Efficacy and Correlation of Intraocular Pressure Measured by Non-Contact, Rebound and Goldmann Applanation Tonometer With Corneal Thickness, True Iop and Corneal Curvature in a Tertiary Hospital.

Abstract

ABSTRACT:
 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), true IOP and corneal curvature.
 Reliability of each tonometer.
 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. Kvalues were measured using an autorefractometer. 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. There was no significant correlation between K and IOP in our study.
 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. All the tonometers show significant correlation with CCT with GAT showing the strongest correlation. So, it is always advisable to measure the corrected IOP for each patient after considering the CCT.
 Keywords- Non-contact tonometer; Goldmann applanation tonometer; central corneal thickness; intraocular pressure; Rebound tonometer, true IOP, Corneal curvature.

Assessment of intraocular pressure measurement between Goldman applanation tonometer, rebound tonometer, non-contact tonometer, and its correlation with central corneal thickness

“…[ 14 ] found a good agreement. In a study by Das et al ,[ 6 ] NCT values were higher than the RBT values; the difference noted was 0.6 mmHg, which was statistically significant. In our study, RBT values were much closer but lower than the GAT values; the difference noted was 0.45 ± 2.22 mmHg, which was statistically significant but clinically insignificant.…”

“…Similar results were found in studies done by Chakrabarty[ 3 ] (difference of 1.24 ± 1.38 mmHg) and Das et al . [ 6 ] (difference of approximately 1 mmHg). A study from Taiwan[ 11 ] also showed similar findings.…”

“…In studies conducted by Das et al . [ 6 ] and Chen et al ,[ 10 ] the authors found that RBT values were higher than the GAT values. In both the studies, the difference was <0.4 mmHg, which was statistically insignificant.…”

“…Various studies have been conducted, and it is an accepted fact that thinner corneas underestimate IOP values, whereas thicker corneas overestimate them. [ 6 ] Keeping this in mind, we wanted to compare the IOP readings taken with the GAT, the NCT, and the RBT and compare their correlation with central corneal thickness (CCT) in our patient population.…”