Structural changes in the corneal subbasal nerve plexus in keratoconus

Abstract

Background: Corneal confocal microscopy (CCM) allows visualizing slightest alterations within the corneal subbasal nerve plexus (SNP). Recent CCM studies based on the analysis of three-five CCM images per eye assumed a reduced corneal nerve fibre length (CNFL) in keratoconus (KC).

Methods: The SNP of KC patients (n = 23, 13 contact lens wearing, 10 noncontact lens wearing) and patients without KC (n = 16) was examined by 10 CCM images of one eye per patient. The CNFL per frame area was calculated, and the SNP tortuosity was quantified by measuring (a) the amplitude of the curves and (b) the area under the curve (AUC) formed by the SNP.

Results: Analysing 390 non-overlapping confocal images revealed the CNFL (mm/mm² ) to be significantly lower in KC (16.4 ± 1.9 mm/mm² ) than in healthy corneae (23.8 ± 3.3 mm/mm² , p < 0.0001; mean ± SD; p-value calculated using the Mann-Whitney U-test), without a difference between contact lens wearing and noncontact lens wearing KC patients (p = 0.4). Amplitudes and AUCs analysed as median with 25th and 75th percentile were significantly increased in KC (amplitude 33/23/41 µm and AUC 2839/1545/3444 µm² ) compared to healthy corneae (amplitude 24/18/28 µm and AUC 1870/1193/2327 µm² , p < 0.0001).

Conclusions: Corneal confocal microscopy (CCM) visualizes slightest alterations within the SNP in KC including (a) a significantly lower CNFL and (b) an enhanced winding course of the SNP. The significantly lower CNFL observed in KC may support the hypothesis of a neurodegenerative aspect of the disease and might be a measure to be correlated with the severity and progression of the disease.

Keywords: corneal confocal microscopy; corneal nerve fibre length; keratoconus; subbasal nerve plexus.