Variables affecting refractive outcome following LASIK for myopia

Predictive Factors for Successful High Myopia Treatment Using High-Frequency Laser-In-Situ Keratomileusis

Aim

To evaluate the predictive factors of LASIK procedure for high myopia with or without astigmatism using a combination of high-frequency femtosecond-assisted LASIK followed by an excimer laser.

Methods

This study was a retrospective interventional case series study to evaluate myopic eyes undergoing high platform LASIK with FEMTO LDV Z2 intervention, followed by WaveLight®EX500 excimer laser machine. Subjects were divided into 2 groups: high myopia (SE of -6.01 to -9.00 D) and very high myopia (SE of -9.01 D or higher). Myopic eyes (Spherical Equivalent/SE) less than -13 D were included in this study. Visual Acuity (VA) was evaluated 1 day and 60 days after the procedure. Predictive factors, such as age, degree of sphere, degree of astigmatism, keratometric reading and axial length were analyzed to detect any influences affecting the final VA results.

Results

A total of 316 myopia eyes underwent intervention, mean age: 25.3±3.8 years. Target treatment was achieved in 96.1% of patients with high myopia and 69.9% of patients with very high myopia. High degree of sphere and astigmatism constitutes an important factor influencing final VA.

Conclusion

Modern machines provide a more promising efficacy and success of LASIK procedure in high myopia: important predictive factors were a high degree of sphere and astigmatism for achieving the optimal final outcome.

Safety, efficacy and refractive outcomes of LASIK surgery in patients aged 65 or older

PURPOSE

Report on the safety, efficiency and refractive outcomes of LASIK surgery in patients aged 65 or older.

METHODS

This study includes a case series of patients ≥65 years that underwent corneal refractive surgery during the period June 2010 to June 2015 at Hospital Zambrano Hellion, Monterrey, Mexico. Inclusion criteria were normal topography, central corneal thickness >500 μm, preoperative manifest refraction spherical equivalent (MRSE) up to -8.5 D and +6.0 D, cylinder up to -6.0 D, CDVA of 20/25 or better and with no other ocular pathology.

RESULTS

A total of 44 eyes (24 patients) were included. Mean age was 67.2 ± 2.1 years (range 65-80), with mean follow-up of 12.2 ± 1.3 months. Conventional LASIK was performed in 20 patients (group 1, 36 eyes) to improve UDVA (10 eyes myopic LASIK and 26 eyes hyperopic LASIK) and presbyopic LASIK (monovision) in 4 patients (group 2, 8 eyes) to restore near-vision performance. Preoperative MRSE group 1 was myopic: -2.79 ± 1.88 D; hyperopic +2.19 ± 1.88 D; and +2.10 ± 0.87 D in group 2. Preoperative UDVA in group 1 was 0.67 ± 0.30 LogMAR; 0.46 ± 0.18 LogMAR; and Jaeger ≥4 in 90% in group 2. Postoperative MRSE: -0.29 ± 0.86 D (myopic LASIK) (p < 0.001), +0.34 ± 0.62 D (hyperopic LASIK) (p < 0.001) and -1.25 ± 0.59 D (non-dominant eye) in presbyopic LASIK. Postoperative UDVA in myopic LASIK was 0.15 ± 0.30 (p = 0.001) and 0.11 ± 0.11 (p < 0.001) for hyperopic LASIK. In group 2, binocular UDVA was 0.16 ± 0.17 (p = 0.12) and UNVA was ≥J2 in 100% of the patients.

CONCLUSION

Even though elder patients may present greater LASIK restrictions due to lens and other ocular age-related changes, patients ≥65 years that were candidates for conventional and presbyopic LASIK showed satisfactory and safe refractive and visual outcomes.

Laser in situ keratomileusis in 2012: a review

Laser in situ keratomileusis (LASIK) is a safe and effective treatment for refractive error. A combination of technological advances and increasing surgeon experience has served to further refine refractive outcomes and reduce complication rates. In this article, we review LASIK as it stands in late 2012: the procedure, indications, technology, complications and refractive outcomes.

A microscopy study of the structural features of post-LASIK human corneas

Purpose

To study the structural features of human post-LASIK corneas.

Methods

A pair of post-mortem donor corneas, from a 55-year old patient who underwent uncomplicated LASIK surgery five years previously, were bisected and fixed in 4% paraformaldehyde. The right cornea and one half of the left cornea were processed for light microscopy and scanning electron microscopy. One half of the right cornea was also examined by transmission electron microscopy.

Results

The flap-bed interface could be easily detected several years after LASIK and, although the flap appeared to be in close association with the stromal bed, there was a noticeable absence of reconnection between adjacent severed lamellae. Tissue gaps were evident at the flap margin, which once free of cellular components revealed the presence of a few bridging fibres.

Conclusion

Examination of corneas five years after LASIK revealed evidence of primitive reparative scar development at the wound interface, but no reconnection of severed collagen lamellae. Such findings may explain the occurrence of flap dislocation following trauma in some patients months or years after surgery.

Real-time measurement of ArF excimer laser corneal tissue ablation rates using cross-correlation of laser waveforms

The current popularity of excimer laser refractive surgery suggests a need for continued research and refinements to further improve clinical outcomes. A fundamental limitation of current clinical systems is the lack of real-time feedback specifically addressing the laser-tissue interactions as directly related to laser ablation rates. This paper reports data to assess the feasibility of a novel approach that holds promise as a real-time feedback scheme based on comparison of the incident and reflected laser pulse waveforms, as quantified using a cross-correlation algorithm. The approach is evaluated for ablation of bovine cornea over a range of clinically relevant laser fluences. A linear relationship was observed between several cross-correlation metrics and the directly measured corneal ablation rate, yielding an average RMS predictive error of 3.9% using a 25-shot average reflected waveform. Assessment of the cross-correlation approach for single-shot ablation data revealed a brief transient corresponding to the first few laser pulses, which is attributed to a slight hydration gradient near the surface of the de-epithelialized cornea. Clinical refractive data are necessary to assess the precision of this approach for actual refractive surgery.