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L.J. Nagy, S. MacRae, G. Yoon, I. Cox, K.R. Huxlin; Ocular wave aberrations after laser refractive surgery – a comparison of human and cat eyes. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):163.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Recent measures of ocular wave aberrations in cat and human eyes have shown that optical quality in the two species is very similar (Huxlin et al., ARVO 2003). Our present goal was to compare the higher order aberrations (HOA) induced by laser refractive surgery (LRS) in cat and humans eyes. Methods: Aberration measurements were carried out in fixating cats and humans using a Shack–Hartmann wavefront sensor. Six eyes from 4 adult cats, and 9 eyes from 9 adult humans were imaged pre–op, as well as 1 and 3 months after LRS. Cats underwent PRK; humans underwent LASEK or LASIK. Three cat and 6 human eyes underwent 6D myopic ablations. Three cat and 3 human eyes underwent 4D hyperopic ablations. All ablations were carried out with the Technolas 217z laser over a 6 mm optical zone. Individual Zernike terms were calculated through the 5th order over a 6 mm pupil. Results: While cats experienced about half the defocus change seen in humans for the same intended corrections, both species exhibited significant increases in the amount of HOA. The mean increase in human higher order RMS (HORMS) 1 month post–op was 0.29 + 0.06µm (mean + sem) while in cats, it was 0.73 + 0.22 µm. Both changes remained stable to 3 months post–op. Thus, for matched ablation magnitudes, cats exhibited a significantly larger increase in HORMS post–op than humans (p<0.05, student's t–test). This difference applied to most HOA, especially vertical coma, trefoil Z33 and secondary astigmatism Z24, whose post–op increase in cats was double that observed in humans. Vertical coma accounted for ∼ 50% of the inter–species difference. However, both species experienced similar changes in magnitude and sign for spherical aberration, trefoil Z –33, and horizontal coma. For instance, myopic ablations increased positive spherical aberration by 0.16 + 0.11 µm in humans and 0.18 + 0.11 µm in cats. Hyperopic ablations increased negative spherical aberration by 0.58 + 0.04 µm in humans and 0.46 + 0.36 µm in cats. Conclusions: Cat and human eyes react similarly to LRS, exhibiting significant increases in HOA. For spherical aberration, trefoil Z–33, and horizontal coma, the magnitude and sign of the change were similar in the two species. For other HOA, especially vertical coma, cat eyes exhibited a larger post–op change than human eyes, possibly due to the difficulty in centering ablations vertically on cat eyes. Overall however, the cat eye appears to be an excellent model for the human eye's optical reaction to LRS, validating its use in studies of the biological substrates of HOA induced by this procedure.
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