EYE. 



189 



Regise Gottingenses, gives the following 

 account of the discovery. " On the 27th of 

 January, 1791, while I examined the eyes of a 

 very fine and healthy young man, a few hours 

 previously drowned in the Rhine, being per- 

 fectly fresh, transparent, and full, and sup- 

 ported in an appropriate fluid, with the in- 

 tention of exhibiting a perfect specimen of the 

 retina to my pupils in the anatomical theatre, 

 I so clearly detected in the posterior part of 

 the retina, which was expanded without a 

 single fold, on account of the perfect state 

 of the eye, a round yellow spot, that I 

 was convinced it was a natural appearance, 

 and not a colour produced by any method of 

 preparation. In examining this spot more 

 accurately, I perceived in its centre a little 

 hole occupying the situation of the true centre 

 of the retina. With the same care I examined 

 the other eye and found it exactly similar. 

 I then communicated the discovery to my 

 pupils in the public demonstrations." " In this 

 precise spot, or in the very centre of the re- 

 titin, is found an actual deficiency of the me- 

 dullary layer, or a real hole perfectly round, 

 with a defined margin a fourth of a line in 

 diameter." " The transparent vitreous humour 

 and black pigment are so clearly seen through 



this hole, that there can be no doubt that 

 it is a real aperture, which briin; situated 

 in the centre of the retina may be appro- 

 priately termed the t'uramcn ccntmlr. Sur- 

 rounding this foramen centrale the remark- 

 able yellow colour resembling that of gum 

 gutt<r is so disposed that it appears much 

 deeper toward the margin, and totally dis- 

 appears at a distance of a line. This 

 colour varies much according to the age of 

 the individual, being very faint in infants, 

 much deeper at puberty, on account of the 

 thickness and whiteness of the retina at 

 that period, appearing of a deep yellow 

 brownish or crocus colour. In more ad- 

 vanced age the colour is less intense, prin- 

 cipally on account of the diminished 

 whiteness of the retina, which also appears 

 extenuated at that period. Even the 

 choroid, where it corresponds to this fora- 

 men, sometimes appears a little deeper- 

 coloured." 



In the paper above alluded to, published 

 in the Medico-Chirurgical Transactions, I 

 have given the result of some careful in- 

 quiries into the structure of this part, from 

 which the following observations are ex- 

 tracted. " Sommerring describes it as a 

 hole in the retina with a yellow margin, 

 mentioning as accidental a fold which 

 occupies the situation of this hole and 

 tends to conceal it, and thus accounting 

 for its remaining so long unnoticed. This 

 appearance is so constant and remarkable, 

 that its existence may be very rationally 

 considered essential to correct vision, and 

 it therefore becomes an interesting object 

 of speculation. The circumstances which 

 it seems important to ascertain, are, whe- 

 ther it is actually a hole in the retina with 

 a yellow margin ; whether, in addition 

 to this hole, the retina is folded or puckered in at 

 this part ; or whether the appearance of a hole 

 arises from a deficiency of the medullary layer of 

 the retina without any orifice in its vascular layer. 

 Both Sommerring himself and many others seem 

 to consider that the fold is accidental and the 

 consequences of changes occurring after death. 

 It is here necessary to call to mind what those 

 changes are with respect to the retina. If the 

 eye had become flaccid previous to dissection, 

 the retina on being exposed presents an irre- 

 gular surface, arising from a number of folds 

 diverging from the optic nerve as from a centre, 

 and evidently produced by the loss of support 

 from the partial evaporation of the fluid of the 

 vitreous humour. These folds, however, never 

 observe any regular form, or preserve precise 

 situations, and may be obliterated by changing 

 the position of the eye in the water. They 

 disappear altogether after the part has remained 

 some time in water, in consequence of the 

 vitreous humour becoming again distended 

 from imbibing the fluid in which it is im- 

 mersed. It however requires no very great 

 care or experience to distinguish between those 

 accidental folds and the peculiar one in ques- 

 tion. If the examination be made from with- 

 out, removing the sclerotic and choroid behind, 



