Paper - On the growth of the human eyeball and optic nerve

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Scammon RE. and Armstrong EL. On the growth of the human eyeball and optic nerve. (1925) J. Comp. Neurol. 33(2):165-219.

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This historic 1925 paper describes the development of the human eye.


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On The Growth Of The Human Eyeball And Optic Nerve

Richard E. Scammon And Ellery L. Armstrong

Department of Anatomy and Department of Ophthalmology and Otolaryngology, University of Minnesota .


Twenty Figures (1925)

Introduction

Considering the amount of work which has been done on the general development of the human eye, the growth of this structure has received comparatively little attention. Occasional remarks on the relative size of the eyeball in the fetus and the child are encountered in some of the anatomic literature of the eighteenth century, but the first extensive quantitative work on the subject seems to be that of Krause(24) who, in 1832, published a set of measurements of the eye of the newborn. A little later, Huschke(41) included a few weights of the eyeball of the newborn and child in his edition of Sommerring’s anatomy of the sense organs and, in 1850, Eng1e(14) presented a table which contained some observations on the length of the optical axis and the diameters of the globe in children and adolescents. In 1861, von Jaeger (21) published a summary of a large series of measurements of the diameters of the eye of infants under one month of age and compared them with similar measurements in the adult. Little more was written on the subject for the next thirty years until the appearance of a careful quantitative study of the newborn eye by Merkel and Orr(26). Some five years later, Weiss(45, 46) published a series of papers which form our most complete study of the postnatal growth of the eye. He measured the major diameters, and weighed and determined the volume of the eyeballs of a series of twentyfive cases ranging in age from birth to fifteen years. He also examined quantitatively a number of emmetropic adult eyes in order to establish norms for comparison with the various measurements observed in children. Most of the figures on the growth of the eye quoted in present-day texts are derived, either directly or indirectly, from this source. Three other rather extensive quantitative studies have appeared since VVeiss’ work. Halben(18) determined the sagittal diameter of the bulbus in thirty—eight children less than three years of age and in one girl of nine years. Baratz (1) made certain measurements of the eyeballs of twentyseven children under one year of age. Unfortunately, his work, which is embodied in a Russian doctor’s dissertation, is available in this country at the present time only in the form of abstracts. The last collection of data on the subject is apparently that of Grod(17), who gives the transverse diameters and volumes of a few eyes of infants in connection with his study of congenital cataract. Besides these studies of the growth of the eyeball as a whole in postnatal life there are several investigations of the growth of various parts of the organ, particularly of the cornea, which will be considered later in this paper.


Less is known of the growth of the eye in prenatal life. A few individual determinations of the weight and volume of the eyeballs in the latter part of the fetal period have been recorded by Bishoff(4), Welcher and Brandt(47), Jackson (20), and Usher(42), but no systematic observations have been made on the subject. The only extensive observations on the dimensions of the eye in the fetus are, first, those of K6nigstein(22), who measured the diameters of the bulbus and the cornea in sixteen specimens ranging in age from four to ten fetal months; second, those of Collins(8), who recorded the average diameters of the eyeball in nineteen fetuses of the fourth to ninth month, inclusive, and, third, those of Seefelder(36), who published a table including measurements of the horizontal and sagittal diameters of the eyeball, the vertical and horizontal diameters of the cornea, pupil width, and the breadth of the lens in forty—two fetuses and newborn children. Seefelder’s data were published in connection with a study of coloboma, and he does not enter into a discussion of his findings except as regards the width of the pupil.


There seem to be no published data on the dimensions of the optic nerve in the developmental period aside from a few observations recorded by Baratz(1).


The above summary indicates on what a relatively small amount of information our knowledge of the growth of the eye in man actually rests, and the need for further data on this subject, both for determining the normal ‘course of growth of the organ and for the interpretation of its anomalies in the size and form in later life. The following study was undertaken with the hope of filling a part of this gap in our knowledge through a systematic quantitative study of the growth of the eyeball in volume and dimensions in prenatal life and a colligation of the scattered published data on the postnatal growth of the organ. To this we have added a certain amount of data on the growth of the optic nerve which became available in the course of our work. We have applied to the study of this material some of the simpler methods of graphic analysis and numerical expression which are outlined in the section of this paper given to technical methods.

Material

The material used in the study of prenatal growth consisted of seventy-one fetuses, of which thirty-five were males and thirty-six were females. They ranged from 85 mm to 501 mm in total crown-heel length. Table 1 below shows the distribution of these specimens according to crown-heel length and to age in fetal or lunar months.


These specimens were all selected from a large collection of material, care being taken to secure individuals in which the eyeballs showed no evidences of shrinkage or distortion. Most of the material was preserved in 10 per cent formalin, but a few specimens had been placed in 10 per cent formalin solution containing 1 per cent chromic acid to harden the tissues. All specimens had been in formalin at least six months previous to dissection.


The collated data which we have used for following the postnatal growth of the various dimensions have been gathered from a large number of sources which are quoted in, the bibliography. They consist of measurements of the weight and volume of the eyeball, the diameter and radius of the cornea, and the length and breadth of the optic nerve.

Technical Methods and Measurements

Eight quantitative determinations were made on the right and left eyes of each specimen — a total of some 1000 observations. Of the eight measurements, seven were dimensional and one volumetric. The technique of making these determinations is given in detail below.

1. L/meal determinations

These measurements were made of the organ in situ with a sliding, stop-brake, steel Vernier caliper graduated to 1 mm. on the major and to 0.1 mm. on the minor scale. All readings were taken to 0.1 mm.

The anteroposterior or sagittal diameter of the eyeball was taken in the sagittal plane of the structure from the vertex of the cornea to the most distant point on the posterior surface of the bulbus oculi. In the majority of cases the latter corresponds approximately to the position of the macula.

The transverse or horizontal diameter of the eyeball was measured by taking the greatest distance in the transverse plane between the lateral and the medial surfaces of the eye ball, and at right angles to the median sagittal plane of the structure.

The superior~inferior or vertical diameter of the eyeball was taken in the median vertical plane of the bulbus from the most superior point on the upper surface to the most inferior point on the lower surface.

The transverse diameter or breadth of the base of the cornea was measured from the lateral or temporal margin of the limbus cornae to the median or nasal margin, in a line at right angles to the vertical axis of the eyeball.

The vertical diameter of the base of the cornea was measured from the inferior to the superior margin of the limbus cornae in the vertical axis of the eyeball. T

The length of the optic nerve was measured from the middle of the medial margin of the juncture of the optic nerve and the eyeball to the median point on the anterior margin of the optic chiasma.

Table 1
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Distribution of fetal material according to total bodylmgth and calculated age in fetal months

B§3$_‘fi:§§T;°fC‘;f.) Nulgfglfs °F CALCULATED AGE IN FETAL MONTHS Nulgfsyg °F

5 to 10 3 Third 3 10 to 15 8 Fourth 12 15 to 20 6 Fifth 16 20 to 25 14 Sixth 8 25 to 30 5 Seventh 7 30 to 35 6 Eighth 8 35 to 40 7 Ninth 8 40 to 45 9 Tenth and newborn 9

45 to 50 8

50 to 55 5 Total 71 Total 71


The diameter of the optic nerve was measured from the lateral to the median surface of the nerve at right angles to its long axis at a point about 2 mm. posterior to its juncture with the eyeball and behind the slight terminal construction of the structure.

2. Volumetric determinations

The eyeball was first dissected free of all muscular attachments, fatty tissue, and the like, and the optic nerve was detached at its connection with the bulbus. The bulbus was first immersed in water, then withdrawn, and the superfluous moisture removed by placing the specimen on a pad of gauze for about ten seconds in each instance. The volume was then determined with a Jones volumetric apparatus, readings being taken to 0.01 cc.

Methods of Treatment of Data

All measurements were made before any attempt was made to analyze the data. The measurements were then grouped by 5-cm. intervals of crown—heel or total body-length and the average of each dimension determined for each of these intervals. Where measurements were taken on the right and left sides of the same specimen, the two values were averaged before being combined in the totals from which the final averages were determined. The results of these preliminary calculations were arranged in tabular form and constitute a part of tables 2, 6, 7, 8, 12, 13, 17, and 18, inclusive, of the present paper.

The data were also examined by some of the simpler methods of graphic analysis. A field graph was made of the measurements of each value, the value in question being used as the ordinate and the crown—heel or total length of the body as the abscissa. These graphs form figures 1, 4, 5, 6, 9, 10, 12, and 13, inclusive, of this paper. The average value for each 5-cm. interval of crown—heel or total body—length was then indicated on these graphs by a special symbol, its exact position in relation to the abscissa being determined by weighting for the average crown-heel length of the specimens in the interval. Curves representing the growth of A each dimension were then drawn on the field graphs by inspection.


Empirical formulae for the numerical expression of these curves were then computed and their reliability tested by determining the average absolute and the average percentage deviation of the observed values, as represented by the 5—cm. interval averages, and the calculated values, at corresponding body-lengths, as given by these empirical formulae (sixth, seventh, and eighth columns of tables 2, 6, 7, 8, 12, 13, 17, and 18).


There are several reasons for obtaining empirical formulae for expressing these various curves in numerical form. The most important is that with such formulae one can make accurate interpolations at any point on the curve and thus determine the calculated value of a given measurement at any given body-length. Second, by the use of such formulae one may shift scales readily and reduce measurements of unlike magnitude to similar scales for comparison. Third, it is possible to obtain values for approximate ages from the body-length with little computation. And, finally, the empirical formula of a curve often aids one in determining the general character of the growth of a part and assists in comparing its growth with that of other parts of the body which have been studied with a similar technique.

It should be pointed out, however, that values obtained from inspected curve by this method are, in theory at least, no more accurate than those obtained from the original inspected curve. The empirical formula presented here will not hold good, in the majority of instances, below 7.2 cm. total body-length or three fetal months, since the character of growth in the earlier embryonic period is evidently quite different from that of the fetal period which is considered in this paper.


After these preliminary steps, the calculated values were computed for each dimension at 5-cm. intervals of total bodylength beginning at 10 cm. and terminating at 50 cm. These values are given in tables 3 and 9. Second, the Values were determined for each fetal or lunar month of gestation from three months to birth. These values were computed from the total body-length by the use of the empirical formula:

2.5L L?

