Effects on visual function of approximations of the corneal-ablation profile during refractive surgery

We offer an analysis that shows that the approximations made for the ablati on depth during practical refractive surgery, in which the square-root term s are replaced by the first two terms of the series expansion, can limit th e visual function of the observer by reducing the modulation transfer funct ion (MTF). To simulate the refractive-surgical operation, we considered two groups of myopic patients with different ametropia who were emmetropized w ith different ablation profiles. We made the MTF calculations by taking the spherical aberration into account. In addition, a fuller analysis showed t hat these approximations limit the possibility of considering surfaces that are aspherical for reshaping the anterior cornea to optimize the observer' s visual function. (C) 2001 Optical Society of America.