Comparative Study of Intraocular Pressure Measured by Non-Contact and Goldmann Applanation Tonometer and their Correlation with Corneal Thickness in a General Population

Abstract

To compare the intraocular pressure (IOP) measured by Non-Contact tonometer (NCT) and Goldmann Applanation tonometer (GAT) and their correlation with central corneal thickness (CCT) as well as the reliability of each tonometer. Methods: 500 patients (1000 eyes) attending the ophthalmology OPD aged 18 years and above were taken up for the study. Patients with anterior and posterior segment pathologies like corneal ulcer, leukoma, staphyloma, corneal lacerations, ectatic corneal conditions, corneal dystrophies, oedema, perforations, acute angle closure glaucoma, retinal detachments, vitreous haemorrhage and unwilling patients were excluded from the study. IOP was recorded using NCT and GAT after assessing the patient's visual acuity.Following IOP measurement, central corneal thickness (CCT) value of each patient was measured using pachymetry. All the data were collected and tabulated for statistical analysis to obtain results. Results: In the present study there were 256 males (51.2%) and 244 females (48.8%). The mean CCT in males was 0.5350 mm and in females 0.5340 mm respectively. The mean IOP measured by NCT is 16.43 mm hg whereas the mean IOP measured by GAT is 15.43 mm hg. IOP measured by NCT is significantly higher than the IOP measured by GAT (p<0.001). When correlated with CCT all the tonometers show significant correlation with GAT showing the strongest significant correlation. NCT overestimates IOP in normal, thin and thicker corneas when compared to GAT and are statistically significant. Conclusion:From the present study we can conclude that IOP measured by NCT is higher than GAT. NCT values are significantly higher than GAT values in thin and normal corneas whereas it overestimates more in thicker corneas. All the tonometers show significant correlation with CCT with GAT showing the strongest significant correlation in this study. So, it is always advisable to measure the corrected IOP for each and every patient after taking into account the CCT of that particular person.