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The Ophthalmologist: Clinical and Therapeutic Journal

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Comparison between the real corneal ablation excimer laser and the theoretical munnerlyns formula and the residual corneal thickness after lasik compared to safety limits

Author(s): Pateras Evangelos* and Kontogeorgou Evangelos

Aims: The purpose of this research is to compare the real corneal ablation (excimer Laser) with the theoretical (Munnerlyn’s Formula) and the residual corneal thickness after lasik compared to safety limits.
Sample and study design:
The comparing data of 70 eyes, involved patients aged 19-59 years, undergone Lasik surgery for myopia. The data concerned the corneal flap measured by the excimer laser the real corneal ablation with the theoretical (Munnerlyn’s Formula) and the comparison of the residual corneal thickness after lasik to safety limits such as 300 μm.
Methodology, place and duration of study:
University of west attica department of biomedical science course optics and optometry in collaboration with private ophthalmology clinic “Athens Opthalologiko” during the period between May 2018 until September 2018. All the refractive error surgeries were performed by the same experienced surgeon and the patients selected had healthy myopic eyes with no other ophthalmic pathology or systemic eye diseases. The myopia ranged from -1.00 to 9.25 Diopters. All participated voluntarily, maintaining their anonymity due to the protection of their personal data. Patients underwent refractive surgery with the excimer lasik method.
Results: The real flap thickness, recorded by the excimer laser was 119.74 μm ± SD 19.50. The actual ablation thickness ranged from 19.25 μm to 126.29 μm with an average value of 64.74 μm ± SD 28.39 μm and a median of 65.29 μm. The theoretical ablation thickness ranged from 12 μm to 118.52 μm, with a numerical average value of 57.79 μm ± SD 26.97 μm and a median of 53.69 μm, with correlation coefficient 0.9603 (P<0.0001). The calculated thickness of the residual stromal bed, (RSB) ranged from 308.14 μm to 490.28 μm with an average value of 374.84 μm ± SD 41.18 and median 374.10 μm. The difference of the residual stromal bed (RSB), from the safety limit of 250 μm for avoiding ektasia after Lasik, ranged from 58.14 μm to 240.28 μm, with an average value of 124.84 μm ± SD 41.18 μm and median 124.10 μm. The RSB was also compared with a safety thickness limit of 300 μm with a difference ranged from 8.14 μm to 190.28 μm, with an average value of 74.84 μm ± SD 41.18 μm and a median of 74.10 μm.
Conclusion:
Our results of the ablation thickness with excimer laser lasik refractive surgery compared between the theoretical Munnerlyn’s formula and the one given by the excimer laser correlated strong with correlation coefficient 0.9603. The RSB difference with a safety thickness limit of 300 μm ranged from 8.14 μm to 190.28 μm, with an average value of 74.84 μm ± SD 41.18 μm and a median of 74.10 μm which is crucial for refractive surgery safety.


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