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Epithelial thickness mapping (ETM): transepithelial photorefractive keratectomy (tPRK) vs mechanical photorefractive keratectomy (PRK)

Poster Details

First Author: A.El Shahed EGYPT

Co Author(s):    R. El Shahed                    

Abstract Details


The aim of the study was to compare both trans-epithelial photorefractive keratectomy (tPRK) and mechanical PRK for correction of mild and moderate myopia with respect to epithelial thickness mapping (ETM).


Almashreq Eye Center, Cairo-EGYPT.


This prospective, comparative study, included 40 myopic eyes (20- patients), with spherical equivalent  -1.50 to -5.00 D. Eyes were divided into two groups; Group-A included the right eyes (OD) of all patients, while Group-B included the left eyes (OS). Group-A underwent mechanical  PRK using “Hockey stick” & Excimer Laser (Mel-90).  Group-B underwent tPRK using Mel-90 with 250 Hz mode (with 0.7-mm spot scanning). Uncorrected visual acuity  was measured pre-operatively & at first week, 1 month, and 3 months (post-operatively);  along with manifest refraction. ETM was measured (using OptoVue, AS-OCT) pre-operatively, and 1-week, 1-month & 3-months post-operatively. Postoperative pain was assessed.


Pre-operative UCVA ranged from 0.1 to 0.4 (OU), while BCVA ranged from 0.8 to 1.0 (OU).The mean UCVA was 0.46 (OD) & 0.51 (OS) after one week that was improved to 0.96 (OD) & 0.98 (OS) after one- & 3-month. Manifest refraction was comparable in both groups, however it was slightly better in group-B. Patients reported post-op pain (in the 1st post-op day) that was more in the tPRK group. ETM showed a faster epithelial regeneration in group-B that was manifest in 1-week & 1-month visits.  All cases that showed post-op. haze were < grade 1.0 (Hanna’s scale).


tPRK & mechanical PRK provide very similar results 3-mon. post-op. These procedures are predictable, effective, and safe. Patients reported post-op pain (in the 1st post-op day) that was more in the tPRK group.  tPRK group expressed a faster epith. regeneration than the other group ( at 1-wk post-op, however at 1-mon. post-op.; corneal epith. reaches an almost  normal thickness in both groups.  Visual  recovery was noted to be faster in tPRK.

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