Clinical Observation Of Laser Subepithelial Keratomileusis For High Myopia

Laser subepithelial keratomileusis (LASEK)is a new way totreat refractive errors.It has been progressing gradually since2001 .LASEK is based on Photorefractive keratectomy (PRK)with afew minor improvements. In this technique, the anterior corneaepithelium is retained and the chance of corneal stromalcells'death is decreased.The death of the corneal stromal cellsis one of the factors that initiate the cornea's concrescencereaction. By avoiding the death of corneal stormal cells,there canbe a reduction in refracting regreession and corneal haze .Presently, many investigtions demonstrated that LASEK was the idealmethed for moderate and low degree myopia. Compared to PRK, thepostoperative ache was weaker,the refractive result was better, andthe rate of corneal haze was lower .In China,laser in situ keratomileusis(LASIK)is the majorsurgical procedure for treating refractive errors.LASIK reservesthe anterior cornea epithelium and the lamina elastic anterior,aswell as the inherent corneal configurations. The rate of refractingregression and corneal haze after performing LASIK is relativelylow. Clinical results show LASIK is ideal for high degree myopia.However due to the necessity of creating a cornea flap,some severecomplications may occur.A 130-160μm cornea flap that is made withthe thin residual bed will influence corneal intensity. Presentlymany studies have proved that in LASIK if more than 250μm of theresidual bed was preserved under the corneal cap , the procedurewould be relatively safe. If 325μm of the residual bed could bepreserved ,then the procedure would be much safer. In some casesthat the patients have high degree myopia and thin cornea,they willnot have enough residual preserved after the surgery.these patientswill go to receive LASEK surgery. In this study,we reviewed the data on 55 patients (total of109eyes) with high degree myopia who have received LASEK surgeryto observe the clinical outcome of the surgery.These patients havea refractive index ranging from –8.0D～-15.25D, they were dividedin to three groups: group Ⅰwith 36 eyes (range:-8.0～-10.0 D);groupⅡwith 40 eyes (range:-10.25～-12.0D);and groupⅢwith 33eyes(range:-12.25～-15.25D).All operations were performed by thesame doctor,and used the TECHNOLAS217c excimer laser in a similarmanner to PRK. In the operation the anterior corneal surface wastreated with 20% alchol for 30 seconds to make the intact cornealflap. Following laser ablation, the epithelial flap was thenreplaced to cover the cornea bed. The follow-up period was 12months. The execution and survival of the epithelial flap wassuccessful. 105(96.33%)eyes'epithelial flap successfully healedwithin 3-4 days after the surgery. Pain was reported on the firstpostoperative day and alleviated on the second day. Eyesightrecovered to the best spectacle corrected visual acuity (BSCVA)within 10-15 days. The percentage of uncorrected visual acuity(UCVA)that reached BSCVA after 12 months was as follows:groupⅠ75.0%;groupⅡ72.5%;groupⅢ48.5%。The percentage of groupⅠandⅡwere statistically significant (p<0.05) from group Ⅲ.Regressions were observed in allthree groups.In groupⅠandⅡ,theregression followed a pattern while group Ⅲshowed no observablepattern. Regreession was very obvious within group Ⅲ.Thepercentage of refraction greater or equal±1.0D at 12 months was:for groupⅠ, 80.56%;for groupⅡ,75%;and for groupⅢ,51.52%。Again, the percentage for group Ⅰand Ⅱwere statisticallysignificant (p<0.05) from group Ⅲ. No or very mild haze wasdetected in groupⅠandⅡ. In groupⅢ, 6.06% of haze falled underclass 1,and 3.03%of haze falled under class 2.No keratoconus wasobserved in any of the 3 groups . The refractive regression occurred more commonly after LASEKfor high myopia. Refractive regression was rate between -8.0D and-12.0D range,and it could be prevented by add to the amount of thecorrection. Refractive regression wasn't jarless when refractive≥-12.25D;At 12 months, no or very mild haze was detected in groupⅠandⅡ,but the rate of corneal haze was relatively high in groupⅢ; The fatalness of keratoconus was low after LASEK.To sumup,LASEK is effective for the correction of the myopia with therefraction between –8.0D and –12.0D . But some severecomplications may occur when refraction≥-12.25D.