In vivo confocal microscopy of hereditary sensory and autonomic neuropathy

Purpose: To observe the morphology of the corneal cells and corneal nerve fibers in patients with type IV or V hereditary sensory and autonomic neuropathy (HSAN) by in vivo confocal microscopy and elucidate the mechanism leading to the loss of corneal sensation in this disease. Methods: In vivo confocal microscopy was performed on the central cornea of the right eye in 3 patients with HSAN (ages 17, 20, and 32 years), and their corneal morphology was compared with that of 3 healthy subjects (ages 28, 30, and 36 years). Corneal sensation was tested with a Cochet-Bonnet esthesiometer. Results: The superficial epithelial cell density was lower in the HSAN patients compared with the healthy subjects (1525, 1225, and 1250/mm2 vs. 2225, 1750, and 2500/mm2), but the basal epithelial cell density of the patients was similar to that of the healthy subjects. Nerve bundles were clearly observed in the sub-basal nerve plexus layer of the cornea in the healthy subjects, but were undetectable at the central cornea in the patients with HSAN. The corneal sensation of the patients with HSAN was much weaker than that of the healthy subjects (2.79, 40.30, and 132.50 g/mm2 vs. 1.47, 1.47, and 1.47 g/mm2). Conclusions: Superficial keratopathy accompanied with neurotrophic keratopathy and tear film instability observed clinically agrees with the large keratinized cells in the superficial corneal epithelium by in vivo confocal microscopy in these patients. Our findings suggest that the loss of corneal nerves contributes to impairment of corneal sensation in patients with type IV or V HSAN.