The instability of tear film in dry eye often affects the visual quality after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). The prediction for visual quality following FS-LASIK was difficult in the past because of the limiting of examination method.OQAS-Ⅱis a quantitative checking system of visual quality, which is helpful for the evaluation of the relationship between tear stability and visual quality following FS-LASIK.

This study was to investigate the predicting effects of the quality of tear film on visual quality after LASIK.

A prospective cohort study was performed.One hundred and twenty eyes of 120 myopic patients who wanted to receive FS-LASIK were enrolled in Nanjing First Hospital from August to December 2015 after informed consent.The objective scattering index (OSI) was 1.2 in the patients.The patients were divided into mild dry eye group (71 eyes) and non-dry eye group (49 eyes) based on the Expert Consensus on Clinical Diagnosis and Treatment of Dry Eye(2013).FS-LASIK was performed in the non-dry eye group, and 0.1% sodium hyaluronate eye drops was topically administered for 1 month firstly and then the operation was carried out in the same way in the mild dry eye group.Slit lamp microscope, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), spherical equivalent (SE) were examined, and the safety index and availability index were assessed.OQAS™ Ⅱ analysis system was employed for the defection of Schirmer Ⅰ test (SⅠt), breakup time of tear film (BUT), modulation transfer function cut-off frequency (MTF cut off) and mean OSI before and after surgery.

The safety index was 1.05±0.11 and 1.03±0.09, and the availability index was 1.02±0.14 and 1.01±0.12 in the non-dry eye group and mild dry eye group, respectively, showing significant differences between the two groups (t=0.391, 0.147, both at P>0.05). The BUT was evidently shortened 1 month and 3 months after surgery in comparison with before surgery in both non-dry eye group and mild dry eye group, and BUT in the mild dry eye group was shorter than that in the non-dry eye group in postoperative 3 months, with a significant differences between them (P<0.05). The mean OSI was increased and MTF cutoff was reduced 1 month, 3 months and 6 months after surgery in comparison with before surgery in both mild dry eye group and none-dry eye group, and mean OSI was higher and MTF cutoff was lower in the mild dry eye group than that in the non-dry eye group, with significant differences between them (all at P<0.05). In postoperative 12 months, BUT, mean OSI and MTF cutoff were near normal in both groups.

FS-LASIK can improve objective visual quality, and preoperative tear film quality is associated with objective visual quality after FS-LASIK.The unstable tear film affects visual quality after FS-LASIK.OQAS™Ⅱsystem can diagnose and monitor tear change of dry eyes, which is helpful for the screening of indicator of FS-LASIK and rational prediction of postoperative visual quality.

Tear film; Femtosecond laser/therapy use; Laser in situ keratomileusis; Visual quality; Modulation transfer function; Scattering index