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T. Giannakopoulou, S. Plainis, A. Pallikaris, I. G. Pallikaris; Correlating Higher Order Aberrations Following Refractive Surgery With Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1568.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of increased ocular higher order aberrations following refractive surgery on the contrast sensitivity function (CSF).
Twenty subjects (age: 25.2±5.0), undergone LASIK or PRK for the correction of low to moderate myopia, volunteered to participate in the study. Best spectacle-corrected contrast sensitivity of the dilated dominant eye was evaluated, pre-operatively and three months post-operatively, using Gabor patches of vertical gratings (of 1.2 deg s.d. at 2m distance) displayed on a CRT display, by means of a VSG2/5 stimulus generator card. Average screen luminance was 30 cd/m2. Contrast sensitivity was assessed for six spatial frequencies (1, 2, 4, 8, 12 and 16 c/deg) and for artificial pupils of 3 and 6mm diameter. A neutral density filter was used to equalise retinal illuminance for both pupil sizes . Threshold was determined using a binary-search staircase with a contrast resolution of 1dB. Ocular aberrations were recorded at 6 mm pupil using a COAS wavefront sensor (Wavefront Sciences Ltd). Objective image quality metrics, e.g. Modulation Transfer Function (MTF) and Root Mean Square (RMS) wavefront error, were calculated using custom-written scripts in Matlab.
CSF and horizontal MTF were fitted using third-order polynomials. The area calculated by the integral of the fitted functions was used as a measure of performance. CSF was found depressed for 6 compared to 3 mm pupil diameter, especially for higher spatial frequencies, but no difference was found between pre-operative and post-operative measures. MTF decreased significantly post-operatively with the effect being more pronounced for higher spatial frequencies. No significant correlation was found between the difference in CSF area for 6 and 3 mm pupils, and the respective difference in MTF area or other image quality metrics.
Although higher order ocular aberrations increase significantly following refractive surgery, resulting to reduced objectively-assesed retinal image quality, best-spectacle corrected contrast sensitivity is not adversely affected. There is a strong indication that the patients "adapt" to the new pattern of ocular aberrations induced after refractive surgery.
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