73‘ + 731;

In this formula, as developed by Scammon and Calkins(33), ‘T’ is the age in fetal or lunar months, ‘L’ is the total bodylength in centimeters, and the numerical values are empirically determined constants. These values are given in tables 4, 10, 14, and 19. finally, in order to reduce the various measurements considered to a common basis for comparison, their values were computed from the formulae in terms of the per cents of their newborn and their adult values. The results of these secondary computations are shown in tables 20 and 21.


The data on the postnatal growth of the eyeball were, in our opinion, too heterogeneous and too scanty to permit the form of analysis outlined above for the fetal measurements, and the graphs illustrating postnatal growth which are presented here are, with one exception (fig. 19), simple point-topoint curves.

Summary of Observations

1. The growth of the eyeball in volume and weight

The growth of the eyeball i11 volume and weight is shown in tables 2 to 5, inclusive, and is illustrated by figures 1, 2, and 3.

Considering first the growth in the fetal period, from the close of the third fetal or lunar month of gestation to birth, it is found that when the average volume of the eyeball is plotted against the total body-length, it forms a shallow curve which rises very slowly until a body-length of 20 to 25 cm. is reached and then increases very rapidly from this stage to 50 cm. or birth. This curve may be expressed approximately by the empirical formula:

Eyeball volume (cc.) 2 0.0] [(0.23 body-length)‘-3’ + 12.0].

The Values calculated by this formula show an average weighted departure of approximately 0.05 cc. from the corresponding observed averages for the 5—cm. intervals of bodylength from 5 to 55 cm., inclusive. The corresponding percentage deviation is about 9 per cent. The larger part of this divergence lies in the 10 to 15 and 20 to 25 intervals of crown-heel body—length. The first is a plus and the second a minus deviation (table 2).

According to this formula, the average volume of the eyeball is nearly one—fifth of 1 co. in fetuses 10 cm. in length, approximately three-fourths of 1 cc. at 25 cm., and 3.24 cc. in the full-term fetus of 50-cm. body-length. Computing the age in fetal months from total body-length according to the empirical formula given on page 171, we obtain a calculated eyeball volume of about 0.6 cc. at five fetal months, or the middle of prenatal life, and about 3:]: cc. at birth. Thus the eyeball has acquired less than one-twentieth of its natal volume at three months, between one-fifth and one-sixth at five months, about one-third at six months, and about one—half between seven and eight months. In other words, nearly three-fourths of the intra-uterine period passes before the eye reaches one-half of-its natal size.

'51o15 zo :5'3o 55 40 45 5055cm.

Fig. 1 Field graph, with curve of the empirical formula, of the growth in volume of the eyeball in the fetal period. Abscissae: total body-length in cm. Ordinates: eyeball volume, cc. Individual case indicated by dots. Averages for 5-cm. intervals of body-length indicated by croses. Curve drawn to the empirical formula:

Eyeball volume (cc.) = 0.01 [(0.23 body-length)‘-“ + 12.0].

While these figures on absolute volume indicate that the eyeball accomplishes the greater part of its growth in the latter part of the fetal period, the relative rate of growth of the organ is much more rapid in the early part of prenatal life than later, for, as will be seen from the figures given in table 4, the organ increases a little over 100 per cent in volume in the course of the fourth month, and this rate drops very rapidly to approximately 50 per cent for the sixth month, 30 per cent for the eighth month, and to about 25 per cent in the last month of gestation.

Table 2
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TABLE 2

Volume of the eyeball in the fetal period (5.9 cases)

Empirical formula: Eyeball volume (cc.) = 0.01 [(0.23 body-length (cm.))’-"" + 12.0]

TOTAL OBSERVED EYEBALL Diz}hF'i‘Fii::§ifz)E BODY-LENGTH VOLUME CALCU‘ ossmcvnn AND (CM.) P we.) Egggign CALCULAVTED Nvggfifi _. vonvmn M.V_A.LU. “M1,.-- CASES Range 1‘ Mean Max. Min. Mean (Col) cc. C221; 5 to 10 I 8.5 I 0.2 0.1 0.17 0.17 1 710 [ : o_o 3 10 to 15 13.5 0.3 0.1 0.21 0.26 + 0.05 I -1-23.8 5 15 to 20 17.4 0.4 i 0.3 0.36 ‘ 0.38 + 0.02 + 5.3 5 20 to 25 22.3 0.8 0.3 0.65 0.56 —- 0.09 —-13.9 13 25 to 30 1 27.2 1.1 0.7 0.89 0.86 — 0.03 -——-~ 3.4 5 30 to 35 32.2 1.6 1.0 1.30 1.20 -— 0.10 —— 7.6 6 35 to 40 37.6 I 1.8 ‘ 1.5 1.70 1.70 t 0.00 i 0.0 6 40 to 45 41.9 2.5 1.8 2.00 2.20 + 0.20 +10.0 8 45 to 50 46.7 3.3 1.5 2.90 2.60 —— 0.30 —10.3 7 50 to 55 50.1 3.4 3.4 3.40 3.20 -—- 0.20 —- 6.2 1

The volume of the eyeball in the newborn as determined by this study (3.25 cc. at 50.2 cm. total or crown-heel length) is distinctly above that of 2.185 cc. given by Weiss(40), which is generally quoted as the standard figure. The reason for this difference between VVeiss’ natal value and our own is obvious if one examines the data regarding the body-weight and length of the specimens in these two series of cases, for the average weight of Weiss’ specimens was but 2290 grams, the maximum being 2400 grams, and the minimum 1900 grams. These Weights indicate a body length of approxiGROWTH OF THE EYEBALL AND OPTIC NERVE

mately 45 cm., which is the average body-length of fetuses of about thirty-four weeks’ gestation. Thus the specimens which Weiss considered as newborn cannot be properly regarded as representing mature, full-term newborn infants. Weiss found that the volume of the eyeball at three months after birth (in specimens of 3490 and 3480 grams bodyweight, respectively) was 3.35 cc. These figures for children having about the average weight of the normal infant at birth are quite similar to those for the natal volume of the eye as determined in this study.

Table 3
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TABLE 3

Calculated volume of the eyeball at 5—cm. intervals of body-length in the fetal period

BODY—LENGTH (CM) CALCULATED VOLUME or EYEBALL (cc.)

5 0.12 10 0.19 15 0.30 20 0.49 25 0.73 30 1 . 05 35 1.43 40 1.96 45 2.54 50 3.24

VVe have made no direct observations on the weight of the eyeball at birth. According to Weiss’ figures, the specific gravity of the bulbus at birth is 1.048, and applying this value to our figure for volume the weight of the natal eyeball may be estimated at 3.40 grams.

The figures of various observers on the growth of the eyeball in weight in postnatal life are summarized in table 5. Although they are few in number, they are sufficient to indicate the general course of the ponderal growth of the organ after birth. The curve shown in figure 3 which is based on these figures illustrates these postnatal changes. In this graph the figure used for the newborn is that determined in this study as, for reasons stated above, we feel that the lower figures usually quoted are far too small. Taking the average for the full-term newborn child at 3.25 cc. (or 3.40 grams) we find that the average weight for the first year falls below the latter figure by 0.07 gram. This is undoubtedly an artifact and the true value for the year is probably considerably higher. Very’ low average weights are obtained for almost all organs for the first year after birth, unless the material is carefully selected. The reason for this lies in the fact that the death rate of premature children in the first year is

Table 4
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TABLE 4

Calculated volumes of the eyeball and the optic nerve from the third fetal month to birth 7-" 8 TQM VOLUME on THE EYEBALL -W VOLUME or orvnc NERVE K ($151111 1 BOW 1* ’ “ ‘ "‘ MONTHS) Lfilglggni Absolute volume Per cent of vo1ume,Abso1ute volume Per cent of volume ' i (cu.mm.) in newborn (eu.mm.) in newborn _ . 7 , i . J ,, 1--.,‘ ,___ , , ,_- , 3 7.2 152.7 I 4.68 1.10 7.32 4 15.6 321.4 I 9.86 7.68 5.11 5 22.8 611.3 1 18.76 18.47 12.29 6 29.2 998.4 30.65 35.11 23.37 7 35.0 1465.0 l 44.97 58.05 38.64 8 40.4 D 2004.0 61.51 80.86 53.82 9 45.5 2611.0 t 80.14 108.30 72.08 10.0 (birth) 50.2 3258.0 , 100.00 150.24 I 100.00


very much higher than that of children born at term, and therefore figures on organ Weights in this period, unless much more carefully selected than was possible in this study, represent those of fetuses which have lived a short time rather than the organ Weights of normal young infants. Omitting this figure, the Weight of the eyeball increases nearly 40 per cent by the middle of the second year and nearly 70 per cent by the fifth year. Thereafter our figures are too scanty to trace the growth year by year, but it is probable that there is slow increase up to maturity. The total postnatal increment is a little less than 4 grams, or approximately 110 per cent over the Weight at birth.

These results are quite different from those usually quoted, due, as has been pointed out above, tothe underestimates of the Weight of the eye at birth through the inclusion of premature material in the natal averages.


Fig. 2 Curve of the growth of the eyeball in volume in the fetal period as calculated from the empirical formula for the eyeball volume given in connection with figure 1, and from the Scammon-Calkins formula for determining fetal age from body-length. Abscissae: age in fetal or lunar months. Ordinates: eyeball volume in cc.

2. The growth of the diameters of the eyeball

The growth of the various diameters of the eye in prenatal and postnatal life is illustrated by tables 6 to 12 and 20 and 2]. and by figures 4 to 8 and 12 to 15, inclusive, and 20. These figures and tables indicate that the general character of the growth of all of these diameters is much the same, although each dimension shows some minor individual peculiarities.


