People equate the phrase “20/20 vision” to perfect eyesight, unaided by eyeglasses or contact lenses. But have you ever wondered what the number 20/20 stands for? Your local eye specialists at Northview Eye Care shares the answer.
What is 20/20 Vision?
The term “20/20” is a fraction that represents visual acuity measurements. Eye professionals refer to it as the Snellen fractions after Herman Snellen, the Dutch ophthalmologist who developed this system in 1862. The top number in a Snellen fraction represents the viewing distance between a patient and an eye chart, which is typically 20 feet.
A typical eye chart has several rows of letters that decrease in size as you read down the chart. During an eye exam, a patient is first asked to identify these letters unaided. One of the smaller lines near the bottom is standardized to “normal” visual acuity. If the patient can identify the letters in this line, then the patient is said to have 20/20 vision. The larger letter sizes correspond to worse visual acuity, so a patient with vision problems may have 20/40, 20/60 and so on. The largest letter, typically the letter “E” is at 20/200. If a patient can’t see this without corrective lenses, they can be pronounced as legally blind. It is also possible for a person to have better than 20/20 vision.
Clarity of Vision
It must be noted that 20/20 vision does not equate to perfect eyesight. Rather, it indicates clarity or sharpness at a distance. Other vision skills such as peripheral or side vision, coordination, depth perception, color vision and the ability to focus all contribute to overall visual ability.
For example, a person afflicted with hyperopia or farsightedness may be able to see objects at a distance clearly, but can’t do the same with nearby objects. People afflicted with myopia or nearsightedness may be able to read a Snellen chart at a distance closer than 20 feet. This is why an eye doctor runs a series of tests during a comprehensive eye examination. This helps determine whether the patient will require eyeglasses or contact lenses, or if a vision therapy program would be more suitable.
If you need to see an eye doctor, visit Northview Eye Care. Give us a call at (616) 202-1095 or fill out our contact form to schedule an appointment. We serve clients in Northview, MI, and surrounding areas.