Subclinical corneal inflammation and subbasal nerve alterations in keratoconus detected by in vivo confocal microscopy: a cross-sectional study.

Purpose: To investigate the intracorneal inflammation and subbasal nerve alterations in keratoconus.

Methods: This prospective cross-sectional study recruited patients with keratoconus, who were diagnosed and graded the severity based on clinical examination and Schiempflug tomography. Laser in vivo confocal microscopy (IVCM) was performed on the corneal subbasal layer centrally to explore the inflammatory cells (ICs), subbasal nerve density (SND), and nerve tortuosity. Keratoconus severity and related factors including ocular allergy, systemic atopy, eye rubbing, floppy eyelids, and contact lens use were recorded. Association between the factors, IC density, SND and keratoconus severity were analyzed.

Results: Thirty-four keratoconus eyes were enrolled, and their IVCM findings were compared with those of 20 age-matched normal eyes. Keratoconus showed a significant increase in ICs (44.25 ± 7.01 vs. 13.06 ± 7.51 cells/mm², p < 0.001) and a significant decrease in SND (16.54 ± 0.79 vs. 20.62 ± 0.72 mm/mm², p < 0.001) when compared to controls. The alterations were pronounced in severe keratoconus as the IC density was significantly higher (p < 0.001), whereas SND was lower (p = 0.001) in high-graded keratoconus than in low-graded keratoconus. However, there was no significant correlation between the number of IC and SND in keratoconus eyes (p = 0.835). Corneal sensitivity and nerve tortuosity were not different between keratoconus and the controls. No keratoconus-related factors were associated with IC density except the severity of keratoconus (p < 0.001, 95% CI [0.70, 0.95]).

Conclusion: Keratoconus, a clinically noninflammatory corneal disease, demonstrates subclinical corneal inflammation and subbasal nerve decline as shown by IVCM. These alterations correlate considerably with the severity of keratoconus.

Key messages: What is known Traditionally, Keratoconus is a clinically noninflammatory corneal disease. What is new Our study suspected keratoconus may be subclinical corneal inflammatory disease. In our research, A Keratoconus patient was discovered to have corneal inflammation and a reduction in sub-basal nerve density through the use of In Vivo Confocal Microscopy. Increase in corneal inflammation is considerably correlated with the severity of keratoconus.