Evaluation of a rebound tonometer for measuring intraocular pressure in dogs and horses

OBJECTIVE: To compare intraocular pressure (IOP) measurements obtained with a rebound tonometer in dogs and horses with values obtained by means of applanation tonometry and direct manometry. DESIGN: Prospective study. ANIMALS: 100 dogs and 35 horses with clinically normal eyes, 10 enucleated eyes from 5 dogs, and 6 enucleated eyes from 3 horses. PROCEDURES: In the enucleated eyes, IOP measured by means of direct manometry was sequentially increased from 5 to 80 mm Hg, and IOP was measured with the rebound tonometer. In the dogs and horses, results of rebound tonometry were compared with results of applanation tonometry. RESULTS: For the enucleated dog and horse eyes, there was a strong (r2 = 0.99) linear relationship between pressures obtained by means of direct manometry and those obtained by means of rebound tonometry. Mean +/- SD IOPs obtained with the rebound tonometer were 10.8 +/- 3.1 mm Hg (range, 5 to 17 mm Hg) and 22.1 +/- 5.9 mm Hg (range, 10 to 34 mm Hg) for the dogs and horses, respectively. Mean IOPs obtained with the applanation tonometer were 12.9 +/- 2.7 mm Hg (range, 8 to 18 mm Hg) and 21.0 +/- 5.9 mm Hg (range, 9 to 33 mm Hg), respectively. Values obtained with the rebound tonometer were, on average, 2 mm Hg lower in the dogs and 1 mm Hg higher in the horses, compared with values obtained with the applanation tonometer. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the rebound tonometer provides accurate estimates of IOP in clinically normal eyes in dogs and horses.