Intraocular Pressure Measurement by Goldmann Applanation Tonometer and Noncontact Tonometers Taking Consideration of Central Corneal Thickness- A Comparative Cross-Sectional Study

Abstract

BACKGROUND Intraocular Pressure (IOP) is one of the key physiological factors, which can regulate the ocular health and homeostasis. Accurate measurement of IOP depends on several factors among which instrument factor plays significant role. Considering Goldmann Applanation Tonometer (GAT) as a "GOLD" standard, we have compared Noncontact Tonometers (NCT) with GAT taking Central Corneal Thickness (CCT) into consideration. MATERIALS AND METHODS In this comparative cross-sectional study in a tertiary care hospital, after inclusion and exclusion, patients were thoroughly examined clinically and GAT, NCT and CCT tests are performed using standard technique by single competent ophthalmologist on the same day. Values are tabulated in excel sheet and statistical calculations done using SPSS version 20. RESULTS In the study population, 57.7% were males and 42.3% females (M:F = 187:137). The mean age of the population is 45.16 ± 19.58 years (SD) and mean intraocular pressure of males was found to be 16.63 ± 3.72 (SD) mm of Hg by GAT method and 16.75 ± 3.53 (SD) mm of Hg by NCT, and in females, it was found to be 16.12 ± 3.51 (SD) mm of Hg by GAT method and 16.29 ± 3.28 (SD) mm of Hg by NCT. The difference between methods was statistically significant (P <0.05). Mean central corneal thickness of the study population was found to be 546.10 ± 34.87 (SD) µm, whereas central corneal thickness of males 547.11 ± 33.93 (SD) µm and females were 544.71 ± 36.13 (SD) µm. The difference in IOP measurement between methods was statistically significant (P<0.05) for the entire group and in the subgroup with central corneal thickness more than 575 µm. The reliability indices for the noncontact tonometer considering the Goldmann applanation tonometer as gold standard are highly correlating as coefficient of correlation is near to +1 in all the subgroups in respect to central corneal thickness. CONCLUSION The difference in measurements by noncontact tonometer and the Goldmann applanation method was statistically significant. The measurements by noncontact tonometer were reasonably accurate (coefficient of correlation is near to +1).