Changes in corneal sensory nerves activity and the protective mechanisms during ocular surface pathologies

Abstract

The prevalence of dry eye complaints due to tear production disorders is steadily increasing, mainly due to increased life expectancy and changes in lifestyle (contact lens wear, increased time spent in front of computer screens). However, the prevalence of subjective complaints and clinical symptoms of tear production disorders is variable, with only 10%–30% of the population having both subjective complaints and clinical symptoms. A number of in vivo confocal corneal microscopy (IVCM) studies have been performed to qualitatively and quantitatively examine the corneal nerve network in patients with dry eye disease in an attempt to elucidate the changes in corneal innervation and their clinical significance in the disease. Most studies have reported a decrease in nerve density, which may lead to nerve damage, followed by altered sensitivity of the regenerated nerves in patients with dry eye disease, resulting in hyperalgesia or allodynia. This presentation will summarize the role of corneal sensory nerves in the control of tear secretion in healthy eyes and the changes in some pathologies, particularly in dry eye disease. The changes in corneal sensory function in dry eye disease will be described in detail based on animal and human clinical studies. Knowledge of these changes will help to understand the contradictory relationship between objective symptoms and subjective complaints in dry eye patients.