If there's one aspect of optometry that everyone recognizes, it's the traditional eye chart, with its rows of big letters on top, which gradually become smaller the farther down you go. This chart is usually known as the Snellen chart.
What is an Eye Chart?
An eye chart is one of the tools your eye doctor uses to assess your eyesight. Based on how well you can see various letters on the chart, your optometrist will determine whether you have myopia (nearsightedness), hyperopia (farsightedness), presbyopia (age-related farsightedness) or astigmatism, and will measure the prescription that will give you the clearest, most comfortable vision.
Are All Eye Charts The Same?
There are a number of variations to the standard Snellen eye chart. The one an eye doctor uses depends on the personal needs and abilities of the patient. For example, eye doctors will use charts with pictures or patterns for younger children who may not have learned to read or identify letters and numbers. There are also certain charts that specifically measure distance vision, while others are better for measuring near vision.
History of the Snellen Eye Chart
The Snellen eye chart was developed by Dutch eye doctor Hermann Snellen in the 1860s. Before this standardized eye chart was developed, each eye doctor had their own chart that they preferred to use. For the first time, the Snellen eye chart allowed a person to provide a standardized prescription from any eye care provider they chose to any eyeglass maker, and get the same optical lenses to accurately correct their vision.
How The Snellen Chart Is Used in Eye Exams
The standard Snellen chart displays 11 rows of capital letters, with the first row consisting of a single large letter. The farther down the chart you go, the smaller the letters become. Your eye doctor will ask you to look through a phoropter and look at the Snellen chart placed 20 feet away. In many offices, where 20 feet of space may not be available, you'll be asked to view the chart through a mirror.
If you have 20/20 vision, it means you can see what an average person can see on an eye chart from a distance of 20 feet. If you have 20/40 vision, it means you can only see clearly from 20 feet away what a person with perfect vision can see clearly from 40 feet away.
Does 20/20 Visual Acuity Mean Perfect Vision?
No. While eye chart tests identify refractive errors, they can't detect signs of visual skill deficiencies or diseases such as glaucoma, cataracts or macular degeneration. These are diagnosed using advanced equipment as part of a comprehensive eye exam. For more information, give us a call at (614) 793-0700 or visit us in person at EyeCare Professionals of Powell today!