1) The previous results obtained from ophthalmoscopic studies on the ocular fundus of fish were reviewed.

2) The results of histopathological investigations of carp, in which fundi were diagnosed to be in various pathological conditions by ophthalmoscopic observations, were reported. From the results of these investigations, it was inferred that fundus abnormalities in carp such as dilatation and tortuosity of vitreal vessels and retinal pigment degeneration might be caused by renal insufficiency.

3) Funduscopic photography of specimens of bigeye (Priacanthus macracanthus) which have a very high falciform process, and of specimens of red sea bream (Pagrus major) which have a low falciform process, were shown.

As an animal model of drug-induced retinopathy, beagle dogs were orally treated with zinc pyridinethione (ZPT) and subjected to time-lapse ophthalmological, electrophysiological, and histopathological examinations.

Administration of 40mg/kg ZPT 3 days a week for 1 to 3 weeks resulted in typical ocular disorders: abnormal pupillary response to light, edema and hemorrhage in the fundus (tapetum lucidum), and retinal detachment. Histopathological observation revealed degeneration of the tapetum lucidum and pigment epithelium, and intense neutrophil infiltration. Three weeks after the last dosing, the pigment epithelium and tapetum lucidum disappeard, the retina atrophied and the optic fibers degenerated.

Administrition of 20mg/kg ZPT 3 to 5 days a week for 2 months produced decrease in amplitude of ERG and VEP waves and decrease in ocular tension from the 2nd dosing week on. Reflection of light from the tapetum lucidum also became weaker with the progress of successive administration. Histologically, mild disarrangement of laminal structure in the tapetum lucidum was the only detectable morphological change in these mildly involved dogs. In a follow-up study, the dogs recovered in a week after drug withdrawal from the slight functional disorder induced by ZPT.

We have been conducting ophthalmic examinations in rats and accumulating back ground data during the past 6 years. Approximately 1000 SD rats have been examined with a fundus camera or binocular indirect ophthalmoscope. Slight tortuosity of retinal vessels, prominant choroidal vessels and persistent hyaloid remnant were not uncommon findings in our laboratory control animals. Preretinal arteriolar loop, focal sacculation of retinal arterioles, preretinal hemorrhage, focal retinal atrophy, retinal detachment, and coloboma were also observed.

Ocular toxicity can result from topical or systemic administration of various chemicals and is evaluated histologically on a routine basis in safety assessment studies. As a result of its peculiar architecture, the eye is one of the more difficult tissues to process and artifacts are difficult to avoid with formalin-fixed specimens. We have adopted a procedure which was presented at a meeting of the Japan Association of Histotechnology which provides superior fixation and has significantly increased the quality of our routine eye sections from rodent and non-rodent species. This presentation will review our technique and variations resulting from different fixatives on hematoxylin and eosin stained eye specimens of rats.

This study was made to establish the methods of measurement, recording and evaluation of the a, b wave and oscillatory potentials of electroretinogram (ERG) in rabbits and other experimental animals.

The appropriate selections of electrodes, photostimulators, amplifiers and fixation of animals to record the ERG were discussed. The amplitude versus stimulus intensity curve was used to decide the condition of the photostimulation intervals and intensity. To obtain reproducible data, the following statistical methods were introduced: experimental design, nonlinear least square method, transformations of data, analysis of variance test, coefficient of variation (C. V.), and signal-to-noise ratio (S/N), etc. Moreover, we emphasized that it was necessary to study the isolated ERG and neurotransmitters for further understanding of the retinal functions.

A screw electrode was implanted on the intracranial dura mater of guinea pigs, and after dark adaptation, 50 photic stimuli at the interval of 10 sec were given with a xenon lamp intensity of 2.0 joule, and the ERG and VEP were recorded. The ERG showed no change after 3 months and 24 applications of ethylacetate in the control group, but in the TDI-treated group α and β waves showed prolonged latency and decreases in amplitude. The VEP showed no remarkable change in the control group, but in the TDI-treated animals some changes were seen in P1-N1 amplitude. These changes suggested that repeated exposure to TDI causes a decline in the retinal function.

The ocular fundi of 18 eyeballs from 9 domestic goats ranging in age from one day to 15 weeks were studied. Six of the animals were reared with their mothers until they were weaned naturally. The other three babies were separated from their mothers just after birth and fed milk replacer for calves until 3 days of age, and then they were reared with their mothers until they were weaned naturally. The results were as follows: The colors of the tapetum lucidum, optic disc, tapetum nigrum and retinal blood vessels were constant on and after birth in kids fed colostrum. However, the color of the tapetum lucidum of babies which did not receive colostrum was more yellowish than that of babies fed colostrum until 72 hours after birth. Retinal hemorrhages were observed in about 75 percent of the examined eyeballs of babies fed colostrum, but not observed in babies not receiving colostrum. The persistent hyaloid artery was observed in all of the examined eyeballs thoughout the investigation.