A “vision score” is a standard measurement eye care professionals use to evaluate how clearly a person sees. It quantifies visual ability, providing a consistent way to assess sight. It represents a ratio comparing a person’s vision to that of someone with normal vision. This measurement helps identify potential vision impairments and is a fundamental part of routine eye health assessments.
Measuring Vision Acuity
Visual acuity, or sharpness of vision, is measured using a Snellen eye chart. This chart features rows of letters that decrease in size, with the largest at the top. The test involves standing 20 feet away from the chart and reading the smallest line of letters possible, one eye at a time.
The vision score is expressed as a fraction, such as 20/20 or 20/40. The top number, 20, represents the distance in feet from which the test is conducted. The bottom number indicates the distance at which a person with normal vision could read the same line of letters. For instance, 20/20 vision means one sees at 20 feet what a person with normal vision sees at 20 feet, whereas 20/40 indicates one must be at 20 feet to see what a person with normal vision can see at 40 feet. A higher bottom number indicates reduced vision.
What Scores Indicate Impaired Vision
A vision score of 20/20 is considered normal visual acuity, though it does not imply perfect vision. Many individuals can achieve better than 20/20 vision, such as 20/15 or 20/10, meaning they can see details at 20 feet that a person with normal vision would need to be closer to see. Conversely, scores with a higher denominator indicate impaired vision.
Visual impairment is categorized by acuity thresholds. Moderate vision impairment falls between 20/60 and 20/200. Low vision is defined as visual acuity of 20/70 or poorer in the better-seeing eye, which cannot be corrected with eyeglasses.
Legal blindness is a classification. A person is considered legally blind if their best-corrected visual acuity in the better eye is 20/200 or worse. This means they can only see at 20 feet what a person with normal vision can see at 200 feet. Legal blindness can also be defined by a visual field of 20 degrees or less, even if central acuity is better.
Common Reasons for Reduced Vision
Reduced vision scores stem from refractive errors, which occur when the eye’s shape prevents light from focusing correctly on the retina. The length of the eyeball or the curvature of the cornea can cause these errors.
Myopia, or nearsightedness, is a refractive error where distant objects appear blurry because light focuses in front of the retina, often due to an eyeball that is too long or a cornea that is too curved. Hyperopia, or farsightedness, is the opposite, causing nearby objects to appear blurry because light focuses behind the retina, typically due to a short eyeball or a flat cornea. Astigmatism results from an irregularly shaped cornea or lens, leading to distorted or blurred vision at all distances as light focuses unevenly on the retina.
Beyond refractive errors, presbyopia and cataracts are common age-related conditions that affect vision scores. Presbyopia involves the eye’s lens becoming less flexible, making it difficult to focus on close-up objects. Cataracts occur when the eye’s lens becomes cloudy, leading to blurred or foggy vision.
Next Steps for Vision Concerns
If you notice changes in your vision, such as blurriness, or are concerned about your vision score, scheduling a comprehensive eye exam is important. An eye care professional can accurately assess your vision and diagnose any underlying issues. Regular eye exams are important for detecting problems early, sometimes even before noticeable symptoms appear.
During the exam, the doctor will evaluate your visual acuity and overall eye health. Corrective measures like eyeglasses or contact lenses can improve vision affected by refractive errors. Surgical options may be recommended to restore clearer vision. Following your eye doctor’s recommendations for treatment and follow-up care is important for maintaining eye health.