Inter-optometrist variability of IOP measurement for modern tonometers and their agreement with Goldmann Applanation Tonometry.

Clinical relevance: Accuracy of tonometers is of vital importance in the detection and treatment of glaucoma.Background: This study investigates: agreement in intraocular pressure measurements between three tonometers and Goldmann applanation tonometry (GAT); inter-optometrist agreement for each tonometer; intra-optometrist agreement for GAT; association between central corneal thickness (CCT) and IOP measurements with each tonometer.Methods: IOP was measured using: CT-1P Non-Contact Tonometer (NCT) (Topcon Corporation, Tokyo, Japan), Pulsair IntelliPuff (Keeler Ltd., Windsor, UK) and Icare rebound tonometer (Icare, Helsinki, Finland) by two optometrists in a random order. Two GAT readings were obtained by each optometrist in a randomised masked manner. Mean differences, and 95% limits of agreement (LoA) for each measurement were calculated. CCT was measured by CT-1P pachymeter.Results: Forty-one participants' IOPs were measured. Mean differences (95% LoA) between NCT, Pulsair, Icare compared to GAT for one optometrist were: 0.8 (-5.4 to 6.9) mmHg, -1.7 (-8.2 to 4.8) mmHg, -1.6 (-9.0 to 5.9) mmHg. Mean differences (95% LoA) in inter-optometrist agreement for GAT, NCT, Pulsair and Icare were: 0.3 (-6.7 to 7.3) mmHg, 0.4 (-2.1 to 2.9) mmHg, -0.9 (-3.6 to 1.9) mmHg and -0.2 (-4.9 to 4.5) mmHg, respectively. Mean differences (95% LoA) for intra-optometrist agreement for GAT were 0.2 (4.3 to -4.7) mmHg and 0.1 (3.6 to -3.9) mmHg for each optometrist, respectively. There was a weak positive association between CCT and both GAT (r2 = 0.11) and NCT (r2 = 0.12).Conclusion: Pulsair and Icare may measure IOP lower than GAT. Mean differences for inter-optometrist agreement for all tonometers were < 1 mmHg; Pulsair showed a statistically significant difference. Intra-optometrist agreement for GAT was good. IOP measurements taken by two community optometrists are comparable using tonometers used in community practice.