Refractive regression after photorefractive keratectomy.

To the Editor: We thank Drs. Talamo and Abad and Mr. Lim (Refractive Regression after Excimer Laser Photorefractive Keratectomy. J Refract Surg 1996;12:757[letter]) for their comments and are gratified that their findings support our hypothesis that the refractive regression after photorefractive keratectomy (PRK) is not a result of the thicker regrowth of connnective tissue or epithelium in the center of the operated zone. We are sorry that they had difficulty measuring refractive changes in the rabbit. We achieved reproducible results when whoever was holding the animal observed the image of the eye on the topographic screen in a mirror, as described in our paper (Ramirez-Florez S, Maurice DM. Inflammatory cells, refractive regression, and haze after excimer laser PRK. J Refract Surg 1996;12:370-381). Perhaps their larger ablation zone made centering more difficult. Similarly, we avoided major distortion of the sections by maintaining the intraocular pressure during fixation. Shrinkage should not be a facter in determining relative changes in thickness of a layer in a section since it should affect all parts of it equally. SUSANA RAMIREZ-FLOREZ, MD DAVID M. MAURICE, PhD