In Pigs. 26, 27, 28 we observe a narrow white ring which intervenes between the margin of the optic disc and the vascular part of the choroid, and which is well defined next the optic disc, but shades off into the vascular part of the choroid. It is often observed in glaucoma.
The optic disc in Pig. 28 appears hyperæmic.
Changes peculiar to increased tension of the eyeball were observed especially in the smaller veins of the retina; these appeared thinner in the optic disc, and where they passed over the white rim, than in the retina.
Fig. 27.
Fig. 27 represents the change in colour of the optic disc, and the disturbance in the circulation of the blood in the blood-vessels of the retina, where they pass through the disc, as the result of sudden and greatly increased tension of the eyeball.
The optic disc appears anæmic (pinkish-white) in the centre, the rest of it bluish-white and opaque. The red rim surrounding the disc represents the vascular choroid, upon which we see the veins of the retina gorged with blood; upon the white rim and in the optic disc itself are the retinal vessels more or less empty, and scarcely traceable.
The optic disc (after iridectomy), in Pig. 26, has a more uniform pinkish-grey and opaque colour. A striking change has occurred in the retinal blood-vessels, which pass through the disc, compared with those represented in Pig. 27. The numerous full veins of the retina are seen passing uninterruptedly from the retina into the optic disc.
The retinal arteries, though more numerous, appear nearly as thin as they did before the iridectomy. The white rim round the optic disc appears hardly altered.
Fig. 29.
Left eye. The optic disc and the immediately adjoining retina, choroid, and sclerotic, from a person suffering from glaucoma in both eyes. The optic disc represented in the middle of the figure appears well-defined, and has a greyish-blue colour most marked in the left half of the disc (the one nearest the yellow spot).
