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A. Guirao, M. Gomez-Valcarcel, J. Tejedor; Optical Corneal Changes Induced by Myopic LASIK. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1040.
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To study optical changes in the corneal anterior surface induced by myopic LASIK, and the explanatory variables involved.
We studied 17 eyes of 10 myopic subjects treated with LASIK (Technolas 217z100, Bausch & Lomb). Preoperative refractive errors ranged from -0.75 D to -6.25 D (mean: -3.1 D). Preoperative corneal thickness was measured in all eyes. The ablation diameter, flap thickness, and the ablation depth, were tabulated, and from these variables we also estimated the residual stromal bed. We measured corneal topography (Orbscan, Orbtek, Inc.) preoperatively, one week, and one month after surgery. Corneal aberrations up to fourth order were obtained by ray-tracing from the corneal elevations for a 6-mm pupil. Pre and postoperatively corneal shape and aberrations were compared. We studied correlations of the aberrations induced by the surgery with: refractive correction, ablation depth, and residual stromal bed.
High-order aberrations increased on average after surgery (from RMS=0.53 to 0.79 microns). Induced aberrations decreased slightly from one week to one month after surgery, although the difference was not statistically significant. The increase in spherical aberration ranged from 0.1 to 0.7 microns (average: 0.3 microns), and statistically correlated with the refractive correction (p=0.006) and the ablation depth (p=0.003). The mean induced coma ranged from 0 to 0.8 microns (average: 0.4 microns), and correlated with the refractive correction (p=0.007), the ablation depth (p=0.008), and the residual stromal bed (p=0.05). Induced high-order aberrations correlated with correction and ablation depth (p=0.03), and with the residual stromal bed (p= 0.007). Induced aberrations including astigmatism statistically correlated with the astigmatic correction (p=0.01).
LASIK induces changes in the corneal surface producing a significant increase of optical aberrations that stabilizes after one week following surgery. The main factor responsible for changes in spherical aberration seems to be the correction pattern that includes refractive correction and ablation diameter. However, for other aberrations such as coma, the preoperative corneal thickness (and then, the residual stromal bed) is also an explanatory variable. Corneal biomechanics could play a main role to explain corneal asymmetries induced by surgery.
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