LASIK Flap Thickness Accuracy after Using Mechanical Microkeratome

Transcription

1 Med. J. Cairo Univ., Vol. 84, No. 1, June: , LASIK Flap Thickness Accuracy after Using Mechanical Microkeratome AYA H. FARAG, M.Sc.; RANIA M. SOBHY, M.D.; MOHAMED H. HOSNY, M.D. and MAHMOUD H. ABOSTEIT, M.D. The Department of Ophthalmology, Faculty of Medicine, Cairo University Abstract Purpose: To asssess the accuracy of flap thickness after using the mechanical microkeratome in LASIK surgery. Design: This prospective case series study includes 20 eyes of 10 myopic patients with a refractive error ranging from 1D to 9D, with astigmatism up to 4D. Method: All surgeries were done under topical anesthesia, by the same surgeon, and the flap thickness was measured in the center, and 2mm nasal and temporal to the center, 1 month after surgery using anterior segment OCT. Results: The mean central flap thickness was µm ±3.95 (ranging from 120µm to 133µm), the mean thickness at 2mm nasal to the center was 132.6µm±4.6 (ranging from 123µm to 136µm), the mean flap thickness at 2mm temporal to the center was 133.4µm±4.4 (ranging from 124µm to 139µm), the mean flap thickness was µm±4 (ranging from 122.6µm to 137µm), the deviation from the 110µm intended flap thickness was ±4 (12.66 to 27). Conclusion: LASIK flap thickness is larger than intended when the mechanical microkeratome is used. Key Words: LASIK flap thickness Mechanical microkeratome Myopia. Introduction MYOPIA is a common refractive error all over the world, [1] many methods can be used for correction of myopia, either non surgical or surgical. Non surgical (spectacles and contact lenses), surgical (Lasik, surface ablation, phakic IOLs, CLE, bioptics and ICRS [2,3]. However LASIK is the most common surgery used to correct myopia. In which a flap is created, and the cornea is ablated with the excimer laser, irrigated with BSS, and the flap is reapplied again on the cornea [4]. Correspondence to: Dr. Aya H. Farag, The Department of Ophthalmology, Faculty of Medicine, Cairo University A critical step in LASIK surgery is flap creation, that can be done either mechanically using mechanical microkeratome, the SBK, or with the femtosecond laser [5]. The microkeratomes use shear force traveling across the corneal stroma with an oscillating blade to create a flap [6]. Flap thickness and morphology became the main concern in LASIK surgery [7]. Most of LASIK complications are microkeratome related, such as free cap, button hole, irregular cut, incomplete cut and flap striae [4]. Aim of work: To measure the flap thickness accuracy after using the mechanical microkeratome in LASIK surgery, for myopic patients. Patients and Methods A prospective study was performed on 20 eyes of 10 patients, who underwent LASIK surgery. Study was done between February 2012 and Dec Patients were informed about the method of LASIK flap creation, (mechanical microkeratome Moria, 90 head; Moria Inc., Antony, France). Inclusion criteriae: Patients included were: 1- Myopes ( 1 to 9, and or astigmatic up to 4). 2- Normal corneal topography. 3- Corneal thickness >500 microns. 4- No other ocular pathologies. 733

