Table 2.
Literature reporting the changes in tear neuromediators following refractive surgery
| Author | Study design | Surgery type and patient number | Findings on neuromediators |
|---|---|---|---|
| Mertaniemi et al. (1995) | Prospective | PRK (n = 14 eyes) | Tear CGRP increased at d 1, peaked at d 2, and decreased at d 7 after PRK. |
| Lee et al. (2005) | Prospective | PRK (n = 70 eyes) and microkeratome LASIK (n = 76 eyes) | Up to 1 mon postoperatively, LASIK resulted in significantly lower tear NGF/total protein ratio compared to PRK, but differences were not significant at 3 and 6 mon. |
| The mean NGF/total protein values at 1 d and 1 wk postoperatively correlated with corneal sensation, TBUT and Schirmer score at 6 months postoperatively for both groups. | |||
| Wu et al. (2009) | Rabbit model | Microkeratome LASIK (n = 24 eyes) and epi-LASIK (n = 24 eyes) | Tear NGF level was significantly lower in LASIK as compared to epi-LASIK on 1 d and 3 d, but differences were not significant at 7 d and 1 mon. |
| Chen et al. (2014) | Monkey model | Microkeratome LASIK (n=20 eyes) | NGF mRNA increased to 5.4-fold at day 3 and 2-fold above preoperative levels at d 7, and then returned to preoperative levels at 3 mon. |
| Increased NGF mRNA level correlated with CNFD at 3 and 7 d postoperatively. | |||
| Pérez-Santonja et al. (1999) | Prospective | PRK (n = 18 eyes) and microkeratome LASIK (n = 17 eyes) | Tear NGF level was significantly lower in LASIK than PRK during the first 3 mon, with no significant differences after 6 mon. |
| Chao et al. (2015) | Prospective | Microkeratome LASIK (n = 40 eyes) | Tear SP level increased during the early post-LASIK period, and did not return to the preoperative ranges until after 3 mon. |
| CNFD following LASIK was inversely correlated with dry eye symptoms and tear SP. | |||
| Chao et al. (2016) | Cross-sectional | Microkeratome LASIK (n = 40 eyes) | Tear SP level was positively and significantly associated with decreased CNFD and increased dry eye symptoms. |
| Tear CGRP level was significantly higher than that of controls at 12 mon. | |||
| Gao et al. (2014) | Prospective | FSL-LASIK (n = 64 eyes) and SMILE (n = 30 eyes) | Tear NGF peaked on the first day, recovered to preoperative values at 3 mon after SMILE, but remained slightly elevated after 3 mon following FSL-LASIK. |
| Zhang et al. (2016) | Prospective | FLEx (n = 18 eyes) and SMILE (n = 23 eyes) | FLEx resulted in significantly higher tear NGF level for the first 1 mon, and significantly higher TGF-β1 for the first 1 wk postoperatively, compared to SMILE. |
| NGF was significantly correlated with OSDI in both the FLEx and SMILE groups. NGF also had a significant association with NI-BUT in the FLEx and SMILE groups. |
CGRP: Calcitonin gene-related peptide; CNFD: corneal nerve fiber density; epi-LASIK: epi-laser in situ keratomileusis; FLEx: Femtosecond Lenticule Extraction; FSL-LASIK: Femtosecond Laser in Situ Keratomileusis; LASIK: Laser in Situ Keratomileusis; NGF: nerve growth factor; NI-BUT: non-invasive TBUT; OSDI: ocular surface disease index; PRK: photorefractive keratectomy; SMILE: Small Incision Lenticule Extraction; SP: substance P; TGF: transforming growth factor.