Objective To study corneal nerve damage and changes in the quantity of nerve growth factor (NGF) in tears by observing the NGF in tears,corneal subepithelial nerve plexus density,corneal sensation,tear secretion and tear film stability (BUT) after laser in situ keratomileusis (LASIK) surgery.Methods Two hundred and four eyes of 102 postoperative patients were examined in this self-controlled study.Tear secretion quantity,BUT and the NGF level in tears were measured preoperatively and 1 day,1 month and 3 months after surgery.Nerve plexus density under the corneal epithelium and corneal sensation were measured preoperatively and 1 day,1 month,3 months,6 months,1 year and 2 years after surgery.All data were analyzed.Results The NGF level in tears in preoperative patients was 51.97±3.66 pg/ml and was 225.29±33.64 pg/ml 1 day after surgery and 104.77±+2.19 pg/ml 1 month after surgery,both of which were higher compared to the the preoperative measurement (t1 day=11.39,t1 month=5.79,both P＜0.05).The NGF quantity at 3 months after surgery had reverted to the preoperative level (t3 months=0.47,P＞0.05).Tear secretion quantity in preoperative patients was 26.59±0.10 mm,and was 12.12±1.03 mm 1 day after surgery and 17.24±0.77 mm 1 month after surgery,both of which were lower compared to the preoperative level (t1 day=9.63,t1 month=8.52,both P＜0.05).Tear secretion quantity at 3 months after the operation had reverted to the preoperative level (t3 months=2.09,P＞0.05).BUT in preoperative patients was 10.06±0.45 s,and was 1.47±0.21 s 1 day after surgery and 4.71±0.23 s 1 month after surgery,both of which were reduced compared to the preoperative level (t1ay=19.25,t1month=10.00,both P＜0.05).BUT at 3 months after surgery had reverted to the preoperative level (t3 months=1.11,P＞0.05).Corneal subepithelial nerve plexus density in preoperative patients was 1582±175 μm and was 208±32 μm at one day,254±31 μm at 1 month,588±65 μm at 3 months,634±79 μm at 6 months and 938±119 μm at 1 year,all of which were significantly decreased after surgery compared to the preoperative level (t1 day=7.71,t1 month=7.35,t3 months=5.48,t6 months=4.72,t1 year=2.73,all P＜0.05).Corneal subepithelial nerve plexus density 2 years after surgery had basically reverted to the preoperative level and the difference was not statistically significant (t=0.15,P＞0.05).Corneal sensation in preoperative patients was 58.82±0.53 mm and was 0.59±0.40 mm at 1 day,15.59±2.67 mm at 1 month,41.18±1.4 mm at 3 months and 51.36±0.83 mm at 6 months,all of which were significantly decreased after surgery compared to the preoperative level (t1 day=79.20,t1 months=15.04,t3 months=7.44,t6 months=5.40,all P＜0.05).Corneal subepithelial nerve plexus density at 1 year after the operation had basically reverted to the preoperative level and the difference was not statistically significant (t1 year=1.14,P＞0.05).Conclusion After LASIK surgery,the NGF quantity in tears increased and then recovered gradually to the preoperative level.Corneal subepithelial nerve plexus density,tear secretion quantity,BUT and corneal sensation initially decreased and then recovered gradually to preoperative levels.NGF quantity in tears,tear secretion quantity and BUT had recovered by 3 months after surgery.Corneal sensation recovered to the preoperative level by 1 year after surgery while nerve plexus density under the corneal epithelium basal cells recovered to the preoperative level by 2 years after surgery.