Paper - Absence of the lens occurring in the human embryo (1922)
|Embryology - 19 Apr 2021 Expand to Translate|
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|vision development with absence of the lens.
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Absence of the lens occurring in the human embryo
By Ida C. Mann, M.B., B.S.
From the Department of Anatomy and Embryology, St Mary’s Hospital.
The subject of this communication is a human embryo (one of Professor Frazer’s collection) which, as far as I know, is unique in that it shows failure of development of both lenses: the optic cups are of normal size and the rest of the embryo shows no evident malformation with the exception of the state of the brain shortly noticed below.
After sectioning, the embryo measured 8-64 mm. It was compared with a normal 13 mm. human embryo (measuring 8-67 mm. after sectioning) with regard to its general development and they were found to have reached the same stage as evidenced by the condition of the submaxillary outgrowth (just appearing in both) and the situation of the posterior nares. The embryo was not in good histological condition and the sections were considerably fissured. The thin walls of the intracranial portion of the central nervous system were much folded, as might be expected in an embryo not in perfect condition, but in addition to this—without going into details—there is, I think, clear evidence of some dilatation of the cavities. The cerebral vesicles are clearly recognisable in their normal hinder portions, but do not appear to have grown in front so that they cannot be definitely marked off from the telencephalon. In spite of these peculiarities the general structure of the substance of the brain appears to be that normal for the stage.
The condition of the eye is the same on both sides. The optic cups occupy their normai position on the side of the head. Their invagination and differentiation have proceeded normally, but the choroidal fissure, which does not extend quite into the optic stalk, has not yet closed, whereas in the normal 13 mm. embryo it has closed except for a notch at the pupillary margin. The hyaloid vessel is present and is well developed and full of blood. It breaks up into numerous blood spaces in the pupil and these drain into scattered channels in the surrounding mesoderm and into a vessel larger than normal running in the line of the cleft outside the optic cup. There is no lens whatever, and the only suggestion of it is the presence of a small blunt-pointed epithelial projection from the deep layer of the surface ectoderm almost opposite the centre of the pupil. This may represent an abortive lens thickening which has failed to differentiate.
The case is interesting both on account of the confirmatory evidence it _ Offers on the subject of independent differentiation of the optic cup (shown experimentally by Lewis, Spemann and others) and also as throwing some light on the clinical controversy as to the possibility of the occurrence of congenital aphakia in an otherwise normal eye. Rabl has described an Amblyostoma embryo which showed unilateral failure of development of the lens, but there was also extensive failure of other ectodermal structures. A few cases in man have been reported clinically, but were not verified by microscopical examination and were generally associated with microphthalmos.
Apams (1915). ‘‘Congenital aphakia with microcornea.” Ophth. Rec. Chicago, vol. xxIv. p. 581.
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Cite this page: Hill, M.A. (2021, April 19) Embryology Paper - Absence of the lens occurring in the human embryo (1922). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Absence_of_the_lens_occurring_in_the_human_embryo_(1922)
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