Therefore, in the description of our findings we will present a somewhat detailed account of the development of the sagi.ttal diameter, concerning which we possess the more complete data, while our description of the growth of the vertical and horizontal diameters will be limited mainly to a consideration of the differences between them and the sagittal diameter.

ct. The growth of the sagittal diameter. When plotted against the total body—length, the sagittal diameter of the eyeball in the fetal period forms a shallow concave curve which rises rather rapidly between 5- and 30—cm. body-length

Table 5
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TABLE 5 Weight of the eyeball in postnatal life (39 cases)

I AGE AVERAGE WEIGHT (GRAMS) ‘NUMBER OF CASES

Birth . . . . . . . . . . . . . . . . . . . 3 .25 (Calculated)

1st year . . . . . . . . . . . . . . .. 3.33 8

2nd year . . . . . . , . . . . . . . . 4.67 3

3rd and 4th years . . . . . . . 5.07 2

5th year . . . . . . . . . . . . . . . . 5. 7] 2

7th and 8th years . . . . . . 5.69 4

9th and 10th years . . . . . .* 6.43 2

14th year . . . . . . . . . . . . . . 5.95 1

16th year . . . . . . . . . . . . . ..1 6.50 1

Maturity . . . . . . . . . . . . . . 7.18 16 l

and more slowly thereafter. This curve may be expressed approximately by the empirical formula:

Sagittal diameter of eyeball (mm.) = 0.1[21 body-length(cm.)°-"—9.0].

The calculated values of this formula show an average weighted absolute deviation of 0.14 mm. from the observed averages for 5-cm. intervals of body-length from 10 to 55 cm., inclusive. The corresponding weighted percentage deviation is 1.2. The fit of the calculated curve to the observed data, therefore, seems to be quite a close one, considering the nature of the material.

According to the values obtained by this formula, the sagittal diameter of the eyeball at 10—cm. total body-length is approximately 4.6 mm. This rises to 11.7 mm. at 20-cm. bodylength and increases more slowly thereafter to 17.4 mm. at 50-cm. body-length.

When the diameter is computed in relation to time i.n fetal months, by the formula cited on page 171, it is found to be 3.3 mm. at three lunar months, and from this rises rapidly to 11.4 mm. at six months, and then more slowly to 17.6 mm. at birth.


Fig. 3 Curve of the postnatal growth in weight of the eyeball. Based upon the data in table 5. Abscissae: age in years. Ordinates: weight of the eyeball in grams.

When considered in terms of the size of the eyeball at birth, it is seen that the sagittal diameter accomplishes a little over one-‘sixth of its entire prenatal growth before three fetal months, a little less than two-thirds by six months, and over nine-tenths by the beginning of the ninth fetal month.

The computed value of 17 .6 mm. for the sagittal diameter at birth, as given by our formula, does not differ greatly from the averages obtained by several other observers. Von J aeger( 21), who made a series of fifty measurements of this diameter in children under two weeks of age, found an average diameter of 17.49 mm.; M: rkel and Orr(26) obtained an average of 17.5 from thirty—tWo cases; Seefelder(36) one of 17.7 from four cases, and Kiinigstein one of 17.7 from three cases. Weiss’ figures are much lower, the average of fourteen cases being 16.4 mm. Thus his value for diameters, like his figures for volumes and Weights, seems to be greatly influenced by the prematurity of his material.

It may be pointed out that the above figures give an excellent test of the effect of fixing fluids on the size of the eye

Table 6
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TABLE 6

Saglttal diameter of the eyeball in the fetal period (68 cases) Empirical formula: Sagittal diameter (mm.) =0.1 (21 body—length (cm.)°-75——~9.O

DIFFERENCE TOTAL OBSERVED SAGITTAL BETWEEN BODY-LENGTH DIAMETER ‘I71‘;‘,I“‘]7§‘I7)' OBSERVED AND NUMBER (CM.) (MM.) SAGITTAL CALCULQERD OF DIAM. -§;__w_ CASE s » - (MM’) Per ‘ Range Mean Max. Min. Mean mm. cent . 1 E

5 to 10 I 8.5 6.0 4.0 4.7 4.0 —— 0.7 ——14.9 1 3 10 to 15 13.5 6.8 5.0 5.9 6.0 + 0.1 + 1.7 6 15 to 20 17.4 8.0 6.9 7.5 7.5 i 0.0 i 0.0 5 20 to 25 22.3 11.6 7.5 9.1 9.2 + 0.1 + 1.1 14 25 to 30 27.2 12.0 10.9 11.3 10.8 I -— 0.5 —- 4.4 5 30 to 35 32.2 13.4 11.6 12.7 12.4 — 0.3 — 2.4 6 35 to 40 37.6 15.0 12.0 13.8 14.0 + 0.2 + 1.4 7 40 to 45 I, 41.9 16.4 13.9 15.4 15.3 —~ 0.1 — 0.7 9 45 to 50 47.6 18.0 15.0 16.8 16.9 + 0.1 + 0.6 8 50 to 55 , 51.5 18.3 17.0 17.9 17.9 i 0.0 i 0.0 5

ball, since our material was preserved in a formalin or formalin-chromic acid mixture, and Merkel and Orr ’s specimens were also preserved in a number of fixing fluids, while the material of the other investigators quoted above was measured when in the fresh condition. The slight differences in the various averages indicate that the effect of the commonly used fixing fluids on the size of the eyeball is so small as to be negligible.

From the literature available to us, we have assembled 303 records of the sagittal diameter of the normal eye in postnatal life. These data are shown in summary in the first column of table 11, and the curveglrawn in solid line in figure 8 represents the postnatal growth of this dimension. These data indicate that the eyeball grows Very little in the first half year after birth, but it is most probable that the figures for this period are too low because of the inclusion of premature cases, as has been pointed out in connection with the weight of the eyeball. By the middle of the second year the diameter has increased to a little over,20 mm., or about one-seventh over the dimension at birth. . Thereafter the growth is relatively slow and our data are not sufficiently numerous to allow us to follow its exact course in detail. The average sagittal diameter in the adult, as determined from measurements of 124 normal eyes of both sexes, is 24.4. mm. This represents an increase in this diameter of approximately 7 mm., or about 40 per cent, between birth and maturity.


Fig. 4 Field graph, with curves of empirical formula, of the growth of the sagittal diameter of the eyeball in the fetal period. Abscissae: total body-length in cm. Ordinates: sagittal diameter of the eyeball in mm. Individual cases indicated by (lots. Averages of 5—cm. intervals of body-length indicated by crosses. Curve drawn to the empirical formula:

Sagittal diameter of eyeball (mm.) = 0.1[21 body-length(cm.)°-'“‘——9.0].

A comparison of these figures on postnatal growth of the sagittal diameter with those on its fetal growth shows to what a degree the growth of the eyeball is a prenatal activity, for the absolute increment in this dimension in the latter half of fetal life, from five fetal months to birth, is greater than the entire growth between birth and maturity.

Table 7
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TABLE 7

Transverse (horizontal) diameter of the eyeball in the fetal period (68 cases)

Empirical formula: Transverse diameter (mm.) =0.1 (20 body-length (cm.))°-"-7.0

DIFFERENCE TOTAL OBSERVED DIAMETER BETVVEEN BODY-LENGTH or EYEBALL CALCU. OBSERVED AND (CM.) (MM.) LATED CALCULATED NU1(‘)‘;“7R 1)1AM_ VALUES (MM) « CASES Range Mean Max. Min. Mean mm. fgilrt 5 to 10 8.5 5.6 4.0 4.4 4.0 — 0.4 —— 9.1 3 10 to 15 13.5 6.1 4.8 5.6 6.0 + 0.4 —— 7.1 6 15 to 20 17.4 7.6 7.0 7.2 7.4 + 0.2 + 2.4 5 20 to 25 22.3 11.3 7.4 8.8 9.0 -1- 0.2 + 2.3 14 25 to 30 I 27.2 11.7 10.2 10.9 10.6 — 0.3 —- 2.6 5 30 to 35 32.2 13.1 11.4 12.2 12.1 — 0.1 — 0.8 6 35 to 40 37.6 13.9 11.8 13.3 13.7 + 0.4 + 3.0 7 40 to 45 42.0 16.1 13.5 14.9 14.9 1‘ 0.0 i 0.0 9 45 to 50 47.6 17.7 10.9 16.4 16.4 1' 0.0 I 0.0 8 50 to 55 51.5 18.7 17.3 17.8 17.5 — 0.3 —— 1.1 5

b. The growth of the transverse (horizontal) diameter. The growth of the transverse diameter of the eyeball in the fetal period seems to be a little less rapid than that of the sagittal diameter. The empirical formula used for computing the growth of the diameter in relation to body-length in the fetal period is:

Transverse diameter of eyeball (mm.) =0.1[20 body-length(cm.)°-“-7.0].

The average weighted absolute deviation of the values of this formula from the observed 5 cm. averages, from 10 to 55 cm. of crown-heel length, inclusive, is 0.185 mm. and the average weighted percentage deviation is 1.9 per cent.

At 10—cm. total body-length the calculated transverse diameter of the eyeball is equal to that of the sagittal diameter (4.6 mm.), at 30—cm. body—length it has increased to 11.4 mm. and at 50 cm. to 17.1 mm.

The calculated transverse diameter is 3.4 mm. at three fetal months, this is more than doubled to 9.2 mm. at five months, and is increased about fivefold to 17.1 at birth.


Fig. 5 Field graph, with curve of empirical formula, of the growth of the transverse (horizontal) diameter of the eyeball in the fetal period. Abscissae: total body-length in cm. Ordinates: transverse diameterlof the eyeball in mm. Individual cases indicated by dots. Averages for 5-cm. intervals of body-length indicated by crosses. Curve drawn to the empirical formula:

Transverse diameter of eyeball (mm.) =0.1[20 body-length(cm.)°:”—7.0].

The calculated transverse diameter of the eyeball at birth, as determined by our empirical formula, falls midway between the observed values obtained by Schneller (17.0 mm. as an average of thirty-three cases) and by von J aeger (17.2 mm. as an average of fifty cases). Seefelder(36) measured this dimension in four large newborn infants and found a distinctly larger figure (18.2 mm.). The average given by VVeiss is 16.0 mm., being far below those reported by all other observers.

The data on the postnatal growth of the transverse diameter are much less extensive than those on the sagittal diameter. They are given in table 11 and are shown in the form of a curve, drawn in broken line, in figure 8. According to these figures, the general course of the postnatal growth of the transverse diameter is much like that of the sagittal diameter. It increases’ about 4 mm., to approximately 21 mm., in the first year, about 1 mm. in the second year, and rises to 23.8 mm. (unweighted average of eighty-nine cases) in maturity. Thus the total postnatal increase is 6.7 mm., or almost exactly 40 per cent of the diameter at birth.

