Electroretinography (ERG) is a useful method for the quantitative evaluation of retinal function. In the fields of clinical veterinary medicine and drug safety research, ERG has largely been evaluated according to the international standard protocol used in the human clinical field as recommended by the International Society for Clinical Electrophysiology of Vision (ISCEV) in recent years. In this study, we performed ERG on rabbits treated with sodium iodate (SI), a retinal toxicant, according to the ISCEV protocol using a Ganzfeld dome (Ganz) or a contact lens electrode with a built-in white light-emitting diode (LED), which provides full-field light stimulation. The studies were conducted in two different laboratories and the differences in ERG changes between the two light stimulations were compared. ERG included rod response (RR), combined rod-cone response (COR), oscillatory potentials (OPs), cone response, and 30Hz flicker response (FR). ERG with both Ganz and LED showed an increase or decrease in the amplitudes of the RR and b-wave of the COR at 3 h after dosing. At 8 h after dosing, these amplitudes increased with Ganz but decreased with LED. The latencies of all responses, except OPs, were prolonged or tended to be prolonged with both Ganz and LED from 3 h after dosing. The RR and FR disappeared at 48 h after dosing and the other responses disappeared at 96 h after dosing in the case of both Ganz and LED. Histopathological examination revealed sequential retinal changes from the pigment epithelial layer to the external granular layer in both the laboratories. These results suggest that ERG analyses using both Ganz and LED enable the early detection of the toxic effects of SI on the rabbit retinal function. There were no significant differences in ERG changes between the two light stimulations.

In non-clinical studies for ophthalmic products, three breeds of rabbits have been frequently used; Japanese White (JW), New Zealand White (NZW) and Dutch-belted (DB) rabbits. There is limited information available for the differences of the ocular anatomical features across the breeds and aging currently. In this study, we compared the ocular anatomical features (the sizes of eyeball, lens and vitreous) among these breeds of rabbits at different age levels; the juvenile (6 weeks old), the young-adult (13-22 weeks old) and mature periods (80-96 weeks old).

As a result, all ocular anatomical parameters increased with age in all the three breeds. Comparing the parameters among breeds, the values were comparable between JW and NZW rabbits at each age level, while those in DB rabbits were generally lower than those in the other breeds. The breed-difference in ocular parameters was not caused merely by that in the body weights. As for the aging, the growth rate of the whole eyeball from the juvenile to young-adult period was higher than that from young-adult to matured period without breed-differences. The growth ratios of the lens-weight and -volume were higher than that of the other parameters.

The present study would provide essential information for ocular anatomical features concerning the breeds and ages in rabbits, and would enable us to plan the study and to evaluate the study results accurately by consideration of the eye size in the ophthalmic research using rabbits.

An 11-year-old, female neutered, miniature dachshund presented with a soft, slow-growing, black tumor mass measuring of 10 × 8 mm since 3 months before, on the sclera of the left eye, and full-thickness sclera was excised together with the tumor mass. Subsequently, glycerin-preserved full-thickness homogeneous sclera was implanted into the scleral defect. Critical complications and graft rejection were not observed except for a partial conjunctival suture dehiscence at the surgical site. There was no recurrence of the tumor at 1 year and 7 months after surgery, and vision was maintained. Histopathological diagnosis of the excised tumor mass revealed limbal melanocytoma. Even in an aged dog, it was possible to excise a limbal melanocytoma without affecting vision, by using glycerin-preserved full-thickness homogeneous scleral grafting.

The Mongolian gerbils (Meriones unguiculatus) are one of the experimental animal models which were established in Japan¹⁾. Abnormally larger eyes were found unilaterally, either right or left, in five out of 686 post-weaning Mongolian gerbils, in our breeding colony, which was started from four pairs of MGW inbred albino strain gerbils and maintained for around one year. Ophthalmological and histopathological examinations were conducted on the eyeballs from four out of these five animals. The affected eyeballs were swollen and showed anterior synechia in all four cases. The lens with opacity of one animal moved freely in the intraocular space depending on the direction of animal's head and those of the other three animals were unevenly located near the Ciliary body or posterior position, and these ocular lesions were diagnosed as lens luxation. Histopathological examination revealed imperfect formation of the ciliary body and zonula ciliaris (Zinn's zonule), suggesting lens luxation due to abnormal formation of the zonula ciliaris that plays a role as a supporting system of the lens. However, these ocular lesions were accompanied by phenomena indicating elevated intraocular pressure, such as enlarged eyeball, edematous cornea, thinning of the cornea and retina, atrophy of the optic nerve, and cupping of the optic disk, and glaucoma was suggested. Thus, such abnormal zonula ciliaris (and its consequent lens luxation) might have occurred following glaucoma. It is suggested that genetic background might be involved in these ocular lesions because all four cases were occurred in the colony, although the prevalence was low.