Real-time pachymetry during photorefractive keratectomy using optical low-coherence reflectometry

Optical low-coherence reflectometry (OLCR) was used as a noncontact method to measure the central corneal thickness of three patients intraoperatively during photorefractive keratectomy. Continuous on-line measurements were performed on the intact cornea immediately before the beginning of surgery, after the removal of the corneal epithelium, during laser tissue photoablation, and for 3 min after the ablation process. Corneal thinning due to evaporation was studied on a separate patient with the OLCR instrument, and it was found to be -0.14 mum/s during the first 5 min after epithelium removal. This baseline corneal thinning rate was used as a fit parameter to calculate actual from measured ablation depths. The measurements showed a maximum difference of +/- 10 mum between planned ablations (34-92 mum) and measured ablation depths. (C) 2001 Society of Photo-Optical Instrumentation Engineers.