Paper - A description of the histology of the eyes in two anencephalic fœtuses (1910)
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Oakden WM. A description of the histology of the eyes in two anencephalic fœtuses. (1910) J Anat. 44(4): 370–376. PMID 17232857
|vision abnormalities in anencephalic fetuses.
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A Description of the Histology of the Eyes in Two Anencephalic Foetuses
By W. M. Oakden, B.A. (Peterhouse, Cambridge).
(From the Anthropological Laboratory, Cambridge.)
In making the following observations, stained sections of the eyes obtained from two anencephalic foetuses, together with similar sections of the eye of a normal foetus of a corresponding age, were placed at my disposal by Dr Duckworth.
The abnormal fcetuses will be referred to as No. I. and No. III. No. III. appeared to be a full-term foetus of large size, and apparently normal except for the condition of anencephaly which it exhibited. The spinal cord was present in its full extent, and there was no spina bifida. The basis cranii was strongly convex, and some cranial nerve-roots were visible. Lying on the cranium was a mass of red spongy tissue, such as is not infrequently present in cases of anencephaly. Sections were made of this pulp, and on microscopic examination proved to consist partly of practically normal cerebral cortex with pyramidal cells, and partly of a tissue deeply infiltrated with large sinuses containing numerous red blood-corpuscles. This infiltra- tion by large blood spaces is very characteristic of the tissue which in these anencephalic monsters represents the central nervous system.
The foetus No. I., a female, was somewhat smaller than the previous one, and of about the seventh month. As in the previous case, the neck was absent, but in addition the head was retroflexed so that the face was directed upwards (iniencephaly). There was, further, a large exomphalos. The degree of anencephaly was probably higher in No. I. than in No. IIL, as there was less pulp on the base of the cranium of the former.
The different parts of the sections of the three eyes were compared with one another, with the following results. Judging from the sections, the eye of No. III. was distinctly larger than that of either No. I. or the control, which were about the same size.
The Cornea. — Comparatively much thinner (about half the thickness) in the abnormal than in the normal eye. Showed a greater tendency to break up into its component lamine.
The Sclerotic — No marked differences were exhibited. In No. I. this coat was considerably narrower and more broken up into lamine than in the control. On the other hand, in No. III., where the sclerotic was as thick as, if not thicker than, in the control, this tendency was unnoticeable. In No. III. the blood-vessels were very dilated.
The Choroid. — The condition of this coat was apparently the same in No. I. and the control. In No. III. the choroid was in places reduced to quite a narrow band, in other places being of normal thickness. The blood- vessels were much enlarged, and in consequence: there was a practically continuous layer of blood spaces in the substance of the whole choroid.
Fig. 1. — Retina of normal eye. Ganglion cells (A) numerous, nerve-fibre layer deep.
The Iris — In No. III. the iris was narrower, was composed of much denser tissue, and possessed a very much smaller blood-supply than that of either No. I. or the control. The iris of No. I. resembled very closely that of the control in point of width, density of tissue, and size of blood-supply.
Since none of the sections, either anencephalic or otherwise, were equatorial, the iris was continuous across the anterior chamber of the eye. In the sections of No. III. it lay in contact with the posterior surface of the cornea, whereas in No. I. and the control it was freely suspended in the anterior chamber of the eye.
The Lens. — In No. I. and No. III. the lens was more flattened and larger than in the control, in which it was almost circular in section. The lens of No. III. was slightly larger than that of No. I.
In the anencephalic eyes the elongated lens cells were arranged in a somewhat concentric manner; in the control they were, as usual, disposed chiefly antero-posteriorly.
The Retina. — The most marked points of divergence were to be found in the retinal layers. A striking feature of the retine of the normal eye and of No. III. (but not of No. I.) was the presence of one or more papille caused by the invagination into the posterior chamber of all the constituent layers of the retina with the exception of the pigment layer. The elevations were of varying height, being as much as two to two and a-half millimetres in the normal eye, but only about one millimetre in No. ITI. They were as a rule situated near the posterior pole of the eyeball. In the normal eye, there were, besides the one large elevation, several smaller ones.
Fig. 2. — Retina of Anen, I. Ganglion cells (A) few, nerve-fibre layer (B) shallow.
The layers of the retina composing these elevations were generally thickened, the layer of ganglion cells and the inner nuclear layer especially so. The outer nuclear layer and, in the control, the molecular layers were not so much affected; but in No. III. the molecular layers participated in the thickening.
