【精品文献】LASIK术中负压吸引时间对猪角膜瓣厚度和直径的影响

【精品文献】LASIK术中负压吸引时间对猪角膜瓣厚度和直径的影响 论文范文 题目:LASIK术中负压吸引时间对猪角膜瓣 厚度和直径的影响 编辑:司马小 作者:马小力,徐建刚～刘汉强 【摘要】 目的:探讨准分子激光原位角膜磨镶术,LASIK,术中负压吸引时间对角膜瓣厚度和直径的影响。方法:根据负压吸引时间的不同将60只猪眼随机分为3组:组1,10s,、组2,20s,和组3,30s,～使用法国产Moria M2型角膜板层刀分别吸引角膜10s～20s和30s后切削角膜瓣～利用角膜超声测厚仪测量角膜瓣厚度～应用镀铬游标卡尺测量角膜瓣直径。结果:组1、 2和3角膜瓣厚度分别为146.05〒13.46～157.35〒18.95和169.25〒21.02μm～各组间比较有 显著性差异(P,0.001)。各组的平均角膜瓣直径分别为8.63〒0.19mm,组1～10s,～8.89〒0.24mm,组2～20s,和9.06〒0.18mm,组3～30s,。各组间比较有显著性差异(P<0.01)。结论:LASIK术中随着负压吸引时间的延长～角膜瓣厚度和直径均增加。 【关键词】 负压吸引,角膜瓣厚度,LASIK Abstract AIM: To determine the effect of suction duration on thickness and diameter of corneal flap created by microkeratome in porcine eyes in laser in situ is (LASIK).METHODS: Sixty porcine eyes were randomly assigned to three groups according to different suction durations: group 1 (10 seconds), group 2 (20 seconds), and group 3 (30 seconds). A Moria M2 microkeratome (Moria, France) with a 160μm head was used to create a corneal flap. Corneal flap thickness was measured by automated ultrasonic pachymetry, and the flap diameter was measured by a vernier caliper.RESULTS: The flap thickness of group 1, group 2 and group 3 was 146.05〒13.46μm, 157.35〒18.95μm and 169.25〒21.02μm, respectively. There was a statistically significant difference among three groups (P=0.001). The mean flap diameter in groups 1, 2 and 3 was 8.63〒0.19mm, 8.89〒0.24mm and 9.06〒0.18mm, respectively. A found among groups (P<0.01).CONCLUSION: In LASIK in porcine eyes, an increase in suction duration resulted in a thicker and greater flap. KEYWORDS: suction duration; lamellar corneal flap thickness; LASIK INTRODUCTION Since its introduction in 1990, laser in situ keratomileusis (LASIK) has become currently the most frequently used surgical treatment to correct refractive errors worldwide[2,3]. LASIK involves a primary procedure of creating a corneal flap by microkeratome. The flap thickness based on the distance between the fixed microkeratome plate and the edge of the metal blade. Some studies found variables that affect LASIK flap thickness include corneal curvature, corneal thickness, the amount of vacuum obtained during the procedure, microkeratome blade translation and oscillation of different suction durations on flap thickness in LASIK. MATERIALS AND METHODS Materials Porcine eyes were obtained from a local abattoir. The eyes were kept at 4? in moist chambers and used for experiments within 12 hours of enucleation. The status of the epithelium in each eye was checked, and eyes with epithelial defects were excluded to avoid any bias in corneal thickness and incision angle measurements. Porcine eyes were randomly assigned to three groups, which were exposed to different suction durations: group 1 (10 seconds, 20 eyes), group 2 (20 seconds, 20 eyes), and group 3 (30 seconds, 20 eyes). Methods Preoperative examinations The intraocular pressure(IOP) of porcine eyes was controlled by the injection of normal saline through the optic nerve and maintained within 20mmHg tonometer (TOPCON, Japan). The IOP of each porcine eye was measured three times and then averaged. Measurements of central corneal thickness (CCT) and keratometry were performed using Micropach 200 automated keratometer (Canon, Japan). The CCT and keratometry of each porcine eye were measured three times and then averaged. Microkeratome and surgical techniques A Moria M2 microkeratome (Moria, France) with a 160μm head was used to according to the manufacturer’s instructions. The porcine eyes were placed on a stand with sufficient support for the surgical procedure. The same surgeon performed all procedures. A drop of normal saline was used to moisten and lubricate the cornea to facilitate the flap resection. The incision using the microkeratome was made from the midpoint of the temporal and inferior side to the nasal side (superior hinge) after the vacuum pressure of the Moria 2 control unit reached 108mmHg. Using different suction durations, the corneal flaps were made with microkeratome. The suction ring was removed and the corneal flap was retracted, exposing the underlying corneal stroma. Measurement of Flap Thickness and Diameter After resection, the remaining corneal stromal thickness was measured centrally three times by the automated pachymeter. The difference in the corneal thickness and the remaining stromal thickness was defined as the flap thickness[11,12]. The diameter of the flap were measured three times using vernier caliper (Fushun measurement equipment factory, China). Tukey’s multiple comparison tests were used to evaluate the differences after various suction durations. P?0.05 was considered statistically significant. RESULTS Preoperative CCT and Keratometry There were no differences in corneal thickness and keratometric values among the three groups (CCT: F,0.035, P,0.996,keratometry: F,0.032, P,0.969; Table 1). Flap Thickness Values for the flap thickness varied with the suction duration. The thickness of group 1, group 2 and group 3 was 146.05〒 13.46μm (10 seconds), 157.35〒 18.95μm (20 seconds), and 169.25〒21.02μm (30 seconds) respectively. There was a statistically significant difference among 3 groups (P=0.001, Table 1). The flaps of group 1 (10 seconds) were statistically thinner than those of group 3 (30 seconds, P<0.01). However～there was no statistical