The annular dark shadow (ADS) reflex may be useful in identifying patients with keratoconus (KC) and KC suspects and determining its severity, according to a study published in Ophthalmic and Physiological Optics.
Researchers enrolled 58 patients in the study consisting of healthy control participants (n=37; eyes, 37; 17 women) and individuals with KC or KC suspects (n=21; eyes, 37; 10 women). Participants underwent comprehensive eye examinations including slit-lamp evaluation, retinoscopy, and corneal topography and tomography. An investigator determined KC severity using ABCD grading which included the anterior radius of curvature (A), back surface radius of curvature (B), corneal pachymetry at the thinnest point (C) and distance best-corrected vision (D). A second examiner imaged the ADS, which was measured from its thickest point to its lowest point.
The ADS was observed in all patients with KC and KC suspects (mean height, 2.24 mm), but not in any of the control group participants. Patients with KC had a significant difference in ADS height compared with KC suspects (1.89 vs 2.88 mm; P <.001). A significant positive correlation was found between the height of the ADS and KC severity for parameters A (r=0.74; P <.001), B (r=0.72; P <.001), C (r=0.58; P <.001) and D (r=0.34; P =.04), according to the report.
The researchers stress the significance of using the ADS reflex as a method of early detection and intervention in patients with less severe KC. “Early detection of KC, especially before vision deteriorates, is important since treatment with collagen crosslinking may stop the progression of the disease.” the study author note. “While it is relatively straightforward to diagnose KC, it is challenging to diagnose early KC and KC suspects.”
Study limitations include failure to assess agreement and repeatability for measurements.
Said AGA, Piñero DP, Shneor, E. Revisiting the oil droplet sign in keratoconus: utility for early keratoconus diagnosis and screening. Ophthalmic Physiol Opt. Published online November 16, 2022. doi:10.1111/opo.13066