Table 8
(to be formatted)

TABLE 8

Vertical diameter of the eyeball in the fetal period (68 cases)

Empirical formula: Vertical diameter (mm.) = 0.1 (20 body-length (cm.))‘’-’“— 7.0

DIFFERENCE , TOTAL OBSERVED DIAMETER BETWEEN BODY-LENGTH or EYEBALL CALCU. OBSERVED AND (CM.) (MM.) LATE]; CALCULATED NU:‘)‘F‘_3ER ])1AM. VALUES CASES I 1 (MM-) "jjmj Range . Mean { Max. ‘ Min. f Mean mm. gift 5 to I0 8.5 5.9 3.9 4.6 3.9 — 0.7 -15.2 3 10 to 15 13.5 6.6 4.6 5.6 5.8 + 0.2 + 3.6 6 15 to 20 17.4 7.7 6.5 7.1 7.1 i 0.0 1 0.0 5 20 to 25 22.3 10.2 7.2 8.8 8.7 — 0.1 — 1.1 14 25 to 30 27.2 11.8 10.3 10.9 10.2 —— 0.7 —— 6.4 5 30 to 35 32.2 13.0 10.5 12.0 11.7 —— 0.3 — 2.5 6 35 to 40 37.6 14.0 11.9 13.2 13.2 i 0.0 '_*: 0.0 7 40 to 45 42.0 15.8 13.7 14.5 14.4 —— 0.1 —- 0.7 9 45 to 50 47.6 17.4 10.6 15.8 15.9 + 0.1 + 0.6 8 50 to 55 51.5 17.6 16.2 16.9 16.9 1 0.0 i 0.0 5


0. The growth of the vertical or superior-trLfer1'.or diameter.

The prenatal growth of the vertical diameter of the eyeball is much like that of the horizontal diameter, although the former is a little less throughout the fetal period. The growth of the vertical diameter in relation to the growth in total body—length may be expressed approximately by the empirical formula:

Vertical diameter of eyeball (mm.) =0.1[20 body—length(cm.)°-’“—7.0]

The computed values of the 5—cm. — interval body—length averages, from 10 to 55, inclusive, have an average weighted absolute deviation of 0.14 mm. and an average weighted relative deviation of 1.4 per cent from the corresponding observed means.


Fig. 6 Field graph, with curve of empirical formula, of the growth of the vertical (superio-inferior) diameter of the eyeball in the fetal period. Abscissae: total body-length in cm. Ordinates: vertical diameter of the eyeball in mm. Individual cases indicated by dots. Averages for 5-cm. intervals of body-length indicated by crosses. Curve drawn to the empirical formula:

Vertical diameter of eyeball (mm.) =0.1[20 body-1ength(cm.)"-“‘“—7.0]

This formula gives the vertical diameter of the eye at 10-cm. total body-length as 4.5 mm., or 0.1 mm. less than the sagittal or the transverse diameter. At 20 cm. of body-length it has risen to 11.0 mm. (0.4 mm. less than the transverse and 0.7 mm. less than the sagittal diameter), and at 50 cm. it is 16.5 mm., or 0.7 mm. less than the vertical and 0.9 mm. less than the sagittal diameter. These figures indicate that the vertical diameter of the eye is not only slightly less than that of the other axes at the beginning of the fetal period, but also that it grows at a slower rate during that period.

Calculated for age according to the formulae previously stated, the vertical diameter is 3.3 mm. at three fetal months. It rises to 8.9 mm. by five months and is increased fivefold (to 16.5 mm.) by birth.

Table 9
(to be formatted)

TABLE 9

Calculated dimensions of the eyeball, cornea, and optic nerve at 5~cm. intervals of body/—length in the fetal period

DIAMETERS or rm: EYEBALL DIAMETERS or THE DIMENSIONS or (3151,) CORNEA (M.VI.) OPTIC NERVE (MM.) BODY-LENGTH (cM.) 1 ; Sagittal ‘ Transverse Vertical V Transverse Vertical Length Breadth

10 4.6 4.6 4.5 2.6 2.6 4.0 0.9 15 6.6 6.5 6.3 3.5 3.4 6.6 1.2 20 8.4 8.2 8.0 4.4 4.2 9.1 1.4 25 10.1 9.9 9.6 5.3 5.0 11.7 1.6 30 11.7 11.4 11.0 6.2 5.8 14.2 1.8 35 13.2 12.9 12.5 7.1 6.6 16.8 2.1 40 14.7 14.3 13.8 8.0 7.4 19.3 2.3 45 16.2 15.7 15.2 8.9 8.2 21.8 2.5 50 17.4 17.1 16.5 9.0 9.0 24.4 2.7

There is very little published material on the vertical diameter of the eyeball at birth with which to check our findings and calculations. Von J ager’s measurements of fifty eyes of infants between four and ten days old gave an average of 16.36 mm. as against 16.5 mm. which we obtained as a calculated value——a relatively small difference of less than 1 per cent. Weiss reports a diameter of 15.5 mm. from a series of measurements of fourteen premature newborn children.

There are also fewer available data on the postnatal growth of the vertical diameter of the eyeball than there are on either the sagittal or transverse (fig. 8 and table 11), but there seem to be no marked differences in the general course of growth of the three dimensions.

The average vertical diameter in the adult, as determined from measurements of eighty—seven eyeballs of both sexes, is 23.5 mm.—an increase of 6.0 mm., or about 36 per cent over the natal diameter. Thus the percentage as well as the absolute postnatal increase of the vertical diameter of the eye is less than that of either the transverse or the sagittal diameter.

3. The growth of the cornea The growth of the cornea was studied by measurements of the transverse and vertical diameters of the base of the structure. No attempt was made to measure the height of the cornea, for it was thought that this dimension was too small in the fetus for accurate determination with the available methods, and also that it might be considerably effected by the process of fixation.


Table 10
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TABLE 10 Calculated dimensions of the eyeball in the fetal period

DIAMETERS or THE EYEBALL (MMJ AGE BODY-LENGTH (FETAL MONTHS) (CM) Sagittal Transverse Vertical 3 t 7.2 3.3 3.4 3.3 4 } 15.6 6.8 6.7 6.5 5 22.8 9.6 9.2 8.9 6 { 29.2 11.4 11. 10.8 7 ‘ 35.0 13.2 12.9 12.5 8 40.4 14.8 14.5 14.0 9 1 45.5 16.2 15.9 15.2 10 50.2 17.6 17.1 16.5


a. The prenatal growth of the cornea. The growth of the horizontal diameter of the base of the cornea iii the fetal period is illustrated by tables 9, 13, and 20, and by figures 9, 13, 14, and 15. VVhen the various determinations of this dimension are plotted against the total body-length of the specimens studied, as is shown in figure 9, the average values for 5-cm. intervals tend to fall in the course of a straight line which may be expressed approximately by the empirical formula: Transverse diameter of corneal base(mm.) =0.1S body-length(cm.) +0.8.

The calculated values of this formula for the 5—cm. intervals of body—length, from 10 and 55 cm., inclusive, show an average Weighted absolute deviation of 0.1 mm. and an average Weighted percentage deviation of 1.9 per cent from the observed means for the same intervals.


Fig. 7 Comparative growth of the several diameters of the eyeball in the fetal period as shown by curves of their empirical formulae. Abscissae: total body-length in cm. Ordinates: diameters of the eyeball in mm.

According to this formula, the absolute growth of the transverse corneal diameter is proportional to the growth in total body-length, and for every increase of 5 cm. in bodylength there is a corresponding increase of 0.9 mm. in the corneal diameter. The corneal diameter thus rises from 2.6 mm. at 10 cm. total body-length to 9.8 mm. at 50 cm. bodylength.


According to this formula and the formula for estimating fetal age from body-length, the diameter is 2.1 mm. at three lunar months, and this value is more than doubled (4.9 mm.) at five fetal months, and is increased over four and one—half times (9.8 mm.) by birth.

The fetal growth of the Vertical diameter of the base of the cornea is much like that of the transverse diameter. The

Table 11
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TABLE 11

Growth of the diameters of the eyeball in postnatal life (number of cases lnclicafed in parentheses)

A ml. SAG ITTAL TRANSVERSE VERTICAL ‘ " ‘ DIAMETER (.\mr.) DIAMETER (.\tM.) DIAMETER (.\IM.) Birth A . . . . . . . . . . . . . . . . . . . . . . . .. 17.5‘ 17.1‘ 16.51 0 to 6 months . . . . . . . . . . . . . . . . .. 17.7 17.6 16.5 (110) (61) (55) (5 to 12 months . . . . . . . . . . . . . . . . .. 18.5 18.0 18.0 (4) (1) (1) 1to2years . . . . . . . . . . . . . . . . . . . .. 20.2 20.5 20.2 (9) (3) (3) 2to5 years . . . . . . . . . . . . . . . . . . . .. 20.3 21.1 21.1 (7) (4) (4) 5to 10 years . . . . . . . . . . . . . . . . . l .. 21.8 21.8 21.3 (11) (9) (7) 10 to 15 years . . . . . . . . . . . . . . . . . .. 21.2 21.9 21.5 (4) (4) (4 Females . . . . . . . . . . . . . . . . . . . . . . . 23 . 9 23.4 23.0 (12) (12) (12) Adult males . . . . . . . . . . . . . . . . . . . . 24.5 24.2 23.6 (92) (90) (2?) Both sexes . . . . . . . . . . . . . . . . . . . . . 24.4 23.8 23.5 ' (124) (89) (87)

‘ Computed with enlpirical formulae.

average values when plotted against the total body-length also approach a straight line which, in this instance, is approximately expressed by the empirical formula:

Vertical diameter of corneal base (mn1.——().'l.6 body-1engt11(em.) +1.0

The average weighted absolute and relative deviations of the calculated values, computed with this formula, from the corresponding observed averages for the 5-cm. crown-heel ranges from 10 to 55 cm., inclusive, are 0.09 mm. and 1.9 per cent, respectively.

