Optical Aberrations in the Normal and Anesthetized Mouse Eye

Abstract

Abstract: : Purpose: The mouse is a common animal model for ocular pathologies. There is an increasing interest in the mouse as a model for myopia. Knowledge of the optical properties of the mouse eye is important for in vivo retinal imaging (usually under anesthesia) and to understand the emmetropization process (natural viewing conditions) Methods: Five 30–40 days old wild type mice (C57BL/6) were used. Ocular aberrations were measured using custom–built Laser Ray Tracing (LRT, ingoing aberrometry) and Hartmann–Shack (HS, outgoing aberrometry) wavefront sensors. Both systems are well tested and provide similar aberrations on artificial and human eyes. Illuminating light was 768 and 680 nm respectively. The pupil was continuously monitored under IR illumination. Four animals were tested. One under anesthesia (ketamine 10%, lidocaine 2% and sterile saline) in the LRT system and three under natural viewing conditions in the HS. Refractive errors were corrected with a Badal system. Wave aberrations were obtained from the estimated centroids in the aerial images (captured sequentially as the entry beam moves across the pupil in the LRT; and from the multiple–spot image in the HS). Optical quality was described in terms of the RMS wavefront error, and individual Zernike terms or orders. Results: HS images obtained under anesthesia were too degraded to allow appropriate processing. However, the larger dynamic range of the LRT system provided good data under anesthesia. Refractive errors ranged from –1.8 to +1.5 D (LRT) and from –1.4 to +7.15 in the normal eyes (HS). Pupil diameters ranged from 0.75 to 1 mm (all data were processed for 0.75 mm). Average third and higher order RMS under anesthesia was 0.281±0.009, third order RMS was 0.22 ±0.01, and spherical aberration 0.004±0.003 microns. Average third and higher order RMS under normal viewing conditions was 0.06±0.01, third order RMS was 0.05±0.01, and spherical aberration 0.002±0.006 microns. Measurement variability was low under anesthesia, and higher in awake mice (particularly defocus and spherical aberration). Changes in the sign of spherical aberration correlated with changes in the sign of refraction. Conclusions: Mice show highly degraded optics. Optical aberrations obtained under anesthesia were significantly higher in magnitude than those obtained under normal viewing conditions

Keywords: optical properties • emmetropization • refractive error development