Though laser in situ keratomileusis (LASIK) surgery is now one of the most common operations performed worldwide, few studies have been published on long term outcome and safety.
Photorefractive keratectomy (PRK) and LASIK have been shown to be comparable in terms of refractive outcome and visual performance for both myopic and hyperopic corrections. LASIK has become more popular because it is a pain free procedure and gives faster visual rehabilitation. However, LASIK is a more invasive procedure than PRK. LASIK surgery involves the formation of a flap at a level of 160 µm from the corneal surface. This, theoretically, could disturb the organisation of collagen fibres that make up the corneal stroma at this level which could lead to compromise in corneal strength. Thus, there has been concern expressed over the long term refractive and biomechanical stability associated with LASIK surgery.
PRK has been shown to offer long term stability for up to 12 years. In contrast, the longest follow up of myopic LASIK has been 6 years and it showed modest results in terms of refractive, and visual outcome for high myopes. In this study we report the long term refractive stability for all levels of myopic correction and we review patient satisfaction with this procedure.
DISCUSSION
LASIK surgery is still a controversial issue despite almost 10 years of experience and eight million patients treated worldwide. The recent publication by the National Institute of Clinical Excellence (NICE) in the United Kingdom, although fundamentally flawed, highlighted the need for long term evaluation of the procedure. Several studies have published good short term results for LASIK surgery; however, few have addressed long term outcome.
Sekundo et al, in a study of 33 eyes with 6 years of follow up, reported a cumulative unaided visual acuity of more than 0.4 logMAR in 66% of patients and only 46% of patients were within plus or minus 1.0D of attempted correction at the end of the study. Furthermore, they reported that 75% of their patients experienced night-time glare, yet 81% of patients were quite happy with overall result.
The long term results for PRK showed that postoperative refraction remained stable over 12 years. In 68 patients studied, it was found that 75% of those who underwent a -2.0D correction and 65% of patients who received a -3.0D correction were within 1D of intended correction at 12 years. This fell to 25% and 22% for patients having a -6.0D and -7.0D correction, respectively. The 5 year results for hyperopic LASIK were recently reported by Jaycock et al. They reported that at 5 years post-treatment 71% of eyes treated for +1.0 to +3.0D of hyperopia were within plus or minus 1.0D of intended correction, whereas only 37.5% of those between +3.5D and +6.0D were within plus or minus 1.0D of intended correction.
In contrast with Sekundo’s study where the mean preoperative SE was -11.4D, the patients in our study had a broader range of preoperative refraction (mean SE = -4.83, range = -1.5 to -13D). Sixty per cent of eyes were within plus or minus 0.5D and 83% within plus or minus 1.0D of attempted correction at 5 years. Furthermore, 89% of eyes had a cumulative unaided vision of 6/12 or better with 57% having a visual acuity of 6/6 or better. The superior results are no doubt because of the inclusion of mild myopes in the study population. But if we exclude the high myopes in the study the results are even better, with 93% having an unaided vision of 6/12 or better. Our findings show that LASIK surgery is predictable for mild to moderate myopia; however, beyond -6.0D its efficacy decreases with a trend towards myopia over 5 years. However, though we see a myopic trend over 5 years it is notable that 96% of patients would have the surgery again and 96% are currently happy with their level of vision.
Like many other studies glare is a common side effect. We were unable to assess changes in glare sensitivity as these measurements were not performed preoperatively. In contrast with Sekundo’s study, which reported glare in 75% of patients only 24% of our patients reported haloes/glare. Contrast sensitivity was not recorded preoperatively in our patients therefore we were unable to compare the levels of contrast sensitivity preoperatively to those at 5 years. Contrast sensitivity is important in the evaluation of patients post-LASIK as it has been found that contrast sensitivity can be poor in the presence of good Snellen acuity. However, the evidence so far seems to suggest that LASIK causes a temporary reduction in contrast sensitivity with gradual normalisation by at least 6 months. The range of methods available for the measurement of contrast sensitivity and the difficulties producing ambient conditions suitable for accurate assessment often deters surgeons from performing this exam in routine practice. Furthermore, even a slight decrease in contrast sensitivity can be within the normal range of a healthy control population.
Overall, there was a 5% re-treatment rate during the 5 years. These re-treatments were performed in the first 6 months after surgery. All three patients were high myopes with spherical equivalents of -13D, -8.5D, -9.5D, and -6D, respectively. Following re-treatment at 5 years two eyes have achieved their best corrected visual acuity, one eye is within one line of best corrected acuity, and one eye is within two lines of best corrected acuity.
No patient developed corneal ectasia and 6% of patients reported dry eyes with only 4% requiring tear substitutes at 5 years.
Importantly, the safety profile of LASIK in this study is excellent. No eye lost more than one line of best spectacle corrected vision and 31 eyes gained one line of vision.
In conclusion, the findings in this study are significant. It is the largest long term outcome study published to date showing good unaided visual results with excellent safety profile. Overall patient satisfaction with the procedure is high with 98% reporting that they would have the surgery again. The emergence of better laser nomograms, safer keratomes, larger optical zones, and improved understanding of aberrations and their significance will lead to improvements in patient outcome in the future.
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