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Results of LASIK Surgery

Alka Rani, Balasubramanya R, Elankumaran S, Rasik B Vajpayee

Laser assisted in situ keratomileusis (LASIK) has been performed world-wide for the primary correction of myopia, hyperopia and astigmatism and also for residual refractive errors following ocular surgery.

The results of LASIK like any other procedure are determined on the basis of certain parameters that include efficacy, safety, predictability, stability and patient satisfaction. The results that have been highlighted here are tabulated from the various published articles as well as abstracts.

Efficacy

The efficacy of LASIK surgery is determined by the postoperative uncorrected visual acuity (UCVA) attained by the patient. Most studies have quantified the results as the attainment of UCVA 20/40 or better, although attainment of a UCVA of 20/20 or better is a more qualified index.

Safety

The safety of a refractive procedure is reflected by the percentage of the patients who retain their best corrected visual acuity (BCVA) within 2 lines of their preoperative level.

Predictability

Although in the older studies predictability was defined in terms of within ±1.00D, in the more recent studies the limits have been decreased to within ±0.5D of correction postoperatively

Stability

In most studies refraction stabilizes by 3 to 6 months after LASIK surgery. It is inversely proportional to the amount of regression. Regression is defined as a change of refraction within ±0.5D over a period of time following LASIK.

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Myopia

For low to moderate myopia, results from studies in the literature have shown that LASIK is effective and predictable in terms of obtaining good to excellent UCVA postoperatively. For moderate to high myopia, the results are more variable.

Low Myopia

Results of LASIK surgery in low myopia of less than 4D have demonstrated the highest predictability and minimum complications (Table 12.1).

Table 12.1: Results of LASIK low to moderate myopia (−1 to −10D)

NR=Not reported

In a study by Salah1, et al 93% of eyes had refraction within ±1.00D in a group of patients with myopia of 2.0 to 6.0D at a mean follow-up of 5.2 months.

Similar results for low myopia have been reported by Bas and Onnis2. At the final follow-up (range; 6 to 25 months), 89% patients of low myopia group (3 to 6D) had achieved a UCVA of 20/40 or better and 30% eyes obtained a visual acuity of 20/ 20 or better. In the first month, 82% of eyes were within ±1D. At the final check-up, the mean spectacle corrected refraction was −0.42±0.98D.

Moderate to High Myopia

The results of LASIK surgery for moderate and high myopia have not been as good as in low myopes (Table 12.2). Knorz et al7 reported the results of a study in which myopia was divided into three categories: −5 to −9.90D; −10 to −14.9D; and −15 to −29.0D. An UCVA of 20/40 or better was obtained in 87.5% in the first category; 77.8% in the second category and 33.3% in the third category. Also, in this group (−15 to −29D) only 38.9% of the operated eyes were within ±1D as compared to 60% in-group 2 and 100%

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in group 1. The authors concluded that the accuracy of the surgery and the patient satisfaction were sufficiently poor to advise against LASIK in myopia of more than 15D.

Waring et al8 published the data for simultaneous LASIK in 378 eyes with myopia ranging from −2 to −22.5D. The predictability of obtaining a refractive error of ±1D was 84.5% and 88.9% of eyes achieved a UCVA of more than 20/40.

Hersh et al9 performed LASIK on 115 eyes with a myopia ranging from −6 to −15D. 55 % of the eyes achieved an UCVA of 20/40 or better.

Perez-Santonja10 performed LASIK in 143 eyes with myopia ranging from −8 to −20D, at the end of 6 months follow-up only 46.4% of eyes could achieve a UCVA of 20/40 or better. From the study group, 1.4% eyes demonstrated a loss of 2 or more lines of best corrected Snellen’s acuity.

Gimbel11 reported the results of LASIK in his first 1000 consecutive cases in myopia ranging from −1 to −23D. At the end of 6 months, a follow-up was available in 906 eyes, which had no intraoperative or postoperative complications. Seven hundred and ninetysix (87.8%) of these eyes were within ±1D of targeted spherical equivalent and 557 eyes (61.5%) were within ±0.5D.

In a study reported by Guell12, 71.4% of eyes gained a UCVA of 20/40 or better after LASIK, performed to correct myopia ranging from −7.0 to −12.0D. However, such an achievement was possible in only 45% of eyes having preoperative myopia of >12.0D.

At the end of 12 months follow-up, Helmy13 reported a predictability of ±1D in 85.7% of eyes that had undergone LASIK for myopia ranging from −6 to −10D. The same study reported a UCVA of 20/40 or better in 75% of operated eyes.

