Comparison of the rebound tonometer (TonoVet®) with the applanation tonometer (TonoPen XL®) in normal Eurasian Eagle owls ( Bubo bubo)

Abstract

Objective To examine the feasibility and accuracy of a handheld rebound tonometer, TonoVet^®, and to compare the intraocular pressure (IOP) readings of the TonoVet^® with those of an applanation tonometer, TonoPen XL^®, in normal Eurasian Eagle owls. Animals studied Ten clinically normal Eurasian Eagle owls (20 eyes). Procedures Complete ocular examinations, using slit-lamp biomicroscopy and indirect ophthalmoscopy, were conducted on each raptor. The IOP was measured bilaterally using a rebound tonometer followed by a topical anesthetic agent after 1 min. The TonoPen XL^® tonometer was applied in both eyes 30 s following topical anesthesia. Results The mean ± SD IOP obtained by rebound tonometer was 10.45 ± 1.64 mmHg (range 7–14 mmHg), and by applanation tonometer was 9.35 ± 1.81 mmHg (range 6–12 mmHg). There was a significant difference ( P = 0.001) in the IOP obtained from both tonometers. The linear regression equation describing the relationship between both devices was y = 0.669 x + 4.194 ( x = TonoPen XL^® and y = TonoVet^®). The determination coefficient ( r²) was r² = 0.550. Conclusions The results suggest that readings from the rebound tonometer significantly overestimated those from the applanation tonometer and that the rebound tonometer was tolerated well because of the rapid and minimal stress-inducing method of tonometry in the Eurasian Eagle owls, even without topical anesthesia. Further studies comparing TonoVet^® with manometric measurements may be necessary to employ rebound tonometer for routine clinical use in Eurasian Eagle owls.