“Your vision in 20/25.” For more than 100 years the measurement and description of a person’s vision has been tied to the results of the Snellen acuity test. But the letter chart test measures only visual acuity and measures it under almost ideal contrast conditions (deep black letters on a white background), an environment that does not represent the world we actively inhabit.

There’s much more to your vision than just your acuity number. In addition to acuity, activities of daily living such as reading, cooking, using a computer, walking the streets and recognizing faces rely on visual components such as contrast sensitivity, visual field, color perception, stereoscopic acuity, dark adaptation, fixation and more.

Of these aspects of vision, the three most important are:

• Visual acuity – the ability to see small details.
• Contrast sensitivity – the ability to perceive small differences in brightness.
• Visual field – the ability to respond to stimuli outside the area of central vision.

While doctors often focus on visual acuity as a measure of vision, there’s more to vision than just that acuity number. Reduced contrast sensitivity, for example, can significantly affect vision quality, including affecting one’s acuity! Someone with low contrast sensitivity may have difficulty navigating his or her environment, even if they have good acuity. Disruptions to the visual field can affect one’s vision even with “good” acuity… tbd

Acuity     Contrast sensitivity     Visual field