| PrefaceLaser in situ keratomileusis(LASIK) is one of the most quickly developing methods to correct the refraction error in rescent years.The techniques include negative pressure suction and creation of a hinged lamellar corneal flap which diameter is 9.5mm with a microkeratome,then excimer laser is used to make a refractive cut on the underlying stromal bed and flap is repositioned.We have discovered some complications during and after surgery along with doing more and more basic and clinic research on LASIK.For example forming a thin flap , a free and/or incomplete flap etc during LASIK.There are other complications such as keratectasia,kertoconus and refractive regression etc after LASIK.Commonly believed there is a direct relation between corneal flap thickness and flap complications.In order to reduce these complications and to elevate the effect of operation,it is important to study the factors that affect the flap thickness in LASIK.During the flap cuting,the distance between the fixed microkeatomeplate and the edge of the metal blade determines the thickness of the flap,and it is known to vary within a certain range for any given microkeratome because of the effect of several factors such as corneal thickness and curvature,suction pressure,intraocular pressure , turbine and translational velocities of the microkeratome,the degree of wetness in the operation room etc.This experiment is to study the effect of suction duration on corneal flap thickness in LASIK,so to reduce corneal flap complications.Materials and methodsl.Materials:45 porcine eyes were kept at 4c in moist chambers and were used for experiments within 4 hours of enucleation.The status of epithelium in each eye was inspected by slit lamp before experiment,and eyes with epithelial defect were excluded to avoid any bias in corneal thickness, Moria M2 microkeratome, Non-contact ophthalmotonomete, Automatic keratometer.Automatic ultrasonic pachymeter.Slit lamp.Stop watch.slide gaud.etc2.Methods:The intraocular pressure (IOP) of each porcine eye was controlled by the injection of normal saline through the optic never and maintained from 20 to 25 mmHg.They were measured corneal thickness and curvature and were assigned to three groups, 10 seconds group(n=15eyes ),20 seconds group(n=15 eyes ),and 30 seconds group(n=15 eyes ).Then simulated LASIK surgery of the right eye,Corneal flap were made by using an suction ring which diameter is 9.5mm and suction time was 10 sec,20 sec and 30 sec respectively.The remaining corneal stromal thickness was measured centrally.The difference in corneal thickness and the remaining stromal thickness was defined as the flap thickness.The diameter of corneal flap is measured by using slide gaud.3.Statistical analysisrStatistical analysis was performed with t tests by SPSS 10.0 software.ResultsMean corneal flap thickness in group 1(10 sec ),group 2 (20 sec ) and group 3 (30 sec ) was 147.2 15.96um,157.33 24.85um and 167.6 22.37um respectively.There was a statistically significant difference between group 1 (10 sec ) and group 3 (30 sec ) (P=0.008).The mean corneal flap diameter in groups 1,2 and 3 was 8.668 0.1601mm,8.8627 0.2534mm and 9.06 0.2238mm,respectively.A statistically significant difference was found amomg groups.DiscussionThere are many factors that can affact corneal flap thickness duringLASlK,and there are some reports on this subject,but few are concerned about the effect of suction duration on corneal flap thickness.I think because the eyeball is relatively malleable,continuous suction delievered by a suction ring can change the shape of the cornea and eyeball,causing oculi axes to stretch and cornea to bulge above the cutting plane,resulting in the changes of flap thickness and diameter.Corneal flap thickness can be controlled by suction duration is useful in several clinical aspects. One can minimize the risk of cutting an overly thick flap by decreasing suction duration,which helps to maintain a residual stromal bed thicker than 250um,which reduces...
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