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

ABSTRACT

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.

KEYWORDS:

• Comparison
• intraocular pressure
• optometry
• tonometer

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This project is supported by Research Development Fund Pump Priming, City, University of London.