PURPOSE: To evaluate visual function in rats with chronic elevation of intraocular pressure (IOP). METHODS: Chronic ocular hypertension was induced in the left eye of 14 adult Brown Norway rats by cauterizing 3 vortex veins and 2 major episcleral veins; the right eye served as a non-operated control. A control group (n=5) was sham operated on the left eye. Prior to surgery, the IOP was measured with a Tonopen, the pupil light reflex (PLR) evaluated with a custom-made computerized pupillometer and electroretinograms (ERGs) were recorded simultaneously from both eyes post surgically: IOP was measured on weeks 1, 3, 5 and 8 post-operatively, pupil light reflexes on weeks 1, 4 and 8 post-operatively, and ERGs on weeks 4 and 8 post-operatively. Sixty five days postoperatively, rats were euthanized and optic nerves and eye globes were prepared for histological analysis. RESULTS: Seven days after surgery 5/14 rats developed significant elevation of the IOP in operated eyes (control eyes: 25.1+/-0.5mmHg; operated eyes: 34.1+/-0.6mmHg; mean+/-SEM; p=0.0004; Paired t-test). Elevation of the IOP was sustained at 3 (p=0.002) and 5 (p=0.007) weeks postoperatively. However, IOP values did not significantly differ between control and operated eyes 8 weeks postoperatively (p=0.192, Paired t-test). Sham operated animals showed no elevation of the IOP 7 days postoperatively. When the ratio between consensual and direct PLR (PLR(ratio)=consensual/direct PLR; pupil of unoperated eye recorded) was examined in rats which developed elevation of the IOP, preoperative values were 92.2+/-4% (mean+/-SEM), 1 week postoperatively 65+/-4% (significantly different from preoperative values, p0.05, n=5). Rats whose IOP values did not rise after surgery and sham operated rats did not develop pupil deficits 4 weeks postoperatively. Rats with elevated IOP displayed a significant decrease in ERG amplitudes in operated eyes at 4 weeks (a-wave(operated)/a-wave(control) (a-wave ratio)=42+/-14% (mean+/-SEM); b-wave(operated)/b-wave(control) (b-wave ratio)=43+/-16%) but not at 8 weeks postoperatively (a-wave ratio=88+/-8.4%; b-wave ratio=82.9+/-9%). Sham operated and rats whose IOP values remained non-elevated after surgery did not develop ERG deficits 4 weeks after surgery. Histological analysis did not reveal any damage in the eyes of animals with elevated intraocular ocular pressure with the exception of one rat, which still had ERG and pupil deficits at the end of experiment. CONCLUSIONS: Development of ERG and PLR deficits are proportional to the elevation of the IOP in the rat model of chronic ocular hypertension. Functional monitoring of the ERG and PLR are useful objective techniques for the detection of retina and optic nerve deficits.
CASE DESCRIPTION: A 7-year-old Siberian Husky-type dog with heterochromia irides was evaluated because of signs of pain associated with the right eye. CLINICAL FINDINGS: Unilateral panuveitis, iris bombé, and secondary glaucoma were detected in the right eye. Tear production was low bilaterally. Facial and truncal poliosis and vitiligo were also evident; skin biopsy specimens were obtained from the nasal planum. Uveodermatologic syndrome was diagnosed on the basis of histopathologic findings of a lichenoid interface dermatitis and pigmentary incontinence within the dermis. Immunohistochemical analysis was performed on skin samples retrospectively, and findings were inconclusive. TREATMENT AND OUTCOME: Treatment involved topical (ocular) and oral administration of corticosteroids, oral administration of azathioprine, and topical (ocular) administration of a carbonic anhydrase inhibitor and a lacrimostimulant. The secondary glaucoma was refractory to treatment, and the right eye was enucleated. Uveodermatologic syndrome was confirmed via histologic examination of ocular tissues. The left eye remained free of inflammation 16 months after the initial diagnosis. The periocular skin and skin of the nose partially regained pigment, but the hair did not. CLINICAL RELEVANCE: Some breeds in which uveodermatologic syndrome has been reported (eg, Siberian Huskies, Old English Sheepdogs, Australian Shepherds, and Shetland Sheepdogs) often have heterochromia irides. This case highlights the fact that dogs with asymmetric uveal pigmentation may have unilateral ocular changes; therefore, uveodermatologic syndrome should not be excluded as a differential diagnosis on the basis of unilateral clinical signs.