SECTION VII 

 HISTOLOGY OF THE RETINA 



THE retina is a delicate membrane lying inside the choroid coat of the eye. 

 Its internal surface lies in contact with the hyaloid membrane of the vitreous 

 body. It is thus supported on both sides. The retina itself consists of 

 two layers, the outer or pigmented, and the inner or nervous. Whereas 

 embryologically the retina covers the whole internal surface of the eye includ- 

 ing the ciliary processes and the iris, this is not the case with the nervous 

 layer, because this stops near the equator of the eye at the ora serrata, and 

 is here replaced by a layer of columnar epithelium. Opposite the pupil a 

 yellow spot is seen on the retina, the macula lutea, and in the centre of 

 this there is an oval depression, the fovea centralis. The optic nerve enters 

 the eyeball through an aperture in the sclera and choroid, and then passes 

 through the posterior surface of the retina to spread out over the internal 

 surface. In the fovea however this is not the case, for the depression at 

 this point is caused by the absence of nerve fibres. The point at which 

 the optic nerve enters the eye is easily recognised from inside the eyeball 

 because the numerous white nerve fibres, as they bend over the edge of the 

 aperture in the retina, form a characteristic white mound called the colliculus, 

 at the centre of which is a depressed portion called the optic cup. It is in 

 the centre of this cup that the central artery of the retina and the corre- 

 sponding vein first make their appearance. These have the important func- 

 tion of nourishing the retina ; the additional blood supply through the inti- 

 mate contact between the retina and the vascular choroid, although important, 

 is quite insufficient to supply the needs of vision, as is shown by the immediate 

 and permanent blindness which follows blocking of the central artery of the 

 retina. 



When sections of the retina are examined under the microscope it is found that 

 they consist of the following layers from within outwards: 



1. Layer of nerve fibres and vessels 



2. Layer of ganglion nerve cells 



:?. Inner molecular or plexiform layer 



4. Inner nuclear or granular layer I ****** fr "' ****** !** 



tatei molecular or pferfotm layer " f P tlC ve8K>K 



<>. Outer nuclear or granular layer 

 7. Layer ut' rods and enm-s (kaeillary layer) 

 s. Layer if pigmented epithelium .. .. |),.-\el.iped from posterior layer. 



5-10 



