Preliminary Evaluation of Corneal Sensitivity to Mechanical and Chemical Stimuli Following Lasik

Abstract

Abstract: : Purpose: : To evaluate the effect of LASIK on corneal sensitivity to air and carbon dioxide stimuli, nerve morphology and tear film characteristics. Methods:A cross sectional study design was used. Eighteen subjects (8M:10F, mean age 36.9±11.2) who had undergone bilateral LASIK for low myopia within 18 months prior to the study, and 28 controls (16M:12F, mean age 27.2±7.7) were recruited. Central and inferior corneal thresholds to mechanical (air) and chemical (air plus carbon dioxide) stimuli, were determined using a staircase technique. Stimuli of 1second duration at 34^oC (on eye) , were delivered using a CRCERT-Belmonte aesthesiometer. Images of sub-basal nerves in the central cornea were captured using confocal microscopy and nerve morphology was classified as either no nerves present, short nerves (<175µm) or long nerves (>175µm). Non-invasive tear break up time (TBUT) was measured using a tearscope and the phenol red thread test was used to measure tear volume. Differences between groups were evaluated using ANOVA, and associations between variables were evaluated using parametric or non-parametric correlation, where appropriate. Results: Central corneal mechanical sensitivity was significantly reduced in the post LASIK group (p<0.001), however, inferior mechanical sensitivity and chemical sensitivity at both sites was unaffected. Nerve morphology was associated with mechanical threshold. Nerve morphology, mechanical sensitivity and TBUT showed improvements during the first 1-3 months after surgery with little change thereafter. Chemical sensitivity was associated with tear volume (p<0.05). Conclusions: Central corneal mechanical sensitivity is reduced in subjects following LASIK, with recovery seen 3 months after surgery. A similar recovery trend is observed for nerve morphology.

Keywords: cornea: clinical science • innervation: sensation • refractive surgery: LASIK