Soluble Fas and Fas ligand in human tear fluid after photorefractive keratectomy

Background/aims-The Fas-Fas ligand system is thought to be involved in stromal cell apoptosis after corneal wounding. The aim was to measure changes in human tear fluid levels of soluble Fas (sFas) and Fas Ligand (sFasL) following myopic photorefractive keratectomy (PRK). Methods-Tear samples of 59 patients were collected preoperatively, and 1 or 2 days after PRK. Tear fluid sFas or sFasL concentrations were determined using sandwich ELISAs. Subsequently, tear flow corrected concentrations (releases) were calculated to compensate for the postoperative tear hypersecretion. Results-The preoperative tear fluid flows (TFF) were 6.4 (1.7) mu l/min (mean (SERI)) in sFas group (n = 18), and 7.5 (1.5) mu l/min in sFasL group (n = 39). Postoperatively TFFs increased to 37.9 (10.9) mu l/min (p = 0.003) and 58.3 (7.0) mu l/min (p = 0.000), respectively. The mean preoperative sFas concentration (24.3 (11.6) U/ml) decreased to 9.7 (4.1) U/ml (p = 0.001) postoperatively, and the mean sFasL concentration (299.1 (28.8) ng/l) to 118.7 (15.9) ng/l (p = 0.000). However, the release of both substances increased significantly: sFas from 87.3 (29.4) mU/min to 229.4 (82.9) mU/min (p = 0.002) and sFasL from 1620.6 (226.4) fg/min to 4777.1 (596.1) fg/min (p = 0.000). Conclusions-Both sFas and sFasL are normal constituents of human tears. Despite a decrease in concentrations related to reflex tears, the release of sFas and sFasL increases significantly after excimer laser photorefractive keratectomy, which suggests that they are involved in corneal healing after PRK in humans.