Researchers Describe the “Halo Sign” in Keratoconus

The newly described halo sign may help clinicians identify advanced keratoconus. While a lot remains unknown about this optical phenomenon, researchers believe that a metric they devised called the Halo Morphology Index has clinical relevance and can assist future investigations looking to uncover more about this manifestation.  Click image to enlarge. Vogt’s striae and Fleischer’s rings are not the only clinical signs of keratoconus detectable using slit lamp examination. A new ocular feature presentable under slit lamp has been discovered, which researchers call the halo sign because of its characteristic shape, which appears when light illuminates the cone apex. However, this phenomenon is not fully understood, remains as a preliminary characterization of keratoconus and requires further research to strengthen its diagnostic validity.In China, researchers conducted a study observing patients with keratoconus under the slit lamp. Since the halo sign appears in cases of advanced keratoconus, the team’s objective was to determine if differences in morphology were apparent in cases of varying severity. Examinations of corrected distance visual acuity (CDVA), Amsler-Krumeich (AK) stage, thinnest corneal measurement, keratometric indices, keratoconus vertex distance and corneal higher-order aberrations (HOAs) were analyzed. OCT images were assessed as well, but only for patients with such scans in their records.Researchers used a concept called the Halo Morphology Index (HMI) in their study, which they state in their paper “provides an operational, image-based descriptor of halo outline anisotropy.” Values calculated using this index range from 0 (no detectable halo) and up, with 1 indicating a near-circular halo outline and higher values indicating greater outline elongation. In the paper, it was noted that this calculation does not measure completeness of halos. “Measurable HMI values were observed only in advanced-stage eyes, indicating that higher HMI reflects halo restriction to advanced disease in this sample.”Eleven patients (22 eyes) diagnosed with keratoconus were examined by the researchers. Under the slit lamp, clinicians discovered eight eyes had halo signs, while the remaining 14 eyes did not.Classification with AK revealed that all eight halo eyes were at stage 4, the highest AK stage. Non-halo eyes appeared in varying stages ranging from 1 to 4. A similar classification system using OCT imaging resulted in a higher stage for eyes with halo signs and lower for non-halo eyes.Other characteristics, like CDVA, corneal thickness, keratometric indices, vertex distance and presenting HOAs, were comparatively different between the two groups. Eyes with halos had worse CDVA, thinner corneas, steeper keratometry, greater cone decentration and a higher prevalence of corneal scarring than non-Halo eyes. Also, HOAs and coma aberrations were more prevalent for eyes with halos.HMI values for eyes with halo signs were wide-ranging. Three eyes fell between 1 and 2, with 1.1 recorded as the lowest value and 1.9 as the highest. However, the halo outlines of five eyes were greatly elongated, according to HMI values. These remaining eyes had values more than 3, with 3.3 as the lowest value and 3.9 as the highest.“HMI provides an operational descriptor of halo outline anisotropy for documentation and future research,” concluded the researchers. “Larger prospective studies with standardized imaging and prespecified analyses are needed to validate these observations and clarify the roles of severity, scarring, and cone decentration.”Click here for the journal source. He H, Niu S, Qu L. A novel optical sign in keratoconus: The Halo Sign and its clinical characteristics. BMC Ophthalmol. March 14, 2026. [Epub ahead of print].  This article was developed by the editorial staff in conjunction with experts in the field. In the process, AI may have been among the editorial tools used to meet the goals of human editors, who approved all content.