Objective: Trypsin digestion and scanning electron microscopy techniques were utilized in conjunction with computerized image analysis to examine the surface of the scleral lamina cribrosa in normal and glaucomatous horse eyes.

Sample Population: Six normal horse eyes were compared to eight glaucomatous equine eyes.

Procedure: The trypsin digestion procedure enzymatically removed all neural, vascular and glial components of the optic nerve leaving only the connective tissue framework of the scleral lamina cribrosa. Measurements of the vitreal surface of the scleral lamina cribrosa were made of individual laminar pore areas, total laminar pore number, and individual pore form factor for each eye.

Results: Statistical results demonstrated that the glaucomatous equine lamina cribrosa had a significantly higher mean total pore count (glaucoma: 959±218 pores vs. normal: 560±258 pores; p=.01), a larger mean sectional pore density (glaucoma: 70±20 pores/mm2 vs. normal: 43±25 pores/mm²; p=.04), smaller individual mean median pore areas (glaucoma: 1,952±544μm² vs. normal: 5,282±2,089μm²; p=.0005), and a more circular, or less flattened, pore shape (p=.004), especially near the center, when compared to laminar pores of the normal equine lamina cribrosa. The intralaminar optic nerves of glaucomatous horses contain a higher percentage of connective tissue (74.2%) than the optic nerves of normal horses (67.4%).

Conclusions: The intralaminar optic nerve of glaucomatous horses contains a significantly larger total number of laminar pores, pores of significantly smaller individual area, and pores of rounder shape than the intralaminar optic nerve of normal horses. These differences may represent an anatomic variation found in horses predisposed to develop glaucoma, as well as changes resulting from intraocular pressure-induced radial stress forces causing stretching of the scleral lamina cribrosa.

Clinical Relevance: Morphologic information is provided that may partially explain the ability of the horse eye to retain vision in spite of sustained elevated intraocular pressure.

This study documents the presence of metallothionein (MT) in retinal tissues of pigs. To evaluate any effects of dietary zinc level and light stress on retinal MT, pigs were fed low normal or high levels of zinc, and eighteen animals were exposed to high intensity intermittent or continuous light stress. Four animals served as unexposed controls. Effects of dietary zinc level and/or light stress on metallothionein levels in kidney, liver and retina were evaluated. The neural retinas were separated from the retinal pigment epithelium/choroid of both eyes from each animal immediately after sacrifice. A cadmium binding assay was used to quantitate metallothionein in kidney, liver, and retinal tissues. The assay was successfully applied to the neural retinal tissues. There was no significant effect of diet or light on neural retinal metallothionein levels. The mean neural retinal metallothionein in young pigs is 40±20ng/mg protein (n=22). The 95% confidence interval was 35-52ng/mg protein. Ocular metallothionein was not significantly correlated with kidney or liver metallothionein nor with the degree of light-induced retinal damage.

The neural retina of the pig possesses much less MT than has been found in human retinal pigment epithelium (RPE) cell cultures. This may represent a species-specific difference but is probably due to the common finding of abundant metallothionein in epithelial tissues like the RPE. This study documents the presence of metallothionein in neural retina which suggests that this ubiquitous protein may also participate in zinc metabolism in the inner retinal layers.

To determine the biochemical features of late onset hereditary cataracts in UPL rats, Raman spectroscopic analysis was applied on the investigation of the lens of the rats at the age of 6 weeks. There were no significant changes in I₇₆₀/I₈₈₀ (Tryptophan) and I₈₃₂/I₈₅₅ (Tyrosine). I₆₂₄/I₆₄₄ (Phenylalanine/Tyrosine) obtained from L-type rat lenses indicated that the lens nucleus was shifted anteriorly in the lens. Shifts of the Raman bands derived from amide III (1239cm^-1) and I (1669cm^-1) were not observed. These results suggested that aggregation and/or conformationchanges in lens protein were not present before and at this period.

In order to establish a new method of electrophysiological visual function test in toxicity studies in beagles, we examined the pattern reversal electroretinogram (P-ERG).

P-ERG (transient and steady-state) were recorded on 5 to 11 male beagles (about 10 months of age, body weight 10 to 12kg) sedated by subcutaneous administration of the mixture of xyladine and atropine sulfate, and after complete mydriasis by a drop of mydriatica. The tests were conducted twice at an interval of 1 week through 1 month for assessment of its reproducibility. Both of transient P-ERG and steady-state P-ERG of the beagles were very similar to the corresponding P-ERGs in human respectively. One positive wave was recorded between 36 and 39 msec and another negative wave was recorded between 89 and 105 msec with good reproducibility in the transient P-ERG of the beagles. The amplitude of the transient P-ERG of the beagles was affected by checker size and size of 18 cm gave the highest amplitude. Three peaks (32 through 40, 236 through 242 and 440 through 450 msec) were recorded for 500 msec in the steady-state P-ERG of the beagles.

These findings suggest that the P-ERG can be used in electrophysiological visual function tests in toxicity studies in beagles, because P-ERG were recorded with good reproducibility in beagles, as in human.

The recent widespread applications of fluorescein fundus angiography using indocyanine green as a contrast medium in the clinical field in humans are very much contributing to a number of active investigations conducted on various choroidal diseases such as age-related disciform macular degeneration, central serous chorioretinopathy and angioid streaks of retina. In this study, a novel case of indocyanine green angiographic application to cynomolgus monkeys is illustrated. Indocyanine green was first observed in choroidal vessels after 5.4±0.3 sec. of the intravenous administration of indocyanine green, and then in retinal arteries and veins. Immediately after the administration, a high level of insertion light caused overexposure, making the images of vessels obscure; therefore, the observations accompanied by the careful adjustment of the level of insertion light were needed. As fluorescence intensity in the vessels was getting to decline with the passage of time, the observations were conducted with an increasing level of insertion light aiming at obtaining the optimal images. The additional different angles of view for angiography were introduced, as demanded, to the analysis for the wide-ranging examinations on morphology and distribution patterns of individual vessels. After 9±1 min. of the administration, indocyanine green could no longer be observed in either retinal or choroidal vessel, but diffuse fluorescence throughout choroid.

The progressive degeneration was found at the macular area of both eyes in a colony-born 128 months old female cynomolgus monkey by using indocyanine green video-angiography (ICG) and the fluorescence angiography (FAG). By the fundascopic examination, slight abnormal changes were found in the macular area at the age of 30 months and they progressively got worse. At the age of 128 months, the legion was expanded into an ellipsoidal shape centering at the fovea centrialis with the horizontal span of approximately four times of the diameter of the optic disc and the longitudinal span of approximately two times of the diameter of the optic disc. Hyperfluorescent parts of micro-granular shape corresponding to the degenerated lesion were demonstrated by FAG. The findings obtained by the later stage of ICG suggested the choroidal neovascularization occurred in the lesion.