Evaluation of intraocular pressure in conscious ferrets (Mustela putorius furo) by means of rebound tonometry and comparison with applanation tonometry

Abstract

To determine normal intraocular pressure (IOP) values by means of rebound tonometry in unanaesthetised ferrets, and to compare rebound and applanation tonometry, 55 clinically healthy ferrets were included in an observational, prospective, blinded study. On 52 ferrets, IOP was measured by means of rebound and applanation tonometry. On 3 ferrets, rebound tonometry was performed every two hours over a 24-hour period. Mean IOPs of the 104 eyes obtained with the rebound tonometer were 14.07±0.35 (95% CI 13.37 to 14.77) tonometer-units (TU). The IOP was significantly higher in males than in females, controlling for age and weight. A study-ordered decrease in coefficient of variation (CV) was observed (measurement 1-52=21.2±1.4 per cent v measurement 53-104=14.4±1.1 per cent) and high CVs (>30 per cent) were significantly less frequent in measurement 53-104. A significant difference in IOP during the 24- hour measurements was found, with the lowest IOP recorded at 22:00. The tonometers presented poor agreement, and IOP values were not correlated. The difference in IOP estimation increased with the magnitude of the measurements. Applanation tonometry presented a significant higher frequency of per-eye IOP values exceeding 25 and 30 TU, and a significant lower repeatability (CV=37.1±2.6 per cent v 17.8±1.2 per cent) compared with rebound tonometry. In conclusion, several factors need to be considered when measuring IOP in ferrets.

Reference values for selected ophthalmic tests of the blue-and-yellow macaw (Ara ararauna)

“…It is noteworthy that the sample showed phenotypic homogeneity, and with a substantial number of animals for this species, the results should be reliable. Although the STT was conducted shortly after anesthesia, we cannot rule out the influence of the drug used on the results obtained, since anesthetics lead to a decrease in tear production (Girolamo et al 2013).…”

Intraocular pressure in clinically normal dromedary camels (Camelus dromedarius)

“…[46][47][48] In healthy dairy cattle, the mean ± SD IOP as determined by applanation tonometry was 26.9 ± 6.7 mm Hg (range, 16 to 42 mm Hg). 29 Thus, given that IOP varies among species, it is important to establish a reference interval for IOP in each individual species. [46][47][48] Among all species, the highest mean IOP reported was 32.1 ± 10.4 mm Hg in a rhinoceros, 34 and the lowest mean IOP recorded was 3 mm Hg in a chinchilla.…”

“…Although, the CV is commonly used to determine the precision of a measurement instrument, to our knowledge prior to the present study, only 1 study 51 had assessed the CV for IOP in a species of veterinary interest (ie, cats). 52 In a study 29 in which rebound tonometry was used to measure the IOP of conscious ferrets, there was a study-ordered decrease in the CV. The mean intra-assay and interassay CVs and the associated 95% CIs (Tables 3 and 4) were within acceptable limits.…”

“…In the present study, we calculated the CV to assess the precision of the IOP measurements in both immature and mature camels. The IOP was measured for 104 eyes, and the CV was 21.2 ± 1.4% for the first 52 measurements and 14.4 ± 1.1% for the last 52 measurements, 29 Values are percentages. Results of 1 study 52 indicate that the reproducibility of IOP measurements by rebound tonometry in freshly enucleated eyes of dogs was good, although the reproducibility decreased linearly as IOP increased.…”

Ocular Examination and Corneal Surface Disease in the Ferret

“…Chemical restraint is rarely required for a simple ophthalmic examination, including intraocular pressure (IOP) measurement, but may be needed if more invasive diagnostic procedures are performed or if the ferret is especially aggressive. 2 Because specific literature on the effects of most anesthetic drugs on the ocular parameters of ferrets is lacking, effects similar to those demonstrated in other domestic animals should be assumed. For noninvasive ophthalmic testing procedures, the use of midazolam or butorphanol alone is sufficient.…”