Response of the Cornea for up to Four Years After Photorefractive Keratectomy for Myopia

Abstract

PURPOSE:To analyze the long-term corneal topographic changes 4 years after myopic photorefractive keratectomy (PRK). METHODS:This study comprised 15 patients (30 eyes) who had PRK surgery with a scanning-spot excimer laser (Chiron Technolas 217C; Bausch & Lomb, Dornach, Germany) and were followed up to 4 years after surgery. The eyes were subdivided into three groups according to the preoperative spherical equivalent refraction. Corneal topographic maps were obtained for all eyes with a Placido disc topographer. Preoperative and follow-up topographical data were imported into a custom software program, which computed the average composite corneal maps and difference maps for each study group to quantify the anterior corneal changes following laser ablation. The software delineated three concentric zones of the corneal surface to characterize the regional corneal remodeling following the surgery. RESULTS:A signifi cant central corneal steepening (approximately 0.25 D, PϽ.001) was calculated between the 1-and 4-year postoperative maps in all study groups. A signifi cant steepening (PϽ.001) of the corneal periphery was also noted for the lower myopic ablations whereas a peripheral fl attening (PϽ.001) was observed for the deeper ablations between 1 and 4 years after surgery. CONCLUSIONS:The anterior corneal surface was observed to remodel for up to 4 years after surface ablation, steepening a mean of approximately 0.25 D.

Long-term corneal wavefront aberration variations after photorefractive keratectomy for myopia and myopic astigmatism

“…[33][34][35] When the central portion of the anterior cornea has mechanically stable curvature in the very long-term postoperative period, as reported previously, 23,24,33,34 it contributes to the stability of corneal optical performance.…”

“…The ablation design and parameters, 36-43 epithelial healing, and biomechanics of the corneal tissue [33][34][35] are the main sources of HOA induction, which can influence the optical result after PRK. The increase in spherical aberration in the optical ablation zone after simple myopic ablations could be due to causes other Figure 6.…”

Long-Term Changes of the Anterior Corneal Topography after Photorefractive Keratectomy for Myopia and Myopic Astigmatism

“…Interpolation to the same spaced referenced cornea grid was necessary for this purpose, as discussed in previous works. [7][8][9] A central zone with radius (r) of 1.00 mm from the corneal apex and a peripheral annular zone with 3.00 Յ r Յ 4.00 mm from the apex were delineated for detailed regional analysis of anterior corneal topography changes during follow-up. The choice of the regions' width was based on results of previous studies.…”

“…In previous studies, 8,9 we described the topographic response of the cornea to PRK for myopia and demonstrated how the anterior cornea undergoes minimal changes of the central optical portion up to 6 years after surgery. In the present study, we describe the long-term variation of the whole anterior corneal morphology over an 8-year follow-up after PRK for the correction of myopia or myopic astigmatism.…”

“…1,2 A few works have thoroughly characterized long-term shape changes over the whole anterior cornea, including the peripheral portion of the tissue. [3][4][5][6][7][8][9] Most of the long-term clinical studies have, in general, targeted their scope at assessing stability and predictability of the surgical outcome by measuring refraction and mean simulated keratometry values during follow-up. 10 -25 The results from these works have reported, as common occurrence after PRK, a mean postoperative refractive regression of Ϫ0.50 diopters (D) during the first 1 to 2 years after treatment and a slow myopic regression for up to 14 years postoperatively.…”