Analysis of the effect of keratotopographic parameters on tonometric intraocular pressure

Abstract

BACKGROUND: Applanation tonometers remain popular in most countries of the world; in Russia, the Maklakov tonometer is one of them. When using a Maklakov tonometer, intraocular pressure values are obtained indirectly through the cornea, which has individual characteristics, which certainly introduces its own errors into the accuracy of the measurement results.
 AIM: The aim of this study was to investigate the influence of keratotopographic parameters on tonometric intraocular pressure.
 MATERIALS AND METHODS: A study of 16 keratotopographic indices (using ALLEGRO Oculyzer Wavelight Oculyzer II) and of tonometric intraocular pressure values obtained using Maklakov tonometer (NGm2-“OFT-P”) was carried out in 500 patients (1000 eyes). Among the study population there were patients with both emmetropic refraction — 8 eyes (0.8%), and patients with refractive errors 992 eyes (99.2%), among them: 978 eyes (97.8%) had myopic refraction 14 (1.4%) eyes had isolated refraction with myopic astigmatism. 889 eyes (88.9%) combined myopic refraction with myopic astigmatism.
 RESULTS: Based on the analysis of 16 keratotopographic parameters and tonometric intraocular pressure values, 500 patients (1000 eyes), the greatest influence of 13 studied parameters of the cornea was determined, such as: K1 (keratometry of flatter meridian); K2 (keratometry of steeper meridian); Km (mean keratometry); Rf (radius of the flatter meridian); Rs (radius of the steeper meridian); Rm (mean radius of curvature); Rmin (minimal radius of curvature); Rper (average radius of curvature between the 6 mm and 9 mm zone center); IVA (index of vertical asymmetry); ISV (index of surface variance); CKI (central keratoconus index); Thickness (thickness); IHD (index of height decentration) — on intraocular pressure values.
 CONCLUSIONS: Based on the results obtained, we determined the effect of topographic parameters of the cornea on tonometric intraocular pressure, and created a formula for correcting intraocular pressure values based on the original formula we developed: Pt keratotopographic corrected = Pt + (±ISVp) + (±IVAp) + (±Rmp) + (±Kmp) + (±CKIp) + (±Thicknessp), where Pt keratotopographic corrected is the corrected tonometric intraocular pressure and Pt is the tonometric intraocular pressure.