Impact of Preoperative Corneal Curvature on the Outcome of Penetrating Keratoplasty in Keratoconus


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Abstract

Purpose.To assess the impact of the patient's preoperative corneal curvature on the refractive outcome after penetrating keratoplasty (PK) in keratoconus before and after suture removal.Patients and Methods.In this retrospective cross-sectional clinical study, 236 keratoconus patients (mean age 37 ± 11 years) were divided into four groups based on their preoperative keratometric (K-) readings: group 1, <50 diopters (D) (n = 24); group 2, <60 D (n = 52); group 3, ≥60 D (n = 101); group 4, irregular corneal shape with unmeasurable K-reading (n = 59). An 8.0/8.1-mm central round PK was performed using 193 nm Meditec excimer laser trephination along metal masks with eight “orientation teeth/notches.” A 16-bite double running cross-stitch suture was applied in all cases. Postoperative examinations were performed before removal of the first suture (ie, 12 months) and after removal of the second suture (ie, 18 months). The outcome measures included central power (C-power), keratometric astigmatism (AST), surface regularity index (SRI), surface asymmetry index (SAI), spherical equivalent (SEQ), refractive cylinder (Cyl), and best corrected visual acuity (BCVA). In addition, the regularity of Zeiss keratometry mires was classified semiquantitatively (0, regular; 1, mildly irregular; 2, moderately irregular; 3, unmeasurable).Results.Before/after suture removal, median C-power was 43.4/43.3 D; AST was 3.0/3.0 D; SAI was 0.6/0.6; SRI was 0.9/0.9; Cyl was 2.5/2.5 D; BCVA was 0.7/0.7. After suture removal, the percentage of regular keratometry mires increased from 37% to 61%. Comparisons among the four groups revealed no significant differences for any parameters tested either before or after suture removal.Conclusions.With laser trephination and a double running suture, the refractive and visual outcome of PK for keratoconus seems to be independent on the patient's preoperative corneal curvature or irregularity. Suture removal did not effect an increase of corneal astigmatism but did increase the proportion of regular keratometry mires. Thus, our policy of not performing PK in keratoconus eyes before the patient becomes contact lens intolerant is well supported.

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