Abstract
Purpose: :
To investigate the morphology of the corneal sub-basal nerve plexus (SBNP) in soft and orthokeratology contact lens wearers using laser-scanning confocal microscopy (LSCM).
Methods: :
Forty-three subjects (age range: 18 to 76 yrs) were recruited in a cross-sectional study and grouped into three categories: daily wear soft (SCL, n=17, median lens wear experience 10yrs), overnight orthokeratology (OK, n=8, median lens wear experience 2yrs), and non-lens wearers (NL, n=18). Nerve morphology was assessed by sampling a 1x1mm area of the SBNP using the Heidelberg Retina Tomograph with Rostock Corneal Module at two locations: corneal apex and temporal mid-periphery approximately 2.5mm from apex. Nerve fibre density (NFD) was calculated by measuring the total length of all nerve fibres and branches per square millimetre. A stylus and tracing tool in an image-processing program (Image Pro Analyser 7.0) was used to measure nerve length. One way independent ANOVA and post hoc paired t-tests (with Bonferroni correction) were used to compare groups.
Results: :
There was a significant difference in central NFD between the groups (SCL: 24,870 ± 4,793 µm/mm2, OK: 18,466 ± 4,872 µm/mm2, NL: 24,931 ± 4,259 µm/mm2; ANOVA p<0.01). NFD was significantly less in OK than SCL (p<0.01) and NL groups (p<0.01). SCL was not different from NL (p>0.05). There was no difference in mid-peripheral NFD among all the groups (SCL: 23,544 ± 3,987 µm/mm2, OK: 22,677 ± 3,301 µm/mm2, NL: 22,435 ± 3,993 µm/mm2; ANOVA p>0.05).
Conclusions: :
This study reveals an apparent decrease in central corneal nerve density in the SBNP in OK lens wear. This suggests that the mechanism underlying refractive change during OK treatment may also impact on the corneal nerve morphology in lens wearers. The implications of this finding in relation to corneal sensitivity require further study.
Keywords: contact lens • microscopy: confocal/tunneling • cornea: epithelium