A Laboratory For the Study of Objective Measurement of Visual Acuity

视力客观测量研究实验室

• 批准号: 0100820
• 负责人: Carlos Davila
• 金额: $ 7.46万
• 依托单位: Southern Methodist University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0100820&HistoricalAwards=false
• 关键词: Laboratory; Study; Objective; Measurement; Visual

0100820DavilaVisual acuity (VA) is a measure of how well the visual system can resolve closely spaced objects. The Snellen eye chart is the most common method of measuring VA in adults however it is useless when measuring VA in infants and other non-verbal patients. Preferential looking, optokinetic nystagmus, and photoscreening have been used to assess VA in infants, however all of these methods have been found to have their shortcomings. Diseases such as amblyopia, which occurs in 2-3% of the population, if not diagnosed by age 6 can lead to permanent visual loss, and this can lead to learning and behavioral difficulties. Standard pre-school visual screening programs can fail to diagnose ocular disease in as any as 2% of the population. The visual evoked potential (VEP), an electrical potential generated in the visual cortex of the brain in response to a visual stimulus, has been used to measure VA in infants. This is done by determining the maximum spatial frequency in the stimulus which elicits a detectable VEP. However, this method does not yield very repeatable measures and has a higher variability than psychophysical measures of VA. The PI's group has developed VEP detectors which are capable of detecting very low-level VEP's at much higher stimulus spatial frequencies than other detectors; nevertheless, long measurement times are still required. The goal of this proposal is to obtain the laboratory equipment necessary to study objective measurement of visual acuity based on a new model of the visual system. This model, if validated, will enable VA to be measured using the VEP by simply computing its temporal frequency spectrum (which is much faster than existing swept spatial frequency methods). The spacing of photoreceptors in the eye is not a good predictor of limits on spatial resolution. The average spacing of cones on the foveal of the retina would actually predict a much higher visual resolution limit than the often quoted value of 60 cycles/deg. The proposed model is based on the premise that the eyes are constantly in motion and hence the luminance falling on any given photoreceptor in the retina is constantly changing with time. The main hypothesizes is that resolution in foveal vision is determined entirely by the temporal dynamics of the visual system. The model for VA consists of a photoreceptor, a ban of temporal bandpass filters, and a detector at the output of the filter bank. The temporal bandpass filters have the same effect as the spatial frequency filters which have been used to model the visual system. A second hypothesis associates the temporal filter-based model for VA with the VEP. A number of psychophysical and electrophysiologic experiments are proposed which are designed to validate the two hypotheses. One experiment is based on the classical psychophysical adaptation experiments of Blakemore and Campbell but rather than adapting to a constant spatial frequency, we propose to adapt to a constant temporal frequency. This will be done by stabilizing the drift rate of the stimulus grating with respect to eye motion. By measuring the contrast sensitivity function (CSF) at two different drift rates and a fixed spatial frequency, the temporal filter model would predict a result which the spatial frequency channel model would completely fail to explain. Experiments co paring psychophysical and electrophysiologic spatiotemporal CSF's will also be performed which are designed to insure that the psychophysical results carry over to the electrophysiologic domain. The equipment needed for this research consists of a high accuracy dual Perkinje image eye tracker, an optical image stabilizer, a high scan rate, fast phosphor video monitor, and a psychophysical graphics generation system. The PI's institution has agreed to cost-share 30% of total project costs. This research will have important theoretical ramifications in understanding the basic processes in human vision. In addition, it will also impact the quality of health care by enabling an accurate method of electrophysiologically measuring VA in infants and non-verbal patients.

0100820视敏度（VA）是衡量视觉系统分辨近距离物体的能力的指标。 Snellen视力表是测量成人视力的最常用方法，但在测量婴儿和其他非语言患者的视力时，它是无用的。 优先注视、视动性眼球震颤和光筛选已被用于评估婴儿VA，然而所有这些方法都被发现有其缺点。 弱视等疾病，发生在2-3%的人口中，如果在6岁之前没有诊断出来，可能会导致永久性视力丧失，这可能会导致学习和行为困难。 标准的学龄前视力筛查计划可能无法诊断任何2%的人口的眼部疾病。 视觉诱发电位（VEP）是大脑视觉皮质响应视觉刺激而产生的电位，已用于测量婴儿的VA。 这是通过确定刺激中的最大空间频率来完成的，该最大空间频率引起可检测的VEP。 然而，这种方法不能产生非常可重复的测量，并且具有比VA的心理物理测量更高的可变性。 PI的小组已经开发出VEP检测器，其能够在比其他检测器高得多的刺激空间频率下检测非常低水平的VEP;然而，仍然需要长的测量时间。 本提案的目标是获得必要的实验室设备，以研究基于视觉系统新模型的视力客观测量。 该模型，如果验证，将使VA测量使用VEP通过简单地计算其时间频谱（这是比现有的扫描空间频率的方法快得多）。 眼睛中光感受器的间距不是空间分辨率限制的良好预测器。 视网膜中央凹上的视锥细胞的平均间距实际上将预测比经常引用的60周/度的值高得多的视觉分辨率极限。 所提出的模型是基于这样的前提下，眼睛是不断地在运动，因此亮度落在视网膜中的任何给定的感光器是不断地随着时间而变化。 主要的假设是，中央凹视觉的分辨率完全由视觉系统的时间动态决定。 VA的模型由感光器、时间带通滤波器组和滤波器组输出处的检测器组成。 时间带通滤波器具有与用于模拟视觉系统的空间频率滤波器相同的效果。 第二个假设将VA的基于时间滤波器的模型与VEP相关联。 提出了一些心理物理和电生理实验，旨在验证这两个假设。 一个实验是基于经典的心理物理适应实验的Blakemore和坎贝尔，但不是适应一个恒定的空间频率，我们建议适应一个恒定的时间频率。 这将通过稳定刺激光栅相对于眼睛运动的漂移速率来完成。 通过在两个不同的漂移速率和固定的空间频率下测量对比敏感度函数（CSF），时间滤波器模型将预测空间频率通道模型完全无法解释的结果。 还将进行比较心理物理学和电生理时空CSF的实验，这些实验旨在确保心理物理学结果延续到电生理学领域。 本研究所需的设备包括高精度双Perkinje图像眼动仪，光学图像稳定器，高扫描速率，快速荧光视频监视器，和心理物理图形生成系统。 PI的机构已同意分担项目总成本的30%。 这项研究将对理解人类视觉的基本过程产生重要的理论影响。 此外，它还将通过实现婴儿和非语言患者的电生理测量VA的准确方法来影响医疗保健的质量。