The rate of growth of the vertical diameter of the base of the cornea is a little less rapid than that of the transverse diameter, being, according to the formula, 0.8 mm. for each 5 cm. growth in total body—length. The absolute calculated values increase from 2.6 mm. at 10 cm. of body—length to 9.0 mm. at 50 cm. Thus while the transverse and vertical. diameters of the corneal base are equal at the beginning of the fetal period, the transverse diameter is about one—tenth the greater in the newborn. In other words, the corneal base is approximately circular in the embryo and young fetus, but becomes broadly elliptical or oval by birth.


Fig. 8 Curves of the postnatal growth of the sagittal, vertical and transverse diameters of the eyeball in postnatal life. Based on the data presented in table 11. Abscissae: age in years. Ordinates: eyeball diameters in mm.


The calculated diameters of the cornea at birth, as given by these formulae, agree quite closely with the figures obtained by Schneller(35), who has published the largest set of observations on these dimensions in the newborn. The average transverse diame.ter, as determined by this author from the examination of thirty-three cases, was 9.9 mm. and the average vertical diameter was 9.2 mm. Other investigators, examining much smaller series of cases, have generally reported higher values. K6nigstein(22) found an average transverse diameter of about 10 mm. at birth, and Seefelder(36) reports an average of 10.4 mm. from measurements of four very large newborn infants. G~r0d(17) observed a distinct sex difference in the transverse corneal diameter at birth, his averages being 9.25 mm. for six male and 10.25 mm. for four female newborn infants. This difference is not found in‘ the figures of other investigators.

Table 12
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TABLE 12

Transverse diameter of the base of the cornea in the fetal period (71 cases)

Empirical formula: Transverse diameter (mm.) = 0.18 body-length (cm.) + 0.8

DIFFERENCE TOTAL OBSERVED TRANSVERSE BETWEEN BODY-LENGTH DIAMETER CALCU. OBSERVED AND (CM.) (MM.) LATED CALCULATED NUMBER mAM_ VALUES 01’ (MM) _______ CASES Range Mean Max. 5 Min. 1 Mean mm. 5921; 9 1

5 to 10 8.5 2.9 2.5 2.7 2.3 —— 0.4 ———17.4 3

10 to 15 13.5 3.7 2.8 3.1 3.2 + 0.1 + 3.1 8

15 to 20 17.4 4.4 3.6 3.9 3.9 i 0.0 i 0.0 6

20 to 25 22.3 5.9 4.1 4.9 4.8 — 0.1 —~ 2.1 14

25 to 30 27.2 6.4 5.5 6.0 5.7 — 0.3 — 5.3 5

30 to 35 32.2 6.8 6.0 6.6 6.6 i 0.0 1 0.0 6

35 to 40 37.6 8.5 6.3 7.2 7.5 + 0.3 + 4.0 7

40 to 45 42.0 10.4 6.8 8.3 8.4 + 0.1 + 1.2 9

45 to 50 47.6 9.7 8.7 9.2 9.3 + 0.1 + 1.1 8

50 to 55 51.5 10.9 10.0 10.4 10.3 —- 0.1 -— 1.0 I 5


b. The postnatal growth of the cornea. Tables 15 and 16 give the data which we have collected from the literature on the postnatal growth of the corneal base. While these data are rather scanty for infancy and early childhood, they are sufficient to show the more striking postnatal changes in the size of this structure. figure 11 illustrates the course of postnatal growth as indicated by three types of corneal measurements available: 1) measurements made on cadavers; 2) measurements made on the living, and, 3) measurements of the radius of the cornea in the living. The curves of these several types of measurements are in substantial agreement, although they exhibit some minor differences. They all show a rapid increase in the early part of the first decade and little increase or even an apparent decrease thereafter. Examining first the curves of the growth of the diameter of the corneal base, it is seen that the curve based on measurements on cadavers begins at 9.65 mm. at birth and, as is the ease with all unselected material, shows little apparent increase in the first year. As has been previously pointed out, this is no doubt an artifact, and probably the growth is much more rapid in the first part of infancy than is indicated. The curve rises to 11.5 mm. in the second year and then increases much more slowly to a maximum of nearly 12 mm. at seven and one—half years. Thereafter the average figures show a slight drop. The curve based on measurements of living subjects rises much more slowly to about 11.3 mm. at approximately three years, and then increases slowly to a maximum of about 11.7 mm. at fifteen years. We think that the curve ‘a’ based


Fig. 9 Field graph, with empirical formula, of the growth of the transverse diameter of the base of the cornea tn the fetal period. Abscissae: total bodylcngth in cm. Ordinates: diameter of the cornea in mm. Individual cases indicated by (lots. Averages for 5-em. intervals of body-length indicated by crosses. Curve drawn to the empirical formula:

Horizontal diameter of co)-nea(mm.) =0.18 body-1ength(cm.) + 0.8.


Table 13
(to be formatted)

TABLE 13

Vertical diameter of the base of the cornea in the fetal period (71 cases)

Empirical formula: Vertical diameter (mm. =0.16 body-length (cm.) + 1.0

DIFFERENCE TOTAL OBSERVED vmvrxcnr. BETWEEN BODY-LENGTH DIAMETER cALou. OBSERVED AND (CM.) (M.\[.) mun CA:glILJ73;:ED NU4g‘1l}E“

_.j‘_ CASES

Range Mean Max. Min. Mean mm. 32:‘;

5 to 10 8.5 2.8 2.2 2.5 2.4 — 0.1 — 4.0 3 10 to 15 13.5 3.6 2.5 2.9 3.2 + 0.3 +10.3 8 15 to 20 17.4 4.2 3.6 3.8 3.8 i 0.0 ‘.1: 0.0 6 20 to 25 22.3 5.2 3.8 4.6 4.6 1 0.0 i 0.0 14 25 to 30 27.2 5.8 5.3 5.5 5.4 —- 0.1 — 1.8 5 30 to 35 32.2 6.2 5.7 6.0 6.1 + 0.1 + 1.7 6 35 to 40 37.6 7.9 6.0 I 6.9 7.0 + 0.1 + 1.5 7 40 to 45 42.0 8.8 6.5 7.7 7.7 .1: 0.0 .'*_' 0.0 9 45 to 50 47.6 9.1 8.0 8.5 8.6 + 0.1 + 1.2 8 50 to 55 51.5 10.4 9.1 9.5 9.2 — 0.3 — 3.2 5

on measurements on cadavers probably represents more accurately the true course of postnatal growth of the cornea than the curve ‘b’ for the following reasons: 1) the cadaver material is more extensive than the living material for the periods of infancy and early childhood; 2) the measurements on living children in this period were made, in the majority

of instances, by a distinctly inaccurate method (rule and_

compass); 3) the curve based upon cadaver measurements agrees more closely in type with the measurements of the corneal radius than does that based on measurements of living subjects.

Measurements of the radius of the cornea are not, of course, true expressions of the growth of the base of this part of the eye, since they involve the increase in height and change in curvature of the structure as well. However, they are included as ancillary to the data given above. They show the same general characteristics of an early rapid increase in infancy and early childhood and little change thereafter.


Fig. 10 Field graph with curve of empirical formula of the growth of the vertical diameter of the base of the cornea i11 the fetal period. Abscissae: total hody—length in cm_. Ordinates: diameter of the cornea in mm. Individual cases indicated by dots. Averages for 5-cm. intervals of body-length indicated by crosses. Curve drawn to the empirical formula:

Vertical diameter of cornea(mm.) = 0.16 body-length(em.) + 1.0.


All of these curves of postnatal corneal growth show that this structure is larger at some time in childhood than in maturity. Figures on the diameter and radius of the cornea in maturity and old age apparently indicate that there is a

Table 14
(to be formatted)

TABLE 14 Calculated diameters of the base of the cornea in the fetal period

195

AGE TOTAL BODY-LENGTH TRANSVERSE (HORIZONTAL) VERTICAL DIAMETER

(FETAL MONTHS) (cM.) DIAMETER (MM.) (MM.) 3 7. 2 2.1 2. 1

4 15.6 3.6 3.5

5 22.8 4.9 4.6

6 29. 2 6. 0 5 . 7

7 35.0 7 . 1 6. 6

8 40.4 8.0 7.5

9 45.5 9.0 8.3

10 50.2 9.8 9.0

Table 15
(to be formatted)

TABLE 15

Horizontal diameter of the base of the cornea in postnatal life as determined by dtferent observers (number of cases given in parentheses)

OBS]-IRVERS AND AVERAGE DIAMETERS (MM.)

von Reussl

P. Smith?

‘GE ('81) (‘85) G(r’§§)f3 (013514 both sexes males females males females males 0 females Newborn 9(-62)5 First year (E1313 9.0 9.2 03;; 10800 Second year 9.5 9.5 11(.45) Third year 11-4 9'9 10.3 11 62 11 75 Fourth year (20) (4) (53) Fifth year j 11 '4 ' 11 '0 1(14-)5 132-)0 5 to 10 years } if; 1(15.47)4 1(14.(§7 12.0 11.6 11525 1%é<))s 10 to 20 years $23) 11.6 11.4 115.0 1137 20 to 40 years } 1&6 1(22.)0 40m goyem ('0) 11.52 11.43 “'3 “-2 11.44 11.00 (100) (100) (3) (4)

‘Total of 184 cases, living subjects and ten infant cadavers.

rule and compass.

‘Total of 804 living subjects. “Total of 200 living subjects. ‘Total of 78 cadavers.

Measured. with keratometer. Measured with 1-Iorstmann pupillometer. Measured with compass.

Measured with slight shrinkage in the size of this dimension in senility, and it is within the range of possibility that this process begins in childhood or adolescence. VVe do not think, however, that the data here presented are either sufficiently homogeneous or extensive to warrant a final conclusion on this subject, although it may be said that we have examined the material for any artifacts which might produce this effect, and so far have found none. More data, obtained from homogeneous material by uniform and accurate methods, are needed on this subject.

