Visual acuity measures the clarity of a person’s sight, typically using a Snellen chart displaying rows of letters that decrease in size. The resulting fraction, such as 20/20, indicates how well the eye is functioning at a specific distance. These measurements are a fundamental part of eye examinations, providing data necessary for understanding overall eye health and visual performance.
Translating the 20/70 Measurement
The fraction 20/70 compares a person’s vision to “normal” 20/20 vision. The first number, 20, indicates the person is standing 20 feet from the eye chart. The second number, 70, signifies that a person with 20/20 vision can clearly read that same line of letters from 70 feet away. This means an individual with 20/70 vision must move significantly closer to an object to see it clearly.
If uncorrectable with glasses or contact lenses, the World Health Organization (WHO) classifies 20/70 as moderate visual impairment or moderate low vision. While this level is far from legal blindness (20/200 or worse in the better eye), it is substantially below the acuity required for many routine activities. For example, 20/70 falls short of the 20/40 level often required for an unrestricted driver’s license.
Daily Life Impact of Reduced Vision in One Eye
Having 20/70 acuity in only one eye while the other retains good vision is known as monocular vision. The most significant consequence is the reduction of stereopsis, the depth perception that relies on two equally strong eyes. Judging distances becomes more challenging, affecting activities like navigating stairs, catching a ball, or pouring liquid.
The brain adapts by relying on less accurate monocular cues, such as relative size and motion parallax. This adaptation can cause increased visual fatigue or eye strain, as the better eye overcompensates for detailed work. Some individuals experience physical discomfort, such as neck pain, from tilting their head to position the better eye optimally. These limitations can impact hobbies, sports, and employment tasks requiring precise hand-eye coordination.
Common Reasons for 20/70 Acuity
A 20/70 visual acuity reading in one eye stems from various underlying medical conditions. Simple refractive errors, such as uncorrected nearsightedness (myopia) or astigmatism, are the most common and easily treatable causes. More serious causes include amblyopia, or “lazy eye,” where the brain fails to develop a strong connection with the affected eye, often due to untreated childhood issues like strabismus.
In adults, reduced vision may indicate early stages of progressive conditions. These include cataracts (clouding of the lens) or age-related macular degeneration (AMD), which affects central vision. Other potential causes are diabetic retinopathy (damage to retinal blood vessels from high blood sugar) or early glaucoma (damage to the optic nerve). A comprehensive eye examination is necessary to diagnose the specific cause and determine if the loss is temporary or permanent.
Driving and Legal Standards for Monocular Vision
Safety and legal requirements for driving licenses are a major consideration for those with reduced vision in one eye. In the United States, regulations vary by state Department of Motor Vehicles (DMV). Most states require a minimum corrected acuity of 20/40 in the better eye for an unrestricted license. If the better eye is 20/70, the individual usually will not qualify for a standard license.
Having 20/70 in the worse eye while the other eye maintains 20/40 or better is typically acceptable. If the best corrected vision in the primary eye is 20/70, a restricted license, such as “daylight only” driving, may be an option. This often follows a vision specialist’s evaluation and sometimes a practical driving test. These standards ensure drivers have sufficient reaction time and visual information to safely operate a vehicle.