NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust & UCL Institute of Ophthalmology, London, United Kingdom.
Invest Ophthalmol Vis Sci. 2012 Oct 9;53(11):7063-70. doi: 10.1167/iovs.12-9864.
Vanishing optotypes (VOs) are pseudo high-pass letters whose mean luminance matches the background so that they "vanish" when the recognition acuity threshold is reached in the fovea. We determined the effect of increasing blur on acuity for these optotypes and conventional letters, in both foveal and extrafoveal viewing.
Detection and recognition thresholds were determined separately for each of the 26 letters of both a conventional and VO alphabet, both in the fovea and at 10° in the horizontal temporal retina, under varying degrees of positive dioptric blur.
In the fovea, detection and recognition thresholds were similar for individual VOs, increased steadily with blur, and separated somewhat at higher levels of defocus (3 diopters [D]). While the recognition thresholds for VOs changed on average by 0.28 logarithm of the minimum angle of resolution (logMAR)/D, those for conventional letters changed more rapidly by 0.35 logMAR/D. In the periphery, recognition thresholds were significantly higher than detection thresholds for the VOs at 0 D blur; both thresholds increased steadily thereafter, converging as blur increased. Peripheral recognition acuity displayed a loss of only 0.09 logMAR/D. In both the fovea and periphery, the interletter variation in recognition acuity was much lower for VOs than conventional letters (0.04 vs. 0.09 logMAR).
Outside the fovea, high-pass VOs display significant differences in their detection and resolution thresholds up to +7 D blur, with a logMAR/D loss of a quarter that of the fovea. The lower interletter legibility differences indicate that VO letters may be better stimuli from which to design clinical letter charts.
消失视标（VOs）是一种伪高通字母，其平均亮度与背景相匹配，因此当在中央凹达到识别锐度阈值时，它们“消失”。我们确定了这些视标和常规字母在中央凹和 10°以外颞视网膜的不同模糊度下的锐度的影响。
分别确定了常规字母和 VO 字母的 26 个字母中的每一个字母的检测和识别阈值，在不同程度的正屈光度模糊下，在中央凹和水平颞视网膜的 10°处进行测量。
在中央凹，个体 VO 的检测和识别阈值相似，随着模糊度的增加而稳步增加，并在更高的散焦水平（3 屈光度[D]）略有分离。虽然 VO 的识别阈值平均变化 0.28 个最小角度分辨率（logMAR）/D，但常规字母的变化更快，为 0.35 logMAR/D。在周边，在 0 D 模糊时，VO 的识别阈值明显高于检测阈值；此后两者都稳步增加，随着模糊度的增加而收敛。周边识别锐度仅损失 0.09 logMAR/D。在中央凹和周边，VO 的识别锐度的字母间变化明显低于常规字母（0.04 与 0.09 logMAR）。
在中央凹以外，高通过 VOs 在高达+7 D 模糊的情况下，其检测和分辨率阈值存在显著差异，损失的 logMAR/D 为中央凹的四分之一。较低的字母间可辨认性差异表明，VO 字母可能是设计临床字母图表的更好刺激物。
