Aspects of vision – Acuity

How the EYES functionHow YOU function

Raising a red flag

eyesfuncitonAlthough acuity is but one of many parameters of vision, it is a very useful indicator of a wide variety of eye problems; there are few eye conditions in which visual acuity is not affected (glaucoma being one).

Because of its broad sensitivity, visual acuity loss is non-specific. Visual acuity is not a diagnostic test; visual acuity alone cannot determine the cause of someone’s vision loss. Visual acuity loss is, however, a valuable red flag which can lead to further examination of many additional factors, ultimately leading to a diagnosis.

Visual acuity is well suited to detect problems in the optics of the eye. Optical problems that affect the eye’s ability to deliver a clear image of the outside world to the retina include:

        • lack of correction or under-correction of refractive errors (often correctable with glasses or contact lenses)
        • A cataract, a clouding of the lens in the eye (usually correctable with surgery).
        • Retinal disorders such as macular degeneration and glaucoma (requiring medical treatment).
          Macular degeneration…


Visual acuity in the real world

youfunctionVisual acuity loss can have wide-ranging effects on one’s activities of daily living. We rely on visual acuity for reading, recognizing faces an gestures, and for navigating the world.

The results of a visual acuity test provide concrete information for adopting ways to compensate for acuity loss. If, for example, your visual acuity is 20/40 (1/2), you need letters that are twice as close or twice as large to see as when your acuity was 20/20. The most common form of adaptation to visual acuity ___ is corrective lenses, usually eyeglasses or contact lenses.

When corrective lenses are not adequate to bring your visual acuity to close to normal, there are a wide variety of visual aids and magnification devices that can be utilized.

Link to modules on rehabilitation, strategies and tools >>>



Reading the letters on a letter chart at a reasonable visual acuity does not necessarily mean one’s vision is adequate for the tasks of everyday living.

If your visual acuity test results are “good” or”normal” but you find you are having difficulty with activities of daily living such as reading, driving at night, or climbing stairs, other aspects of vision such as contrast sensitivity and visual fields should be evaluated.

The MeyeSight Test – acuity

phoneappThe visual acuity sequence of the MeyeSight test determines the smallest detail that can be recognized when presented with high contrast. When the response is correct, the next symbol shown is one step smaller; if the response is incorrect, the next symbol is one step larger, with each step corresponding to one line on a letter chart. You continue the test until a satisfactory endpoint is reached. to be written


Introduction    Contrast sensitivity    Visual field