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L. Diaz-Santana, K. Martin, C. Noack; Contact Lens vs Coverslip: Comparing Two Methods for Optimisation of the in vivo Optical Quality of the Rat Eye. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1579.
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The optical quality of an anaesthetised rat eye decreases quickly due to a rapid increase in scattering over time. This has a strong effect in the quality of retinal images and of wave front measurements needed for adaptive optics correction for high resolution retinal imaging. Protecting the cornea with a cover slip or a contact lens can be used to reduce this problem. In this work we characterised the optical quality of the anaesthetised rat eye in terms of aberrations and scattering present when using two different corneal covers
A custom made Shack-Hartmann (SH) sensor was built to measure the optical quality of the rat eye. The ocular aberrations from the eyes of four Sprague Dawley rats were measured while wearing a prototype contact lens (CL) (Material PMMA, front surface r=3.94mm, Back surface r=4.50mm, apical distance=0.34 mm) and measured again while using a microscope cover slip (CS) (thickness=0.130mm, Glass BK7) to cover the cornea. Viscotears (Novartis) were used to couple the CS or CL to the cornea. SH data from 1 Sprague Dawley and 2 Wistar rats were also collected without any corneal cover. We compared the amount of scattering and aberrations in each case.
The uncovered eyes presented the largest amount of scattering while the ones with a cover slip presented the minimum. The width of the scattering spread was statistically different between all 3 cases (p <0.05). 92% of the individual Zernike coefficients were found to differ significantly between the CL and CS sets (p0.05). The scattering present in the uncovered eyes was too high for reliable wave front measurements.
The amount of aberrations found were in line with modelling predictions based on Campbell and Hughes' rat eye model. The increased amount of scattering observed with the CL might be due to inferior surface quality of our prototype CL compared to the high quality surface of the CS made for microscopy applications. Our modelling predicts that optimisation of the CL shape can help to reduce aberrations and improve image quality. Future work will address CL improvement both in terms of aberrations and scattering management.
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