Influence of Central Corneal Thickness (CCT) on the Intraocular Pressure (IOP) Measurements Taken From Goldmann Applanation Tonometer, Tonopen, and Airpuff Tonometer.

Abstract

Introduction: Intraocular pressure (IOP) is one of the basic and most important investigations. Central corneal thickness influences IOP measured by various devices.

Objective: In this study, we attempt to determine the agreement and influence of the central corneal thickness in the measurement of IOP obtained by Goldman applanation tonometer, Airpuff tonometer and tonopen.

Methodology: A cross-sectional analytical study of Central corneal thickness (CCT) was done using Ultrasonic pachymetry. IOP was adjusted using Ehler's formula. Mean and the standard deviation was measured using the observed and predicted values for each instrument for its accuracy irrespective of the CCT.

Results: 200 eyes of 100 patients were included in the study. Mean IOP measured was 16mmHg (SD 4). Tonopen was found to have closer observed values when compared with the predicted values to IOP obtained by Goldmann's applanation tonometer after CCT adjustments with Mean difference of 0.0134 mmHg with SD of 0.814. Air Puff tonometer was found to be the least accurate with Mean difference -2.08mmHg and SD of 4.704. Linear regression analysis also predicted that while the tonopen tend to underestimate the IOP levels by 5 %, Airpuff tonometer had a tendency to overestimate the IOP by 13%.(p<0.05).

Conclusion: Tonopen had the greatest agreement and significant correlation with the GAT over a range of IOP and CCT and replicate measurements that are closest to the values obtained by using GAT after CCT adjustments. CCT adjustments may not even be required or has very little influence on IOP when using Tonopen.