Reduced Optokinetic Response in Mouse Ocular Hypertension

Abstract

Purpose: : To determine non-invasively whether the optokinetic response, a visuomotor reflex, is altered in mouse ocular hypertension.

Methods: : Unilateral ocular hypertension was induced in 5 male young adult pigmented SV-129 mice by intracameral injection of latex microspheres (Invitrogen). In controls (n=6), vehicle was injected intracamerally. Intraocular pressure was measured using Tonolab (Colonial Medical Supply) at baseline and 3-5 day intervals for a period of 6 weeks. Optokinetic response was measured at baseline and 6 weeks after the first IOP reading above 25mmHg. A custom-made optokinetic apparatus composed of motorized drum with alternating black and white strips giving spatial frequencies of 0.033 and 0.066 (cycle/degree) was used. The unrestrained mouse was placed on a central stationary platform and the drum rotated at speeds ranging from 1°/sec to 60°/sec, clockwise and counter-clockwise. The frequency of extinction (FE; cycles/sec), defined as the maximum speed at which an optokinetic head response could be observed, was recorded. Student t-test and Mann-Whitney test was used to compare IOP and FE between two groups, respectively.

Results: : In ocular hypertension and control groups, mean IOP was 24.1 mmHg ± 0.45 and 14.5 mmHg ± 0.37 (SD), respectively, and the difference in IOP between groups was statistically significant (p< 0.005), At a spatial frequency of 0.066 cycle/degree, frequency of extinction was significantly lower in ocular hypertensive mice compared to controls (0.9 ± 1.78 cycle/sec vs. 5.9 ± 1.03 cycle/sec p< 0.05). The difference in frequency of extinction between two groups was not significant at lower spatial frequency (0.033 cycle/degree) (p > 0.05).

Conclusions: : Short-term ocular hypertension induced significantly reduced optokinetic response. Optokinetic response is a visuomotor reflex that can be exploited to assess visual function non-invasively in rodent glaucoma models. This functional disturbance may be relevant to ocular hypertensive patients.

Keywords: eye movements • neuroprotection • intraocular pressure