Laser in situ keratomileusis (LASIK) surgery is increasingly being utilized, throughout the world, for the correction of myopia and associated myopic astigmatism. Rapid recovery of vision, minimal discomfort, short periods of medication application, and high patient satisfaction are factors that have led many surgeons and patients to adopt LASIK as their procedure of choice for both primary and retreatment surgical procedures. This article reports the results of primary and retreatment LASIK for myopia and astigmatism, performed by three experienced corneal surgeons in a large series of 353 eyes, in a single center. Our data were analyzed in four different groups: Group I: primary treatment including all patients; Group II: primary treatment group excluding retreatment patients; Group III: retreatment patients; and Group IV: overall results from combining primary and retreatment results (Groups II and III). Analysis of these combined results has not been reported in previous studies. This combination of data allows for a more accurate assessment of LASIK-surgery predictability and safety, providing results that can be shared prospectively with patients who may be considering the procedure.
MATERIALS AND METHODS
Patients and data collection
Three hundred and fifty-three consecutive eyes underwent myopic-astigmatic LASIK surgery, performed by three surgeons (J.P.M., R.W.B., and H.D.C.) at the Zale Lipshy University Hospital Laser Center for Vision, between May 1997 and September 1998. The equipment used was the VISX Star excimer laser (VISX, Inc. Santa Clara, CA), the Automatic Cornea Shaper, and the Hansatome (Chiron Vision, Emeryville, CA). Before and after surgery, the patients underwent thorough examinations, including pachymetry, keratometry, and computerized corneal topography (TMS, Tomey Technology, Cambridge, MA).
At our center, LASIK treatment has been limited to patients of at least 20 years of age, with stable refractive errors. Patients had none of the following: clinical or topographic signs of keratoconus, previous ocular surgery, corneal infection, or systemic diseases that could effect corneal healing. Patients wearing contact lenses were required to remove soft contact lenses for 7 to 10 days and soft toric or gas-permeable lenses for 2 to 3 weeks before their initial evaluation.
Examination data were recorded preoperatively and at 1 day, 1 week, 1 month, 3 months, 6 months, and 12 months intervals after surgery. UCVA, best spectacle-corrected visual acuity (BSCVA), sphere and cylinder correction, and spherical equivalent correction were analyzed.
Topical anesthesia was achieved with three drops of 0.5% proparacaine. The cornea was focused and centered under the excimer laser, and alignment marks were placed on the cornea using a marker coated with methylene blue dye. The suction ring was positioned on the cornea with slight nasal (Automatic Cornea Shaper [ACS]) or superior (Hansatome) decentration; suction was maintained at or above 28 mm Hg by the Chiron system suction pump, and intraocular pressure was verified to be at least 82 to 83 mm Hg on a pneumotonometer. When visible fluid was present on the stromal bed, a merocel sponge (Xomed Surgical Products, Jacksonville FL) was used before and during laser ablation to remove the fluid. After ablation, the flap was carefully replaced onto the bed using an irrigation cannula, painted into position with a moist merocel sponge, and allowed to seed into place for a total of 5 minutes. The flap position was verified by slitlamp microscopy immediately after surgery, and the patient was discharged with a clear plastic eye patch. When required, retreatment was performed after manually lifting the flap. The Bansol-Kay nanogram was applied to all cases. Immediately after all procedures, ciprofloxacin drops were administered every 5 minutes 3 times. A drop of ciprofloxacin also was applied to the ablated bed before repositioning the flap. After painting the flap in place for 1 to 2 minutes, ciprofloxacin drops were used to keep the ocular surface moist. Postoperative medication consisted of 1 drop of ciprofloxacin 4 times daily and 1 drop of rimexolone 4 times daily for 1 week only. Artificial tears were used by the patient as needed postoperatively.
