Corneal Metrics May Signal Risk of Keratoconus in Frequent Allergic Conjunctivitis

Tomography and biomechanical index (TBI) may indicate increased risk of keratoconus (KC) in patients with allergic conjunctivitis (AC), research in Eye and Vision shows.

Prior research has suggested that patients with AC and eye rubbing may be linked with KC. The investigators sought to further investigate the link between AC and the early risk factors for KC.

(NAC) and 30 eyes in 30 patients with AC from a university ophthalmic center. They scored eye rubbing frequency and ocular symptoms in the patients with AC, and obtained various corneal images.

They found that the AC group had significantly higher TBI (P =.04) and average densitometry in the total cornea and anterior layer compared with the NAC group (P <.001). Compared with the NAC group, the AC group had significantly thinner average epithelial thickness in the 2 mm to 5 mm and 5 mm to 7 mm annuli and minimum epithelial thickness within 7 mm (P <.05).

They discovered that index of surface variance (ISV), index of vertical asymmetry (IVA), keratoconus index (KI), index of height decentration (IHD), and Belin-Ambrosio enhanced ectasia total deviation index (BAD-D) were significantly higher among the patients with AC than those in the NAC group. TBI was linked with ISV, IVA, KI, IHD, and BAD-D. ISV and KI were inversely correlated with average epithelial thickness in the 2-5 mm and 5 mm to 7 mm zones and minimum thickness, and they were associated with epithelial thickness standard deviation (SD) (P <.05 for all).

Eye rubbing was linked to IVA and BAD-D. It was inversely correlated with average epithelial thickness in the 2 mm to 5 mm annulus and the 5 mm to 7 mm annulus and the minimum epithelial thickness. 

Ocular allergic symptoms increased in severity as ISV, BAD-D, TBI and epithelial thickness SD increased and when average epithelial thickness in the 2 mm  to 5 mm annulus and 5 mm 7 mm annulus decreased.

“To the best of our knowledge, this is the first study to reveal corneal epithelial thinning and an uneven corneal thickness distribution in AC patients, indicated by a thinner average corneal epithelial thickness with greater variation,” according to the researchers. “Furthermore, we found that the decrease in corneal epithelial thickness was closely related to the eye rubbing frequency in AC patients.”

The researchers said ophthalmologists should urge patients with AC to avoid rubbing their eyes. Pediatric patients and those going through puberty are of particular concern since KC progresses more quickly at younger ages, the researchers report.

Limitations of the study included small sample size.

Reference

Wang Q, Deng Y, Li S, et al. Corneal biomechanical changes in allergic conjunctivitis. Eye and Vis. Published online May 3, 2021. doi:10.1186/s40662-021-00241-7