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M. Bird, M. C. W. Campbell, M. L. Kisilak, K. Bunghardt, N. J. Gibson, E. L. Irving; Variability in the Optical Quality Within a Single Strain of Pigmented Rats. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3961.
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Campbell and Hughes (1981) published a rat schematic eye showing overcorrected spherical aberration (SA), in agreement with measurements on pigmented DA rats. In this case, the optical power decrease in the periphery of the gradient refractive index lens is not completly balanced by the power increase in the peripheral cornea. More recently, we showed that the total root mean square (RMS) higher-order aberrations (HOA) of Long Evans rats within 20 degrees of the optical axis agreed with the model’s predictions. However, we have also shown variability in refraction among rat strains used as models of disease and others have reported variability in the sign of SA. Here we investigate SA in pigmented, Long Evans rats experimentally and by modeling.
: Hartmann-Shack (H-S) measurements were acquired from the eyes of Long Evans rats, either awake or under sedation with natural or dilated pupils. SA was assessed with retinoscopy in 2 additional animals. The relative speed of the retinoscopic reflex in the pupil centre and periphery was assessed. A Zemax model of the rat eye, including a gradient refractive index lens, was used to assess the sensitivity of SA of the eye to corneal shape.
For many measurements, the H-S patterns could not be analysed due to poor tear film and optical quality issues. All Long Evans rats were hyperopic, in agreement with the published eye model. The average Zernike coefficient for SA across 7 eyes at a 1.47 mm pupil was 0.04 waves, ranging from -0.007 waves (overcorrected) to 0.1 waves (undercorrected). Pupil sizes of 1.88 mm (5 eyes) and 2.3 mm (3 eyes) gave average SA values of 0.018 waves and -0.01 waves respectively. Retinoscopy reflexes were consistent with undercorrected SA in the 4 eyes measured. For the corneal asphericity measured for DA rats (-0.14), the model predicted an overcorrected SA of -0.02 waves (1.47 mm pupil), -0.05 waves (1.88 mm) and -0.12 waves (2.3 mm pupil). However, reducing the corneal asphericity in the model reduced SA progressively. It changed to undercorrected SA at a corneal asphericity of 0.06.
Eyes within a single strain of pigmented rats exhibit SA of differing sign. Although the schematic eye correctly predicts the RMS HOA of Long Evans rats, it does not predict the average SA. Our analysis shows that SA is sensitive to the asphericity of the rat cornea. Variability in refraction and SA needs to be taken into account when designing contact lenses and imaging the fundus of the rat, an important animal model of disease.
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