The neurophysiology and psychophysics of vision provide the basis for vision channels. Vision channels are the foundation of understanding spatial vision. This understanding has led to the development of a general model of visual perception and tests of functional vision. The channel model is shown to predict the Gestalt of many objects and perceptual distortions in a wide variety of spatial patterns misnamed as "visual illusions". Contrast sensitivity has been shown, more than visual acuity, to relate to functional vision and the visual quality of everyday objects viewed at work and play. The channel model and differences in contrast sensitivity help explain why people such as drivers with similar good visual acuity can complain of the quality of vision in one eye and not the other from eye disease and can dete4ct and identify objects at significatnly different distances. The peak of the contrast sensitivity function, about 3 to 6 cpd, is most sensitive to detecting objects at low contrast and is shown to relate to the visibility of a variety of objects in a night driving simulator. Using the contrast sensitivity function from sine-wave grating contrast sensitivity charts, EyeView software creates images that relate to the quality of vision.
Contrast sensitivity has emerged as an accepted, comprehensive tool which measures visual function. More capable than Snellen acuity, contrast sensitivity provides early detection of eye disease and the measurement of visual capability and performance-'2 Sine—wave gratings have been recognized as the gold standard for contrast sensitivity for over 29 years in the scientific, clinical and applied communities. Low contrast letter acuity has emerged the last 10 years as an alternative to gratings for contrast testing. The advantages and disadvantages of each approach to contrast testing have been discussed before.3 Here is offered a set of criteria and a methodology for evaluating any contrast test, whether composed of gratings, letters or any other target.