Young Laura K, Love Gordon D, Smithson Hannah E
Department of Experimental Psychology, University of Oxford, 9 South Parks Road, Oxford OX1 3UD, UK.
Vision Res. 2013 Sep 20;90:57-67. doi: 10.1016/j.visres.2013.06.007. Epub 2013 Jul 20.
Advances in ophthalmic instrumentation have allowed high order aberrations to be measured in vivo. These measurements describe the distortions to a plane wavefront entering the eye, but not the effect they have on visual performance. One metric for predicting visual performance from a wavefront measurement uses the visual Strehl ratio, calculated in the optical transfer function (OTF) domain (VSOTF) (Thibos et al., 2004). We considered how well such a metric captures empirical measurements of the effects of defocus, coma and secondary astigmatism on letter identification and on reading. We show that predictions using the visual Strehl ratio can be significantly improved by weighting the OTF by the spatial frequency band that mediates letter identification and further improved by considering the orientation of phase and contrast changes imposed by the aberration. We additionally showed that these altered metrics compare well to a cross-correlation-based metric. We suggest a version of the visual Strehl ratio, VScombined, that incorporates primarily those phase disruptions and contrast changes that have been shown independently to affect object recognition processes. This metric compared well to VSOTF for letter identification and was the best predictor of reading performance, having a higher correlation with the data than either the VSOTF or cross-correlation-based metric.
眼科仪器的进步使得在活体中测量高阶像差成为可能。这些测量描述了进入眼睛的平面波前的畸变，但没有描述它们对视觉性能的影响。一种从波前测量预测视觉性能的指标使用在光学传递函数（OTF）域中计算的视觉斯特列尔比率（VSOTF）（蒂博斯等人，2004年）。我们研究了这样一种指标在捕捉散焦、彗差和继发性散光对字母识别和阅读影响的实证测量方面的效果如何。我们表明，通过在介导字母识别的空间频率带对OTF进行加权，使用视觉斯特列尔比率的预测可以得到显著改善，并且通过考虑像差引起的相位和对比度变化的方向可以进一步改善。我们还表明，这些改变后的指标与基于互相关的指标相比表现良好。我们提出了一种视觉斯特列尔比率的版本，VScombined，它主要纳入了那些已被独立证明会影响物体识别过程的相位干扰和对比度变化。该指标在字母识别方面与VSOTF相比表现良好，并且是阅读性能的最佳预测指标，与数据的相关性高于VSOTF或基于互相关的指标。
