Visual acuity measures the clarity or sharpness of a person’s vision. When eye examination results include high numbers, such as 20/100 or 20/200, these fractions indicate a significant deviation from standard visual capability. This information clarifies the meaning behind these visual acuity scores and outlines the functional implications for daily living.
What Visual Acuity Scores Mean
Visual acuity is determined using the Snellen fraction system, commonly seen on eye charts. The first number (numerator) represents the distance in feet at which the test is conducted, typically 20 feet. The second number (denominator) indicates the distance at which a person with standard 20/20 vision could clearly read that same line of letters. A score of 20/100 means an individual must be 20 feet away to see an object that a person with 20/20 vision can see clearly from 100 feet away.
A score of 20/100 represents a substantial impairment of distance vision, but it does not meet the criteria for legal blindness. Legal blindness is a specific classification used for legal and governmental purposes. The threshold for legal blindness in the US is a central visual acuity of 20/200 or worse in the better eye, even after correction. While 20/100 vision is severely reduced, it is still significantly better than the 20/200 benchmark.
How Vision Loss Affects Daily Life
A 20/100 visual acuity score results in a world where distant details are blurred and difficult to distinguish. Tasks relying heavily on sharp distance vision become challenging. For instance, reading street signs while driving or navigating an unfamiliar environment requires much closer proximity to the object than for a person with normal vision.
Recognizing faces across a room is a common difficulty associated with this level of reduced acuity. The ability to safely operate a motor vehicle is directly impacted by a 20/100 score, as most jurisdictions require corrected vision of 20/40 or better for an unrestricted driver’s license. Uncorrected 20/100 vision makes activities like watching a movie on a large screen or identifying a bus number nearly impossible.
Common Reasons for Poor Vision Scores
The cause of reduced visual acuity can be categorized into two groups: those correctable with standard lenses and those caused by underlying eye disease. Refractive errors are the most common cause, occurring when the eye does not properly focus light onto the retina. Severe nearsightedness (myopia) results from an eyeball that is too long, causing distant images to focus in front of the retina. High levels of uncorrected astigmatism, resulting from an irregularly shaped cornea or lens, can also scatter light and cause blurriness.
Other causes involve damage or clouding of the eye’s structures that may not be fully correctable with glasses alone. Cataracts, the clouding of the eye’s natural lens, scatter light entering the eye and diminish visual clarity. Conditions that damage the retina or optic nerve also lead to poor scores. These include advanced diabetic retinopathy, which damages retinal blood vessels, and glaucoma, which progressively damages the optic nerve.
Options for Improving or Managing Vision
Addressing a low visual acuity score starts with determining the best corrective measure. For refractive errors, prescription eyeglasses or contact lenses are the most straightforward solutions, accurately redirecting light onto the retina. If vision loss is due to a cloudy lens, cataract surgery can replace the damaged lens with an artificial intraocular lens, dramatically restoring acuity.
Surgical Correction
Surgical procedures like LASIK or PRK offer permanent reshaping of the cornea to correct refractive errors, potentially eliminating the need for daily corrective wear.
Disease Management
For chronic eye diseases, management involves targeted medical treatments to slow or halt disease progression. This may include eye drops or laser therapy for glaucoma to manage intraocular pressure, or specialized injections to control the progression of macular degeneration or diabetic retinopathy.
Low-Vision Aids
When best-corrected vision remains poor, low-vision aids can help maximize remaining sight for daily tasks. These aids include specialized magnifiers, telescopic lenses, or electronic screen readers.