Three hundred fifty-three LASIK-surgery cases were performed on 191 patients. There were 86 women and 105 men, with an average age of 40.39 ± 9.22 (range 20–62) years. Preoperatively, the mean sphere was −6.37 ± 2.93 D (range −0.75–6.75 D), with a mean cylinder of +1.01 ± 0.9 (range 0.0–+4.75D) (Table 1). Forty eyes of 28 patients (11.33%) required retreatment (Table 1). The initial refraction of the patients who needed retreatment was 7.42 ± 2.49 D (range −3.5– −15.25 D) with a mean cylinder of +1.0 ± 0.61 D (range 0.0 to +2.75 D). Seventeen (42.5%) patients had spherical equivalent within −3.0 to −6.0 D, 15 (37.5%) patients were within −6.0 to −9.0D, 5 (12.5%) patients were within −9.0 to −12.0D, and 3 (7.5%) patients were within −12.1 to −17.0 D range. The mean retreatment preoperative spherical equivalent was −1.68 ± 0.74 D (range −0.75– −4.0D) with a mean cylinder of +0.42 ± 0.43 D (range 0.0 – +1.25D). Eight (20%) patients had refractive errors within 0 to −1.0 D, 24(60%) patients within −1.1 to −2.0 D, 6 (15%) were within −2.1 to −3.0 D, and 2 (5%) patients were higher than −3.0 D. The mean retreatment time was 6.6 ± 2.7 months (range 1.5–14.5 months); among them, 3 (7.5%) patients were retreated between 1 to 3 months, 27 (62.5%) were between 3 to 6 months, 10 (25%) were between 6 to 12 months, and 2 (5%) patients were retreated over 12 months.
Primary Treatment Including Retreatment Patients
Postoperative uncorrected visual acuity (UCVA) results at 1 month, 3 months, and 6 months were: 20/40 or better 90.5%, 87.2%, and 89.5%; and 20/20 or better 52.0%, 48.9%, and 59.6%. UCVA results after 6 months by refractive error: 0.0 to −3.0 D 90% 20/20; −3.1 to −6.0 D 70% 20/20; −6.1 to −9.0 D 60% 20/20; −9.1 to −12.0D 46% 20/20; and greater than −12.0 D 44% 20/20 (Table 2). At 6 months postoperatively, 67.9% of patients were within ± 0.5 D; 84.9% of patients were within ± 1.0 D of intended spherical correction, whereas 87.7% of patients were within ± 0.5 D, and 94.3% were within ± 1.0 D intended cylindrical correction (Table 3). Two patients gained two lines of BSCVA, and 18 patients gained one line. Four patients lost one line of BSCVA, and no patient lost two lines. Stability of group refractive values was reached between 1 week and 1 month; stability of individual refraction change not greater than ±0.5 D and ±1.0D: from 1 week to 1 month was 81.4% and 96.0%; from 1 month to 3 months was 84.1% to 94.2%, and from 3 months to 6 months was 89.0% and 96.5%.
Primary Treatment Excluding Retreatment Patients
Postoperative UCVA results at 1 month, 3 months, and 6 months were: 20/40 or better 95.0%, 95.2%, and 95.7%; 20/20 or better 52.0%, 62.6% and 63.8%. UCVA patients, grouped by refractive error, at 6 months postoperatively were: 0.0 to −3.0 D; 20/40 or better 98.8%; 20/20 or better 90%; −3.1 to −6.0 D; 20/40 or better 96.2%; 20/20 or better 78%; −6.1 to −9.0D; 20/40 or better: 94%; 20/20 or better 64%; −9.1 to −12.0D; 20/40 or better 93.6%; 20/20 or better 57%, and >12.0 D; 20/40 or better 89.4%, 20/20 or better 50% (Table 4). At 6 months postoperatively, 81.5% of eyes were within ± 0.5 D, and 92.7% were within ± 1.0 D of intended sphere correction, whereas 93.1% were within ±1.0 D intended cylinder correction. Two patients gained two lines of BSCVA; 18 patients gained one line. Four patients lost one line of BSCVA, and no patient lost two lines (Table 5). Predictability and accuracy at 6 months postoperatively were 72.5% within ± 0.5 D, 87.5% within ± 1.0 D, 99% within ± 1.5 D, and 100% within ± 2.0 D. At 1 month postoperatively, the mean refraction was −0.22 ± 0.34 D, at 3 months −0.24 ± 0.41 D, at 6 months −0.24 ± 0.35 D. Stability by individual patient values is demonstrated in Table 6. Eighty-four percent of the patients had ≤ ± 0.5 D change between months 1 and 3 and 89.5% between months 3 and 6.
At 1 month, 3 months, and 6 months after retreatment 80%, 76%, and 77% of patients had UCVA 20/20 or better, and 97.5%, 97.5%, and 100% of patients had 20/40 or better (Table 7). Four patients gained one line, and two patients gained two lines BSCVA (Table 8). No patient lost any lines of BSCVA. Eighty-three percent were within ± 0.5 D, and 100% were within ± 1.0 D of intended sphere correction; and 95% were within ± 0.5 D of intended cylindrical correction at 6 months after retreatment. Although 100% 20/40 or better was achieved within all refractive error groups, the trend toward higher refractive error achieving lower visual results was seen at a 20/20 or better endpoint (Table 9). The group with greater than −12.0 D achieved 100% 20/20 or better but only contained 3 patients. This small number may not represent the normal outcome. Predictability and stability are illustrated in Table 10.
