Comparison of two rebound tonometers in healthy horses

Abstract

Objective To obtain a reference range for evaluation of intraocular pressure (IOP) in horses using Tonovet Plus®, to compare the IOP readings obtained with Tonovet® and Tonovet Plus®, and to evaluate the repeatability of readings. Animals studied and Procedures Intraocular pressure of 30 client‐owned horses (60 eyes) with no signs of illness or ocular disease was evaluated using Tonovet® and Tonovet Plus® rebound tonometers. Horses’ mean age was 10.7 (range 6‐17) years. Triplicate measurements were performed without using sedatives or local anesthetics, with minimal restraint. Results Calculated reference intervals (the CLSI robust method) were 14.4‐27.2 mmHg for Tonovet® and 16.0‐26.1 mmHg for Tonovet Plus®. Mean values (± standard deviation, SD [± coefficient of variation, CV]) obtained with Tonovet Plus® (21.6 ± 2.45 mmHg [11.3%]) were on average 0.6 mmHg higher than with Tonovet® (21.0 ± 3.14 mmHg [15.0%]), and a negligible statistical difference between the devices was found using the paired sample t test (P = .049). The correlation coefficient for the averaged triplicate measurements was 0.73. The average CV was 4.6% and 4.4% for Tonovet® and Tonovet Plus®, respectively. Conclusions The repeatability of measurements was very good with both devices. The readings between the two devices differed statistically significantly, but the correlation was considered good and the variation was numerically small, and thus, the difference was considered clinically irrelevant. When monitoring disease process or treatment response in an individual patient, repeated readings are best performed using a similar device to avoid false interpretation of results.

Ocular abnormalities in the Icelandic horse with a focus on equine recurrent uveitis: 112 Icelandic horses living in Denmark and 26 Icelandic horses living in the United States

“…This finding was also reported by Knollinger et al (2005) 34 . It has been recommended that the same type of tonometer should be used when IOPs must be repeated 33,34 …”

“…Data from this study revealed a significant difference between the two rebound tonometers (TonoVet and TonoVet Plus) with the TonoVet measuring mean IOP slightly higher than those recorded by TonoVet PLUS. A recent study by Mustikka et al 33 (2020) reported opposite results: In this study, the TonoVet PLUS measured a significantly higher mean IOP in horses than the TonoVet. Operator variables or environmental conditions (heat or humidity) related to geography or time of year could also have affected IOP values.…”

“…34 It has been recommended that the same type of tonometer should be used when IOPs must be repeated. 33,34 In conclusion, the three most common ocular abnormalities found in the Icelandic horse breed were follicular conjunctivitis, cataracts, and multifocal chorioretinopathy ("bullet hole chorioretinopathy"). Incipient cataract was the most common cataract type in this breed and was found in young as well as older horses.…”

Effect of topical cyclopentolate alone or combined with phenylephrine in healthy horses

“…In fact, the IOP was significantly increased (p = .02) in phase 2 (at the baseline and T2) compared with phase 1. The IOP was within normal range values 14,15 at these times, and there was no effect of the treatment. For these reasons, the significant difference was not considered clinically significant and could be attributable to the measurement technique or to the daily variation of the IOP.…”

Noninvasive diode laser–an effective and safe treatment of iris cysts in 46 eyes of 35 horses

“…In 3/48 eyes, large iris cysts were in contact with the endothelium leading to localised corneal oedema. Based on the treating veterinarian's assessment, intraocular pressure (IOP) was measured in 10 horses and was within normal limits (16–30 mmHg) in all of them 24,25 …”