Publication:

Goldmann applanation tonometry versus non-contact tonometry: a comparative study

Background Intraocular pressure (IOP) measurement is a routine procedure in complete ophthalmologic examination and finds importance in diagnosis and monitoring of glaucoma. Goldmann applanation tonometry and non-contact tonometry, though age old, are still widely used methods of measuring IOP, especially in developing countries like India. This study was undertaken to compare IOP measured with Goldmann applanation tonometer (GAT) and non-contact tonometer (NCT) and to determine the correlation between intraocular pressure and central corneal thickness (CCT).

Methods This was a cross sectional and observational study wherein adult patients visiting a medical hospital were included. IOP measurements of one hundred and forty four eyes (glaucomatous and non-glaucomatous) were performed using GAT and NCT. The IOP values were compared in different IOP ranges using Bland Altman graph. CCT was measured and its correlation with GAT and NCT analyzed using linear regression analysis.

Results Both methods of tonometry correlated significantly with each other. The mean of paired difference between GAT and NCT was 1.24±1.38 mmHg (r=0.95, p<0.001). A positive correlation between CCT and both GAT and NCT was found with a regression of 0.35 mmHg per 10 micrometer change in corneal thickness.

Conclusions Pressure readings of GAT and NCT are comparable. Ophthalmologists need to keep in mind the variation of IOP with CCT. Suitable correction table needs to be devised when considering different CCT ranges for both methods of tonometry.