Table 16
(to be formatted)

TABLE 16

Radius of the cornea in postnatal life

AGE NUMBER OF CASES AVERAGE RADIUS (Ml\[.) Birth to 6 months . . . . . . . . . . . . . . . . . . . 4 6. 67

6 to 12 months . . . . . . . . . . . . . . . . . . . . . . 4 7.43

1to2years . . . . . . . . . . . . . . . . . . . . . . . .. 3 7.58

2to4years . . . . . . . . . . . . . . . . . . . . . . . .. 6 7.40

4 to 6 years . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.41

6 to 8 years . . . . . . . . . . . . . . . . . . . . . .. 17 7.45

8 to 10 years . . . . . . . . . . . . . . . . . . . . . . . . 18 7.48

10 to 14 years . . . . . . . . . . . . . . . . . . . . . . . 25 7.50

14 to 20 years . . . . . . . . . . . . . . . . . . . . . . . 33 7. 70

20 to 40 years . . . . . . . . . . . . . . . . . . . . . .. 319 7.89

If one accepts Priestly Smith’s figure of 11.7 -1- mm. for the average diameter of the corneal base in the young adult, the total increase of the diameter from the newborn average of 9.8 mm. is approximately 2 mm., or a little over 20 per cent. By far the greater part if not all of this growth takes place i11 infancy and early childhood.

Although the corneal diameter of the adult male is slightly greater on the average than that of the female, we have found no sex difference in our fetal material and the slight differences reported for children seem to be irregular and inconsistent. If a sex difference does exist prior to maturity, our figures are not sufficiently extensive to demonstrate it.


4. The growth of the optic nerve

The growth of the optic nerve has been studied from measurements of its length and breadth. The dimensions of this structure in the fetal period are shown in tables 9, 17, 18, 19, 20, and 21 and in figures 12, 13, 14, 15, 16, and 17. Our measurements of the nerve have proved more variable than those on the eyeball, probably because of greater experimental error in their determination.


Fig. 11 Curves of the postnatal growth of the horizontal growth of the base of the cornea and of the corneal radius. Based on data presented in tables 15 and 16. Abseissae: age in years. Ordinates: diameter and radius in mm.

at. .The growth of the optic nerve in length. Figure 12 is a graph of our measurements of the length of the nerve in fetal life plotted against the total body—length. The measurements thus plotted tend to arrange themselves in the course of a straight line which may be expressed by the empirical formula:

Optic nerve length (mm.) = 0.51 body»1ength (cm.) —1.1. 198 RICI-IARD E. SCAMMON AND ELLERY L. ARMSTRONG

The average weighted absolute deviation between the observed averages for the 5-cm. intervals of body-length from 10 to 55 cm., inclusive, and the values as given by this formula is 0.5 mm. and the average weighted percentage deviation is 3.7. This rather large percentage deviation is caused by some unusually high values in the 30 to 35 and the 35 to 40 cm. intervals of crown—heel length.

According to the values given by this formula, the length of the nerve grows at a constant rate in relation to the total

Table 17
(to be formatted)

TABLE 17

Length of the optic nerve in the fetal period (63 cases)

Empirical formula: Length of nerve (mm.) =0.51 body-length (cm.)——1.1

DXFFERENOE TOTAL OBSERVED LENGTH BETWEEN BODY-LENGTH or NERVE CALCU‘ OBSERVED AND (cM.) (MM.) LATE” CALCULATED NUMBER NERVE MEANS or LENGTH 4 CASES ‘ (nM.) Per Range Mean Max. Mm. Mean. mm. cent

5 to 10 8.5 6.0 2.4 4.0 3.2 -—— 0.8 ——20.0 3

10 to 15 13.5 6.3 4.2 5.4 5.7 + 0.3 + 5.5 6

15 to 20 17.4 9.6 6.7 7.8 7.8 i 0.0 i 0.0 5

20 to 25 22.3 13.1 9.4 10.7 10.3 ——— 0.4 —— 3.6 14

25 to 30 27.3 15.6 13.4 14.6 12.8 —— 1.8 —12.3 5

30 to 35 32.2 20.3 15.8 17.2 15.3 —— 1.9 —11.0 6

35 to 40 37.6 20.3 15.4 17.6 18.1 + 0.5 + 2.2 7

40 to 45 41.9 22.4 17.3 20.0 20.2 + 0.2 + 1.0 8

45 to 50 47.6 25.9 13.4 23.2 23.2 :t 0.0 t 0.0 8

50 to 55 50.1 23.8 23.8 23.8 24.2 + 0.6 + 2.5 1

or crown—heel body~length. The calculated length at 10 cm. of body-length is 4.0 mm., and this rises to 24.4 mm. at 50 cm.

When computed according to age in fetal months, the length of the nerve is 2.2 mm. at three fetal months. This value is more than tripled (6.8 mm.) at four months, increased over sixfold (13.8 mm.) at six months, and about elevenfold (24.4 mm.) by birth.

There seem to be no recorded observations on the length of the optic nerve of the newborn with which to check these findings. In the adult the average length of the optic nerve as computed from the observations of 'VVeiss(_40), Otterski(25), and Vierordt(39) is approximately 37.3 mm. This figure indicates that the nerve increases in lengthabout 13 mm., or a little over 60 per cent, between birth and maturity.


Fig. 12 Field graph, with curve of empirical formula, of the growth in length of the optic nerve in the fetal period. Abscissae: total body-length in cm. Ordinates: optic nerve length in mm. Individual cases indicated by dots. Averages for 5—cm. intervals of body—length indicated by crosses. Curve drawn to the empirical formula:

Optic nerve length (mm.) =0.51 body-length (cm.) —1.1.

b. Ihc growth of the optic nerve in diameter. When the diameter of the optic nerve in the fetal period is plotted against the total body-length, the resulting curve appears to be a straight line, as in the case of the length of the structure. An approximate empirical formula for this line is:

Optic nerve diameter (mm.) =0.045 body-length (cm.) +0.5. 200 RICHARD E. SCAMMON AND ELLERY L. ARMSTRONG

The calculated values for the 5-cm. crown-heel length, from 10 to 55 cm., inclusive, as obtained by this formula, show an average weighted absolute deviation of 0.5 mm. and an average weighted percentage deviation of 3.76 from the corresponding observed means. The greater part of this deviation lies in two intervals, that from 15 to 20 cm., which is negative, and that from 35 to 40 cm., which is positive. Aside from these intervals, the fit of the curve is fairly close to the observed values. A considerable part of this deviation is

Table 18
(to be formatted)

TABLE 18

Diameter of the optic nerve in the fetal period (63 cases) Empirical formula: Diameter of nerve (mm.) = 0.045 body-length (cm.) + 0.5

DIFFERENCE 'ro'r.u. OBSERVED DIAMETER BETWEEN "°".':.‘:.=:°“* °** °:r.m*:.A.=;” xwggax lag‘) MEANS CASES Range ‘ Mean I Max. Min. Mean 1 mm. 5 to 10 8.5 1.2 0.8 0.9 0.9 i 0.0 2 0.0 3 10 to 15 13.5 1.6 0.8 1.2 1.1 ——- 0.1 —- 8.3 6 15 to 20 17.4 1.8 1.4 1.7 1.3 —- 0.4 --23.5 5 20 to 25 22.3 1.9 1.2 1.6 1.5 —- 0.1 —— 6.2 14 25 to 30 27.2 2.0 1.6 1.8 1.7 —- 0.1 —— 5.5 5 30 to 35 32.2 2.1 1.7 1.9 1.9 i 0.0 1 0.0 6 35 to 40 37.6 2.3 1.7 2.0 2.2 —+- 0.2 --I-10.0 7 40 to 45 41.9 2.8 2.1 2.4 2.4 :1: 0.0 I 0.0 8 45 to 50 47.6 3.0 2.0 2.6 2.6 i 0.0 i 0.0 8 50 to 55 50.1 2.7 2.7 2.7 2.7 i 0.0 i 0.0 1

probably due to the technical difliculties involved in making this small measurement on soft tissues.

The calculated values for the diameter of the optic nerve in the fetal period range from 0.9 mm. at 10 cm. total bodylength to 2.7 mm. at 50 cm. total body-length. As the curve of growth is a straight line, the increase in relation to the increase in body-length is a constant one, being 0.2 mm. for each 5—cm. interval. The calculated length at three fetal months is 0.8 mm., and this is almost doubled at six months, and more than tripled (2.8 mm.) at birth.


The only published observation which we have found on the diameter of the nerve at birth are those of Baratz(1), who gives the natal dimension as 0.8 mm. However, we have not encountered as small a diameter as this in any specimen over 10 cm. in total body-length. Baratz’s figure for the diameter of the nerve in the adult is 1.4 mm., while most observers have recorded average diameters of 3 or 4 mm.



Fig. 13 Field graph, with curve of empirical formula, of the growth in diameter of the optic nerve in the fetal period. Abscissae: total body-length in em. Ordinates: diameter of optic nerve in mm. Individual cases indicated by dots. Averages for 5-cm. intervals of body-length indicated by crosses. Curve drawn to the empirical formula: Diameter of optic nerve (mm.) 2 0.045 body—length (cm.) + 0.5.

The discrepancies between Baratz’s figures and those of other observers are so great that we think possibly some clerical error occurred in the published summary of his findings which is available to us, but, since the original Russian work cannot be obtained in this country at present, we are not able to check these with his own publication.

The diameter of the optic nerve in the adult at the level where our measurements were taken (just posterior to the constriction at the bulbus oculi) is given by Vierordt as 3.2 mm. Accepting this figure, the postnatal increase in the breadth of the structure is 0.4 mm., or 13.5 per cent. This small increase is presumably due almost entirely to the myelinization of the optic-nerve fibers—a process which is already under way at birth.

Although we have made no direct volumetric determinations of the volume of the optic nerve, it is possible to make a rough estimate of the changes in volume of the structure by considering its form to be that of a regular cylinder and calculating its volume from its length and diameter. The results of a series of such computations are shown in table 4. According to these calculations, the volume of the nerve is about 1.2 c.mm. at three fetal months, and this is increased to about 146 c.mm. at birth. The calculated volume of the nerve in the adult is approximately 312 c.mm.—a value which is in fairly close agreement with the adult weight of 0.35 gram for the nerve as reported by BischoH(4). Thus there is a postnatal increase of about 166 c.mm., or approximately 115 per cent over the birth volume.

