An ANCOVA analysis of the results of planned and actually obtained hypocorrection after excimer laser surgery in middle-aged patients with myopia

Abstract

Purpose: a covariance analysis of the planned and actually obtained refraction after excimer laser myopia correction surgery in middle-aged patients. Material and methods. 85 patients (170 eyes) aged 35 to 50 underwent excimer laser myopia correction surgery by FemtoLASIK. The patients were divided into 3 groups according to the degree of myopia: group 1 included 13 patients (26 eyes) with myopia from -1.25 to -3.0 D, group 2 had 42 patients (84 myopic eyes) from -3.25 to -6.0 D and group 3 had 30 patients (60 eyes) with myopia of -6.25 D or higher. Results. The patients with low myopia, independently of the age, revealed a postoperative refraction effect closer to that planned than the patients with moderate and high myopia. The difference (delta) between the planned and the obtained results was -0.35 ± 0.08 D (41%) in group 1, -0.58 ± 0.04 D (51.3%) in group 2 and -0.64 ± 0.05 D (46%) in group 3. The divergence between the respective indicators for figures for low and high myopic groups is statistically significant. Conclusion.Patients with low myopia over 35 years old can be recommended a symmetric hypocorrection in binocular format irrespective of the objective data regarding the initial corneal hydration, which affects the ablation volume. To achieve a better agreement between the planned and the actual hypoeffect (and, accordingly, a more precise dosage of the surgery) in patients with moderate and high myopia, it is important to introduce into clinical practice the technology of contactless measurement of corneal hydration.