Clinical Comparison Of Epi-LASIK And Off-flap Epi-LASIK In The Treatment Of Myopia

Epipolis laser in situ ketatom-ileusis (Epi-LASIK) is the mainsurgical option in surface ablation at present. It broadens the rectifiablemyopia surgery range, and it’s suitable for the people with thin cornea, highcorneal curvature, higher myopic degree, and special occupations, such asathletes and soldiers who is not suitable to have LASIK. Compared with PRKand LASEK, there is less postoperative irritant symptoms in the Epi-LASIK,such as haze, and LASIK-related complications. Epi-LASIK is safe andeffective in the treating myopia. Traditional Epi-LASIK, named on-flapEpi-LASIK, resets the epithelial flap after the photorefractive corrections.Some surgeons suggested that procedures with discarded epithelium flapduring surgery be called as off-flap Epi-LASIK. Whether there is differencebetween the two surgery options, is still unknown both in and abroad. Whetherthe epithelial flap, dissected during the Epi-LASIK operation, is highly activeand has intact basement membrane, is still uncertain both in and abroad. Byobserving the morphology of Epi-LASIK corneal epithelial flap, andcomparing on-flap Epi-LASIK and off-flap Epi-LASIK, we try to determinewhether there are differences between them, and provide theoretical basis forour decision of Epi-LASIK operation in the future.PartⅠ The histomorphological observation of Epi-LASIK epithelial flapObjective：To investigate if there is intact basement membrane on theepithelial flap made with Epikeratoma through light microscope and electronicmicroscope observation.Methods：Thirty epithelial flaps of30cases, dissected during the off-flapEpi-LASIK operation, were collected, with10cases, observed by lightmicroscope and20cases, observed by transmission electron microscope.Results：Under the light microscope, there was no intact basement membrane in10cases of corneal flaps; by transmission electron microscopy,only2of the20epithelial flaps were observed with intact basement membraneand18flaps(90%) with discontinuous or no basement membrane.Conclusion：Epithelial flap, made with Epikeratoma, is theoreticallyseparated between epithelial basement membrane and Bowman’s layer, withcomplete basement membrane and active epithelial flap. But through ourobservation of flaps, collected during the actual operation of the Epi-LASIK,there are a large number of epithelial flaps without complete basementmembrane.PartⅡ Clinical comparison of Epi-LASIK and off-flap Epi-LASIK inthe treatment of myopiaObjectives：To compare the clinical effects of off-flap and on-flapEpi-LASIK, and to provide theoretical basis for keeping or removing cornealepithelial flap during Epi-LASIK operation.Methods：According to the equivalent spherical,122eyes of61casesmyopia patients given Epi-LASIK operation were divided into high myopiagroup(≥6.0D,31cases), low-to-moderate myopia group(<6.0D,30cases). Ineach group, one eye had off-flap Epi-LASIK, and the other eye went on-flapEpi-LASIK operation randomly. We compared the postoperative pian, cornealepithelium healing time, postoperative vision, refractive diopters, haze,corneal topographic map(ISV,IVA) and higher-order aberrations(RMSh, coma,SA) between the two groups.Results: High myopia group:1.The stimulus symptom: On the2nd and3rd day after surgeries, the stimulus pain was slighter for the ones receivingoff-flap than for others receiving on-flap，and there was statistical differencebetween the two groups(P <0.05);2.Corneal epithelial healing time: Cornealhealing time for off-flap group(5.06±0.57days) was shorter than that for theon-flap group (5.58±0.99days), and there was significant difference betweenthe two groups(P <0.05).3. The uncorrected visual acuity (UCVA): Atpostoperative1week，1month, and3months, UCVA of off-flap group wasbetter than UCVA of on-flap group, and there was statistical difference between the two groups (P <0.05). There was no statistical difference as tothe UCVA at postoperative6months (P>0.05)4. Refractive diopters: Therewas no statistical difference between off-flap group and on-flap group atpostoperative1month,3months and6months (P>0.05);5. Haze: There wasno more than level1Haze in the two groups, and no statistical differencebetween the two groups in postoperative1month,3months and6months (P>0.05);6. Corneal topographic map: Compared with preoperative states,postoperative ISV and IVA increased(P＜0.05),and no statistical differenceexisted between off-flap group and on-flap group in postoperative1month,3months and6months (P>0.05);7. High order aberration: PostoperativeRMSh, Coma, and SA of both groups rose(P＜0.05). There was no statisticaldifference between off-flap group and on-flap group (P>0.05).Low-to-moderate myopia group:1. The stimulus symptom: On the2ndand3rd day after surgeries, the stimulus pain was slighter for the onesreceiving off-flap than for others receiving on-flap，and there was statisticaldifference between the two groups(P <0.05);2. Corneal healing time: Thecorneal epithelium healing time of off-flap group(4.94±0.68days) wasshorter than that of the on-flap group(5.81±0.91days). There was statisticaldifference between the two groups (P <0.05);3.The uncorrected visual acuity(UCVA): At postoperative1week, UCVA of off-flap group was better thanUCVA of on-flap group, and statistical difference existed between the twogroups (P <0.05), but no statistical difference existed for UCVA atpostoperative1month,3months and6months (P>0.05);4. Refractivediopters: There was no statistical difference between off-flap group andon-flap group in postoperative1month,3months and6months (P>0.05);5.Haze: There were no more than level1Haze in the two groups. There wasno statistical difference between the two groups in postoperative1month,3months and6months (P>0.05);6.Corneal topographic map: Compared withpreoperative states, ISV and IVA increased(P＜0.05), but there was nostatistical difference between off-flap group and on-flap group inpostoperative1month,3months and6months (P>0.05);7.High order aberration: Postoperative RMSh, Coma, and SA of both groups rose(P＜0.05).But there was no statistical difference between off-flap group and on-flapgroup (P>0.05).Conclusion:1In both high myopia group and low-to-moderate myopia group, off-flapEpi-LASIK group had less pain in the early postoperative days, and thehealing time was shorter than that of on-flap Epi-LASIK group.2In both high myopia group and low-to-moderate myopia group, therewas low incidence of postoperative haze in both on-flap Epi-LASIK group andoff-flap Epi-LASIK group. The incidence of haze was not impacted by theexistence of epithelial flap.3In both high myopia group and low-to-moderate myopia group, thecases with off-flap Epi-LASIK operation or on-flap Epi-LASIK operation allgained good vision, and the refractive status were stable at6months aftersurgery. The two groups both had better visual quality.