Table 19
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TABLE 19 Calculated dimensions of the optic nerve in the fetal period

AGE TOTAL BODY-LENGTI-I LENGTH or OPTICNERVE DIAMETER or om-xc NERVE (FETAL Mom-Hs) tom.) (MM.) (mm 3 7.2 2.2 0.8 4 15.6 6.8 1.2 5 22.8 10.5 1.5 6 29.2 13.8 1.8 7 35.0 16.8 2.1 8 40.4 19.5 2.3 9 45.5 22.1 2.5 10 50.2 24.4 2.8


If we accept the comparative values of Baratz, most of this growth is accomplished in the first year after birth where the myelinization of. the nerve takes place. GROWTH OF THE EYEBALL AND OPTIC NERVE 203


Discussion

1. A comparison of the prenatal growth of the optic apparatus with that of certain other organs and that of the body as a. whole

The course of growth of the eyeball in prenatal life is so different from its postnatal history that the two periods will be considered separately. The growth of the eyeball in volume and dimensions in the early or truly embryonic portion of prenatal life is obviously very rapid, but it cannot be accurately compared with tl1at of the organs of the body, since we have no quantitative data on the subject. In the fetal period proper, from the third fetal month to birth, it has been shown that the volume growth of the structure, when compared with the total body-length (fig. 1) or with the calculated age (fig. 2), follows the course of a shallow concave curve which rises slowly to about 30 cm. of body-length, or six fetal months, and then ascends rapidly to birth. This general type of curve is characteristic of the growth in weight and volume of the body as a whole and of all major parts in


Fig. 14 Curves illustrating the fetal growth in volume of the body as a whole, the brain and its several parts, the spinal cord, and the eyeball. All these structures are reduced to a similar scale by computing their values at each 5—em. interval of body-length as per cents of the value at 50 cm. The empirical formulae given in the body of this paper were used as the basis of these computations. Abscissae: total body-length (cm.). Ordinates: per cents of values at 50cm. total body-length.


Table 20
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TABLE 20

Ltneal d1'mer1sirm.s of the eyeball and optic nerve in the fetal period calculated in percentages of their size at birth

MT TOT ‘L HORIZOYI-‘,“‘ DIA.\il<ITERS OF EYI-IBALL DIAMETERS OF CORNEA OPTIC NF.R\'E

(1-‘E'1‘AL B0])Y- HEAT .\Io:<'rI~1s) }.1«:.\'<:TH CIRCI‘-‘l’

IWIRENCE S-agittal Transverse Vertical Transverse Vertical Length Diameter

3 14.34 17.28 18.75 19.88 20.00 21.43 23.33 9.02 28.57 4 31.08 33.50 1 38.64 39.18 39.39 36.73 38.89, 27.87 42.86 5 45.42 47.40 55.68 53.80 53.94 50.00 51.11 43.03 53.57 6 58.17 59.70 64.77 64.91 65.45 61.22 63.33, 56.56 64.29 7 69.72 70.93 75.00 75.44 75.76 72.45 73.33j 68.85 75.00 8 80.48 81.24 84.09 84.80 84.85 81.63 83.33 79.92‘ 82.14

9 90.64 90.91 92.05 92.98 92.12 91.84 92.22‘ 90.57, 89.30 Birth ‘100.00 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00

the fetal period (Scammon, 31). Although all the organs and parts of the body follow this general type of growth curve in fetal life, each shows its own peculiar variant of the type, and a. closer examination enables us to group the Various curves which are more closely related. When such a detailed comparison is made of the growth of the eyeball with that of the other organs, it is found that the fetal growth in mass or volume of the optic apparatus approaches more closely that of the brain stem and spinal cord than that of any other part of the body for which we have quantitative data.

This fact is illustrated by figure 14, which shows a series of growth curves of the volumes of various parts of the brain, GROWTH or THE EYEBALL AND OPTIC NERVE 205

of the eyeball, and of the optic nerve, and of the weight of the body as a whole. These curves represent the calculated volumes or weights of the parts in question plotted against the total body-length. The absolute Vol.umes and weights of the various parts under consideration differ so greatly that it is necessary to reduce them to some kind of common scale for comparison. In the present instance this was done by taking the birth Volume or weight of each part as 1 and calculating the Volume or weight of the part at each 5-cm. interval of fetal body-length as a per cent of the birth weight.

Table 21
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TABLE 21

Lineal dimensions of the eyeball and the optic nerve in the fetal period calculated in percentages of their size in the adult

DIAMETERS or I-ZYEBALL on-re NERVE (£2. :23;

A - . D1 .1: .12 MONTHS) LENGTH ("R01 M‘ “I W 0F

FFRENCE Sagittal Transverse Vertical CORN“ Length Diameter

4.11 11.05 13.52 14.29 14.04 17.95 5.90 25.00

8.92 21.44 27.87 28.15 27.66 30.77 18.23 37.50 13.03 30.33 39.34 38.66 37.87 41.88 28.15 46.88 16.69 38.20 46.72 46.64 45.96 51.28 37.00 56.25 20.00 45.38 54.10 54.20 53.19 60.68 45.04‘ 65.63 23.09 51.98 60.66 60.92 59.57 68.38 52.28 71.88 26.00 58.16 66.39 66.81 64.68 76.92 59.25 78.13 Birth 28.69 63.98 72.13 71.85 70.21 83.76 65.42‘ 87.50

¢QG7\lCTJCJV>Jk0D

It will be seen that the curves of eyeball Volume and opticnerve volume parallel very closely those of pons and medulla volume and of spinal-cord volume, although the eyeball curve runs a little above and the nerve-Volume curve a little _below those of the brain parts and spinal cord.

A further illustration of this resemblance between the growth in the fetal period of the eye and the spinal cord and brain stem is afforded by a comparison of the empirical formulae which may be used to express their growth in relation to body-length. The same general formula may be used for all these structures, viz.:

100 V=aLb+c,


Where ‘V’ is the volume of the part in cc., ‘L’ is the total body-length in cm., ‘a’ is a decimal fractional constant, ‘b’ is a power between a square and a cube, and ‘c’ is a third constant. The specific formulae are:


Midbrain volume X 100 = 0.168 L‘'“‘’ + 12.0 Spinal—cord volume X 100 = 0.17 L’-""’ + 11.0 Pons and medulla volume X 100 = 0.2 L’-" + 20.0 Eyeball volume X 100 = 0.23 L’-35 + 12.0 IOO % 90 80 70 60 50 40 30 *-—-— Length of spinal cord ‘T Bagitral diameter of eyeball """"""" "Tran5ver5e diameter of cornea E0 / ——— — Horizontal head circumference “‘—‘ Toral body length —'——"LengIb of optic nerve I0 0



Fig. 15 Curves illustrating the comparative growth in the fetal period of the sagittal diameter of the eyeball, the horizontal diameter of the base of the cornea, the length of the optic nerve, the length of the spinal cord, the horizontal head circumference, and the total body—length. All these structures are reduced to a similar scale by computing their values at each 5-cm. interval of body—length as per cents of the value at 50-cm. body—length. The computations were made with the empirical formulae given in the body of this paper. Abscissae: total bodylength in cm. Ordinates: per cents of values at 50-cm. total body-length.


In these formulae ‘L’ IS always the total body—length in cm. The formulae for the volume of the brain parts given above are those computed by Dunn(13) from material which was obtained in a large measure from the specimens used in the present study.


Fig. 16 Curves illustrating the comparative growth in the fetal period of the length and the diameter of the optic nerve, the sagittal diameter of the eyeball, the horizontal diameter of the base of the cornea, the horizontal head circumference, and the total b0dy—length. The values for each fetal month are calculated as per cents of the value at birth. Age computed from the empirical for mula of Scammon and Calkins(31) for determining fetal age from the total body-length. Abscissae: age in fetal months. Ordinates: per cents of natal values.


The lineal growth of the optic apparatus in the fetal period also shows some interesting similarities. When the diameters of the eyeball are plotted against the total body-length the resulting curves are shallow ones with the concavities directed downward. The length of the spinal cord in the fetal period follows a similar curve when plotted against the bodylength. A comparison of these is shown in figure 15. As in the preceding figure, the curves have been reduced to the same scale by plotting all values as per cents of the size at 50—cm. crown-heel length. figure 16 is a similar graph with the Various Values computed as per cents of the natal size and plotted against the calculated age in fetal or lunar months. Figure 17 is a similar graph with the Various values computed in percentages of their adult size.



Fig. 17 Curves illustrating the comparative growth in the fetal period of the sagittal diameter of the eyeball, the length and the diameter of the optic nerve, the transverse diameter of the base of the cornea, the horizontal head circumference, and the’ total body-length. The value of each dimension at each fetal month is computed as a per cent of the average value at maturity. Abscissae: age in fetal months as determined byvthe Scammon-Calkins formula. Ordinates: per cents of adult values.

