Comparative study of intraocular pressure measured by non-contact, rebound and goldmann applanation tonometer and their correlation with corneal thickness and true IOP in a general population

Abstract

To compare the Intraocular Pressure (IOP) measured by Non-contact tonometer (NCT), Rebound tonometer (RBT) and Goldmann Applanation tonometer (GAT) and their correlation with central corneal thickness (CCT) and true IOP. Reliability of each tonometer. Materials and Methods: 500 random patients 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, RBT and GAT after assessing the patient's visual acuity. Following IOP measurement, central corneal thickness (CCT) of each patient was measured using pachymetry. All the data were collected and tabulated for statistical analysis to obtain results. Results: 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 NCT and RBT are compared NCT values are significantly higher than that of RBT(p<0.001). Although the mean RBT IOP 15.83 mm hg is higher than the mean GAT IOP of 15.42 mm hg the values are not statistically significant. When correlated with CCT all the tonometers showed significant correlation with GAT showing the strongest correlation. NCT overestimates IOP in normal, thin and thicker corneas when compared to GAT and are statistically significant. RBT also overestimates in the normal and thick corneas when compared to GAT but their values are much closer to GAT values in thinner corneas. The IOP measured by all the 3 tonometers correlated with corrected IOP with NCT showing the best correlation followed by GAT. Conclusion:From the present study we can conclude that IOP measured by NCT and RBT is higher than GAT. NCT values are significantly higher than GAT values in thin and normal corneas whereas it overestimates more in thicker corneas. RBT values are significantly higher than that of GAT in normal and thick corneas. So, it is always advisable to measure the corrected IOP for each patient after considering the CCT.

A Comparative Study Between the Goldmann Applanation Tonometer and the Non-Contact Air-Puff Tonometer (Huvitz HNT 7000) in Normal Eyes

“… 13 Regarding thickness, a study showed that NCT values were higher than GAT values in thin and normal corneas, but that IOP was overestimated in thicker corneas. 14 …”