2 734 LASIK Flap Thickness Accuracy after Using Mechanical Microkeratome Exclusion criteriae: Excluded patients were: 1- Myopes > 9, and or astigmatic > Abnormal corneal topography (Inferior steepening, asymmetrical bowtie, K reading >47D). 3- Corneal thickness <500 microns. 4- Any other ocular pathologies. 5- Single eyed patients. Preoperative preparation: A written informed consent was signed by all patients, preoperative examination included: - General medical and ophthalmic histories. - UCVA. - BCVA. - Slit lamp examination. - Schirmer dryness test. - Indirect ophthalmoscopic examination. - Investigations: Corneal topography (Pentacam, Allegretto Wave Topolyzer). Operative procedure: All procedures were performed by the same surgeon, all eyes were targeted for emmetropia, topical anaesthesia Benoxinate hydrochloride 0.4% was instilled before surgery, all patients were done at a private hospital. Mechanical mirokeratome Moria (90µm, Moria Inc., Antony, France) was used to create the flap with superior hinge, the suction ring selected according to the nomogram either 0 or +1 based on the corneal curvature, the used blade was disposable, the same blade for both eyes starting with the right eye, the flap was lifted, excimer laser ablation was done by VISX S4 IR (Abott Medical Optics Inc., Santa Ana, CA). Corneal flaps were repositioned by rinsing them with balanced saline solution, no corneal contact lenses were used after flap reposition. Postoperative follow-up: Postoperative medications included Ofloxacin 0.3%, Dexamethasone 0.1% eye drops, and artificial tears. Follow-up was done on the same day to make sure of the flap position, 1wk, for UCVA, BCVA, slit lamp examination, at 1 month anterior segment OCT (Fourier-domain OCT, Optovue RTVue-100; Optovue Inc., Fremont, California) was done to measure the flap thickness and evaluate architecture. With a scan rate of axial scans per second, axial resolution of 5µm, transverse resolution of 15µm, and an add-on lens (CAM-L mode: mm) was used to assess the corneal flap morphology. We measured the thickness at the corneal center, and 2mm nasal and temporal from the center, each scan was analyzed by the same observer. Results Preoperative values: Table (1): The mean age was 28±4.6 (ranging from 20 to 35), sex 2 males and 8 females, the mean preoperative K reading was 43.24D ± 1.5 (ranging from 41.5D and 46.45D), the mean preoperative corneal thickness was 545.6µm±27 (rang from 500µm to 584µm, the mean spherical error was 4.2 ±2 (from 1 to 8), mean cylindrical error was 1.25 ±0.8 (from 0 to 2.75), the mean SE was 4.9 ±2.00 (from 1.75 to 8.6) the mean preoperative UCVA was 0.27±0.47 (0.1 to 0.7), the mean preoperative BCVA was 0.95±0.89 (0.7 to 1). Table (1): Preoperative characteristics of patients who underwent LASIK flap creation with the Moria Microkeratome. Mean ± SD (range) Age (yr) Sphere (D) 28±4.6 (20 to 35) 4.2±2 ( 1 to 8) Cylinder (D) 1.25±0.8 (0 to 2.75) Spherical Equivalent (D) 4.9±2.00 ( 1.75 to 8.6) CCT (µm) 545.6µm±27 (500 to 584) Corneal Curvature (D) 43.4±1.5 (41.5 to 46.45) UCVA 0.27±0.47 (0.1 to 0.7) BCVA 0.95±0.89 (0.7 to 1) Postoperative values: Table (2): The mean central flap thickness was µm ±3.95 (ranging from 120µm to 133µm), the mean thickness at 2mm nasal to the center was 132.6µm ±4.6 (ranging from 123µm to 136µm), the mean flap thickness at 2mm temporal to the center was 133.4µm±4.4 (ranging from 124µm to 139µm), the mean flap thickness was µm±4 (ranging from 122.6µm to 137µm), the deviation from the 110µm intended flap thickness was ±4 (12.66 to 27). There was no, correlation between the mean flap thickness and the mean preoperative corneal thickness, as it was with p-value which is statistically insignificant, and there was no correlation between the mean flap thickness

