Impact of refractive surgery on Maklakov tonomery results

Relevance Excimer laser methods for correcting refractive errors, including laser in situ keratomileusis (LASIK), femtosecond-assisted LASIK (FS-LASIK) and photorefractive keratectomy (PRK), are very popular due to their high safety and effectiveness [1–3]. The widespread use of these technologies has led to the need to personalize tonometry methods based on corneal applanation. Despite the obvious advantages of modern surgical methods, it is necessary to take into account their effect on the structural parameters of the cornea. Understanding this process is important for accurate measurement of intraocular pressure (IOP) and glaucoma diagnostics [4, 5]. Objective To evaluate the effect of changes in corneal structural parameters after refractive surgery on the results of Maklakov tonometry. Material and methods The study involved 61 people (121 eyes). The patients were divided into groups: the first (control) - without a history of surgery, the second - after LASIK, the third - after LASIK with femtosecond assisted laser (FS-LASIK) and the fourth - after photorefractive keratectomy (PRK). All patients underwent a standard ophthalmological examination, keratometry (Km), Maklakov tonometry with a 10 g weight and elastotonometry with weights of 5; 7.5 and 15 g. Results In the LASIK group, the diameter of the imprint with weights of 5 and 7.5 g showed a correlation with the curvature of the central and paracentral zone (r = 0.3–0.5), while tonometry with a 10 g weight did not demonstrate such a relationship. When using a 15 g weight, an inverse correlation was found with curvature at the paracentral points (at 4 mm) of the strong meridian (r = -0.5 ... -0.7). In the FS-LASIK group, a significant inverse correlation was observed only for the indentation diameter with a 10 g weight in the paracentral zone (3-4 mm) (r = -0.4 ... -0.5). In the PRK group, weak correlations (r < 0.4) were recorded between curvature and indentation diameter with 7.5 and 10 g weights in the central zone (1-2 mm), while significant correlations were not observed for 5 and 15 g weights. In the control group, there were virtually no correlations for the 5 and 7.5 g weights, but the diameter of the imprint with a 10 g weight showed a uniform correlation with the curvature at all points (r = -0.38 ... -0.6), and the imprint with a 15 g weight mainly correlated with the curvature of the horizontal meridian (r = -0.37 ... -0.49). Conclusion Considering the inverse nature of most correlations, high keratometry can be associated with an overestimation of tonometry results, and low - with an underestimation. Key words: IOP; Maklakov tonometry; LASIK; photorefractive keratectomy (PRK); refractive surgery