Alexander Kenneth R, Rajagopalan Aruna S, Seiple William, Zemon Vance M, Fishman Gerald A
Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL 60612, USA.
Invest Ophthalmol Vis Sci. 2005 Aug;46(8):2967-73. doi: 10.1167/iovs.05-0231.
To evaluate the contrast response of the visual system in retinitis pigmentosa (RP) under conditions designed to emphasize the parvocellular (PC) and magnocellular (MC) pathways.
Visual evoked potentials (VEPs) were measured in 10 patients with RP and in 10 age-equivalent control subjects with normal visual acuity and color vision, by using an array of isolated checks that were presented against a steady yellow background. The checks were modulated sinusoidally, either in isoluminant chromatic contrast (5.6 Hz), to favor the chromatic PC pathway, or in luminance contrast (5.6 and 11.2 Hz), to favor the MC pathway. Response amplitude and phase at the stimulus (fundamental) frequency were derived from Fourier analysis, and contrast response functions were fit with a Michaelis-Menten equation to derive R(max), the maximum response amplitude, and sigma, the contrast necessary to produce R(max)/2.
In the control subjects, the mean amplitude function for chromatic modulation increased approximately linearly with increasing contrast, whereas the function for luminance modulation increased sharply at low contrasts and saturated at contrasts above approximately 30% for both temporal frequencies, as expected. The patients with RP showed primarily a reduction in R(max) with little change in sigma in all testing conditions. The reduction in R(max) was equivalent for chromatic modulation and luminance modulation at 5.6 Hz, but was substantially lower for luminance modulation at 11.2 Hz.
Contrast processing was impaired within both the MC and PC pathways in these patients with RP, but the degree of impairment within the MC pathway depended on temporal frequency. These VEP results are in general agreement with recent psychophysical studies of contrast sensitivity losses in patients with RP, and further they characterize contrast processing deficits in these patients at suprathreshold levels.
在旨在强调小细胞（PC）和大细胞（MC）通路的条件下，评估视网膜色素变性（RP）患者视觉系统的对比度反应。
对10例RP患者和10例年龄匹配、视力和色觉正常的对照受试者进行视觉诱发电位（VEP）测量，使用一系列孤立的方格，以稳定的黄色背景呈现。方格以正弦方式调制，要么采用等亮度颜色对比度（5.6赫兹），以利于颜色PC通路，要么采用亮度对比度（5.6和11.2赫兹），以利于MC通路。通过傅里叶分析得出刺激（基频）频率下的反应幅度和相位，并将对比度反应函数与米氏方程拟合，以得出最大反应幅度R(max)和产生R(max)/2所需的对比度σ。
在对照受试者中，颜色调制的平均幅度函数随对比度增加大致呈线性增加，而亮度调制的函数在低对比度时急剧增加，并且在两个时间频率下对比度高于约30%时达到饱和，正如预期的那样。RP患者在所有测试条件下主要表现为R(max)降低，而σ变化不大。在5.6赫兹时，颜色调制和亮度调制的R(max)降低程度相当，但在11.2赫兹时亮度调制的R(max)降低程度明显更低。
这些RP患者的MC和PC通路内的对比度处理均受损，但MC通路内的受损程度取决于时间频率。这些VEP结果与最近关于RP患者对比度敏感度损失的心理物理学研究总体一致，并且进一步表征了这些患者在阈上水平的对比度处理缺陷。
