Comparison of intraocular pressures estimated by rebound and applanation tonometry in dogs with lens instability: 66 cases (2012-2018)

OBJECTIVE

To compare intraocular pressures (IOPs) estimated by rebound and applanation tonometry for dogs with lens instability.

ANIMALS

66 dogs.

PROCEDURES

Medical records of dogs examined between September 2012 and July 2018 were reviewed for diagnoses of anterior (ALL) or posterior (PLL) lens luxation or lens subluxation.

RESULTS

Estimates of IOP obtained with rebound and applanation tonometry significantly differed from each other for all types of lens instability considered collectively (mean ± SE difference between tonometric readings, 8.1 ± 1.3 mm Hg) and specific types of lens instability considered individually (mean ± SE difference between tonometric readings: ALL, 12.8 ± 2.5 mm Hg; PLL, 5.9 ± 1.7 mm Hg; subluxation, 2.8 ± 0.8 mm Hg). Median (range) differences between rebound and applanation tonometer readings for dogs with ALL was 5 mm Hg (-9 to 76 mm Hg), with PLL was 3 mm Hg (-1 to 19 mm Hg), and with lens subluxation was 3 mm Hg (-9 to 18 mm Hg). In eyes with ALL, rebound tonometer readings exceeded applanation tonometer readings on 44 of 60 (73%) occasions.

CONCLUSIONS AND CLINICAL RELEVANCE

Rebound tonometry yielded higher estimates of IOP than did applanation tonometry in eyes with ALL and with all types of lens luxation considered collectively. Estimates of IOP in eyes with lens instability should ideally be obtained with both rebound and applanation tonometers. Veterinarians with only one type of tonometer should interpret results for dogs with lens instability concurrent with physical examination findings.

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

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.

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

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.

A systematic review of the effects of injectable sedative and anesthetic drugs and inhalant anesthetics on intraocular pressure in the dog

OBJECTIVE

The purpose of this systematic review was to summarize the results of studies that have determined the effect of injectable and inhalant drugs used in anesthesia on intraocular pressure (IOP) in dogs.

DATABASES USED

A comprehensive search of research literature was performed without language restriction. The search utilized the PubMed, CAB Abstracts and the University of Georgia's Galileo electronic databases using a combination of free text terms 'Ophthalmology', 'Intraocular Pressure', 'Anesthetic', 'Anesthesia', 'Canine' or 'Dog'. The time frame searched was from 1970 to October 2018. Any published research paper that dealt with sedatives or anesthetics administered systemically and the canine eye was evaluated.

CONCLUSIONS

The effects of many anesthetic drugs in dogs with ocular pathology are largely unknown. Many anesthetic drugs do not induce clinically relevant changes in IOP in dogs with normal eyes, although some studies demonstrated results with statistically significant changes. The dose, route of administration, experimental conditions, drug combinations, timing of measurements, measurement technology and setting or individual animal characteristics may all produce some heterogeneity in results from multiple studies.

The influence of the tonometer position on canine intraocular pressure measurements using the Tonovet® rebound tonometer

The objective of this study was to assess the variability of readings made using the Tonovet^® rebound tonometer for measurement of intraocular pressure (IOP) in the peripheral cornea and in angulated positions on the canine corneal surface. Forty-six client-owned dogs admitted for ophthalmic evaluation at the Queen's Veterinary School Hospital, University of Cambridge were included in the study. IOP readings were taken at a variety of locations and using the tonometer at a number of different angles to the cornea: 1) Perpendicularly at center of the cornea (CC); 2) At the center of the cornea but with the tonometer positioned at four angles, and 3) At four different points on the peripheral cornea. All values were compared with the values recorded at the recommended CC position. IOP values were significantly underestimated in seven positions, with median and interquartile range from 12.1 ± 4 mmHg (nasal on periphery) to 15 ± 5 mmHg (laterally angled at center), varying between 0 mmHg to 2.9 mmHg from the CC value. While dorsally angled in the central cornea were not significantly different from those at CC (p = 0.09). Median values were lower for measurements in peripheral positions when compared to angled central positions. These results demonstrate that angling the tonometer or measuring in peripheral regions can result in small but statistically significant underestimation of IOP values.

Intraocular pressure in free-ranging anuran species in Oklahoma

Ocular disease appears to be a common issue in anurans. Intraocular pressures were measured for six species of free-ranging anurans in central Oklahoma. No significant differences were identified between left or right eyes. There was a significant negative relationship between the weight of the anuran and intraocular pressure. The intraocular pressure range for the six species was 3-10 mm Hg. Tonometry values in anurans are, to the authors' knowledge, previously unreported and this study provides initial information on intraocular pressure measurement in anurans.