RID-MyC CRISPR Assay in Smear- And Culture-Negative Fungal Keratitis

A prospective diagnostic accuracy evaluation in JAMA Ophthalmology reports on a CRISPR-based Rapid Identification of Mycoses using CRISPR (RID-MyC) assay in a defined clinical niche: patients with suspected fungal keratitis whose conventional corneal smear and culture were nondiagnostic.

Investigators compared RID-MyC results with in vivo confocal microscopy (IVCM) findings, using IVCM as the comparator for estimating test performance in this smear- and culture-negative population. The study was conducted as a prospective diagnostic accuracy investigation at Aravind Eye Hospital, a tertiary referral center, with enrollment from December 2024 to March 2025. Consecutive patients with clinical suspicion of microbial keratitis and negative smear and culture results were eligible. The reported flow was 245 consecutive suspected cases, 82 smear-negative cases, and—after exclusions for contraindications or positive subsequent cultures—41 patients with smear- and culture-negative results included in the final analysis. All included participants underwent corneal scraping for the index test and IVCM imaging, with IVCM used as the reference standard for the performance calculations reported in the study.

Using IVCM as the reference, the authors report that RID-MyC had a sensitivity of 82.1% (95% CI, 63%-94%) and a specificity of 76.9% (95% CI, 46%-95%). The reported positive predictive value was 88.5% (95% CI, 74%-95%) and the negative predictive value was 66.7% (95% CI, 46%-82%). Overall concordance between RID-MyC and IVCM was 33 of 41 cases (80.5%), representing agreement on the presence or absence of fungal keratitis under the study’s comparison framework.

The article also describes how discordant results clustered with certain clinical features. Among patients who were IVCM positive but RID-MyC negative, prior antifungal therapy was reported in most cases (4 of 5). In the opposite direction, all patients who were IVCM negative but RID-MyC positive were described as having smaller lesions, or lesions located peripherally or paracentrally (3 of 3). The authors also report that RID-MyC testing was feasible in all included cases, including some patients in whom imaging was not possible, and they characterize the assay as having rapid turnaround with minimal equipment needs. In their narrative, these observed disagreement patterns are presented alongside a workflow in which the RID-MyC assay could still be completed when imaging constraints arose.

Key Takeaways:

• The report describes a prospective diagnostic accuracy study in smear- and culture-negative suspected fungal keratitis comparing RID-MyC with IVCM as the reference standard.
• The authors report diagnostic performance metrics for RID-MyC versus IVCM and describe overall agreement between the two modalities in most included cases.
• Discordant results were reported alongside patterns involving prior antifungal exposure and lesion size/location, and the authors describe RID-MyC as feasible with rapid turnaround and minimal equipment needs.