Nerve Growth Factor Changes and Corneal Nerve Repair after Keratoplasty

SIGNIFICANCE Measured tear concentration of nerve growth factor is correlated with postoperative corneal reinnervation among patients who undergo keratoplasty. This may be a future therapeutic target for post-keratoplasty corneal nerve regeneration. PURPOSE To determine the relationship between changes in the content of nerve growth factor (NGF) in tear fluid and corneal subepithelial nerve regeneration in patients after keratoplasty. METHODS In this retrospective study, 30 eyes of 28 patients (15 males, 13 females; mean age 42.8 [range 16-73] years) who underwent primary keratoplasty for the first time were recruited through the clinics of the Department of Ophthalmology, Jilin University affiliated First Hospital, between May and December 2015. All patients underwent a complete ophthalmic examination preoperatively. Tear fluid samples were collected to detect the content of NFG at different time points in the follow-up period (day 1 preoperatively and days 1, 7, 30, and 90 postoperatively) and analyzed correlations between NFG content and age, infective factors, and variables of the surgical procedure as well as with subepithelial nerve repair at 30 and 90 days postoperatively. RESULTS The NFG content in tear fluid on day 1 postoperatively was lower than that on the day preceding surgery; however, it was higher than the preoperative value on postoperative days 7, 30, and 90 (F = 5.046, P < 0.05). Further, the NFG content of tear fluid at 30 days postoperatively correlated with the surgical procedure (coefficient = -2.775, P = 0.010); however, no significant correlation was found on postoperative day 1 (coefficient = -1.315, P > 0.05). At all study time points, the NFG content of tear fluid had no correlation with infective factors or age (P > 0.05). Postoperatively, at day 30, small nerve buds were observed in the periphery of the corneal graft in 13 eyes (43.3% of cases) but not in 17 eyes (56.7% of cases), which showed a significant correlation with the NFG content of tear fluid (coefficient = -3.370, P = 0.010). By postoperative day 90, small nerve buds were observed in the periphery of the corneal graft in 24 eyes (80.0% of cases) and showed a significant correlation with the NFG content of tear fluid (coefficient = -2.750, P = 0.006). CONCLUSIONS The NFG content in tear fluid increases with the increasing ratio of small nerve buds indicating corneal nerve regeneration. NFG promotes subepithelial nerve regeneration in patients after keratoplasty.