The effect of central corneal thickness on intraocular pressure values using various tonometers in the dog

Abstract

Objective To compare intraocular pressure readings from three different tonometers, the Tono‐Pen AVIA® (TP), TonoVet® (TV) and TonoVet Plus® (TV+) and to determine how measurements from each tonometer are affected by central corneal thickness (CCT). Animals Ninety dogs. Procedures Normal dogs and dogs with ocular disease were selected for study inclusion. Central corneal thickness measurements were gathered with the Pachette 4 ultrasonic pachymeter, and IOP measurements were gathered with the three tonometers in random order. ANOVA or Wilcoxon tests were utilized for overall group comparisons. Linear regression analyses were utilized to determine the association between IOP and CCT. Results When comparing tonometers to each other, for all dogs, readings from the TV+were significantly different compared to the TV (p = <.0001) and TP (p = <.0001); however, there was no significant difference between the TV and the TP (p = .999). Linear regression did not find any significant correlation between corneal thickness and IOP readings with any tonometer when looking at normal dogs or when including dogs with ocular abnormalities. Discussion This study did not find a significant correlation between an increase in CCT and increase in IOP reading in any tonometer comparison amongst normal and dogs with ocular abnormalities. The TV+produced consistently and significantly higher readings, but measurements did not exceed the expected IOP range in normal dogs. For consistency, the same tonometer should be used when monitoring IOP over time.

Comparison among TonoVet, TonoVet Plus, Tono-Pen Avia Vet, and Kowa HA-2 portable tonometers for measuring intraocular pressure in dogs

“…In both the in vivo and outpatient studies, the IOP values measured by TonoVet Plus averaged 3-5 mmHg higher than those measured with the other tonometers, which is consistent with some recent studies, such as the study by Ben-Shlomo and Muirhead [28], who compared IOP values in healthy dogs, obtained with TonoVet (15.0±3.2 mmHg; range 7-22 mmHg), TonoVet Plus (19.2±3.1 mmHg; range 11-25 mmHg), and Tono-Pen Avia Vet (12.8±2.9 mmHg; range 6-19), and concluded that TonoVet Plus indicated significantly higher IOP values than TonoVet and Tono-Pen Avia Vet. These results were in agreement with those presented by Guresh et al [29], who conclude TonoVet Plus produced consistently and significantly higher IOP readings. Nevertheless, the measurements did not exceed the expected IOP range in normal dogs.…”

Comparison of three rebound tonometers in normal and glaucomatous dogs

“…Similar relationships between CCT and IOP have been described in humans, [35][36][37][38] but they stand in contrast to a few canine data published by others who did not find significant correlations. 23,39 Limitations of this study include a small sample size (50 dogs) with fewer high-pressure readings (9) and the omission of manometric IOP. Larger sample sizes, including different canine breeds, could be considered to compare the new TVA with other tonometers more extensively.…”

“…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][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).…”

“…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).…”