Contrast Sensitivity Functions in ON and OFF Visual Pathways in Myopia

Purpose: The current study investigates the contrast sensitivity (CS) of ON and OFF visual pathways across a broad spatial frequency range in individuals with varying severities of myopia. Methods: The CS function (CSF) was measured in 60 adults (emmetropes, low myopes, and high myopes) using a psychophysical paradigm that could selectively activate the ON and OFF pathways, combined with the quick CSF method. Stimuli included bipolar, increment, and decrement bandpass-filtered noise across 15 spatial frequency levels (0.25-25.85 cycles per degree). Tests were performed under binocular, dominant eye (DE), and non-DE (NDE) conditions. Results: High myopes exhibited significant deficits in ordinary (bipolar) and ON pathway (increment) CS, primarily manifested as reduced peak sensitivity. The increment/decrement (ON/OFF) area under log CSF ratio was significantly lower in the high myopia group than that in the emmetropia group (P < 0.001) and the low myopia group (P = 0.009), indicating a selective ON pathway deficit. The ratio correlated with the spherical equivalent refraction (r = 0.484; P < 0.001) and axial length (r = -0.490; P < 0.001). Conclusions: High myopia exhibited reduced ordinary and ON pathway CS. The ON pathway-selective CS deficits were significantly correlated with myopia severity and predominantly observed at low SFs. These findings provide a theoretical basis for understanding visual function in myopia, developing effective functional evaluation tools, and designing targeted intervention strategies.