The blood-retinal barrier (BRB) is composed of an inner and an outer BRB. The former is located in the endothelial cells of the retinal vessels and the latter in the pigmented epithelial cells of the retina. Morphological evidence from electron micrographs shows the existence of tight junctions (Zonula occludence) between these cells. Clinical methods for evaluation of the function of these barriers are, at present, three: 1) fluorescein angiography (quolitative), 2) vitreous fluorophotometry (quantitative), and 3) fluorescein electroretinography (quantitative). The effect of calcium inhibitor on the barrier function in diabetic retinopathy was evaluated by these methods.

Protein aggregation, impairment of electrolyte transport systems, protein oxidation, and so on, are known as biochemical changes in the human lens accompanying with the development of senile cataract. The report presented here demonstrates that calcium-induced lens protein aggregation is remarkably accelerated by oxidation (or photo-oxidation), and that electrolyte transport systems of cell membrane in the lens are easily damaged by oxidation. From the above results, a possible mechanism of senile cataract formation is proposed as follows; damage to lens cell membrane and denaturation of lens protein proceed during the cataract development by oxidative stress, and aggregation of denatured lens protein, leading to lens opacity, is induced by calcium ions increasing in the lens with the membrane damage.

Using 42 beagles (7 to 10 years old), ophthalmoscopic examinations were carried out in both anterior segment of eye and ocular fundus. The low light transparence was observed in all beagles in the present test. The low transparence is thought to becaused by the facilitation of reflectivity in the lens, since progressing lens nuclea sclerosis with aging was observed and no findings suggesting cataract were noted in the pathological examination.

In ophthalmoscopic and histopathological examinations we observed light tree-like cloudiness in the posterior surface of the lens, a decline in lens epithelial cell density, a marked formation of cysts surrounding the ora serrata in the retina, and hypertrophy of the basement membrane in the retinal capillary.

Since January of 1978, a survey of ocular fundus abnormality has been carried out on pound-derived dogs at a national medical school. Over 3600 animals were checked in the period of 79 months. Almost all dogs were younger than 4, 5 years of age. The ocular examination of these animals was performed in a clean, air-conditioned research facility for laboratory animal science where the dogs were reared on commercial diet. In this period, over 29 breeds were recorded. After premedication with a mydriatric agent (Mydrin P^R, Santen Pharmaceutical Co. Ltd.), the ocular fundi were recorded with a portable ophthalmoscopic camera (Kowa RC-2, Kowa Co. Ltd.). The incidence rate of retinal haemorrhage, retinal detachment, retinal atrophy, and atapetal retina was less than 1.3 percent. Chorioretinitis and retinitis were observed especially in Japanese native breeds such as the Akita.

The eye is one of the organ to be evaluated in toxicity studies. Eye examinations, however, have not been standarized and are totally dependent upon each institute in Japan. In this paper we describe how the eye is assessed in our laboratories for the effects of various test compounds administered in routine toxicity studies using rats and dogs, and we hope that this will stimulate discussion among workers in this field.

The anterior segment of the eye is examined using a slit lamp binocular microscope and an indirect ophthalmoscope without an aspheric lens. We feel it more practical to make the axis of the slit lamp free, so that the light beam may be directed to the subjects with less difficulity, even into the lens of rats, though their eyes are small for slit lamp examinations. In dogs, corneal opacity, lenticular abnormalities and their location may be detected in most cases, although roughly, with an indirect ophthalmoscope.

For the fundus, indirect ophthalmoscopy is employed. Care must be taken when albino rats are subjected to the eye examinations since the diagnosis of light-induced retinopathy may indicate the limits of its use. These examinations are conducted by two or more investigators discussing the findings at which they are looking. Final diagnosis is then made on the basis of results from ophthalmological examinations together with those from histopathological examinations.