Some variables to consider to avoid the need for LASIK surgical enhancements

Abstract

BACKGROUND: The predictability of LASIK refractive surgery is important both to the patient and the surgeon in obtaining an optimal result and in reducing the need for enhancement surgery. Some instruments, large ablation zones and possibly other variables may increase hyperopic overcorrection. METHODS: A retrospective study was undertaken of 345 myopic LASIK eyes (175 patients) treated with a Nidek EC-5000. The need for additional surgery in the form of an enhancement was determined after the patient had a stable refraction. The variables measured in the study were the patient's refractive correction, corneal curvature using an Alcon EH-290 topographer, the patient's age and Nidek excimer laser ablation optic and transition zone size. The same nomogram was used for all eyes and where possible bilateral surgery was conducted on all patients. The effect of ablation sizes, refractive errors, patient age and corneal curvature on the enhancement surgeries was evaluated using SPSS 6.0. RESULTS: The most significant variable that precipitated a LASIK enhancement was an optic zone of 6.5 mm with a transition zone of 7.5 mm (paired t-test, p < 0.0025). Multivariate analysis indicates that the older the patient and the larger the refractive error, the greater the risk of not achieving a residual refractive error of +/- 0.50 D at three months. The steeper pre-operative corneas have a greater chance of enhancement (mean of sample 44.48 +/- 1.47 D and mean of enhancements 45.30 +/- 1.65 D, p = 0.01, independent sample test). The smaller optic zone was associated with a smaller refractive over-refraction after LASIK surgery (mean for 5.5 mm optic zone, +0.71 +/- 0.29 D; mean, for 6.5 mm optic +1.27 +/- 0.50 D, paired t-test p < 0.0001). CONCLUSIONS: In this study, the 5.5 mm optic zone appears to dampen or reduce the undesirable refractive results. The optic zone size of choice with the Nidek EC-5000 laser should be 5.5 mm if the patient has small pupils and steep corneas. In this sample, the targeted emmetropic refractive state (range plano to +0.50 D sphere and plano to -0.50 D cylinder) was achieved in 93.3 per cent of cases after three months.

Slit‐scan tomography evaluation of the anterior chamber and corneal configurations at different ages

“…A well known example is the continuous growth of the lens throughout the lifespan of an individual, which may eventually be closely related to presbyopia and nuclear cataract (Bron et al 2000), and which may also indirectly contribute to increased intraocular pressure (Altan et al 2004), or even, in extreme cases, to narrow‐angle glaucoma (Markowitz & Morin 1984). Age‐related changes in the cornea can be less clinically obvious, but they do occur, and can be reflected in, for example, the response to some surgical procedures (Feltham & Wolfe 2000). A more detailed knowledge of the normal configuration of the eye's anterior segment and its natural change over time can be of importance in the planning of refractive procedures such as phakic intraocular lens (IOL) implantation (Hosny et al 2000; Vetrugno et al 2000; Cosar & Sener 2003), but also in the understanding and quantification of disease processes such as keratoconus (Auffarth et al 2000), cataract and glaucoma (Markowitz & Morin 1984; Altan et al 2004).…”

Variables affecting refractive outcome following LASIK for myopia

“…9,39 Extreme pre-operative corneal curvatures did not present in the current study and perhaps would not have been expected to influence outcome. Additionally, previous studies have frequently examined factors in isolation and have examined correlations between each single factor and the refractive outcome, rather than considering a multivariable analysis.…”

“…Larger ablations with the NIDEK EC-5000 are more likely to result in a greater initial post-operative hypermetropic residual refractive error. 8,9 Conversely, the Technolas 217 Plano scan results in undercorrection, which has since been compensated for in the surgical nomogram. 10 Clearly, refractive success following myopic LASIK is modified by multiple factors such as patient characteristics including age and initial refractive error, [11][12][13] plus changes to corneal stress forces after ablation 14,15 and the wound healing process.…”

The effect of water content on the 193 nm excimer laser ablation

“…Refractive success (± 0.50 DS from targeted ablation) can be as high as 83% 3 to 94% 4 for patients with low myopia and astigmatism 3 months after surgery. The risk of not achieving ± 0.50 DS best sphere after uncomplicated myopic procedures is higher for a correction of ‐5.00 DS or greater; 5 how­ever, the success rate for myopic ablations greater than − 15.00 DS can be as low as 32% 6…”