Many individuals wonder if their eyesight prescription indicates legal blindness. Understanding vision impairment involves specific terms and measurements. This article clarifies what a -5.5 eyesight prescription means and whether it falls under the definition of legal blindness.
Understanding Visual Acuity and Prescriptions
Visual acuity measures the sharpness of your vision, commonly expressed as a fraction like 20/20. The Snellen eye chart, with its rows of progressively smaller letters, is a standard tool used to assess this. When you stand 20 feet away and can read the line designated for 20 feet, you have 20/20 vision, which is considered normal.
A prescription number like -5.5 diopters indicates the optical power of the corrective lens needed for clear vision. Diopters are the unit of measurement for lens strength. A negative value, such as -5.5, signifies myopia, commonly known as nearsightedness, where distant objects appear blurry. This measurement helps determine the appropriate strength for eyeglasses or contact lenses.
Criteria for Legal Blindness
Legal blindness is a specific classification defined by visual limitations, not simply a lack of sight. In the United States, it is defined by the Social Security Administration (SSA) based on criteria established by the American Medical Association. There are two main criteria for legal blindness, both applying to the better-seeing eye with the best possible correction.
The first criterion is a central visual acuity of 20/200 or less. This means that a person must be 20 feet away to see what someone with normal vision can see from 200 feet away. The second criterion involves a restricted visual field, defined as a widest diameter of 20 degrees or less. This condition is often referred to as “tunnel vision.”
Is -5.5 Diopters Considered Legally Blind?
A -5.5 diopter prescription does not indicate legal blindness on its own. This diopter strength measures the degree of refractive error, specifically myopia, and the lens power needed for correction. It does not directly represent a person’s best corrected visual acuity.
Many individuals with a -5.5 diopter prescription can achieve visual acuity significantly better than 20/200 with appropriate corrective lenses. The definition of legal blindness depends on the best corrected vision and the visual field, not solely on the raw prescription number. While -5.5 diopters represents a moderate to high degree of nearsightedness, it is correctable. An eye care professional, such as an ophthalmologist or optometrist, can conduct a comprehensive eye examination to determine if an individual meets the criteria for legal blindness.