ground :- Intraocular pressure is one of the most important modifiable risk factors in the management of glaucoma. Though different tonometers are available, their measurement is not always interchangeable & reproducible. Central corneal thickness is known to affect the accurate IOP measurements & it has different effects on different tonometers. Aim:- To compare measurements of IOP using GAT and NCT in different IOP ranges (<11, 11-25, >25 mm Hg) and evaluate the influence of CCT on IOP measurements by these techniques. Materials and Methods:- IOP was measured by NCT followed by GAT in 218 eyes of 112 patients (both eyes of 106 patients and single eye of 6 patients due to various reasons; eg – one eyed patient, corneal scar in one eye) attending the eye OPD of a tertiary hospital of West Bengal by a single observer. Mean of three consecutive readings were taken for analysis by both techniques. IOP values were compared in the three IOP ranges (<11, 11-25, >25 mm Hg) between the two techniques. CCT values were obtained from them using ultrasonic pachymeter. Statistical analysis was done to know whether the two methods were interchangeable across the three IOP ranges. Results:- Though good agreement was seen between GAT and NCT, the later showed a tendency to overestimate IOP in the lower IOP range and underestimate in the normal and high IOP range. Mean values of GAT and NCT showed a statistically significant difference in the normal IOP range (11 - 25 mm Hg, significance level ) and high IOP range (>25 mm Hg). However in the lower range, the difference did not reach the level of significance. NCT is more influenced by CCT. To conclude, though NCT has good accuracy and predictability to be used as a screening tool, but GAT is accurate in all IOP ranges.

Keywords : Tonometers , Intraocular Pressure, Central Corneal Thickness, Goldmann Applanation Tometry , Non Contact Tonometry.