Comparability and Influence of Central Corneal Thickness (CCT) on Measurements of Intraocular Pressure (IOP) by Goldmann Applanation Tonometry (GAT) and Non Contact Tonometry (NCT) in Different IOP Ranges

Aim : To compare IOP measurements using GAT and NCT in different IOP ranges (<10, ≥10-25 mm Hg and > 25 mm Hg) and evaluate the effect of CCT on IOP measurements by these techniques. Materials and Methods: IOP was measured by NCT followed by GAT in 188 eyes of 100 glaucoma patients attending glaucoma clinic at Chaithanya Eye Hospital , Trivandrum 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 (<10, 10-25, >25 mm Hg) between the two techniques. 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 latter 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 (10-25 mm Hg, significance level <0.08). However in the lower and higher ranges, the difference did not reach the level of statistical significance. NCT is more influenced by CCT. To conclude, though NCT has good accuracy and predictability to be used as a screening tool, it is not suitable for situations where accurate assessment of IOP has paramount importance as in glaucoma clinics. Chaithanya Eye Hospital and Research Institute, Thiruvananthapuram ORIGINAL