A Comparison of NCT, Goldmann Applanation Tonometry Values in Diurnal Variability of Intraocular Pressure and their Relation to CCT in Healthy Subjects

Objectives: To assess the difference of diurnal variation of Intraocular pressure (IOP) measurements obtained by Goldmann Applanation Tonometry (GAT) and Non-contact Tonometry (NCT) and to study their relationship to central corneal thickness (CCT) in non-glaucomatous eyes. Methods: This is a prospective study of 200 eyes of 100 non- glaucomatous subjects of age between 15yrs-80yrs who underwent Intraocular pressure measurements by GAT and NCT. Intraocular Pressure was measured at 8.00AM, 12.00noon, 4.00PM, 8.00PM by both GAT and NCT and diurnal variation was calculated. CCT readings were taken from both eyes of 100 subjects. The effect of CCT was correlated with the GAT and NCT intraocular pressure differences and as well as with diurnal IOP. Results: The mean age was 46.06 yrs. The mean diurnal IOP variations from 8am to 12noon, 8am to 4pm and 8am to 8pm by GAT were 1.09mm Hg, 1.15mmHg, 2.41mmHg and NCT were 1.15mmHg, 1.74mmHg, 2.60mmHg respectively. The average CCT was found to be 546.60m. No statistical difference was observed between GAT and NCT in measuring diurnal variation. No significant correlation was observed among NCT, GAT, diurnal variation and CCT values. Conclusion: In non-glaucomatous eyes differences in diurnal IOP variations measured by GAT and NCT was not statistically significant and no correlation was observed with CCT. Hence NCT could be an alternative to GAT in measuring diurnal variation of Intraocular pressure in clinical practice.