Bhatia Karan, Shastri Aniket, Mishra Deepak, Satyamurthy K V, Manaktala Ruchita, Rati Renuka
M. M. Joshi Eye Institute, Hubli, Karnataka; Regional Institute of Ophthalmology, Sitapur Eye Hospital, Sitapur, Uttar Pradesh, India.
M. M. Joshi Eye Institute, Hubli, Karnataka, India.
Indian J Ophthalmol. 2020 Dec;68(12):2995-2997. doi: 10.4103/ijo.IJO_450_20.
To calculate a modified percentage tissue altered (mPTA) in post laser-assisted in-situ keratomileusis (LASIK) eyes and to validate its role as an independent factor to evaluate ectasia in the Indian population.
A total of 333 consecutive eyes with normal preoperative corneal topography by combined placido and scheimpflug imaging-based topography system (SIRIUS) who underwent LASIK using a microkeratome between 2011 and 2014 at a tertiary level teaching hospital in south India, were retrospectively analyzed. Preoperatively patient's refraction, flap thickness (FT), ablation depth (AD), residual stromal bed (RSB), and thinnest corneal thickness (TCT) were recorded. The formula used was mPTA = (FT + AD)/TCT. mPTA was grouped into <0.4 (low risk), 0.40 - 0.45 (moderate risk), and >0.45 (high risk). All patients were called for follow-up and underwent a topography to look for ectasia.
In total 60.1%, 29.1%, and 10.8% patients had mPTA of <0.4, 0.40 - 0.45 and >0.45, respectively. However, after a minimum follow-up of 2 years, none of the patients had any sign of ectasia.
Careful selection of patients is mandatory before proceeding for LASIK. Factors like corneal thickness, RSB, degree of myopia, and AD are more important. The role of mPTA >0.4 as an independent risk factor for post LASIK ectasia is questionable in Indian eyes. Other factors or a modified formula suitable for Indian eyes needs to be investigated. A larger follow-up period is also required as ectasia has been known to develop even after 2 years.
计算准分子激光原位角膜磨镶术（LASIK）术后眼的改良组织改变百分比（mPTA），并验证其作为评估印度人群角膜扩张的独立因素的作用。
回顾性分析2011年至2014年期间在印度南部一家三级教学医院使用微型角膜刀进行LASIK手术的333只连续眼，这些眼术前使用基于普拉西多和眼前节分析系统（SIRIUS）的联合角膜地形图成像系统检查角膜地形图正常。记录术前患者的屈光度数、瓣厚度（FT）、切削深度（AD）、剩余基质床（RSB）和最薄角膜厚度（TCT）。使用的公式为mPTA =（FT + AD）/TCT。mPTA分为<0.4（低风险）、0.40 - 0.45（中度风险）和>0.45（高风险）。所有患者均被要求进行随访并接受角膜地形图检查以寻找角膜扩张。
分别有60.1%、29.1%和10.8%的患者mPTA<0.4、0.40 - 0.45和>0.45。然而，在至少随访2年后，没有患者出现任何角膜扩张的迹象。
在进行LASIK手术前必须仔细选择患者。角膜厚度、RSB、近视度数和AD等因素更为重要。mPTA>0.4作为LASIK术后角膜扩张的独立危险因素在印度人群眼中的作用值得怀疑。需要研究其他因素或适合印度人群眼的改良公式。由于已知角膜扩张甚至在2年后仍会发生，因此还需要更长的随访期。
