Research On The Influence Of Corneal Thickness On Corneal Flap Thickness In LASIK

PurposeTo evaluate the influence of corneal thickness on corneal flap thickness in LASIK.MethodsAll flaps were created using the Moria M2 microkeratome 160 head . Bilateral LASIK was performed in 162 myopiaus patients (324eyes) ,The same blade was used in fellow eyes, and the right eye was always treated first . Eyes were grouped by order of blade use for statistical analysis ( OD group, OS group). Patients of the two groups were randomly assigned to four groups according to different preoperative corneal thickness: groupl (range 470 - 500um) , group2 (range501 -530um), group3 ( range531 -560um) , group4 ( range561 -590um) . Stromal bed thickness was measured with the ultrasonic pachmeter ( MICROPACH 200P + Sonomed Inc. ) , after the flap was lifed. Flap thickness was calculated by substracting the central stomal bed thickness from the preoperative central corneal thickness. Flap thickness was recoreded for statistical analysis.Results1. Mean preoperative central corneal thickness was 533. 15 ±35. 57 urn ( range466-589um) , the Moria M2 microkeratome (160um head) created thinner flap than predicted. Mean flap thickness was 138. 05 ± 21. 37 urn(range79-186um). 95% limit for both eyes was 135.72-140.38um. Patients were randomly assigned to four groups according to different preoperative corneal thickness. Mean flap thickness of group 1 wasl26. 32 ± 18. 18um, mean flap thickness of group 2 wasl28. 86 ±17. 34um, mean flap thickness of group 3 wasl44. 36 ± 18.00um, mean flap thickness of group 4 wasl47.76 ± 18.72um. Flap thickness varied with different pre - comeal thickness groups (p <0.001). Flap thickness was significantly positivaly correlated with increasing comeal thickness (r=0.510,p<0.001). Difference of 100um of preopretive comeal thickness led changes of 30. 5um of flap thickness.2. In the first eye cut group (OD group) ,mean flap thickness was 144.46 ±20.25um ( range106 - 186um) , 95% limit for right eyes was 141.32 -147.60um. Patients were randomly assigned to four groups according to different preoperative corneal thickness. Mean flap thickness of group 1 was 132. 59 ± 16.28 um, mean flap thickness of group 2 was 134. 13 ± 17. 71 um, mean flap thickness of group 3 was 152. 30 ± 14. 81 um, mean flap thickness of group 4 was 177. 60 ±23. 83 um. Flap thickness varied with different pre - comeal thickness groups (p < 0. 001). Mean flap thickness of group 1 was thinner than that of group3 and group4. Mean flap thickness of group2 was thinner than that of group3 and group4 ( p < 0. 001). Flap thickness was significantly positivaly correlated with increasing corneal thickness ( r =0.536,p <0.001). Difference of 100um of preopretive corneal thickness led changes of 30. 5um of flap thickness.3. In the second eye cut group (OS group) ,mean flap thickness was 131. 64 ±20.46um (range79 - 171um) , 95% limit for right eyes was 128.47 - 134. 82um. Patients were randomly assigned to four groups according to different preoperative comeal thickness . Mean flap thickness of group 1 was 120.05 ± 12.29 um, mean flap thickness of group 2 was 123. 60 ± 15.45 um, mean flap thickness of group 3 was 136. 42 ± 17. 54 um, mean flap thickness of group 4 was 141.62 ± 17.44 um. Flap thickness varied with different pre - comeal thickness groups (p < 0. 001). Mean flap thickness of group3 was thicker than that of group 1 and group2 (p <0.01). Mean flap thickness of group4 was thicker than that of groupl and group2 (p <0.001). Flap thickness was significantly positi-...