Visual impairment or vision impairment is vision loss that constitutes a significant limitation of visual capability resulting from disease, trauma, or a congenital or degenerative condition that cannot be corrected by conventional means, including refractive correction, medication, or surgery. This functional loss of vision is typically defined to manifest with 1) best corrected visual acuity of less than 20/60, or significant central field defect, 2) significant peripheral field defect including homonymous or heteronymous bilateral visual field defect or generalized contraction or constriction of field, or 3) reduced peak contrast sensitivity either of the above conditions. ...

Visual impairment or vision impairment is vision loss that constitutes a significant limitation of visual capability resulting from disease, trauma, or a congenital or degenerative condition that cannot be corrected by conventional means, including refractive correction, medication, or surgery. This functional loss of vision is typically defined to manifest with 1) best corrected visual acuity of less than 20/60, or significant central field defect, 2) significant peripheral field defect including homonymous or heteronymous bilateral visual field defect or generalized contraction or constriction of field, or 3) reduced peak contrast sensitivity either of the above conditions.

Visual impairment is the consequence of a functional loss of vision, rather than the eye disorder itself. Eye disorders which can lead to visual impairments can include retinal degeneration, albinism, cataracts, glaucoma, muscular problems that result in visual disturbances, corneal disorders, diabetic retinopathy, congenital disorders, and infection." Visual impairment can also be caused by brain and nerve disorders, in which case it is usually termed cortical visual impairment (CVI).

Blindness is the condition of lacking visual perception due to physiological(normal body) or neurological(nerve conditions) factors.Various scales have been developed to describe the extent of vision loss and define "blindness."

Total blindness is the complete lack of form and light perception and is clinically recorded as "NLP," an abbreviation for "no light perception." Blindness is frequently used to describe severe visual impairment with residual vision. Those described as having only "light perception" can see no more than the ability to tell light from dark.

In order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as legal blindness. In North America and most of Europe, legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (6 m) from an object to see it with the same degree of clarity as a normally sighted person could from 200 feet (60 m).

By the 10th Revision of the WHO International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 6/18, but equal to or better than 3/60, or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction. Blindness is defined as visual acuity of less than 3/60, or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.