Evaluating the effect of dry eye disease on corneal sub-basal nerve density and morphology

Abstract

PURPOSE: Published studies on diabetes and corneal nerves did not evaluate the tear function’s effect on corneal nerves. To investigate the effect of dry eye disease on corneal sub-basal nerve density and morphology. METHODS: Six participants with dry eye (corneal fluorescein staining grade 2 or above) and 6 controls were recruited. Patients were from a tertiary referral clinic in Singapore. Symptoms (SPEED), Schirmer’s I test (ST), fluorescein staining, conjunctival hyperemia (CH) grading and non-invasive tear break up times were assessed. In-vivo confocal microscopy of the corneas was undertaken by one investigator using the HRT III. Three best central images and another 3 images over the inferior whorl region were analysed using CCModule software. In the central regions, the nerve fiber density, nerve fiber length, nerve branch density, nerve tortuosity (NT) were evaluated, and the nerve fiber length (IWL) was evaluated in the inferior whorl region. RESULTS: The dry eye group had significantly (p<0.05) higher age (mean 66.2±8.2 years) than controls (27.2±2.0). All dry eye participants but only 1/6 controls were women. As expected, there were significantly higher SPEED, ST and CH scores in the dry eye group. Comparison of corneal sub-basal density and morphology between the two groups showed no differences, except NT in the dry eye group was higher (p=0.03) and IWL shorter than in the control group (p=0.05). If the outlying participant is excluded in the IWL analysis, the difference was significant (p=0.01). Corneal sensation was similar between groups. CONCLUSIONS: The results suggest that NT and IWL are altered in patients with dry eye. Previous studies did not find association of either age or gender with NT and IWL. In future studies comparing two groups of patients (eg. diabetics with non-diabetics) it is crucial to objectively assess the ocular surface as a potential confounding factor.