title: Nerve growth factor concentration and implications in photorefractive keratectomy vs laser in situ keratomileusis.
abstract: OBJECTIVE
  To determine whether tear nerve growth factor (NGF) concentration correlates with corneal sensation and ocular surface dryness after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).
  
  
  METHODS
  Prospective, nonrandomized comparative clinical trial.
  
  
  METHODS
  Seventy eyes of 35 patients and 76 eyes of 38 patients underwent PRK and LASIK procedures to correct myopia and myopic astigmatism, respectively. Total tear protein level, tear NGF concentration, tear film breakup time (BUT) and Schirmer values were measured before and 1 day, 1 week, 1 month, 3 months, and 6 months after surgery.
  
  
  RESULTS
  The postoperative mean tear NGF/total tear protein (NGF/tP) ratio increased in both PRK and LASIK patients compared with preoperative levels (P < .0001). At 1 week and 1 month postoperatively, the NGF/tP ratio was higher in PRK than in LASIK subjects (P < .0001). Before 6 months postoperatively, the mean corneal sensation after LASIK in the ablated zone was lower than the preoperative sensation (P < .0001), but this was not the case in PRK subjects. Mean BUT and Schirmer values were significantly lower in LASIK-treated eyes compared with PRK-treated eyes up to 6 months postoperatively (P < .0001). The early postoperative tear NGF/tP ratio correlated with the postoperative 6-month value of corneal sensation, BUT, and Schirmer values.
  
  
  CONCLUSIONS
  The difference in the postoperative corneal sensation and ocular surface dryness between PRK-treated and LASIK-treated eyes might be related to the difference in the early postoperative levels of NGF, which is a potent nerve growth stimulator.
authors.affiliation: Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, 146-92 Shinchon-dong, Sudaemoon-gu, Seoul 135-720, Korea.
authors.forename: Hyung Keun
authors.initials: HK
authors.lastname: Lee
authors.forename: Kyung Sub
authors.initials: KS
authors.lastname: Lee
authors.forename: Hyeon Chang
authors.initials: HC
authors.lastname: Kim
authors.forename: Sung Ho
authors.initials: SH
authors.lastname: Lee
authors.forename: Eung Kweon
authors.initials: EK
authors.lastname: Kim
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000601:surgery; D003315:Cornea / Q000502:physiology / Q000601:surgery; D003316:Corneal Diseases / Q000209:etiology / Q000378:metabolism*; D015352:Dry Eye Syndromes / Q000209:etiology / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005136:Eye Proteins / Q000378:metabolism*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000009:adverse effects*; D054018:Lasers, Excimer; D008297:Male; D009216:Myopia / Q000601:surgery; D020932:Nerve Growth Factor / Q000378:metabolism*; D018903:Photorefractive Keratectomy / Q000009:adverse effects*; D011446:Prospective Studies; D012677:Sensation / Q000502:physiology; D013666:Tears / Q000378:metabolism*
chemical_list: D005136:Eye Proteins; C042434:tear proteins; D020932:Nerve Growth Factor