Intraocular Pressure Measurement by Applanation Tonometry: Baseline Assessment in Exotic Carnivores and Non-Human Primates
Abstract
Intraocular pressure (IOP) is measurement of fluid pressure within the anterior chamber of the eye. Glaucoma or uveitis may present with abnormal IOP. Applanation tonometry measures IOP by the force required to flatten the cornea.4,6,7,10
In domestic animals, IOP can be measured under manual restraint with topical anesthesia.1,2 Although anesthesia can affect IOP,2 general anesthesia seldom can be avoided in exotic species.3,5,8,9 Normal IOP reference ranges have been established for domestic species, but little information is available for exotics.
In this retrospective study of one zoological collection, IOP measurements (n=100) were collected over a five-year period at a single institution in 22 mammalian species opportunistically during annual examinations. In 73% of the individuals, measurements were obtained more than twice at repeated physical examinations, and in 25% of the individuals, measurements were made from juvenile to adulthood. Anesthetic protocols were maintained consistently within each species. Typically, during measurement animals were positioned laterally. Measurements (in mm Hg) were obtained in triplicate using a Tonopen® XL (Medtronic, Jacksonville, FL, USA) and measurements in the dependent eye were recorded.
IOP of the right and left eye was compared by paired t-test by species. No difference was identified at p<0.05 significance. Normal IOP (18 mm Hg) within mammalian species studied was generally consistent. Therefore, differences greater than two standard deviations from this baseline may indicate underlying ocular pathology. Caution should be exercised in interpretation of IOP between eyes of laterally recumbent animals as IOP may be elevated artifactually in the dependent eye.1
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