Corneal Morphology And Visual Quality After LASIK Flap Creation With FEMTO LDV Femtosecond Laser

PARTI Facts Relating to the Corneal Flap Creation With The FEMTO LDV Femtosecond LaserPURPOSE To present the flap characteristics and assess the facts correlating to the thickness and diameter of the cornea flap created with femtosecond laser.METHODS Two hundred sixty consecutive eyes of 130 previously non-operated patients were treated with the FEMTO LDV. Twenty-six patients had an intended flap thickness of 90μm and 104 were 110μm. Intended flap diameter varied from 8.5 to 9.5mm.The flap diameter was measured by callipers. Single variable correlation of flap diameter and preoperative keratometric value K1, corneal thickness or patient age were determined. Similarly, single variable correlations of the flap thickness (measured by optical coherence tomography,OCT) and preoperative keratometric value K1, corneal thickness, patient age, intraocular pressure. flap diameter were calculated at 1 week after surgery.RESULTS The 90μm flap group has a mean flap thickness of 95.12±7.65 (75.50～109.50)μm, while for the 110μm group the mean flap thickness was 104.81±3.09(95.75～112.50)μm. The difference between rignt and left eyes was not statistically significant (tl10μm=-1.223, t90μm=-1.343, P>0.05). Corneal flap thickness was inversely correlated with flap diameter (r110μm=-0.363, r90μm =-0.434, P<0.01), but was not dependent on preoperative patient age, corneal thickness, keratometric value K1, or intraocular pressure (r110μm=-0.160,0.054, -0.011,-0.363; r90μm=0.024,0.074,-0.212,-0.434, all P>0.05). Corneal flap diameter was positively correlated with preoperative corneal keratometric value K1 and thickness (P<0.001, P<0.05). The most common complication was minor bleeding during the procedure, but none prevented further laser ablation.CONCLUSIONS The Ziemer FEMTO LDV laser created LASIK flaps have relatively good predictability and minimal intraoperative complications. Preoperative central cornea thickness and keratometric value K1 of eye dose not affect the thickness of the corneal flap made with femtosecond laser.PARTⅡIn Vivo Corneal Confocal Microscopy Comparison of Ziemer FEMTO LDV Femtosecond Laser and Hansatome Mechanical Microkeratome for Laser In Situ KeratomileusisPURPOSE To assess and compare corneal cellular modifications induced by Ziemer FEMTO LDV femtosecond laser and mechanical microkeratome Hansatome for LASIK.METHODS In this case-control study, FEMTO LDV femtosecond laser (10 patients/20 eyes) and mechanical microkeratome Hansatome (9 patients/18 eyes) assisted flap preparation were both performed during the same period. All eyes were examined with the HRTⅢpre-surgery and 1 week,1 month,3 months post-surgery. The morphological changes at the center and margin of the flaps were observed, and difference of cellular morphology after surgery between the two approaches were evaluated.RESULTS No cornea had clinically significant flap microfolds detected by slit-lamp examination 1 week,1 month and 3 months after the surgery. Both groups showed decreased density of upper stromal cells (all P＜0.001). Hansatome group demonstrated slightly thickened corneal epithelium early after the surgery, which returned to the pre-surgery level at 3 months. FEMTO LDV group demonstrated unchanged before and after surgery.All eyes showed high reflective interface particles, and its density was lower in the FEMTO LDV group than in the Hansatome group (P<0.001). Evaluation of both groups on day 7 showed keratocyte transformation, most likely related to cellular activation beneath the interface. The activation of stromal cells was decreased at 3 months. The FEMTO LDV group showed earlier regeneration of nerve fibers than the Hansatome group. The flap margin after the femtosecond laser technique appeared microscopically as a clear-cut and regular edge 1 week after the surgery. At month 3, irregular secondary fibrosis, adjacent to the still well-defined FEMTO LDV flap edge, was observed, which indicated a stronger healing ability. In contrast, the flap margin of the mechanical microkeratome had the appearance of a less clearly identified fibrotic scar.CONCLUSIONS The FEMTO LDV flap margin showed earlier nerve fiber regeneration and greater fibrotic scarring than that induced by the mechanical microkeratome.PARTⅡComparison of Visual Quality After LASIK Flap Creation With a Femtosecond Laser and a Mechanical MicrokeratomePURPOSE To assess efficacy, predictability and safety after FEMTO LDV femtosecond laser and mechanical microkeratome hansatome LASIK for myopia, and to evaluate the patients'visual quality by comparing the contrast sensitivity(CS), CS under the glare stimulus and aberration changes.METHODS Ninety-eight myopic patients (196 eyes) were treated with LASIK using the Technolas217zl00 laser system. For flap preparation,92 eyes (46 patients, spherical equivalent [SE],-6.88±1.65D) were treated with FEMTO LDV approach, and the other 104 eyes (52 patients, SE,-6.78±1.05D) were treated with Hansatome approach.Zyoptix wavefront-guided LASIK was performed for each of these eyes after the flap preparation. For evaluation of efficacy, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, contrast sensitivity, CS under the glare stimulus and high order aberrations (HOA) were evaluated preoperatively and 1 week,1 month,3 months after treatment.RESULTS (1) Visual acuity. At 1 week after the surgery,59/92(64.13%) patients of the FEMTO LDV group had their UCVA reaching or surpassing the BSCVA, while in the Hansatome group, this rate was 76/104 (73.08%). At 3 months after the surgery, the rate of UCVA>BSCVA was 86/92(93.48%) in FEMTO LDV group and 96/104(92.31%) in Hansatome group. (2) Refraction. The refraction was +0.49D in the FEMTO LDV group and +0.35D in the Hansatome group at 1 week after surgery, while at 3 months, it was +0.16 D in the FEMTO LDV group and-0.15D in the Hansatome group. (3) Contrast sensitivity. The FEMTO LDV group photopic CS was not different before and after the surgery. The mesopic CS decreased to the lowest level at 1 week postoperation, and returned to preoperative level at 1 month after operation.(4) CS under the glare stimulus. Glare didn't influence the photopic CS in the FEMTO LDV group. Mesopic CS was most obviously influenced by glare at 1 week but not 1 or 3 months after surgery, causing decrease of CS at 1.5,3.0,6.0 and 18.0 cpd (P<0.05). However, under photopievision, glare didn't make difference in CS between the 2 groups after surgery. At 3 months, at medium to low spatial frequencies (1.5,3.0,6.0 cpd), the CS of FEMTO LDV group was higher than the hansatome group. (5) HOA. In the FEMTO LDV group, the root-mean-square (RMS) of CHOAs,3 order aberration and Coma were increased at 1 week and 1 month after the surgery, but returned to the preoperation level at 3 months. The RMS of 4 order aberration and spherical aberration were higher than the preoperation level at all periods after the surgery (P<0.05). At 3 months, the HOA and Coma in the FEMTO LDV group were all lower than the Hansatome group (P=0.045, P=0.047). There were no difference in spherical aberration and trefoil between the 2 groups.CONCLUSIONS Femtosecond laser for LASIK surgery greatly mitigates the increase of HOA after the surgery.Patients undergoing femtosecond laser-assisted LASIK have better quality of vision after surgery than hansatome patients. The improvements of CS after the femtosecond laser assisted LASIK surgery may be related to the differences in postoperative HOAs found with femtosecond laser and microkeratome flap creation.