Intraocular pressure measurements using the TONOVET® rebound tonometer: Influence of the probe-cornea distance

Abstract

Purpose: To demonstrate the effect of different probe-cornea distances during intraocular pressure (IOP) data acquisition in dogs and rats.

Animals studied: Twenty-four conscious dogs and 15 anesthetized Wistar rats.

Methods: Three interchangeable three-dimensional printed polylactide plastic spacer collars were used in place of the original Icare TonoVet® collar piece, which provided different distances (4, 6, and 8 mm) between the instrument's probe and the corneal surface. IOP values were obtained in sequence by a single observer, with the tonometer probe at a 4-, 6-, and 8-mm distance from the corneal surface. The dogs were gently restrained, and the rats were anesthetized with isoflurane.

Results: Intraocular pressure values obtained at 4, 6, and 8 mm from the TonoVet® probe to corneal surface distance in both dogs and rats were significantly different (P < .01). There was a small positive correlation between IOP (mm Hg) and probe-cornea distance (mm) (r_s = 0.39 for dogs and r_s = 0.51 for rats). In dogs, the mean IOP (± SD mm Hg) obtained at different distances were 16.2 ± 3.0 at 4 mm; 17.6 ± 3.4 at 6 mm; and 19.8 ± 3.8 at 8 mm. In rats, IOP values were 8.2 ± 1.5 at 4-mm; 9.4 ± 1.8 at 6-mm; and 10.5 ± 1.5 mm Hg at 8-mm distance.

Conclusions: Probe-cornea distance of the Icare TonoVet® significantly affects IOP readings, even within the 4- to 8-mm range recommended by the manufacturer.

Keywords: TonoVet®; dogs; intraocular pressure; probe-cornea distance; rat; rebound tonometry.