Comparison of Central Corneal Thickness Measurement using Optical and Ultrasound Pachymetry in Primary Open Angle Glaucoma Patients

Introduction: A thinner Central Corneal Thickness (CCT) is an important criterion in determining the probability of progression from Ocular Hypertension (OHT) to Primary Open Angle Glaucoma (POAG). The most common devices for measuring CCT are ultrasound and optical pachymeters. Ultrasound pachymetry is a quick and precise approach to quantify corneal thickness that is also portable and inexpensive. The advantages of optical method include operator independency and noninvasiveness. Aim: To compare central corneal thickness using optical and ultrasound pachymetry in patients with POAG. Materials and Methods: This cross-sectional study was conducted at the Department Ophthalmology, ESI Post Graduate Institute of Medical Sciences and Research, Basaidarapur, Delhi, India, from October 2020 to April 2022. There were 105 POAG patients (210 eyes), divided into three subgroups of 35 subjects each (70 eyes each), based on the number of anti-glaucoma medications being instilled, topically (one/two/three drugs), and 35 healthy antiglaucoma controls (70 eyes). Central corneal thickness measurements were taken by Ultrasonic Pachymeter (USP) TOMEY SP-100, and by CEM-530 Non Contact Specular Microscope (NCSM) (optical). Statistical analysis was performed by the Statistical Package for Social Sciences (SPSS) program for Windows, version 17.0 (SPSS, Chicago, Illinois). Results: The mean CCT taken with NCSM and USP was 540.83 +/- 35.51 pm and 538.74 +/- 36.22 pm, respectively, in Right Eyes (RE) of 35 glaucoma patients on one drug, (p-value=0.80). Similarly, Left Eyes (LE), mean CCT with NCSM was 544.17 +/- 33.98 pm, and with USP was 541.69 +/- 36.6 pm (p-value=0.76). Mean CCT taken with NCSM and USP was 539.83 +/- 30,85 pm and 537.66 +/- 30.5 pm, respectively in RT eyes of 35 glaucoma patients on two drugs (p-value=0.76). Left eyes, mean CCT was 541.91 +/- 29.79 pm with NCSM as compared to USP which was 540.11 +/- 29.89 pm (p-value=0.80). On comparing the mean CCT values of RE in glaucoma subjects who were controlled on three antiglaucoma drugs it was found to be 528.37 +/- 26.44 pm using NCSM and 527.09 +/- 26.17 pm using USP (p-value=0.84). The meanvalues of CCT for LE was 521.94 +/- 26.53 pm with NCSM and with USP was 520 +/- 26.52 pm, respectively (p-value=0.81). Comparison of mean CCT measurements using NCSM and USP in 35 age-matched controls RE eye was found to be 517.83 +/- 21.27 pm and 515.97 +/- 20.91 pm, respectively (p-value=0.71). Similarly, for LE mean CCT values were 518.8 +/- 24.21 pm and 516.8 +/- 24.37 pm, respectively (p-value=0.73). Conclusion: The CCT measured using NCSM was found to be higher than that measured using USP in POAG subgroups patients as well as healthy age-matched controls, however the difference was not statistically significant. There was highly significant linear correlation between the CCT measured using NCSM and USP in all POAG subgroups as well as healthy controls. This suggests that the devices could be used interchangeably in glaucoma patients as well as healthy subjects of similar age group.