3 Aya H. Farag, et al. 735 and the mean preoperative K readings was with p-value >0.993 which is statistically insignificant. The mean postoperative spherical error was 0, cylindrical error was 0.12 ±0.12 (ranging from 0 to 0.25), the mean postoperative spherical equivalent was 0.06±0.06 (ranging from 0 to 0.12) UCVA was 0.95 ±0.89 (0.7 to 1), BCVA was 0.95 ±0.89 (0.7 to 1). Regarding complications, we detected on follow-up (on the same operative day) flap striae in one eye which needed operative management by lifting the flap and irrigation with BSS then flap repositioning. Table (2): Postoperative values. Mean ± SD (range) Central flap thickness (μm) μm±3.95 (120 to 133) 2mm nasal to the center (μm) 132.6±4.6 (123 to 136) 2mm temporal to the center (μm) 133.4±4.4 (124 to 139) Mean flap thickness (μm) μm±4 (122.6 to 137) Deviation from intended (μm) 20.79±4 (12.66 to 27) Sphere (D) 0 Cylinder (D) 0.12±0.12 (0 to 0.25) Spherical Equivalent (D) 0.06± 0.06 (0 to 0.12) UCVA 0.95±0.89 (0.7 to 1) BCVA 0.95±0.89 (0.7 to 1) 5 0 Deviation from intended Fig. (1): A column chart showing deviation from the intended flap thickness after using the Moria mechanical microkeratome. Fig. (2): AS OCT of flap created by mechanical microkeratome. Discussion In our study the, the mean central flap thickness was µm±3.95 (ranging from 120µm to 133 µm), the mean thickness at 2mm nasal to the center was 132.6µm±4.6 (ranging from 123µm to 136µm), the mean flap thickness at 2mm temporal to the center was 133.4µm±4.4 (ranging from 124µm to 139µm), the mean flap thickness was µm±4 (ranging from 122.6µm to 137µm), the deviation from the 110µm intended flap thickness was ±4 (12.66 to 27). Yuehua Zhou et al., [8], measured the accuracy of LASIK flaps created by the Moria microkeratome 110-µm head (72 eyes). One month after surgery, using the Visante AS OCT, they measured the flap thickness at the vertex, paracentral (1 to 2mm from the vertex) and peripheral (3 to 5 from the vertex). The mean central flap thickness at 1 month postoperative was ±3.38µm (range: to µm), in the femtosecond group, the mean paracentral thickness nasal and temporal were

4 736 LASIK Flap Thickness Accuracy after Using Mechanical Microkeratome 135 ±5, 143±5 respectively, peripheral nasal and temporal thickness were 142 ± 10, 143± 10 respectively, the mean flap thickness was ±4.70µm. Burkhard Von Jagow et al. [9], measured the flap thickness and morphology of Zioptics XP microkeratome 120µm, using the Visante AS OCT at 0.5mm, 1, 2, 3 from the vertex and 0.5mm from the flap edge, the mean thickness nasally at the same points were 129 ± 16, 135± 14, 145± 15, 160± 18, 175± 16 respectively, and temporally were 132 ± 15, 142± 18, 154±20, 166±24, 165±23 respectively. The mean deviation from the intended 120µm was +12.5µm for the central 2mm, +40.8µm for the periphery. They explained the deviation from the intended flap thickness using the mechanical microkeratome due to mechanical interaction between the cornea and the microkeratome. With the microkeratome the course of the lamellar cut depends on the gap of the blade, oscillation speed, and constancy of compression during the forward movement of the blade at the side of the device, and the steepness and stiffness of the cornea on the other side [9]. Similar to our study Yu Zhang et al., [10] measured the flap thickness and morphology mechanical microkeratome, the Moria 90, and they almost gave very close results. LASIK was performed in 50 eyes using the Moria microkeratome (Moria SA, Antony, France). Visante AS-OCT was used 1 week postoperatively to evaluate the thickness at the center, 2mm and 3.5mm from the center. The mean central thickness was (132.96± µm. The mean standard deviation of the different points within the individual flap (uniformity) was 8.48±2.35µm. Yao et al., [11] found that the mean flap thickness at 1 week postoperatively was 127.9±7.57µm using the Moria microkeratome with an