Comparative evaluation of applanation and indentation tonometers in a community ophthalmology setting in Southern India

Abstract

Purpose: Measurement of intraocular pressure (IOP) is one of the basic investigations in a general ophthalmic workup. In this study, we attempt to determine the agreement in the measurement of IOP obtained by Perkin's applanation tonometer, noncontact tonometer and Schiotz indentation tonometer in patients attending general ophthalmology OPD in a tertiary care centre in South India and its use in a community ophthalmology setting. Methods: A cross-sectional analytical study in which IOP was measured in patients using the three tonometers. Central corneal thickness (CCT) was measured using Ultrasonic pachymetry. Bland Altman analysis was done to evaluate the agreement between instruments. Results: 800 eyes of 400 patients were included in the study. By Bland Altman method, Schiotz indentation tonometer was found to have better correlation to IOP obtained by Perkin's applanation tonometer. Schiotz indentation tonometer was found to be most accurate when CCT was in the range of 501-550 μm and noncontact tonometer was found to be least accurate when CCT was greater than 600 microns. On comparing correlation at different age groups, both the methods had better correlation at <40 years age group. Conclusion: Both the tonometers showed a significant correlation with the gold standard technique (Perkin's applanation tonometer) over a range of IOP and CCT with the Schiotz tonometer better than the NCT. This study proves that Schiotz tonometer can be recommended as a reliable screening tool in community outreach ophthalmology services. The twin advantages of portability and availability make the Schiotz tonometer a popular choice among ophthalmology trainees and optometrists in a developing country like India.