You’ve probably visited your trusted eye exam doctor recently and were told that you have 20/20 vision. If this is the case, you may feel relieved about this, but does it really mean you have perfect vision? To answer this, we’ll first explain the related vision terminology to help you understand how we measure your vision’s quality.
Visual acuity is the term used to express the clarity or sharpness of your vision. This is measured by your ability to identify the letters or numbers on a standardized eye chart while standing at a certain distance. So, for instance, if you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. Similarly, if you have 20/100 vision, it must mean that you can see as close as 20 feet to see what those with 20/20 vision normally see at 100 feet.
20/20 vision doesn’t always mean your eyesight is perfect. For instance, if you’re getting nearsighted, we may recommend that you use our orthokeratology lenses to slow its progression. But then this only indicates how sharp and clear your vision is at a distance. There are also other vision skills that are just as important, such as eye coordination, side vision, focusing ability, color vision, and depth perception.
The Snellen visual acuity system is named after the Dutch ophthalmologist Herman Snellen, who developed the system in 1862. The system uses acuity measurements in fractions of 20/20, 20/40, 20/60, and so on. The numerator or the top number of the Snellen fraction is the distance between the eye chart and the patient. In the U.S., the viewing distance is usually 20 feet while in other countries, it’s 6 meters.
Meanwhile, the bottom number of the fraction corresponds to the visual acuity of the patient. Higher numbers mean less clarity and sharpness in eyesight. For instance, the Big “E” that you see in most Snellen eye charts corresponds to 20/200 visual acuity. If this is the only letter you can discern, then there’s a chance that you may be legally blind unless prescribed with corrective contact lenses.
The Factors and Limits
The major factors that determine visual acuity are as follows:
1. The accuracy of how the lens and cornea of the eye focuses light onto the retina
2. The sensitivity of the nerves in the retina and vision centers in the brain
3. The ability of the brain to interpret information received from the eyes
Visual acuity tests are quite useful in measuring the clarity of your eyesight in standardized conditions, it’s not completely accurate in determining the overall quality of your vision. Some of its limitations are that it can’t measure how well you see colored objects, moving objects, or objects that are similar in brightness to their background.
When you need to have your eyes checked, don’t hesitate to call our team at Lumen Optometric. Call us at (626) 921-0199 or reach us online to schedule your appointment.