intended thickness of 110µm. Zhai CB et al., [12], measured the flap thickness of the Moria created flaps using the Visante ASOCT, at I month after surgery the mean central flap thickness was 118 ± 13, the maximum deviation from the intended flap thickness was 20µm. Du S. et al., [13] compared 3 types of microkeratomes, the Moria One Plus, 90, and 110, using subtraction pachymetry, the mean flap thickness was not significantly different between the right and left eyes (97.5 ± 11.39, 96.73±0.45 in the right and left eye of the Moria one plus group respectively), while it was significantly different in the 90 ( ± versus 123.4± in the right and left eyes respevtively) and significantly different in the Moria 110 group ( ± versus ±.03 in the right and left eyes respectively). Conclusion: LASIK flap thickness is larger than intended when the mechanical microkeratome is used. References 1- HAIYAN L.I., Ph.D., M.D.; TONG SUN, M.D.; MING WANG, Ph.D., M.D. and JIALIANG ZHAO, Ph.D., M.D.: Safety and Effectiveness of Thin-flap LASIK Using a Femtosecond Laser and Microkeratome in the Correction of High Myopia in Chinese Patients. J. Refract. Surg., 26: , JORGEL, ALIO, PABLOPEN A. GARCIA, KETEVAN- PACHKORIA, JORGIL. ALIOII and AMR ELASWAD: Intraocular Optical Quality of Phakic Intraocular Lenses: Comparison of Angle-Supported, Iris-Fixated, and Posterior Chamber Lenses, Am. J. Ophthalmol., 156: , DAVID P. PIÑERO and JORGE L. ALIO: Intracorneal ring segments in ectatic corneal disease-a review. Clinical and Experimental Ophthalmology, 38: , ASHOK G., JORGE L. ALIO, FRANK J., CARLO F., JEROME J., FRANCISCO S., A. JOHN K., D. RAMA- MURTH, KEIKI R., MAHIPAL S., ROBERTO P., FRE- DERIC H., DAVID P., C. BANU C., ARUN C., CYRES C. and BOJAN P.: Surgical techniques in ophthalmology refractive surgery, Vol. 10, p.89-90, MARCELLA Q. SALOMAO, M.D. and STEVEN E. WILSON, M.D.: Femtosecond laser in laser insitu keratomileusis. J. Cataract. Refract. Surg., Jun., 36 (6): , LADAN ESPANDAR and JAY MEYER: Intraoperative and Postoperative Complications of Laser in situ Keratomileusis Flap Creation Using Intra Lase Femtosecond Laser and Mechanical Microkeratomes, Middle East. Afr. J. Ophthalmol., Jan.-Mar., 17 (1): 56-9, TEHRANI M., SCHÄFER S. and DICK H.B.: Evaluation of cut quality using the Amadeus microkeratome with different settings. J. Cataract. Refract. Surg., 30: , YUEHUA ZHOU, M.D.; LEI TIAN, M.D.; NINGLI WANG, M.D.; PAUL J. DOUGHERTY, M.D.: Anterior Segment Optical Coherence Tomography Measurement of LASIK Flaps: Femtosecond Laser vs Microkeratome. J. Refract. Surg., 27 (6): , BURKHARD VON JAGOW and THOMAS KOHNEN: Corneal architecture of femtosecond laser and mechanical microkeratom flaps imaged by anterior segment ocular coherent tomography. J. Cat. Refractive Surgery, 35: 35-41, YU ZHANG, YUE-GUO CHEN and YING-JIE XIA: Comparison of Corneal Flap Morphology Using AS-OCT

5 Aya H. Farag, et al. 737 in LASIK With the WaveLight FS200 Femtosecond Laser Versus a Mechanical Microkeratome. J. Refract. Surg., 29 (5): 320-4, YAO P., XU Y. and ZHOU X.: Comparison of the predictability, unifor- mity and stability of a laser in situ keratomileusis corneal flap created with a VisuMax femtosecond laser or a Moria micro-keratome. J. Int. Med. Res., 39: , ZHAI C.B., TIAN L., ZHOU Y.H., ZANG Q.W. and ZHANG J.: Comparison of flaps made by Femtosecond laser and automated keratomes for the sub bowman keratomileusis. Cchen. Med. Journal (Engl.) July; 126 (13): , DU S., LIAN J., ZHANG L., YE S. and DONG S.: Flap thickness variation with 3 types of microkeratome heads. Journal Cat. Refrac. Surg., Jan., 37 (1): 144-8, 2011.