角膜塑形镜对周边屈光度的影响及其作用机制

Effects of orthokeratology on peripheral refraction and its mechanism

目的研究角膜塑形镜对周边屈光度的影响及其作用机制。方法自身对照研究。11名被试儿童先后在配戴角膜塑形镜前和配戴角膜塑形镜后的1个月，分别进行主觉验光、角膜地形图和眼周边屈光度的测量。在进行周边屈光度测量时，被试儿童依次注视从鼻侧30。到颞侧300的7个5m距离远视标．用开放式红外自动验光仪分别获取6个周边屈光度和1个中心屈光度。周边屈光度减去中心屈光度即得到相对周边屈光度（RPR），然后计算配戴角膜塑形镜前后各个角度上的RPR差值。同时模拟高斯光学系统，用三角函数计算出各个测量角度相应的角膜前表面位置，读取7个位点的角膜前表面矢向屈光力，计算它们在配戴角膜塑形镜前后的差值。配戴角膜塑形镜前后的RPR值比较均采用配对t检验，RPR差值与相应角膜前表面矢向屈光力变化值的关系采用Pearson相关分析。结果配戴角膜塑形镜前，各个角度的相对周边屈光度均呈远视（鼻侧10。除外），幅度随周边角度增加而增大．表现为鼻、颞侧不对称，以颞侧屈光度更偏远视。配戴角膜塑形镜1个月后，所有角度的RPR值发生近视性漂移（鼻侧10。除外），越到周边RPR值变化越大，以颞侧更偏近视。与配戴角膜塑形镜前的RPR值相比，在鼻侧30。和颞侧10°、20°、30°，差异有统计学意义（t=2．32，P=0．043；t=3．01，P=0．013；t=5．92，P〈0．01；t=7．08，P〈0．01）。配戴角膜塑形镜前后各个角度的RPR差值，与相应角膜前表面矢向屈光力的变化值呈显著正相关（r=0．842，P=-0．018）。结论配戴角膜塑形镜能重塑角膜前表面形态，使中央角膜变平、中周部角膜变陡，从而使周边屈光度发生近视性漂移。

Objective To investigate the effects of orthokeratology （OK） on peripheral refraction and its working mechanism. Methods This was a self-controlled study. Eleven enrolled children underwent subjective refraction, corneal topography and peripheral refraction measurements before and one month after OK lens wear. Only right eyes were tested. During peripheral refraction measurements, children were required to view seven consecutive targets at a distance of 5 m from 30°nasal to 30° temporal. An infrared open-field autorefractor was used to obtain six peripheral refractions and one central refraction. The difference between peripheral refraction and central refraction was identified as the relative peripheral refraction （RPR）. RPR changes at each peripheral angle were recorded. The seven corneal positions corresponding to each peripheral angle were identified by simulating the Gauss Optical System and the changes in their sagittal refractive power were recorded and calculated. RPR values before and after lens wear were compared using a paired t test. RPR changes and corresponding sagittal corneal refractive power changes were analyzed with a Pearson correlation test. Results RPR values were hyperopic at all peripheral angles before OK lens wear （except 10° nasal）, showing asymmetry between nasal and temporal visual fields, with more hyperopia in the periphery and temporal visual field. RPR values shifted to myopia at all peripheral angles （except 10° nasal） after 1 month of OK lens wear, with higher myopia in the periphery and temporal visual field. When compared with pre-OK values, differences were statistically significant at 30° nasal and 10°,20°, 30° temporal （t=2.32, P=0.043; t=3.01, P=0.013; t=5.92, P〈0.01; t=7.08, P〈0.01）. Peripheral refractive changes were signifieantly correlated to saginal corneal refraetive power changes （r=0.842, P=0.018）. Conclusion The OK lens reshapes the anterior eorneal surface, making the eornea flatter in the center and steeper in the mid-periphery, thus bringing a myopic shift to peripheral refraction.