Noninvasive Ophthalmic Examinations

The routine ophthalmic examination is an efficient and effective technique to identify ocular toxicity (Munger and Collins, 2013 Wilkie, 2014). Long a required evaluation in Good Laboratory Practice (GLP) safety studies, these examinations can be readily applied to any mammalian in vivo study in which ocular effects are anticipated or observed. Minimal pharmacologic intervention is required to examine the eye, and most typical laboratory animal species require only manual restraint. The examinations are not invasive, and the same animal or cohort of animals can be examined 

Histopathology of the eye is a complementary procedure to the routine ophthalmic examination. Microscopic evaluation of ocular tissue permits identification of specific cell types, 

Intraocular pressure (lOP) measurement can be appUed to laboratory animals (Williams, 2007 Coster et al., 2008 Munger and Collins, 2013). The tonometry procedure requires topical corneal anesthesia. Proparacaine hydrochloride 0.5%, administered as a single drop to each eye immediately before measurement, provides adequate desensitization for this brief procedure. Applanation tonometry requires physical contact between the instrument and the corneal surface a gentle and consistent touch with the tonometer is essential. Unlike tonometry using fixed, tabletop equipment with adult humans, this procedure in laboratory animals demands multiple, consecutive measures that are averaged and displayed by the equipment. Tonometers that rely on air pulses can cause startle reflex activity that interferes with consistent measurement. 

Examination of the nonhuman primate requires sedation (Kuhlman et al., 1992). The highly mobile primate eye and their anxious nature when handled mandate a chemically restrained animal for an adequate examination. Human safety considerations also are a factor. Ketamine hydrochloride works well due to its safety and controllable duration. The time to onset of mydriasis following tropicamide administration must be balanced against the time to the animal s recovery from ketamine s sedative effect. A refinement is the addition of a water-based lubricant eye drop at the time of tropicamide administration. This helps protect the cornea from desiccation while the monkey is sedated and may also aid in achieving prompt and satisfactory dilation by increasing tropicamide residence time in the precorneal tear film. Working with a seasoned technical staff appropriately trained for ketamine injection, the examiner can evaluate many primates in a reasonable time. 

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