significance between neither groups 1 and 2 (P=0.128), nor group 2 and 3 (P=0.103). Flap Diameter The flap diameter increased along with suction duration (Table 1). The flaps of group 1 (10 seconds) were statistically larger than those of group 2 (20 seconds, P<0.01) and group 3 (30 seconds, P<0.01). Moreover～there was also statistical significance between groups 2 and 3 (P=0.028). DISCUSSION Although LASIK is safe, there are some complications, including iatrogenic keratectasia[3,13], which is the most serious late complication following LASIK. Altered biomechanics of the cornea following LASIK predispose it to ectasia despite normal IOP. The strength of cornea following LASIK is determined by the residual stromal bed thickness. If the corneal flap is unexpectedly thicker than intended, inadequate residual stromal thickness may occur, and then keratectasia may occur. Furthermore, variability in flap thickness can also have a direct effect on refractive correction because the depth of keratectomy relates to the amount of intraoperative bioelastic corneal change, which in turn affects the accuracy of the desired curvature change[14,15]. Therefore, the desired thickness of an ideal corneal flap should be consistent, predictable and accurate. LASIK microkeratomes are designed to cut a predetermined flap thickness based on the distance between the fixed microkeratome plate and the edge of the metal blade. Other variables that affect LASIK flap thickness include corneal curvature, corneal thickness, the amount of vacuum obtained during the procedure, microkeratome blade translation and oscillation rates, and bla eyeball is bioelastic, continuous suction delivered by a suction ring can change the shape of the cornea, causing it to bulge above the cutting plane, resulting in inconsistent flap thickness. Therefore, we focused only on the effect of suction duration on flap thickness and tried to control the other factors as precisely as possible in our study. According to our data, values for the flap thickness varied with the suction duration. There was a statistically significant difference among 3 groups (P,0.001). The flaps of group 1 (10 seconds) were statistically thinner than those of group 3 (30 seconds, P<0.01). Therefore, in order to minimize the risk of cutting an overly thick flap and maintain a residual stromal bed thicker, maintaining optimal suction duration is necessary, which depends on practiced, perfect and smooth operation. A thinner corneal flap is of benefit in the prevention of keratectasia. Control of flap thickness can be useful in the other clinical aspects. Very flat corneas with average keratometric power of less than 41 diopters (D) are at a greater risk for cutting a free flap[16]. A smaller area of the cornea is usually exposed to the microkeratome blade in these cases, resulting in a free cap[17]. Sufficient suction duration that thickens the flap would increase the hinge area and decrease the probability of creating a free flap. In conclusion, values for the flap thickness and flap diameter varied with the suction duration. We suggest corneal flap thickness should be routinely measured intraoperatively to ensure that enough tissue remain after surgery. 【参考文献】 1 Pallikaris IG, Papatzanaki ME, Stathi EZ, Frenschock O, Georgiadis A. Laser in situ keratomileusis. Laser Surg Med 2 Sugar A, Rapuano CJ, Culbertson WW, Huang D, Varley GA, Agapitos PJ, de Luise VP, Koch DD. Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy: a report by the American Academy of Ophthalmology. 3 Seiler T, Koufala K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg 1998, 4 Liu KY, Lam DS. Direct measurement of microkeratome gap width by electron microscopy. J Cataract Refract Surg 27 5 Choudhri SA, Feigenbaum SK, Pepose JS. Factors predictive of LASIK flap thickness with the Hansatome zero 6 Flanagan GW, Binder PS. Precision of flap measurements for laser in situ keratomileusis in 4428 eyes. J Refract Surg 7 Flanagan GW, Binder PS. The theoretical vs. measured laser resection for laser in situ keratomileusis. J Refract 8 Gailitis RP, Lagzdins M. Factors that affect corneal flap thickness with the Hansatome microkeratome. J Refract 9 Kasetsuwan N, Pangilinan RT, Moreira LL, DiMartino DS, Shah SS, Schallhorn SC, McDonnell PJ. Real time intraocular pressure and lamellar corneal flap thickness in ker 10 Módis L Jr., Langenbucher A, Behrens A, Seitz B. Flap quality in single versus multiple use of the same blade in the Flapmaker microkeratome. J Refract Surg 11 Spadea L, Cerrone L, Necozione S, Balestrazzi E. Flap measurements with the Hansatome microkeratome. J Refract Surg 12 Seo KY, Wan XH, Jang JW, Lee JB, Kim MJ, Kim EK. Effect of microkeratome suction duration on corneal flap thickness and incision angle. J Refract Surg 13 Tervo TM. Iatrogenic keratectasia after laser in situ 14 Roy AS, Dupps WJ Jr. Effects of altered corneal stiffness on native and postoperative LASIK corneal biomech 15 Wang A, Chen W, He R, Wang X, Liu C. Experimental study on corneal biomechanical properties of rabbit eye after LASIK. Shengwu Yixue Gongchengxue Zazhi 2009;26(2 16 Sridhar MS, Rao SK, Vajpayee RB, Aasuri MK, Hannush S, Sinha R. Complications of laser in situ keratomileusis. 17 Gimbel HV. Flap complications of lamellar refractive surgery. Am J Ophthalmol 1999;1