Overall results at 6 months after primary treatment and not requiring retreatment and results at 6 months after retreatment with UCVA 20/40 or better were 97%, 20/25 or better were 82.1%; and 20/20 or better were 63% (Table 11). UCVA, grouped by refractive error were 0.0 to −3.0D; 20/40 or better 98.8%, 20/20 or better 90%; −3.1 to −6.0 D; 20/40 or better 96.9%, 20/20 or better 80.5%; −6.1 to −9.0 D; 20/40 or better: 94.7%, 20/20 or better 64.4%; −9.1 to −12.0 D; 20/40 or better 93.8%, 20/20 or better 57.1% and greater than 12.0 D; 20/40 or better 89.6%, 20/20 or better 50% (Table 12). Seventy-six percent were within ± 0.5 D, and 94% were within ± 1.0% intended spherical correction (Table 13). Eighty-eight percent were within ± 0.5 D and 97% were within ± 1.0 D cylindrical correction. Four patients gained two lines of BSCVA; 22 patients gained one line. Four patients lost one line of BSCVA, and no patient lost two lines (Table 9). Predictability and accuracy were 76.0% within ± 0.5 D, 94.0% within ± 1.0 D. Stability by individual patients is demonstrated in Table 16. Eighty-six percent of the patients had ≤ ± 0.5 D change between months 1 and 3 and 89.7% between months 3 and 6.
There was one free flap (0.3%) that was carefully repositioned and secured with 4 interrupted 10-0 nylon sutures, and LASIK retreatment was successfully performed at a later time. There were two slipped flaps (0.7%) immediately after surgery, which were repositioned without sequelae; and one inadequate suction (0.3%) required returning to surgery on another day. There were four cases of small epithelial growth at the edge of flap interface, none of which were progressive, and surgical intervention was not required. None of the complications resulted in loss of BSCVA. Twelve cases (4%) in the primary treatment group and eight cases (20%) in the retreatment group encountered intraoperative epithelium defects, which required high-water content, type IV, bandage soft contact lenses for 24 hours. All contact lens wear was discontinued at 1 day postoperatively, however, and no complications of lens use were observed.
Uncorrected Visual Acuity
Primary Treatment Group
Previous clinical trials for correction of myopia and astigmatism are summarized in Table 15. The overall results of this study show the same trend, that is, the lower refractive error group received better outcome and a lower retreatment rate. In the 0.0 D to −3.0 D group no patients required retreatment, and had a 98.8% 20/40 or better UCVA. As refractive error increases to greater than −12.0 20/40 or better, however, UCVA decreased to 82.4%, and 15% patients required retreatment (Table 15), a statistically significant difference. The significance between greater than −12.0 D and 0.0 to −3.0D groups is P < .0005 (t-test). Our results in both UCVA achieved and retreatment rate exceed most of those previously reported (Table 14).
In group II, retreatment patients were excluded to evaluate the results on only non-retreated eyes. This exclusion prevents the skewing of data by the eyes needing retreatment. To the best of our knowledge, there are no data published comparable with this group. Within this group the degree of pretreatment myopia also had a direct effect on the chance of 20/20 outcome. The higher the degree of myopia the less chance of success (Table 4).
Comparing our retreatment patients’ (group III) data with other published data, our results were similar to Perez-Santonja et al 1 who reported UCVA after retreatment was significantly improved. These authors reported pre-retreatment 20/40 or better at 3.38% and post-retreatment 20/40 or better at 61.80%. Zodok 2 et al reported post-retreatment 20/40 or better in 96.2% and 20/20 or better in 38.3%. Rashad 3 reported 20/20 or better at only 31.4% after their retreatment. Our retreatment results were 100% 20/40 or better after retreatment and 77.5% 20/20 or better.
Group IV results represent the overall outcome 6 months after the last treatment. By combining groups II and III in a way not previously done, it is possible to analyze the best outcome. All refractive error groups have improved UCVA (Table 12), demonstrating excellent overall results. As with the other groups, it was clear that, as the degree of myopia increases, a significant decrease in the percentage of patients achieving 20/20 UCVA occurs (Table 12). This is statistically significant between greater than the −12 D group and 0.0 to −6.0 D group (P =0.008), and it is not significant between the −12D group and −6.0D to -12 D group (P =0.64;t-test).
