Visual Acuity: High Contrast and Low Contrast

There are many components of vision. These include visual acuity, contrast sensitivity, visual fields, 3D vision, motion perception, etc. Of all these components, the most important component is visual acuity, the ability of the eye to resolve and perceive small targets. There are various methods and ways to measure this resolution capacity of the eye. All these methods use black letters on a white background. Ironically, none of the real-world scenes and scenarios appear in black and white. The visual function that is more relevant to the real-world scenario is contrast sensitivity. Contrast sensitivity is the ability of the eye to detect the dimmest target and largely depends on the background (for example, a white bead placed on a white tabletop has poorer contrast than a gray bead on a white tabletop). This ability of the eye to distinguish the contrast of the target against the background is also related to the size of the object. If this ability is mapped for different target sizes, we arrive at the contrast sensitivity function (CSF). Interestingly, high-contrast visual acuity (or visual acuity) is only a single-point measurement within the CSF. Yet, we mostly draw conclusions and correlate patients’ complaints and functional vision difficulties (e.g., identifying faces, pouring water into a cup) with the visual acuity value. This chapter gives equal importance to visual acuity, contrast sensitivity, and low-contrast visual acuity.