CLINICAL RESULTS OF LASIK FORLOW MODERATE AND HIGH MYOPIAWITH THE TECHNOLAS 217c EXCIMER LASER
Sujal Shah*, Anand Shroff**
*Consultant Ophthalmic Surgeon, Bhatia & Lilavati Hospital; **Hon. Ophthalmic Surgeon, Bombay Hospital; Mumbai.
Since the first Laser Insitu Keratomileusis (LASIK) procedure performed in 1989, the technique has been considerably refined and millions of people worldwide have experienced the benefit of improved natural vision and reduced dependence on glasses or contact lenses. The use of the excimer laser is a quantum leap in the precision and safety of refractive surgery over the previously dominant techniques such as radial keratotomy (RK) that involved the use of calibrated knives.
First generation excimer lasers (broad beam, small treatment zones, simple spherical and cylindrical treatments) used in 1989 gave way to second -generation lasers (large scanning or slit-beams) and finally to modern third generation lasers (small beam flying spot lasers with active eye trackers, sophisticated algorithms) to allow superior corneal profiles and customized treatments. The coupling of third generation excimer laser hardware and software with modern surgical techniques that use the most advanced instrumentation have made LASIK a safe and consistent procedure resulting in its widespread acceptance as an alternative to spectacles and contact lenses.
The Technolas 217c excimer laser system incorporates a narrow circular beam of 2 mm diameter and software designed for a controlled treatment of a full range of refractive errors including myopia, hypermetropia and astigmatism. This is combined with an active eye tracking that follows minute eye movements to allow precise delivery of laser pulses over the desired area of the cornea. The aim of this article is to critically evaluate the clinical results of LASIK with the Technolas 217c excimer laser system at one year follow-up using standard criteria.
MATERIAL AND METHODS
One thousand three hundred and fifty seven eyes (1357) eyes of 721 patients undergoing myopic LASIK between January 1999 - May 2000 were prospectively enrolled in this study. All surgeries were performed by one of the authors using a standard operating protocol. The patient ages ranged from 21-56 years (mean 26.2 years). The refractive error ranged from -1 Dsph to -15.5 Dsph (mean -7.75 D). A 12-month follow-up was available for all patients. Patients with less than a yearís follow-up were excluded from the analysis, resulting in a study group of 1040 eyes.
All patients underwent a complete eye examination and a standard LASIK evaluation including a fogged manifest refraction, dilated retinal evaluation, central corneal thickness evaluation (pachymetry) and corneal topography. All patients were counseled about the procedure and the risks and benefits of the treatment were clearly explained preoperatively. Patients were required to sign a standard consent form prior to treatment. Patients wearing contact lenses were asked to discontinue lens wear at least one week prior to treatment for soft contact lens wearers and 2-3 weeks for rigid gas permeable lenses, allowing for stabilization of contact-lens induced corneal surface changes.
The excimer laser was calibrated on every single treatment day and between patients. No pre-medication was given.
Topical proparacaine anaesthetic eye drops were instilled. After painting and draping, a self-retaining speculum was applied. The cornea was marked for post-op flap alignment. After application of suction, the intraocular pressure was checked and an ACS microkeratome used to create a flap with a nasal hinge. After lifting off the flap, the active eye tracker was engaged and the treatment performed taking care to protect the flap. The bed was cleaned and the flap aligned. A soft contact lens was placed to enhance patient comfort.
The patient was advised hourly topical medication for the first post-operative day to be continued 5 times a day for a week. Follow-up visits were at one day, one week, one month, three months, six months and twelve months. The same treatment nomogram was followed by all surgeons.
Safety was defined as the preservation of best-corrected visual acuity without any long-term risk to the eye. Best-corrected vision means the maximum number of lines that the patient is able to read on the vision chart with his glasses or contact lenses. The objective of the refractive surgery is to improve the patientís unaided natural vision after treatment to the same level as the patientís best-corrected vision before treatment. A refractive procedure is considered safe when the patientís best-corrected vision remains unchanged or improves after the treatment.
Of 1040 eyes, 21 eyes (2%) lost 1 line of best corrected vision after the treatment, i.e. after the treatment 21 eyes read one line less on the vision chart than they could before the treatment. Similarly, 8 (0.76%) eyes lost 2 lines of best-corrected vision. The reasons for this included irregular astigmatism due to flap folds, flap striae, decentred ablations or irregular ablations. These eyes underwent enhancement procedures to improve vision that finally resulted in 25 (2.4%) eyes being restored to their preoperative best-corrected vision. Four eyes (0.38%) had one line of best-corrected vision loss even after the second treatment due to long standing flap folds that could not be removed. This occurred in patients that were non-compliant with the follow-up schedule. Therefore, in all 2.76% eyes lost lines of best-corrected vision after a single treatment, of which 2.38% were improved to their pre-operative best-corrected vision after an enhancement procedure.
Efficacy of refractive procedures is defined as the ability of the procedure to correct the refractive error and improve unaided vision and is quantified by the extent to which the error is corrected and the patients vision after surgery.
At one year follow-up, 863 eyes (83.1%) were within æ 0.5 Dsph and 981 eyes (94.4%) were within 1 Dsph of the intended correction. 926 eyes (89%) had an unaided natural vision of 6/6 or better and 978 eyes (94%) were 6/12 or better. Only 3% patients experienced the need to wear corrective spectacles occasionally during visually demanding activities after the treatment. Even these patients subjectively felt that they had benefited from the treatment and were satisfied with their decreased dependence on visual aids.
Predictability is defined as the consistency with which the desired result can be achieved or how close the actual clinical outcome is to the intended outcome for the whole group i.e. case after case. The accuracy is reflected by the mean of the residual refractive error and the consistency by the standard deviation of the same. The mean residual refractive error was 0.6 Dsph with a standard deviation of 0.7 Dsph, indicating a high level of accuracy and consistency or predictability.
Overall a very low rate of complications was seen. Visually significant flap folds or wrinkles were seen in eight eyes (0.76%). These were enhanced to improve the visual outcome in 4 eyes. However, 4 eyes reported late and the folds persisted despite enhancement procedures resulting in a mild reduction of visual acuity in these eyes. No cases of infection, interface keratitis, free caps or epithelial ingrowth were encountered. Mild interface debris that was not visually significant was noted in 14 eyes. Irregular astigmatism due to treatment decentration was seen in 2 eyes. No cases of retinal detachment were observed.
Despite 11 years of follow-up and millions of treatments performed worldwide, doubts remain about the safety and efficacy of LASIK. Many clinicians and even ophthalmologists perceive LASIK as a relatively new purely cosmetic procedure that is neither safe nor consistent nor stable. The aim of this study was to address some of these issues.
The results of this study clearly demonstrate that LASIK is a procedure that has an excellent level of efficacy, accuracy, predictability and safety for a very wide range of refractive errors. In this study, two experienced surgeons with a well-maintained third-generation excimer laser system and a personalized nomogram followed a standard operating protocol. The surgeonsí experience is reflected in the consistency of the results as confounding variables due to the learning curve are excluded. Experience coupled with cutting-edge technology and adherence to a standard operating protocol contribute significantly towards consistent excellence in results. It is likely that these results may not be replicated universally and results would vary between different laser systems with different operating protocols and varying level of experience. The incidence of complication was very low indicating a very high level of safety. When complications do occur they can be managed to maintain an excellent visual acuity.