Intraocular pressure after combined photorefractive keratectomy and corneal collagen cross-linking for keratoconus

Abstract

Purpose: The purpose of this prospective study was to evaluate the effect of combined photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) on intraocular pressure (IOP) in patients with keratoconus (KC).

Methods: We included 64 eyes of 34 patients (19 males and 15 females; age: 19-40y) with stages 1-2 keratoconus which had undergone combined wavefront-optimized photorefractive keratectomy and corneal collagen cross linking. Two other groups of patients were added as controls: the PRK group including 110 eyes of 57 patients (23 males and 34 females; age: 18-44y) which had undergone wavefront-optimized photorefractive keratectomy for myopic refractive errors, and the CXL group including 36 eyes of 23 patients (14 males and 9 females; age: 12-38y) with keratoconus, not filling the inclusion criteria for combined PRK and CXL, which had undergone corneal collagen cross-linking. IOP was recorded preoperatively and postoperatively at 3, 6 and 12 months follow-up visits.

Results: Preoperative IOP in both CXL (12.1 ± 2.53 mmHg) and PRK + CXL (13.2 ± 2.50 mmHg) groups was significantly lower than PRK group (15.8 ± 3.10 mmHg) (F = 30.505, p < 0.001). At 3 months postoperatively, IOP showed no statistically significant difference between the three studied groups (F = 1.821, p = 0.164). At 6 months postoperatively, IOP in the CXL group (14.6 ± 2.64 mmHg) was significantly higher than both PRK (13.4 ± 2.27 mmHg) and PRK + CXL (13.3 ± 2.62 mmHg) groups (F = 3.721, p = 0.026). At 12 months postoperatively, IOP in the CXL group (14.3 ± 2.69 mmHg) was significantly higher than the PRK group (13.2 ± 2.23 mmHg) and was higher than PRK + CXL group (13.3 ± 2.59 mmHg) although not statistically significant (F = 3.393, p = 0.035). Regarding the percent of change from preoperative IOP, a statistically significant difference between the three studied groups was detected at 3, 6 and 12 months postoperatively (H = 117.459, 109.303, 122.694 respectively, p < 0.001). The median percent of change from preoperative IOP in the PRK group was -16.7%, -15%, and -16.7%, in the CXL group was + 14.3%, + 19.4%, and + 19.1%, while in PRK + CXL group was 0% at 3, 6 and 12 months postoperatively. (Post-hoc power analysis 75%).

Conclusions: Combined PRK and CXL in patients with KC shows no significant effect on IOP, in contrast to either procedure performed separately.

Keywords: Corneal collagen cross linking; Intraocular pressure; Keratoconus; Photorefractive keratectomy.

Fig. 1

A: Preoperative, B: 6 months post PRK + CXL Scheimpflug tomography of stage 1 KC patient (correction -0.75 D sphere, -0.75 D cylinder, ablation depth 24 µ)

Fig. 2

A: Preoperative, B: 6 months post PRK + CXL Scheimpflug tomography of stage 2 KC patient (correction -2 D sphere, -2 D cylinder, ablation depth 52 µ)

Fig. 3

A: Preoperative, B: 6 months post CXL Scheimpflug tomography of stage 2 KC patient (unfit for PRK + CXL due to age, 15 years old)

Fig. 4

Comparison between the three studied groups according to percent of change from preoperative IOP