Reference Values for the Ophthalmic Schirmer Tear Test and the Intraocular Pressure in Healthy Chinchillas

The objective of this study was to measure the intraocular pressure (IOP) and tear production before and after topical anaesthesia in healthy chinchillas (Chinchilla lanigera). Thirteen healthy non-sedated chinchillas (eight males and five females) were used in this study. The tear production was measured by the novel endodontic paper point tear test (PPTT) using Roeko Colour No. 30 Paper points. Following the PPTT, one drop of 0.4 % oxybuprokainium chloride was added to the eye to anaesthetise the cornea and the IOP was measured using the Tono-Pen Avia®Vet. Excess anaesthetic was removed from the conjunctival fornix using a sterile cotton tipped applicator and the PPTT II was performed. The PPTT I and II were measured in 26 eyes, mean ± standard deviations (SD) were 7.98 ± 1.95 mm.min⁻¹, and 9.71 ± 3.52 mm.min⁻¹ respectively. The IOP was measured in 20 eyes, and the mean ± SD was 28.52 ± 12.48 mmHg (35.50 ± 9.31 mmHg in males and 21.53 ± 11.57 mmHg in females). There was no significant difference in the PPTT results between the left and right eyes or between the male and female groups. The males were found to have a significantly higher IOP than females and the PPTT II was significantly greater than the PPTT I. The PPTT test proved to be effective, easy to use, and reliable, causing little apparent discomfort to the chinchillas and could prove to be a much more effective tool than the Schirmer tear test for the evaluation of the tear production in animals with small eyes and/or low aqueous tear production. The mean intraocular pressure proved to be much higher in this population of chinchillas than those previously studied and so further investigation is warranted before a reliable reference range may be produced.