In normal dogs, Bimatoprost SR was associated with a transient increase in EVP followed by a sustained decrease. Changes in EVP were accompanied by a sustained dilation of aqueous outflow vessels.

Objective  Gonioscopy provides limited quantitative information to compare the iridocorneal anatomy across different species. In addition, the anatomic relationships by histologic examination are altered during processing. As a result, the comparative anatomy of the iridocorneal angle across several mammalian species was evaluated by Optical Coherence Tomography (OCT). Methods  Cats, beagle dogs, minipigs, owl monkeys, cynomolgus monkeys, and rhesus monkeys (n = 6 or 7 per species) were evaluated. Imaging was performed using the OCT. The anterior chamber angle (ACA), angle opening distance (AOD), and the angle recess area (ARA) were evaluated. Results  AC angle: cat (63 ± 6°) > owl monkey (54 ± 4°) > beagle dog (42 ± 4°) > minipig (40 ± 3°) > rhesus monkey (36 ± 1°) > cynomolgus monkey (34 ± 2°). AOD: cat (3.3 ± 0.5 mm) > owl monkey (2.05 ± 0.2 mm) > beagle dog (1.08 ± 0.1 mm) > rhesus monkey (0.92 ± 0.06 mm) > minipig (0.64 ± 0.04 mm) > cynomolgus monkey (0.43 ± 0.03 mm). ARA: cat (3.5 ± 0.1 mm(2) ) > owl monkey (1.41 ± 0.2 mm(2) ) > dog (0.88 ± 0.1 mm(2) ) > rhesus monkey (0.62 ± 0.06 mm(2) ) > minipig (0.21 ± 0.05 mm(2) ) > cynomolgus monkey (0.15 ± 0.01 mm(2) ). Conclusions  This study benchmarks the normative iridocorneal angle measurements across different mammalian species by OCT. These data can be useful to compare iridocorneal angle measurements in disease states as OCT evolves as a common diagnostic tool in veterinary ophthalmic research and practice.

Purpose: To compare the dose–response profiles of bimatoprost sustained-release implant (Bimatoprost SR) and topical bimatoprost in lowering intraocular pressure (IOP) in normotensive beagle dogs. Methods: In 1 study, topical bimatoprost 0.001%, 0.01%, or 0.1% was administered twice daily in the study eye for 5 days. IOP was measured at baseline and up to hour 6 each day. Other studies evaluated the IOP response to a single administration of Bimatoprost SR at dose strengths ranging from 8 to 120 μg. IOP was measured before implant administration and during 3 months of follow-up; IOP in response to topical bimatoprost 0.03% was measured prestudy as an internal control. Results: Mean percentage decrease in IOP from baseline at hour 6 (peak effect) across study days was 15.7%, 36.1%, and 24.8% (2.8, 7.0, and 4.0 mmHg) in animals treated with topical bimatoprost 0.001%, 0.01%, and 0.1%, respectively. After Bimatoprost SR administration, mean percentage decrease in IOP from baseline across 3 months consistently increased with increasing dose strength and was 38.7% (7.2 mmHg) with Bimatoprost SR 120 μg. Mean percentage IOP decrease with topical bimatoprost 0.03% was 27.6% (5.9 mmHg). Conclusions: Topical bimatoprost demonstrated a U-shaped dose–response curve; increasing the bimatoprost concentration to 0.1% resulted in reduced IOP-lowering efficacy. In contrast, the dose–response curve for Bimatoprost SR showed consistently greater IOP lowering as the dose strength increased, with the dose strength producing maximum IOP lowering not yet determined. At 60- and 120-μg dose strengths, Bimatoprost SR produced greater IOP reductions than were achieved with topical dosing.

The increase in EVP in the dog with exposure to topical 0.005% latanoprost has not been observed in other species that have been studied, such as in the mouse and in humans, where the drug had no significant effect on the EVP. This response may be unique to dogs and suggests that dogs may not fully mimic human aqueous humor dynamics with topical 0.005% latanoprost. Although frequently performed in human studies, EVP should not be regarded to be a constant value in aqueous humor dynamic studies in the normal beagle dog.

Female dogs have a significantly smaller AOD vs. males. This difference may render the female iridocorneal angle more susceptible to closure and may partially explain the 2:1 female/male predisposition to PACG. Further studies using goniodysgenic dogs are warranted.