How is visual acuity expressed?

Visual acuity is expressed as a ratio, such as 20/20, which indicates the clarity or sharpness of vision. This ratio compares the distance at which a person can see a specific detail to the distance at which a person with normal vision can see that same detail. For example, a visual acuity of 20/20 means that a person can see at 20 feet what an individual with normal vision can also see at 20 feet, signifying normal vision capacity. Higher numerical values, such as 20/40, indicate poorer vision, while lower values signify better vision.

The other methods mentioned do not accurately represent visual acuity. Degrees of light refraction relate to how light bends as it passes through different mediums, but it does not measure the sharpness of vision. Color perception is a separate aspect of visual perception that deals with the ability to distinguish colors but is not a measure of visual clarity. Distance measured from the lens does not correlate directly with visual acuity; instead, it is more related to focusing ability rather than the clearness of sight. Thus, the expression of visual acuity as a ratio is the most precise and commonly used method in optometry and ophthalmology.