点扩散函数法对近视患者准分子激光角膜原位磨镶术后早期视觉质量的评价

背景目前对屈光手术后视觉功能的评价研究主要是对比敏感度的研究，但易受患者主观因素的影响。点扩散函数（PSF）分析法是一种定量评价术后早期视觉质量的方法。目的研究近视患者行准分子激光角膜原位磨镶术（LASIK）后在明视和暗视两种环境下（3mm和6mm瞳孔直径）视觉系统调制传递函数（MTF）的变化，用PSF分析法评价术后早期的视觉质量。方法回顾性系列病例研究。38例72眼纳入本研究，分为低、中、高度近视组，术前等效球镜值分别为（-2．72±0．52）、（-4．89±0．80）、（-8．00±0．98）D。分别于术前，术后1周、1个月、3个月检查裸眼视力（UCVA）、最佳矫正视力（BCVA）、屈光度，PSF分析仪测量模拟明视、暗视下的MTF值。结果LASIK术前，3／11／71和6Him瞳孔直径下的MTF值差异有统计学意义（P=0．000）。术后1周、1个月、3个月，3mIn瞳孔直径下，低、中、高空间频率的MTF值与术前比较，均有明显先下降后上升的趋势；术后3个月仍未恢复到术前水平，术后各时间点MTF值与术前比较差异均有统计学意义（P〈0．05）；部分高空间频率（18．85～37．70cpd）的MTF值与术前比较，差异无统计学意义（P〉0．05）。6mm瞳孔直径下，低度近视组和中度近视组低空间频率（2．98～7．44cpd）的MTF值与术前比较明显下降，差异均有统计学意义（P〈0．05）；部分中、高空间频率（9．42～37．70cpd）的MTF值下降不明显（P〉0．05）；而高度近视组术后各时间点在所有空间频率段MTF值均下降（P〈0．05），随着时间的推移有逐渐上升的趋势，但术后3个月仍未恢复到术前。结论近视患者LASIK术后MTF值随屈光度及瞳孔直径的增加而下降，随时间的推移呈逐渐好转的趋势。PSF分析可对LASIK术后的视觉质量进行定性和定量分析，有助于准分子激光术后视觉质量的分析和手术方案的改进。

Evaluation of visual quality after laser in situ keratomileusis for myopia by point spread function

Background The evaluation of visual function after laser in situ keratomileusis(LASIK) mainly focuses on the study of contrast sensitivity funetion (CSF).However,CSF measurement is a subjective method and therefore has a limiting in application.A point spread function (PSF) is becoming a study topic because of its objectivity in assessing visual quality.Objective Present study was to evaluate the change of the modulation transfer function (MTF) of eyes and compare the optical and visual quality of human eyes after LASIK.Methods Thirty-six patients(72 eyes) were included in this study.The patients were divided into low myopia(-2.72±0.52 D),moderate myopia (-4.89+0.80 D) and high myopia (-8.00+0.98 D) groups according to the spherical equivalent (SE)diopter before the sugery.The uncorrected visual acuity (UCVA),best corrected visual acuity (BCVA) were examined before and after operation,and PSF data was obtained with Topoeon PSF-1000 analyzer under the 3.0 mm and 6.0 mm pupil size conditions.The follow-up visits of the patients were scheduled at the 7th days,1 st and 3rd months.Written informed consent was obtained from each patient before this study. ResuIts The MTF values among the three refractive groups were significantly different between 3 mm and 6 mm pupil preoperatively (P＜0.05).Under the condition of 3 mm pupil size,the MTF values in the spatial frequencies of 2.98 cpd and 14.88 cpd were significantly declined in different time points after operation in comparison with preoperative ones (P＜0.05).However,the MTF changes had no statistical significance in the spatial frequencies from 18.85-37.70 cpd among various time points(P＞0.05).Under the condition of the 6 mm pupil size,MTF values in low and moderate myopia groups were reduced after operation in comparison with before operation at the spatial frequencies from 2.98-7.44 cpd(P＜0.05),however,there were no obvious difference was found in the spatial frequencies of 9.42-37.70 cpd(P＞0.05).The MTF values of high myopia group was decreased significantly at all spatial frequencies(P＜0.05).The MTF values improved gradually as the prolong of time after operation but was still lower at the 3rd postoperative month than that of preoperation. Conclusion The postoperative visual quality is associated with refractive power and pupil diameter.PSF is a feasible method in assessing the early visual quality after LASIK.