A Comparative Study of Intraocular Pressure Measurement Using Tonopen and Goldmann Applanation Tonometer

Background: Glaucoma is the world's leading cause of preventable irreversible blindness. The most important risk factor of glaucoma is increase in the intraocular pressure.Hence, timely screening by accurate IOP measurements is of utmost importance. In recent years, Tonopen has emerged as an alternative to Goldmann applanation tonometer which is the ‘gold standard’ for IOP measurement because of its various advantages. Since its reliability has not yet been confirmed, this study aims to assess the accuracy of the Tonopen in measuring the IOP as compared to the Goldmann applanation tonometer. Objective: To determine whether Tonopen is accurate and reliable in measuring the intraocular pressure as compared to Goldmann applanation tonometer. Methodology: In this prospective cross-sectional study, 113 patients above 40 years coming for routine eye check-up and who were diagnosed earlier as glaucoma patients their IOP was measured. The Tonopen was used first followed by the Goldmann applanation tonometer. Collected data was analyzed using SPSS version 17.0. The results were expressed in terms of sensitivity, specificity, positive and negative predictive value and accuracy rate. Institutional Ethics Committee clearance was obtained prior to commencement of study. Results: For the right eye, the sensitivity of the Tonopen in detecting glaucoma was 60% and the specificity was 94.44%. The positive predictive value and the negative predictive value were 33.33%and 98.08% respectively. Percentage of false-negatives obtained were 40% and percentage of false-positives obtained were 5.55%. Accuracy rate of the Tonopen was 92.92%. For the left eye, sensitivity was 75% and specificity was 96.33%. The Positive predictive value and negative predictive value were42.86% and 99.06% respectively. Percentage of false-negatives obtained were 25% and percentage of false-positives were 3.67%. Accuracy rate of the Tonopen was 95.57%. Area under the Receiver Operating Characteristic curve was 0.887 with a standard error of 0.085 in case of the right eye. For the left eye, the area under the curve was 0.972 with a standard error of 0.027. Conclusion: According to this study, the Tonopen is an accurate and reliable indicator of Intraocular pressure.