Corneal sensitivity and slit scanning in vivo confocal microscopy of the subbasal nerve plexus of the normal central and peripheral human cornea.

PURPOSE: To determine the subbasal nerve density and tortuosity at 5 corneal locations and to investigate whether these microstructural observations correlate with corneal sensitivity.
METHOD: Sixty eyes of 60 normal human subjects were recruited into 1 of 3 age groups, group 1: aged <35 years, group 2: aged 35-50 years, and group 3: aged >50 years. All eyes were examined using slit-lamp biomicroscopy, noncontact corneal esthesiometry, and slit scanning in vivo confocal microscopy.
RESULTS: The mean subbasal nerve density and the mean corneal sensitivity were greatest centrally (14,731 +/- 6056 microm/mm and 0.38 +/- 0.21 millibars, respectively) and lowest in the nasal mid periphery (7850 +/- 4947 microm/mm and 0.49 +/- 0.25 millibars, respectively). The mean subbasal nerve tortuosity coefficient was greatest in the temporal mid periphery (27.3 +/- 6.4) and lowest in the superior mid periphery (19.3 +/- 14.1). There was no significant difference in mean total subbasal nerve density between age groups. However, corneal sensation (P = 0.001) and subbasal nerve tortuosity (P = 0.004) demonstrated significant differences between age groups. Subbasal nerve density only showed significant correlations with corneal sensitivity threshold in the temporal cornea and with subbasal nerve tortuosity in the inferior and nasal cornea. However, these correlations were weak.
CONCLUSIONS: This study quantitatively analyzes living human corneal nerve structure and an aspect of nerve function. There is no strong correlation between subbasal nerve density and corneal sensation. This study provides useful baseline data for the normal living human cornea at central and mid-peripheral locations.