Thorn F, Schwartz F
New England College of Optometry, Boston, Massachusetts.
Optom Vis Sci. 1990 Jan;67(1):3-7. doi: 10.1097/00006324-199001000-00002.
We compared the effects of dioptric blur on Snellen acuity and grating acuity. Dioptric blur had a strong negative effect on Snellen acuity, consistent with previous studies, but had little effect on grating acuity. Between 1 and 12 D both types of acuity were reduced as a linear function of blur. However, 12 D of blur reduced grating acuity to only 6/24 (20/80), whereas letter acuity was worse than 6/300 (20/1000). We suggest that these differences are due to the presence of "spurious resolution" in which phase-reversed gratings are readily detectable. But the phase reversals so distort the relative positions of linear segments within the letters that the letters become unrecognizable. These results indicate that Snellen letters are more sensitive than gratings to a patient's refractive errors, emphasize the differences between Snellen and grating acuity, and indicate that the minimum angle of resolution (MAR) concept is not applicable to letters.
我们比较了屈光性模糊对斯内伦视力和光栅视力的影响。屈光性模糊对斯内伦视力有很强的负面影响，这与先前的研究一致，但对光栅视力影响很小。在1到12屈光度之间，两种视力都随模糊程度呈线性下降。然而，12屈光度的模糊仅将光栅视力降低到6/24（20/80），而字母视力则差于6/300（20/1000）。我们认为这些差异是由于存在“伪分辨率”，即相位反转的光栅很容易被检测到。但相位反转会使字母内线性部分的相对位置严重扭曲，以至于字母变得无法辨认。这些结果表明，斯内伦字母比光栅对患者的屈光不正更敏感，强调了斯内伦视力和光栅视力之间的差异，并表明最小分辨角（MAR）概念不适用于字母。
