Pupillary responses in the C57BL/6J and congenic IRBP knockout mouse

Abstract

Purpose : The interphotoreceptor retinoid-binding protein (IRBP) knockout mouse exhibits retinal degeneration and profound myopia. We hypothesized that developmental differences would extend to other responses of the eye. Here we tested for additional ocular differences in the IRBP knockout mouse by measuring pupil dilation in response to induced mydriasis.

Methods : Pupil diameters of 90 day old, male IRBP knockout (KO) and C57BL/6J (WT) mice, were measured using a custom photorefraction device. Following an initial measurement in the awake state, mydriasis was induced via topical application of tropicamide, followed 2 minutes later by ketamine/xylazine anesthesia. Pupil diameters were then measured at 2.5 minute intervals for 30 minutes post-mydriatic application. Unpaired t-tests with Welch’s correction and a 2-way ANOVA (genotype and time points as two factors) were used to assess significance between KO and WT groups, as well as time points following mydriatic application.

Results : Measurements of awake-state pupil diameter trended towards differing (p=0.053) between KO and WT (KO: 1.52 ± 0.07mm; WT: 1.30 ± 0.01mm (mean ± standard deviation)). In the anesthetized state, pupil diameter differed significantly at 15 minutes (KO: 2.14 ± 0.07mm; WT: 2.44 ± 0.02mm; p=0.01) and 30 minutes (KO: 2.06 ± 0.07mm; WT: 2.41 ± 0.02mm; p=0.04) post-mydriatic application. Maximum pupil dilation differed (p=0.003) between the two groups (KO: 0.6 ± 0.01mm; WT: 1.2 ± 0.02mm) with KO pupil diameter changing less than WT in response to mydriatic application. No obvious differences in morphology or pigmentation were observed in either the ciliary body or iris.

Conclusions : The IRBP knockout eye differs in several physiologically important ways from C57BL/6J mice. This new assay demonstrates that control of the pupillary response also differs in IRBP deficient mice, as a potential consequence of the KO’s inherent developmental anomalies.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.