Unilateral colobomata nervus opticus was observed in two 6-week-old Slc: Wistar rats. A fixed pupil was found in one rat, and aplasia of the optic disk and the central retinal arteries and veins was detected in both animals. At necropsy, the left optic nerve was completely absent from the posterior pole of the eye to the optic chiasma, and the right optic tract was barely visible in both rats. The eyes appeared normal in size.

Histologically aplasia of the optic disk, retinal atrophy, rosette formation of the retina, and hypoplasia of the ciliary body were observed in both cases.

One of the rats had subretinal hemorrhage and nodular hyperplasia of connective tissues in the choroid. The inner layer of the retina was markedly atrophied, resulting in a definite decrease in the ratio of brain layer to whole layer of the retina.

Although the right optic tract was markedly reduced in volume, there were neither degenerative changes nor inflammatory reaction in the tract. The two cases were histopathologically diagnosed as congenital unilateral aplasia of the optic nerve, accompanied by hypoplasia of the retina.

An aged male rat of the Kyo: Wistar strain showed an intraocular tumor in the left globe. The neoplastic lesion consisted mostly of spindle to polygonal-shaped cells packed closely. The neoplastic cells had oval nuclei and acidophilic cytoplasm, and little atypia. The choroid was increased in thickness by neoplastic proliferation, and the neoplastic tissue extended partly beyond the sclera. The neoplastic cells were strongly positive to the S-100 protein test. Electromicroscopically, the neoplastic cells were almost unconnected to each other and stretched long processes into the intercellular space. The cytoplasm contained many organellae and dense spherical structures which were similar to melanosomes. From these findings, this tumor was diagnosed as malignant melanoma of the choroid.

A simple method for judging visual function in the cynomolgus monkey was designed. The principle of this method is to examine whether a monkey watches the eyes of two observers who wear a face hood with a sheet of neutral density filter paper attached. Thirty-four normal monkeys and eight monkeys with macula degeneration were examined by this method. The monkeys with macula degeneration were inferior in their visual function to the monkeys with normal fundus. In addition, the degree of visual function judged by this method was in accord with the degree of macula degeneration observed ophthalmoscopically.

Zinc pyridinethione (ZPT) was orally administered to laboratory animals (a cynomolgus monkey, beagles, a cat, pigmented and albino guinea pigs, and Mongolian gerbils). The time course of ZPT retinopathy was observed by opthalmological procedures.

Animals without the tapetum lucidum (the cynomolgus monkey, pigmented and albino guinea pigs, and Mongolian gerbils) failed to develop ZPT retinopathy. Administrations of 15mg/kg body weight ZPT 3 days a week for 5 consective weeks to the cat induced discoloration of the tapetum lucidum and decrease in amplitude of “a” and “b” waves in the electroretinogram (ERG). In dogs three dose levels of ZPT, 2.5, 5, and 10mg/kg were selected by reference to the results of previous studies. They showed bilateral ophthalmological abnormalities at all doses.

At 10mg/kg of ZPT, only mild changes in the fundus were observed in 24-month-old dogs, which were less sensitive to ZPT than younger dogs.

The changes recognized in these dogs included discoloration of the tapetum lucidum and a slight decrease in amplitude of “a” and “b” waves in the ERG. No histopathological changes were observed in the tapetum lucidum.

Twelve-month-old dogs treated with 5mg/kg ZPT 5 days a week showed subretinal edema and retinal hemorrhage in the fundus and decrease in amplitude of “a” and “b” waves in the ERG.

At increasing dosage from 2.5mg/kg to 5mg/kg of ZPT, lateral geniculate body nucleus (LGN) evoked potentials and visual evoked potentials (VEP) were recorded in animals in which stainless steel electrodes had been implanted in the LGN and the skull. Dosage of ZPT increased from 2.5mg/kg to 5mg/kg induced decrease in amplitude of the ERG, followed by abnormalities of LGN evoked potentials and VEP.

Ophthalmological observation disclosed discoloration of the tapetum lucidum. Histopathological observation revealed thinning of the tapetum lucidum, and electron microscopic observation showed enlargement of the rough endoplasmic reticulum of the tapetal rods in one of the severely affected dogs.

The ocular fundi of three thousand and eight hundred colony-born and wild-caught cynomolgus monkeys (Macaca fascicularis) were examined with an ophthalmoscope. Lipemia retinalis was found in six monkeys that had been kept for 2 to 15 years after importation, at the time of which they were estimated to be five or more years old. There was a marked change in color of the retinal vessels which appeared as if they contained a milky white or orange yellow-hued substance. Both the arteries and veins were uniform in appearance and difficult to distinguish from each other by the color alone.