Factors affecting crowded acuity: eccentricity and contrast.
Factors affecting crowded acuity: eccentricity and contrast.
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DOI：
10.1097/opx.0b013e31829908a4
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发表时间：
2013-07
期刊：
影响因子：
--
通讯作者：
Chung ST
中科院分区：
文献类型：
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作者：
Coates DR;Chin JM;Chung ST
视力测量是临床上评估视觉功能的基本方法。很少有人知道如何敏锐度测量存在的相邻字母，如在字母表的情况下，改变对比度和非中央凹观看。当患者不能使用他们的中央凹时，这些信息对于使用低对比度图表的敏锐度测量是至关重要的。在这项研究中，我们评估了视标敏锐度，有和没有侧翼，是由对比度和偏心的影响。五名视力正常的年轻人单独或在存在四个侧翼Tumbling-E的情况下识别Tumbling-E的方向。边缘到边缘的字母间距范围从1到20条宽度。刺激在白色背景上呈现150 ms，韦伯对比度范围为−2.5%至− 99%。侧翼的大小和对比度与目标相同。在下视野中的中心凹、3度、5度和10度处进行测试。当绘制为字母间距的函数时，敏锐度保持不受侧翼的存在的影响，直到侧翼在临界间距内，其平均边缘到边缘间距在中央凹处为4.4条宽度，并且在所有三个偏心度处为大约16条宽度。临界间距随着对比度的减小而减小。当绘制为对比度的函数时，对于侧翼和非侧翼情况，只有当中央凹的对比度低于约24%和周边的对比度低于约17%时，敏锐度才会恶化。福尔斯。在所有对比度水平下，常规字母表上的字母间距超过了在中央凹处进行敏锐度测量的临界间距。因此，这些图表是适当的评估中心凹敏锐度。在外围，临界间距大于传统图表上的字母间距。因此，由于拥挤的影响，这些图表可能低估了在周边测量的敏锐度。
Acuity measurement is a fundamental method to assess visual performance in the clinic. Little is known about how acuity measured in the presence of neighboring letters, as in the case of letter charts, changes with contrast and with non-foveal viewing. This information is crucial for acuity measurement using low-contrast charts and when patients cannot use their fovea. In this study, we evaluated how optotype acuity, with and without flankers, is affected by contrast and eccentricity. Five young adults with normal vision identified the orientation of a Tumbling-E alone or in the presence of four flanking Tumbling-Es. Edge-to-edge letter spacing ranged from 1 to 20 bar widths. Stimuli were presented on a white background for 150 ms with Weber contrast ranging from −2.5% to −99%. Flankers had the same size and contrast as the target. Testings were performed at the fovea, 3, 5 and 10 degrees in the inferior visual field. When plotted as a function of letter spacing, acuity remains unaffected by the presence of flankers until the flankers are within the critical spacing, which averages an edge-to-edge spacing of 4.4 bar widths at the fovea, and approximately 16 bar widths at all three eccentricities. Critical spacing decreases with a reduction in contrast. When plotted as a function of contrast, acuity only worsens when the contrast falls below approximately 24% at the fovea and 17% in the periphery, for flanked and unflanked conditions alike. The letter spacing on conventional letter charts exceeds the critical spacing for acuity measurement at the fovea, at all contrast levels. Thus these charts are appropriate for assessing foveal acuity. In the periphery, the critical spacing is larger than the letter spacing on conventional charts. Consequently, these charts may underestimate the acuity measured in the periphery due to the effects of crowding.