Laser In Vivo Confocal Microscopy Demonstrates a Lower Density of Peripheral Corneal Nerve Fibers Compared to the Central Cornea in Normal Subjects

Abstract

Purpose: To quantify subbasal corneal nerve density by in vivo confocal microscopy in the central and four peripheral quadrants of normal subjects.

Methods: In vivo confocal microscopy (IVCM; HRT3/RCM) of the central cornea and 4 peripheral quadrants (superior, inferior, nasal, and temporal) was performed in 37 subjects with normal clinical slit-lamp examination. Three representative images were chosen for each area and quantified using NeuronJ, a plugin for ImageJ (NIH). Two masked observers measured the number and density of total nerves, main trunks and branches. Statistical analysis was performed with ANOVA with Bonferroni correction to compare the differences between the 5 areas. A linear regression model was applied to assess the changes for gender and age.

Results: The average age of normal subjects was 30 years, ranging from 19 to 69 years. The central cornea had a significantly higher number and density of total nerves (16.2 n/frame [14.8-17.6] 95%CI; and 20067.7 µm/mm² [18776.6-21358.8] 95%CI), main trunks (3.3 [2.9-3.6]; and 8848.4 [7915.3-9781.4]), and branches (12.8 [11.4-14.2]; and 11219.3 [10152.2-12286.4]) in comparison to all peripheral areas (p<0.001). All peripheral areas demonstrated similar distribution of the subbasal nerve plexus for all parameters (p>0.05), including the number and density of total nerves for superior (9.2 [7.8-10.6]; and 11638.1 [9834.7-13441.5]), inferior (9.2 [7.5-11.0]; and 11169.3 [9080.2-13258.4]), temporal (8.9 [7.5-10.3]; and 9535.3 [8452.7-10617.9]), and nasal (7.8, [6.2-9.4] and 9621.0, [7832.3-11409.8]). An inverse correlation to age (R=-0.20; p=0.017), but not for gender (p=0.781) was shown for all nerve parameters.

Conclusions: In normal eyes, IVCM shows a higher number and density for subbasal nerve fibers for the corneal center in comparison to the periphery. An inverse correlation is observed for nerve parameters and age. A standardized approach is demonstrated to measure the subbasal plexus for future clinical studies.

Keywords: 550 imaging/image analysis: clinical • 479 cornea: clinical science • 610 nerve fiber layer