Abstract
Purpose:
Many labs use optical coherence tomography (OCT) to determine ocular parameters in the mouse eye when studying refractive development. The optical linear distance obtained with the OCT is converted to geometrical linear distance using the refractive index of the tissue. Since the optical power of the nocturnal mouse eye is largely dependent on the large ocular lens, many published studies have used the refractive index value of 1.433 for C57BL/6J mouse lenses reported by Remtulla and Hallett (Vision Res 25:21-31; 1985) using the Abbé refractometer. Calculations from the mouse paraxial schematic eye model suggest that refractive index increased from 1.568 to 1.605 between 22 and 100 days in C57BL/6J mice (Schmucker & Schaeffel, Vision Res 44:1857-67; 2004 ). The purpose of this study was to measure the refractive index of isolated mouse lenses across age and in different strains using OCT.
Methods:
Lenses were carefully dissected from C57BL/6J wild-type (C57) and nob mice eyes at 4, 10, and 16 weeks of age. Nob mice have an ON pathway defect caused by nyx mutation and have previously been shown to be more susceptible to form deprivation myopia (Pardue et al., IOVS 49:706-12; 2008). Lens thickness (LT) and refractive index (RI) was measured using OCT, as reported by Uhlorn et al. for human ocular lenses (Vision Res 48:2732-8; 2008). Briefly, RI was calculated from optical length differences in Dulbecco’s medium with and without the mouse lens present.
Results:
RI of the mouse lens did not change across age in either strain. However, nob mice had overall higher lens RI than C57 mice (Ave ±SEM: 1.433 ±0.004 vs 1.420 ±0.003, ANOVA main effect, p=0.011). LT increased with age in both strains from 1.253 ±0.01 to 1.471 ±0.01 mm (ANOVA main effect, p<0.001) but was not significantly different between strains.
Conclusions:
C57 mice had lower ocular lens RIs than that reported previously for the mouse eye using refractometry and both strains had lower RIs than that calculated with the schematic eye model. Contrary to the schematic eye calculations, mouse lens RI was stable across age. As expected, lens thickness increased with age; however, no change was detectable between nob and C57 mice. These data suggest that mouse lens RI may need to be more carefully determined in order to accurately measure ocular parameters with OCT techniques and make comparisons between strains.
Keywords: 567 intraocular lens •
677 refractive error development •
605 myopia