Long-term changes of the anterior cornea after photorefractive keratectomy for myopia and myopic astigmatism

PURPOSE. To analyze the anterior corneal topography changes after 8 years after photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism. METHODS. Sixty-six eyes (33 patients) underwent PRK using an excimer laser platform. Patients were subdivided into three groups: the low myopia (13 patients; range, -1.25 to -4.40 diopters [ D]), the high myopia (13 patients; -4.50 to -9.00 D), and astigmatism (7 patients; cylinder component between -2.00 and -5.00 D) groups. The preoperative and 1-, 2-, 4-, 6-, and 8-year postoperative average corneal maps were computed for each study group. Changes inside and outside the optical zone, which was 6.00 mm in diameter for all eyes, during follow-up were further investigated. RESULTS. The topographic central region, 2.00-mm diameter, was almost stable in all study groups, with changes < 0.39 D between 1 and 8 years. The postoperative variations at the peripheral region, 6.00- to 8.00-mm diameter, were related to the type and amount of refractive correction: a higher flattening (P < 0.05) has been assessed in the high-myopia group (-0.85 D) in comparison with the low-myopia group (-0.42 D) between 1 and 8 years. On the contrary, corneal periphery steepened (+2.22 D; P < 0.05) in the astigmatism group during follow-up, mainly at the superior and inferior emimeridians. CONCLUSIONS. The anterior corneal topography continues to change configuration even long term after PRK. Changes are confined outside the functional optical zone of the cornea. PRK for the correction of myopia was shown not to influence the mechanical stability of the corneal tissue at 8 years after surgery.