BackgroundIntegrated transepithelial photorefractive keratectomy (TransPRK) is a new kind of surface ablation and has a fast reepithelialization and uncorrective visual acuity (UCVA) recovery as well as slighter postoperative pain, and epipolis laser in situ keratomileusis (Epi-LASIK) has been recognized to be an effective method for myopia.But there have been few studies to evaluate the dynamic change of the corneal biomechanical properties and posterior corneal elevation after TransPRK.

ObjectiveThis study was to assess and compare the effectiveness and safety between TransPRK and Epi-LASIK for myopia with thin cornea.

MethodsThis study was approved by Ethic Committee of Jinan Mingshui Eye Hospital, and written informed consent was obtained from each patient.In this prospective non-randomized controlled study, 93 right eyes of 93 myopic patients with the central corneal thickness 460 to 500 μm were included in Jinan Mingshui Eye Hospital from June to December 2013 under the informed consent.The eyes were divided into TransPRK group for 46 eyes and Epi-LASIK group for 47 eyes.UCVA, manifest refraction, haze, corneal biomechanical properties, posterior corneal elevation, Q-value and corneal high order wavefront aberration were analyzed before and 1 week, 1 month, 3 months and 6 months after operation, respectively, and the examination results were compared between the two groups.

ResultsThere was no statistically significant difference in the eyes of postoperative UCVA and manifest refraction between the TransPRK group and the Epi-LASIK group at various time points (all at P>0.05). Six months after surgery, the percentage of eyes with UCVA of 1.0 or better was 93.9%, and 90.9% eyes exhibited the targeted refraction in ±1.00 D in the TransPRK group.Corneal haze was most obvious 1 month after surgery in both groups, with the incidence of 32.6% (15/46) in the TransPRK group and 17.4% (8/47) in the Epi-LASIK group, but no significant difference was found in the eye numbers with haze between the two groups ( χ ²=2.841, P=0.092). No significant differences were seen in the corneal hysteresis（CH) values and corneal resistance factor（CRF) values between the two groups（CH: F _group=0.000, P=0.999; CRF: F _group=0.110, P=0.741), however, the postoperative CH values and CRF values were significantly declined in comparison with preoperative ones, with significant differences among various time points (CH: F _time=103.658, P=0.000; CRF: F _time=132.008, P=0.000), while there were no remarkable differences between any two time points in postoperation (all at P>0.05). Posterior corneal surface height shifted rearward 1 week, 1 month, 3 months and 6 months after surgery, showing remarkable differences in comparison with before surgery in both groups ( F _time=12.868, P=0.001), but no significant differences between the two groups ( F _group=1.923, P=0.169). No significant differences were found in Q-value between the two groups ( F _group=0.191, P=0.663). Root mean square (RMS) and spherical aberration values elevated in postoperation compared with preoperation, with significant differences between them（all at P<0.01), but the comparison between intergroup was insignificant (RMS: F _group=0.299, P=0.586; Spherical aberration: F _group=1.290, P=0.259).

ConclusionsTransPRK for myopia with thin cornea is safe and stably effective like Epi-LASIK.TransPRK affects corneal biomechanical properties early after surgery but the effect gradually lessens over time.The posterior corneal elevation shows a tiny backward displacement, while posterior corneal asphericity has no change.