Kumar Preetam, Vaddavalli Pravin Krishna, Campbell Peter, Hull Christopher C, Bharadwaj Shrikant R
Department of Optometry and Visual Science, School of Health and Psychological Sciences, City, University of London, Northampton Square, London EC1V 0HB, United Kingdom; Brien Holden Institute of Optometry and Vision Sciences, L V Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India; Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, L V Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India.
The Cornea Institute, L V Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India.
Vision Res. 2023 Nov;212:108310. doi: 10.1016/j.visres.2023.108310. Epub 2023 Aug 13.
Contrast detection thresholds are elevated with optical quality loss in keratoconus. This study hypothesized that suprathreshold contrast perception is also impaired in keratoconus, with the impairment being predictable from the pattern of loss in threshold-level performance. Contrast detection thresholds were determined across a range of spatial frequencies in 12 cases with mild to severe keratoconus and 12 age-similar controls. These values were used to predict the contrast needed to achieve perceptual matches between reference and test spatial frequency pairs (peak of CSF Vs. 0.3x, 0.5x, 2x or 3x spatial frequency from the peak) for stimuli at 10% and 50% suprathreshold contrast. Contrast thresholds predicted a 1.5 to 6.7-fold increase in the test pattern's contrast to obtain a perceptual match with the reference pattern in keratoconus, relative to controls. Contrary to predictions, the empirical data of contrast matches between test and reference patterns were similar for higher than peak spatial frequencies at both contrast levels. However, as predicted, test patterns required higher contrast than the reference pattern for a perceptual match for lower than peak spatial frequencies. These results were similar to controls and invariant of disease severity, interocular asymmetry and short-term changes in optical quality. Unlike thresholds, suprathreshold contrast perception of resolvable high spatial frequencies appears immune to optical quality losses in keratoconus. These results are discussed in the context of the prevailing models of contrast constancy in healthy humans. Breakdown of contrast constancy at lower than peak spatial frequencies may reflect the properties of the testing paradigm employed here.
圆锥角膜患者的对比敏感度阈值会随着光学质量下降而升高。本研究假设，圆锥角膜患者的超阈值对比度感知也会受损，且这种损害可根据阈值水平表现的损失模式进行预测。在12例轻度至重度圆锥角膜患者和12例年龄匹配的对照者中，测定了一系列空间频率下的对比敏感度阈值。这些值被用于预测在10%和50%超阈值对比度下，参考和测试空间频率对（对比敏感度函数峰值与峰值的0.3倍、0.5倍、2倍或3倍空间频率）之间实现感知匹配所需的对比度。与对照组相比，对比敏感度阈值预测圆锥角膜患者测试图案的对比度需增加1.5至6.7倍，才能与参考图案实现感知匹配。与预测相反，在两个对比度水平下，高于峰值空间频率的测试图案与参考图案之间的对比度匹配的实验数据相似。然而，正如预测的那样，低于峰值空间频率时，测试图案需要比参考图案更高的对比度才能实现感知匹配。这些结果与对照组相似，且与疾病严重程度、双眼不对称性和光学质量的短期变化无关。与阈值不同，圆锥角膜患者对可分辨的高空间频率的超阈值对比度感知似乎不受光学质量损失的影响。本文将结合健康人对比度恒常性的主流模型对这些结果进行讨论。低于峰值空间频率时对比度恒常性的破坏可能反映了此处所采用测试范式的特性。
