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) (rs = 0.39 for dogs and rs = 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.

Comparison of three rebound tonometers in normal and glaucomatous dogs

“…8,9,[11][12][13][14][15][16][17][18][19][20][21][22][23] Numerous variables were shown to affect the IOP measurements, including the probe's angle, cornea-to-probe distance, and central corneal thickness (CCT). 17,[22][23][24][25][26] Recently, a third rebound tonometer, the Tono-Vera® Vet (TVA; Reichert Technologies), was introduced for use in animals (Figure 2). While there are numerous published studies on the use of TV and TVP in animals, 8,9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] to the best of our knowledge, no such studies exist for the TVA.…”

“…17,[22][23][24][25][26] Recently, a third rebound tonometer, the Tono-Vera® Vet (TVA; Reichert Technologies), was introduced for use in animals (Figure 2). While there are numerous published studies on the use of TV and TVP in animals, 8,9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] to the best of our knowledge, no such studies exist for the TVA. This study aimed to compare TV, TVP, and TVA rebound tonometers across a range of IOPs in purpose-bred normal Beagle-derived dogs and dogs with ADAMTS10open-angle glaucoma (ADAMTS10-OAG).…”

“…Their accuracy was studied extensively in dogs and other species and compared to manometry and applanation tonometers in vivo and ex vivo 8,9,11–23 . Numerous variables were shown to affect the IOP measurements, including the probe's angle, cornea‐to‐probe distance, and central corneal thickness (CCT) 17,22–26 …”

TonoVet Plus®: Higher reliability and repeatability compared with Tono‐Pen XL™ and TonoVet® in rabbits

“…Nevertheless, although some variables can be controlled by a consistent technique, not all interference can be completely mitigated. 7 According to Rodrigues et al, 34 differences in distance between the TonoVet® probe and the ocular surface during evaluations, even within the distance limits designated by the manufacturer, can generate differences in the obtained IOP values. In this study, although the evaluations were performed by the same operator with a consideration of the distance between the tonometer and the cornea, changes in distance during the evaluations might have contributed to the differences observed with the TonoVet® between Days 1 and 2.…”

Determination of Reference Values for Tear Production and Intraocular Pressure in Pygoscelid Penguins of the Antarctic Peninsula † ‡

“…As rebound tonometry requires only an instant contact between the probe and corneal surface [32,33]. Being a minimally invasive technique, rebound tonometry can be safely performed for corneal diameters as small as 1.4 mm [5,9,13,25].…”