PURPOSE. The aim of this study was to investigate effects of a local anaesthetic on the morphological appearance of corneal features METHOD. Confocal microscopy, using an in-vivo slit-scanning real-time confocal microscope (Tomey ConfoScan P4, Erlangen, Germany) fitted with an Achroplan 40X/0.75NA immersion objective at X680 magnification, was performed on both eyes of 10 subjects on two occasions, one week apart. At one visit, topical anaesthetic (Benoxinate Hydrochloride 0.4%, Chauvin Pharmaceuticals Ltd) was instilled in both eyes of the subject. At the other visit a drop of saline was used. The order in which anaesthetic or saline was used was randomly assigned.
RESULTS. Qualitative analysis of the epithelial basal cell layer demonstrated the following: in 5/10 subjects the images were similar in appearance, 4/10 showed greater clarity when anaesthetic was instilled, the remaining subject showed greater clarity when saline was used. Quantitative analysis of the epithelial basal cell layer was not possible due to lack of contrast of all images. Anterior keratocyte density, posterior keratocyte density and endothelial cell density did not change between the two visits (p=0.91, p=0.63 and p=0.68 respectively). Subjectively, it was more difficult for subjects to maintain fixation when saline had been instilled.
CONCLUSIONS. The local anaesthetic used within our laboratory to perform confocal microscopy examinations does not seem to affect corneal morphology. However, using saline instead of anaesthetic may have lead to a slight reduction in the clarity of the images, as it was more difficult for fixation to be maintained by the subjects.