A Comparative Analysis of Intraocular Pressure Measurement Accuracy With Reused iCare Probes

Abstract

Purpose: To assess the accuracy of reused iCare probes after disinfection with 70% isopropyl alcohol and ethylene oxide gas compared to new iCare probes and Goldmann applanation tonometry (GAT).

Design: Prospective comparative analysis.

Participants: A total of 118 eyes from 59 patients recruited from the Aravind Eye Hospital glaucoma clinic in Tirupati, South India.

Methods: Intraocular pressure (IOP) was measured on each eye using a new iCare tonometer probe, an iCare probe previously used and disinfected 1 time prior (once used probe) and 5 times prior (multiply used probe), as well as with GAT. Probes were disinfected after each use with 70% isopropyl alcohol swabs and ethylene oxide sterilization.

Main outcome measures: Agreement demonstrated with intraclass correlation coefficients (ICCs), mean difference in IOP values with limits of agreement, and Bland-Altman plots among IOP measurement approaches.

Results: Compared to new iCare probes, both once used probes (ICC = 0.989, 95% confidence interval [CI] 0.985-0.993) and multiply used probes (ICC = 0.989, 95% CI 0.984-0.992) showed excellent agreement, and the mean difference in IOP was minimal for both once used probes (0.70 mmHg, 95% CI 0.29-1.11) and multiply used probes (0.75 mmHg, 95% CI 0.66-0.82) compared to new probes. Bland-Altman plots demonstrated minimal differences between new and reused probes across the spectrum of IOP. When comparing multiply used probes to once used probes, there was a high level of agreement (0.993) (95% CI 0.990-0.995) and negligible mean IOP difference 0.04 mmHg (95% CI 0.32-0.40). Additionally, ICC values for new probes (0.966, 95% CI 0.951-0.976), once used probes (0.958, 95% CI 0.940-0.971), and multiply used probes (0.957, 95% CI 0.938-0.970) compared to GAT were similar and all showed excellent agreement. Both new and reused iCare probes underestimated IOP by 2 to 3 mmHg compared to GAT.

Conclusions: In this prospective comparative analysis, we found that reusing iCare probes up to 5 times does not compromise the accuracy of IOP measurements when disinfected with 70% isopropyl alcohol swabs and ethylene oxide. Reusing iCare probes has the potential to transform care by reducing cost, decreasing environmental waste, and allowing for glaucoma screening camps and increased glaucoma monitoring in low resource settings leading to earlier identification and treatment of glaucoma.

Financial disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Keywords: Goldmann applanation tonometry (GAT); iCare tonometry; intraocular pressure (IOP); rebound tonometry; reused tonometer probes.