Clinical Report: The Halo Sign in Advanced Keratoconus Diagnosis

Overview

The Halo Sign, an annular light projection observed on the iris during slit-lamp examination, has been identified as a novel optical marker in advanced keratoconus. This sign correlates with worse visual acuity, corneal thinning, steeper keratometry, and increased corneal scarring, suggesting its potential utility in assessing disease severity.

Background

Keratoconus (KC) is a progressive corneal ectatic disorder characterized by corneal thinning and protrusion, leading to visual impairment. Traditional slit-lamp signs such as Fleischer’s ring and Vogt’s striae reflect biochemical or biomechanical changes but may not fully capture optical irregularities. The Halo Sign, first described by He and Qu in 2025, represents a novel optical phenomenon seen during slit-lamp examination, potentially offering additional clinical insight, especially in advanced KC. Understanding and quantifying this sign may enhance clinical assessment where advanced imaging is limited.

Data Highlights

Key Findings

• The Halo Sign appears as an annular light projection on the iris when the slit-lamp beam targets the cone apex in keratoconus.
• It was identified exclusively in advanced keratoconus cases (Amsler–Krumeich stage IV) among the studied cohort.
• The Halo Morphology Index (HMI) quantifies halo shape, with lower values indicating circular, well-defined halos and higher values indicating fragmented, irregular patterns.
• Halo-positive eyes showed worse visual acuity, thinner corneas, steeper keratometry, and higher-order aberrations compared to halo-negative eyes.
• Corneal scarring was significantly more common in eyes exhibiting the Halo Sign.
• The Halo Sign may serve as a complementary clinical marker for advanced structural deformation rather than an early diagnostic tool.

Clinical Implications

Recognition of the Halo Sign during routine slit-lamp examination can aid clinicians in identifying advanced keratoconus, especially in settings lacking access to corneal tomography. Incorporating the Halo Morphology Index may further refine assessment of disease severity. However, this sign should complement, not replace, established diagnostic methods.

Conclusion

The Halo Sign represents a promising optical marker of advanced keratoconus detectable via slit-lamp examination. Its presence correlates with significant structural and visual deterioration, underscoring the value of detailed clinical observation in managing keratoconus.

References

1. He and Qu 2025 -- The Halo Sign in Keratoconus: A Novel Optical Phenomenon