Objective To validate intraocular pressure (IOP) readings obtained in cats with the TonoVet® tonometer. Animal Studied IOP readings obtained with the TonoVet® were compared to IOP readings determined by manometry and by the Tono-Pen XL in 1 normal cat and 2 glaucomatous cats. TonoVet® and Tono-Pen XL readings were also compared in a further 6 normal and 9 glaucomatous cats. Procedures The anterior chambers of both eyes of 3 anesthetized cats were cannulated and IOP was varied manometrically, first increasing from 5 to 70 mm Hg in 5 mm Hg increments, then decreasing from 70 to 10 mm Hg in 10 mm Hg decrements. At each point, two observers obtained three readings each from both eyes, with both the TonoVet® and Tono-Pen XL . IOP was measured weekly for 8 weeks with both tonometers in 6 normal and 9 glaucomatous unsedated cats. Data were analyzed by linear regression. Comparisons between tonometers and observers were made by paired student t-test. Results The TonoVet® was significantly more accurate than the Tono-Pen XL (p=0.001), correlating much more strongly with manometric IOP. In the clinical setting, the Tono-Pen XL , underestimated IOP when compared with the TonoVet®. Conclusions Both the TonoVet® and Tono-Pen XL provide reproducible IOP measurements in cats, however the TonoVet® provides readings much closer to the true IOP than the Tono-Pen XL . The TonoVet® is superior in accuracy to the Tono-Pen XL for detection of ocular hypertension and/or glaucoma in cats in a clinical setting.

Citation: Heyne GW, Kiland JA, Kaufman PL, Gabelt BT. Effect of nitric oxide on anterior segment physiology in monkeys. Invest Ophthalmol Vis Sci. 2013;54:5103-5110. DOI: 10.1167/iovs.12-11491 PURPOSE. To determine the effect of the nitric oxide donor, sodium nitroprusside (SNP), and the nitric oxide synthase (NOS) inhibitor, L-nitro-arginine-methylester (L-NAME), on IOP, mean arterial pressure (MAP), pupil diameter (PD), refraction (Rfx), aqueous humor formation (AHF), and outflow facility (OF) in monkeys.METHODS. Monkeys were treated with single or multiple topical treatments of 500 lg SNP or L-NAME to one eye. IOP was determined by Goldmann applanation tonometry, PD with vernier calipers in room light, Rfx by Hartinger coincidence refractometry, AHF by fluorophotometry, and MAP with a blood pressure monitor. OF was determined by two-level constant pressure perfusion following anterior chamber exchange. RESULTS.Following four topical treatments with 500 lg SNP, 30 minutes apart, IOP was significantly decreased from 2 to 6 hours compared with the contralateral control with the maximum IOP reduction of 20% at 3 hours (P < 0.001). PD, Rfx, and AHF were unchanged. Effects on MAP were variable. OF after SNP exchange was significantly increased by 77% (P < 0.05) at 10 À3 M. Topical L-NAME had no effect on IOP, PD, Rfx, or MAP.CONCLUSIONS. Enhancement of nitric oxide concentration at targeted tissues in the anterior segment may be a useful approach for IOP reduction for glaucoma therapy. Additional studies are warranted before conclusions can be made regarding the effect of NOS inhibition on ocular physiology in nonhuman primates.

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