Authors : Santanu Das, Kiran Kumar L
DOI : 10.18231/j.ijceo.2020.010
Volume : 6
Issue : 1
Year : 2020
Page No : 41-49
Aim: 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> RBT are compared NCT values are significantly higher than that of RBT(p<0> 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.
Keywords: Central corneal thickness, Goldmann applanation tonometer, Intraocular pressure, Non-contact tonometer, Rebound tonometer, True IOP.