Andrew Lyle et al14 performed a prospective study, which included 332 eyes having myopia over −10D. The eyes were divided into 3 groups according to the amount of preoperative refraction: i.e. −10 to −11.90D, −12 to −14D, −14.1 to −18D. The mean follow up was 12±5.6 months. At the last visit, 84% of eyes

Table 12.2: Results of LASIK for moderate to high myopia (−6 to −25D)

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−8 to −12 −12 to 46 −16 to −20

NR=Not

reported

were within ±1D of emmetropia and 96.4% were within The UCVA was 20/20 or better in 45.8% of eyes and 20/40 or better in 89.5%. Six eyes (1.8%) lost 2 or more lines of BCVA. Retreatment was done in 37.0% of the eyes at a mean of 6.3±5.3 months after the initial treatment. At the last examination, 86% of eyes with myopia ranging from −10.0D to– 14.0D and 70.0% in group with myopia ranging from −14.1D to −18.0D were within ±1D of emmetropia. The authors concluded that the efficacy, predictability, and safety were significantly less in eyes with myopia greater than −14D.

Merchea M et al15compared LASIK outcomes with the Nidek EC-5000 and Meditec Mel 70 excimer laser. They evaluated 5700 eyes treated for myopia and myopic astigmatism with the preoperative sphere ranged from −0.25 to −15.50D and cylinder ranged from −0.75 to −5.50D. They found that eyes treated for myopia and astigmatism with either of these lasers showed early refractive stability and similar efficacy.

Astigmatism

Laser in situ keratomileusis (LASIK) has been employed to treat astigmatism, either as a component of myopia, hyperopia or existing as a entity itself. However, astigmatic corrections by LASIK have not demonstrated an optimal success.

Chayet et al19 attempted to correct simple myopic, mixed and simple hyperopic astigmatism with manifest cylinder ranging from 2.00 to 6.50D at the end of 3 month follow-up, UCVA was 20/40 or better in 85% of the eyes. 95% of the corrected eyes were within+1.00D of the attempted correction.

Salchow et al20 used LASIK to correct myopic astigmatism ranging from 0.00 to 3.00D, as a simultaneous procedure while correcting myopia. At the end of 6 months of follow-up 96.8% of the eyes were within +1.00D of attempted cylindrical correction and UCVA of 20/40 or better was achieved in 82.5% of eyes.

Argento et al,21 in a prospective non-randomized clinical trial used LASIK to treat simple hyperopic astigmatism (3.37±1.62D), compound hyperopic astigmatism (3.34±1.39D) and mixed astigmatism (3.45±2.15D). Six months after the procedure, refractive cylinder was reduced to +0.58±1.22D in simple hyperopic astigmatism, +0.12±1.23D in compound hyperopic astigmatism and −0.11±1.28D in mixed

Perez-Santonja et al31 evaluated the effect on contrast sensitivity function of LASIK in myopia. Fourteen eyes had LASIK to correct myopia ranging from 6 to 19.50D. They found that although LASIK decreased contrast sensitivity values at low and intermediate spatial frequencies at 1 month after surgery, these values rapidly returned to preoperative values at three months. Their study also suggested that LASIK can improve the quality of vision in eyes with moderate and high myopia.

Yan Z et al32 evaluated near contrast sensitivity function in 93 eyes before, 1 month and 6 months after LASIK. They found that there was a general reduction in near contrast sensitivity at all spatial frequencies at postoperative 1 month. By the end of 6 months, all eyes showed a recovery of static contrast sensitivity function. Eyes with myopia of ≥ −6.00D had higher decrease rate of contrast sensitivity compared with that of myopia < −6.00D. Their study suggested that the near contrast sensitivity in post-LASIK patients at early stage is reduced despite normal visual acuities and this can affect the quality of vision.

Chan JW et al33 in a similar study found a general depression in the contrast sensitivity function after LASIK; 1.5cpd and 3.4cpd being the most affected frequencies. However, contrast sensitivity function recovered at the end of 6 months and the reduction in contrast sensitivity was greater for higher amounts of myopia.

Tsai YY et al34 evaluated the effect of LASIK on colour vision. Twenty-nine eyes were enrolled in the study with a normal colour vision test preoperatively, tested using Farnsworth-Munsell 100-hue test. They found that LASIK did not affect the colour vision.

Table 12.4: Results of retreatment after LASIK

NR=Not reported

Results of Re-LASIK Surgery

Overall, LASIK re-treatment by lifting the flap is an effective and safe procedure (Table 12.4). Overall improvement is seen in the uncorrected visual acuities, postoperative spherical equivalent, spherical equivalent within ±0.5D and ±1.00D and uncorrected visual acuities better than 20/20 and 20/40.

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