low vision
Low vision is a visual impairment that standard glasses, contact lenses, medication or surgery cannot correct, and that interferes with activities of daily living. Acuity of 20/70 to 20/400 inclusive counts as moderate visual impairment or low vision.1
The legal definition of low vision rests on two measures, resolution and field of view. Acuity is measured with the refractive error fully corrected, because the eye reaches its best acuity only when it is correctly focused.2 The impairment can also show as reduced contrast sensitivity, photophobia, diplopia or visual distortion, and its causes may be congenital, hereditary or acquired.1 Typical problems include reading standard-sized print, driving, work tasks, and recognizing familiar faces.1
Legal blindness in the United States requires best-corrected acuity of 20/200 or less in the better eye, or a field of 10 degrees or less from fixation, or a widest field diameter of no more than 20 degrees.1
More detail
The World Health Organization counts low vision when best-corrected distance acuity falls below 0.3 in decimal notation in the better eye.2 The World Health Organization's definition of blindness requires acuity below 20/400 or a remaining field under 10 degrees in the better-seeing eye.1 When an ETDRS chart is used for the US legal standard, a patient who cannot read any letter on the 20/100 line counts as legally blind.1
Sources (14)
- AOA Optometric Clinical Practice Guideline, Care of the Patient with Visual Impairment (Low Vision Rehabilitation), sec. I
- Modern Ophthalmic Optics, ch. 9
- Colenbrander, A. (2003). Aspects of vision loss–visual functions and functional vision. Visual Impairment Research, 5(3), pp.115-136.
- Corn, A.L. and Erin, J.N. eds., (2010). Foundations of low vision: Clinical and functional perspectives. American Foundation for the Blind.
- Massof, R.W. and Lidicker, J.R. (2001). Issues in low vision rehabilitation: service delivery, efficacy, and economic aspects. American Foundation for the Blind.
- Schwartz, S.H. (2013). Geometrical and Visual Optics, 2nd Edition. New York: McGraw-Hill Professional Publishing.
- Wolffsohn, J.S. and Cochrane, A.L. (2000). Design of the low vision service of the future. BMC ophthalmology, 1(1), pp.1-6.
- Low Vision and Legal Blindness Terms and Descriptions
- What Is Low Vision? - American Academy of Ophthalmology
- Aspects of vision loss–visual functions and functional vision
- Foundations of Low Vision: Clinical and Functional Perspectives
- Issues in Low Vision Rehabilitation: Service Delivery, Efficacy, and Economic Aspects
- Design of the low vision service of the future
- Visual Acuity - Webvision secondary
Reviewed October 2026