What Exactly is an Eye Chart?
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. Yet how much do you really know about this eye chart? Are all eye charts the same? How are these eye charts used? And when were they invented?
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. Having so many different eye charts made it impossible to standardize the vision correction available to patients.
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 – an instrument used to test individual lenses on each eye during an eye exam – and look at the Snellen chart placed 20 feet away. Your eye doctor will prescribe the lenses that provide you with the clearest and most comfortable vision.
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. On the other hand, 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. Early diagnosis and treatment of eye conditions are essential to ensuring long-term vision and eye health.
For more information, give us a call at (614) 476-2015 or visit us in person at Eyecare Professionals of Gahanna today!
Q&A
How do you keep your eyes healthy? Make sure to implement the following habits: eating a balanced diet rich in fiber, fruits and vegetables; drinking plenty of water; not smoking; wearing sunglasses to protect your eyes from UV rays; maintaining a normal BMI with regular exercise; and regular visits to your eye doctor.
What health conditions can an eye exam detect? A comprehensive eye exam can often detect certain underlying diseases that can threaten your sight and eye health, such as diabetes, high blood pressure, high cholesterol, tumors, autoimmune conditions and thyroid disorders.