# A comparison of iCare and Goldmann applanation tonometry measurements during the COVID-19 pandemic: a retrospective study

## TL;DR

This study compares two methods for measuring eye pressure in glaucoma patients and finds they agree well on average but can differ significantly in individual cases.

## Contribution

The study identifies factors like age and corneal thickness that influence differences between iCare and Goldmann tonometry in glaucoma patients.

## Key findings

- The ICC between iCare and Goldmann applanation tonometry was 0.90, indicating strong agreement.
- The mean IOP difference was -0.18 ± 2.89 mmHg with a 95% limit of agreement of -5.8 to 5.5 mmHg.
- Age and central corneal thickness were significantly correlated with IOP measurement differences.

## Abstract

To evaluate factors associated with differences in intraocular pressure (IOP) readings between iCare and Goldmann applanation tonometry (GAT) in established glaucoma patients.

This retrospective comparative study included clinical data of 350 eyes from 350 established glaucoma patients who had iCare and GAT IOP measured by an ophthalmic technician and a glaucoma specialist, respectively. The main outcome measure was the difference in IOP measurements of the right eyes with iCare and GAT.

The intraclass correlation coefficient (ICC) between GAT and iCare was 0.90. The mean IOP difference between tonometers was − 0.18 ± 2.89 mmHg. Bland–Altman plots indicated a 95% limit of agreement of − 5.8 to 5.5 mmHg. Central corneal thickness (CCT) and age were significantly correlated with the difference in IOPs of the iCare and GAT. GAT-IOP and age were significantly associated with the absolute difference in measured IOP of the two tonometers. The difference in measurements was not significantly associated with prior glaucoma surgery, average global index of optical coherence tomography, axial length, technician years of experience and certification, and IOP range.

Although there is good agreement between the iCare and GAT mean values, these devices are not interchangeable in glaucoma patients due to the wide range of the limit of agreement.