INCREASED RELEASE OF IMMUNOREACTIVE CALCITONIN-GENE-RELATED PEPTIDE (CGRP) IN TEARS AFTER EXCIMER-LASER KERATECTOMY

The purpose of the study was to quantify the neuropeptide calcitonin g ene-related peptide (CGRP) in normal human tear fluid and to determine the effect of photorefractive excimer laser keratectomy (PRK) on its release in tears. CGRP was assayed in tear fluid samples using an enzy me immunoassay (detection limit 0.2 mu g ml(-1)). Tear-fluid samples w ere collected preoperatively, 1, 2 and 7 days after PRK and analysed f or CGRP. The changes in tear-fluid secretion were also monitored. The intra-assay variation was 3.0-7.0%. Despite the marked hypersecretion of tears, the concentration of CGRP did not decrease following PRK ind icating a concomitant increase in CGRP release by sensory nerves and/o r lacrimal gland(s). Consequently, the release of CGRP in tears increa sed from 197.9+/-36.6 ng min(-1) (mean+/-S.E.M.) to 1723.0+/-402.4 ng min(-1) (P < 0.01) on day 1, and to 2304.2+/-561.1 ng min(-1) (P < 0.0 1) on day 2. On day 7, only minor elevation (377.02+/-83.24 ng min(-1) ) was observed. It is concluded that CGRP is a component of normal hum an tear fluid. The ocular irritation response related to the photoabla tion induces an enhanced release of CGRP in tears. As a compound prese nt in corneal sensory nerves CGRP may have a role in wound-healing.