Change in Best Spectacle Corrected Visual Acuity (BSCVA)
In a previously published report, BSCVA increased one line in 11.76% of patients, two lines in 26.47%; decreased one line in 8.82% and two lines in 8.82% (−10.0 – −22.5 D). 4 In another study, there was −5.0 D to −9.9 D, no loss; −10.0 D to −14.0 D, lost two lines in 6.1%; −15D to −29 D, 6.3% lost 2 or more lines. 5 In a third report, there were no lines lost in the moderate myopic group, but as myopia increased, ≥−10.0 D, the loss of two or more lines increased from 4.3% to 10%. 6 Zodok 2 reported 9.4% of eyes lost one line of BSCVA, 28.3% gained one line in retreatment, with all eyes being 20/50 or better. In our series no loss of any lines of BSCVA were seen any of the retreatment eyes, and no loss of two or more lines occurred in any eyes. These outcomes are better than generally reported in previous studies.
Deviation From Intended Correction
In their mixed group of patients (−3.5D – −19.75 D), Pesando et al 7 reported at 6 months postoperatively 28.26% of patients were within ± 0.5 D and 78.26% of patients were within ± 1.0 D. Tsai 8 reported preoperative spherical power ≤−7.0 D had 86.21% were within ± 0.5 D and 96.55% were within ±1.0 D. Those greater than −7.0 D and ≤−10.0 D were 76.92% within ± 0.5 D and 80.77% within ± 1.0 D. When power was greater than −15.0 D, 31.5% were within ± 0.5 D and 52.63% within ± 1.0 D. Zodok 2 had 100% ± 1.0 D and 90.6% ± 0.5 D in his retreatment patients. Rashad, 3 in his retreatment patients, had 91.5% ± 0.5 D. Other authors 7,9–11 reported similar results. It appears that in cases of high myopia, as refractive power increases, the achieved intended correction decreases. Our results support this conclusion. The difference between greater than −12.0 group and 0.0 to −3.0 D group is statistically significant (P =0.03;t-test). When Group IV is analyzed, however, a marked improvement was noted (same groups, P =0.38, t-test). This supports the findings that by combining treatment and retreatment data, a more thorough assessment of LASIK results can be achieved.
Published predictability data range from 100%, in low to moderate myopia, to 60% in higher (-10 to 14.0D) myopia and were nearly 38.9% in greater than −15.0 D myopia. Predictability usually was less than 50% within 1.0 D in corrections of −12.0 to −15.0 D. 6,7,9,11 Our primary treatment results also reflect this trend. The unusually high consistency of the retreatment results promotes an overall high success rate in final predictability.
Others have reported mixed stability of refraction, in which no regression of more than 1.0 D was 100% in a moderate myopia group (−5.0– −9.9 D); with 8% regression in (−10–15.0 D), and 28% in ≥−15.0 D high myopia group. 5 Helmy et al 12 found regression to be common in both photorefractive keratotomy and LASIK patients with myopia ranging from −6.0 D to −10.0 D. Others 9,13 have reported more regression after LASIK treatment for high myopia than for moderate myopia, with stable results after 6 months. All four of our groups have stability comparable with other reported results, with stability established within 1 month.
Reported LASIK complication rates range from 3.4% to 11.8%, with a higher rate (up to 31%14–19) in retreatment patients. Our total complication rate, including both treatment and retreatment, was 2.2%. Epithelial ingrowths and flap melting are commonly reported complications in LASIK retreatment. Within our retreatment group neither complication was observed. Compared to initial treatment, there was an increased need for bandage soft contact lenses postoperatively for epithelial defect occurring during the procedure.
This study reports for the first time final LASIK results as a whole. Overall, the results demonstrate LASIK to be a safe and effective procedure for correcting low to high degrees of myopia and associated astigmatisms. Visual outcome is acceptable with good stability. The degree of myopia has a significant effect on the predictability of outcome, with low myopia achieving better results, whereas the percentage of 20/20 or better results decrease as myopia increases. In patients with unsatisfactory primary treatment results, retreatment has shown to be an excellent recourse. When performed carefully by experienced surgeons, the LASIK complication rate is low—lower than that previously reported by many authors. The overall analysis, when viewed in the context of Group IV, is favorable and demonstrates the potential of LASIK as a safe and efficient alternative to other methods of refractive correction. 13
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