The presence of these elevations has apparently not been explained. Since there was no indication of them in No. I., and since they were present both in No. III. and in the control, they would appear to have no connection with the anencephalic condition. They have been attributed to the action of the hardening agent used.
At first sight the retina of No. I. appeared to be quite normal. It was a perfectly regular band, and no peculiarity was observed in the pigment layer, the layer of rods and cones, or either of the nuclear or molecular layers. The layer of ganglion cells, however, on comparison with the control was found to be poorly represented, the actual number of ganglion cells being much diminished.
Fig. 3. — Eye of Anen, I. in neighbourhood of optic nerve. Almost complete absence of nerve-fibres at the blind spot.
The innermost layer of the retina, that of nerve-fibres, was much narrower than in the control. Whereas in the latter, in the neighbourhood of the blind spot, this layer measured roughly one-third of the total retinal thickness, in the former the number of: nerve-fibres was so small that the ganglion cells lay in close proximity to the vitreous humour. Not only in the peripheral parts of the retina was this layer exceedingly thin, but the normally thick mass of diverging fibres at the blind spot itself was almost entirely absent.
The retina of No. III. was less regular and normal in appearance than that of No. I, whilst the total thickness of the retina varied considerably from place to ‘place.
There was no definite cell structure visible in the layer of rods and cones. In the ganglion cell layer there were even fewer ganglion cells than in the previous specimen, but the layer of nerve-fibres was if anything rather thicker on the whole.
In both the anencephalic specimens the bases of the fibres of Muller were more clearly seen than in the control.
In the sections of the eye of No. I. there was present a short length of the optic nerve measuring roughly 5 mm. This was quite slender and measured less than one-half of the thickness of the optic nerve in control sections. In the sections of No. III. there was no evidence of a portion of the optic nerve attached to the orbit.
Fig. 4. — Eye of Anen. III., showing one of the retinal elevations. A, pigment- layer of retina ; B, large blood-spaces in choroid and sclerotic.
It has been shown by the descriptions of anencephalic foetuses by various observers that the degree of anencephaly or absence of the central nervous system may vary enormously. On the one hand, only a relatively small portion of the brain may be absent, while on the other hand ‘the entire brain may be unrepresented ; and in addition, a considerable portion or the whole of the spinal cord may be deformed or even non-existent. The cause of the varying degrees of this condition is unknown. The question as yet remains unanswered as to whether this condition is to be ascribed to the non-development of the portion of the central nervous system involved, or to the destruction by some agency of the nervous system developed along normal lines up to a certain point.
The retinal element of the eye is described as developing at an early stage of foetal life in the form of a diverticulum, known as the optic vesicle, from the forebrain. The stalk of the vesicle becomes attenuated and eventually forms the optic nerve, while the peripheral portion becomes invaginated so that the enclosed space is obliterated and the retinal cup is thereby formed.
Fig, 5. — Eye of Anen. III., showing large blood-spaces in substance of choroid and sclerotic coats (thick black band, A). 3B, large retinal vessel ; C, pigment layer.
In the eyes of the anencephalic foetuses described the retina does not depart widely from the normal appearance. The most noticeable deficiency is in the optic nerve, the layer of nerve fibres and of ganglion cells, which portions are most nearly related to the brain.
From the high degree of development of the eye one would expect the brain similarly to have attained a late developmental stage. But in the foetuses described it is practically non-existent, so that one is led to imagine that the deficiency is due to destruction after normal development rather than to want of development. This idea is strengthened by the fact that the reddish pulp removed from the cranium of No. III. was found to contain an isolated portion of cerebral cortex with well-marked pyramidal cells, embedded in a mass of loose blood-infiltrated tissue. This infiltration was also noticed in the sclerotic and choroid coats of No. III., and may be indicative of an inflammatory process which had involved the brain and, to a less extent, the eye.
The degenerative change which overcame the brain appears to have extended to the outgrowth from the brain, and involved to some extent the optic nerve, the layer of nerve fibres, and the layer of ganglion cells of the retina.
Cite this page: Hill, M.A. (2020, November 1) Embryology Paper - A description of the histology of the eyes in two anencephalic fœtuses (1910). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_A_description_of_the_histology_of_the_eyes_in_two_anencephalic_f%C5%93tuses_(1910)
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