The empirical formula for the length of the spinal cord (as developed by Dunn, 13),‘ and the formulae'for the Various diameters of the eyeball are much alike, having the general form: “

D:aL"—c,

where ‘D’ is the dimension in question, taken in mm., ‘L’ is the total or crown—heel body—length in cm., ‘a’ is a constant larger than 1, ‘b’ is a fractional power, and ‘c’ is a third constant. The specific empirical formulae for these dimensions are:

Spinal cord length = 10 L°""—— 4.0 Sagittal diameter of the eyeball X 10 2 21 L°-”— 9.0 Transverse diameter of the eyeball X 10 = 20 L°-"——7.0 Vertical diameter of the eyeball X 10 = 20 L"-'"’——7.0

On the other hand, when the dimensions of the base of the cornea are plotted against the total or crown—heel length, they are found to follow the course of a straight line which may be expressed by the general formula:

D=aL+b,

where ‘D’ is the dimension in question, taken in mm., ‘L’ is the total body—length in cm., ‘a’ is a constant in the form of a decimal fraction, and ‘b’ is a second constant. This type of growth is also characteristic of all the external dimensions of the head, and in fact of the great majority of the external dimensions of the body (Calkins, 5, 6). Thus the cornea, which forms a part of the external surface of the body, grows like the other dimensions of this surface, and not like the remainder of the eyeball. These similarities are shown graphically in figures 15 and 16 and are also illustrated by the following specific empirical formulae:

Horizontal head circumference = 0.675 L + 5.0 Bimalar diameter of the head = 0.1375 L —+- 0.25 Transverse diameter of the corneal base (X 10) = 0.18 L + 0.8 Vertical diameter of the corneal base (X 10) = 0.16 L + 1.0


The length and breadth of the optic nerve also appear as straight lines when plotted against the body-length, but the ‘c’ constant in the empirical formula for the former dimension is a negative instead of a positive one. The straight-line type growth of the optic nerve may be related to the growth of the lineal dimensions of the cerebral hemispheres and the dimensions of the anterior portion of the base of the skull

Table 22
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TABLE 22

Average dimensions of various structures of the eyeball in the newborn and adult (based, for the newborn, on the data of Merkel and Orr, and, for the adult, on the data of Merlcel and Kalltus, Salzmann and Vierordt)

NEWBORN ADULT hm.) (MM ) Thickness of the cornea at the vertex . . . . . . . . . . 0.81 0.8

Thickness of the cornea at the margin . . . . . . . . . 1.03 1.1

Thickness of the sclera anteriorly . . . . . . . . . . . . . . 0.51 0.6

Thickness of the sclcra at the equator . . . . . . . . . 0.41 0.4

Thickness of the sclera posteriorly . . . . . . . . . . . . 0.92 0.9

Thickness of the chorioid anteriorly . . . . . . . . . . . 0.05 0.1~0 15

Thickness of the chorioid posteriorly . . . . . . . . . . . 0.09 0.2

Greatest thickness of the ciliary body . . . . . . . . . . 0.50 1 . 1

Greatest length of the M. ciliaris . . . . . . . . . . . . . . 2.10 3.5

Breadth of the iris . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.30 4 (3—6)

Greatest thickness of the iris . . . . . . . . . . . . . . . . . . 0.17 0.4

Diameter of the papilla of the optic nerve . . . . . . 1.00 1.50 Thickness of the retina near the optic papilla. . . 0.34 0.40 Thickness of the retina near the equator . . . . . . . 0.21 0.30 Thickness of the retina at the ora serrata . . . . . . 0.18 0.20

which also appear as straight lines when plotted against the total body—length.

2. The postnatal growth of the optic apparatus

Those parts of the eyeball concerning which we have quantitative data all seem to follow the same general course of postnatal growth, being characterized by a rapid increase in infancy and early childhood and a much slower increment thereafter. But both the absolute and the relative amount of postnatal increase of these Various parts is quite different. Thus the diameters of the eyeball increase about two-fifths between birth and maturity, while the diameter of the base of the cornea increases but one-fifth and the diameter of the optic nerve but one—seventh. Wliile no special study has been made of the growth of the several coats of the eye, the data given in table 22 allow us


Fig. 18 Curves illustrating the postnatal growth in weight of the eyeball, the brain and its major parts and the spinal cord. To reduce these values to a common scale, the natal weight of each structure was considered as unity and the values in postnatal life were calculated in units of the natal Weight. Abscissae: age in years. Ordinates: units of natal values.

to make some speculations regarding it. According to these figures, the average thickness of the entire wall of the bulbus is approximately 0.92 mm. at birth and about 1.28 mm. in maturity. If, for the purpose of making a rough comparison, we regard the bulbus as a sphere having a diameter equal to its transverse axis, we may estimate the volume of all its coats with the formula:

V: D3 _ (D—t)3


Where ‘V’ is the volume desired, ‘D’ is the external diameter of the eyeball, and ‘t’ is the thickness of its coat. This computation gives values of about 0.178 cc. at birth and about 1.28 cc. at maturity—an increase of approximately five and one-half times in postnatal life as compared with that of one and one—tenth times in the eyeball as a whole. While these calculations are rough ones and of comparative value only, they seem to indicate fairly definitely that the wall of the eyeball undergoes a much greater relative postnatal increase than do the contents.


Fig. 19 Curves illustrating the comparative growth in postnatal life of the weights of the eyeball, the brain, and the body as a whole. The curves represent the per cents of the entire postnatal gain in weight of each organ attained at each year from birth to twenty years.


We have made no determinations of the Weight or volume of the lens in our specimens, for we thought that the effect of fixation upon this structure would render such data unreliable.

The figures of Clapp(7), Collins(8,9), Deutschmann(12), and Smith(37, 38) on the growth of the lens show that this structure weighs about 0.1 gram in the newborn and 0.18 gram in the young adult——a postnatal increase of about fourfifths, or considerably less than that estimated for the wall of the eyeball, and probably distinctly less than that of the remainder of the eyeball contents. However, it should be recalled in this connection that the lens increases in mass to senility, when its weight may be between two and three times that of the newborn.

Almost as soon as any data on the weight and dimensions of the eyeball became available for study, observers noted the resemblance between the postnatal growth of this organ and that of the brain. This similarity was particularly emphasized by Fuchs(15) and Weiss(46), who published comparative curves of the postnatal growth of the eyeball weight, the diameter of the corneal base and the weight of the brain. In all of these structures growth proceeds very rapidly in infancy and early childhood and declines or even ceases in later childhood and adolescence. This type of growth is also characteristic of the other portions of the central nervous system, the neural portion of the skull and the dura, certain parts of the auditory apparatus, and probably of the lachrymal gland and the extrinsic muscles of the eyeball.


These similarities are best shown graphically by plotting the percentages of the total postnatal gain of the various structures at one-year intervals from birth to twenty years, inclusive, against the age in years. The curves of this type of the ponderal growth of the eyeball, the brain, and the body as a whole are shown in figure 19. Similar curves of the dimensional growth of the corneal base, the eyeball, the horizontal head circumference, and the total body-length are included in figure 20. These curves show the essential similarity of the growth of the various neural structures as compared with the growth of the body as a whole.


While the general course of growth of all of the neural structures is much the same, both the absolute and the relative amount of growth of the Various members of the group may be quite different. Thus the brain shows an increase of about 294 per cent in weight between birth and maturity (Scammon and Dunn, 34), while the corresponding increase in the eyeball weight is only about 110 per cent and that in the volume of the optic nerve may be estimated at about 115 per cent. Similarly, the horizontal head circumference is increased about 50 per cent between birth and maturity, the various diameters of the eyeball between 36 and 40 per cent, the transverse diameter of the cornea about 20 per cent, the diameter of the optic nerve about 15 per cent, and the greater diameter of the tympanic membrane, according to the figures of Rodgers(29), about 10 per cent. On the other hand, the contrast between postnatal increases of all these structures and that of the body as a whole is much more marked for the body—weight increases in the neighborhood of 2000 per cent between birth and maturity and the body—length or height increases over 200 per cent. The increases of the various parts of the central nervous system and of the eyeball over their birth—weights are shown in graphic form in figure 18.


Fig. 20 Curves illustrating the postnatal growth of the transverse diameter of the base of the cornea, the sagittal diameter of the eyeball, the horizontal head circumference, and the total body-length. The curves show the per cent of the entire postnatal gain of each dimension attained at each year from birth to twenty years.


Summary

The results of this study may be summarized as follows:

  1. The growth in volume of the eyeball in the fetal period (three lunar months to birth) follows the general course characteristic of the weight or volume of the body as a whole and of all the organs and parts which have been quantitatively studied to the present time. More specifically, the growth is very similar to that of the spinal cord and brain stem.
  2. At birth the volume of the eyeball is about 3.25 cc. and the estimated weight is about 3.40 grams. These values are distinctly above those usually quoted, because the natal values reported by certain investigators are based upon the examination of premature children.
  3. The eyeball a little more than doubles its weight between birth and maturity. Most of this growth is made in the first five years of postnatal life. No definite evidence was found of a puberal increase in eyeball weight in man.
  4. The growth of the diameters of the eyeball in the fetal period is rapid to the sixth fetal month and much slower thereafter. It seems most similar in character to the lineal growth of certain parts of the central nervous system.
  5. The calculated diameters of the eyeball in the full—term newborn child are: sagittal diameter 17.6 mm., transverse diameter 17.1 mm., and vertical diameter 16.5 mm. These values agree fairly closely with those reported by previous observers, excepting those of Weiss, which they exceed considerably.
  6. There is a slow but constant change in the comparative dimensions of the various diameters of the eye in prenatal life, the vertical diameter growing more slowly than the Sagittal or transverse diameters.
  7. Most of the increase in the diameters of the eyeball in postnatal life takes place in infancy and early childhood. The sagittal and transverse diameters increase about 40 per cent between birth and maturity and the vertical diameter about 36 per cent.
  8. During the fetal period the growth of the diameters of the corneal base is proportional to the increase in general body-length. The dimensional growth of the cornea, in this period, resembles that of other external dimensions of the body surface of which it forms a part, and is quite different from the dimensional growth of the eyeball proper.
  9. During the fetal period the transverse diameter of the cornea grows more rapidly than the vertical diameter. Consequently, the outline of the corneal base changes from a circular to an eliptical form during this period. The calculated transverse diameter at birth is 9.8 mm. and the calculated vertical diameter is 9.0 mm.
  10. The increase in the average diameter of the corneal base between birth and maturity is nearly 2 mm., or about 20 per cent. Most of this increase takes place in the first few years of postnatal life. All of our compiled data indicate that the cornea is absolutely as well as relatively larger in later childhood than in maturity, but we think that more carefully controlled observations are necessary before it can be definitely stated that this is a constant phenomenon.
  11. The growth in length and diameter of the optic nerve in the fetal period is directly proportional to the growth in total body—length. The calculated length of the nerve at birth is 24.4 mm., the calculated diameter is 2.7 mm., and the estimated volume (considering the nerve as a regular cylinder) is about 150 cu.mm.
  12. In postnatal life the optic nerve increases about 60 per cent in length, between 13 and 14 per cent in transverse diameter, and, in rough estimate, about 115 per cent in volume. While we have no reliable data on the time of this postnatal growth, it probably takes place mainly in infancy.
  13. The general character of the postnatal growth in mass of the optic apparatus is similar to that of the brain and related structures. The amount of postnatal growth is much less, both absolutely and relatively (with respect to newborn values).
  14. It is estimated that the coats of the eye form the greatest part of the postnatal growth, the contents of the bulbus, including the lens, comes next, and the cornea makes the least postnatal increase.

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