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M.C. W. Campbell, M.L. Kisilak, N.J. Gibson, L. Huang, E.L. Irving; HARTMANN–SHACK MEASUREMENTS OF IMAGE QUALITY IN THE RAT EYE . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1079.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The fundus in the small rat eye can be imaged with potentially better resolution than in larger eyes, making it an important animal model. However, fundus image quality will depend on the optical quality of the eye. The source of degradation in the optical point spread function is controversial. Here we objectively assess the optical quality using a Hartmann–Shack device. Methods: The wavefront aberrations of eight eyes of four awake female breeding rats (Long Evans) aged 140 days and raised on a 12 hour light: dark cycle were measured. Measurements were made in 633nm light through plus lenses used to correct the refractive errors estimated from retinoscopy. These were later corrected for lens magnification. Measurements were taken along the optical axis and pupils ranged from 1.6 mm to 3.2 mm. Results: Eyes of all rats measured were highly hyperopic in both retinoscopic and Hartmann–Shack data. The Zernike defocus calculated from the Hartmann–Shack patterns was up to 16D hyperopic. This was 5D more hyperopic than retinoscopy. There was little astigmatism present and no evidence of accommodation. Higher order root mean square wavefront aberrations were larger than in human eyes with corresponding pupil sizes. RMS aberrations increased with increasing pupil size. Hartmann–Shack images had circular gaps, which varied in size and location in the pupil with time. These appear to be due to tear film irregularities, which are different from those in human eyes. Shadows of whiskers sometimes occluded part of the Hartmann–Shack patterns. As well as the effect of classical Zernike aberrations, overall image quality will be adversely affected by poor optical quality of the tear film and diffraction due to the whiskers. Conclusions: Hartmann–Shack measurements can be performed on awake rats. The more hyperopic refraction in the Hartmann–Shack measurements could arise from a combination of chromatic aberration, a difference in the source of the reflection in the two methods and the paraxial nature of the Zernike defocus term. Image quality will be degraded by diffraction and classical monochromatic and chromatic aberrations. Moreover, tear film optical quality will potentially degrade the overall image quality.
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