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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?

Here’s everything you need to know about eye charts and more!

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. Eyeglass makers didn’t receive the defined measurements they needed to accurately design, manufacture and measure the optical prescriptions their patients needed.

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 – 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.

In many offices, where 20 feet of space may not be available, you’ll be asked to view the chart through a mirror. This provides the same visual experience as if you were standing 20 feet away.

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.

If you have 20/200 vision, the legal definition of blindness, this means what a person with perfect vision can see from 200 feet away, you can see from 20 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 with your local eye doctor. 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 or visit us in person at , today!

Q&A With Your Local Optometrist

How do you keep your eyes healthy?

You only have one set of eyes – don’t take them for granted!

Make sure to implement the following habits for healthy eyes (and body). These include:

  • Eating a balanced diet rich in fiber, fruits and vegetables
  • Drinking plenty of water to hydrate your body and eyes
  • Not smoking, and avoiding 2nd-hand smoke
  • Wearing sunglasses to protect your eyes from ultraviolet (UV) rays
  • Maintaining normal BMI with regular exercise
  • Regular visits to your eye doctor as recommended

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. This is why having your eyes checked regularly is key. The earlier the diagnosis and treatment, the better the outcome and the higher your quality of life.

Cataracts

When looking at an object, light is received through the pupil. It is then focused onto the the back of the eye, where there is a collection of light sensitive cells called the retina. A cataract occurs when the eye’s normally clear lens becomes fogged up, making it hard or even impossible for light to travel properly through the lens and be clearly focused on the retina.

Cataracts are often considered a common part of aging. The lens, which is made of mostly water and protein, grows excess layers on its surface as the years go by. When these layers harden, protein in the lens may form clumps and become cloudy, forming a cataract. Although cataracts are usually considered an eye condition of old age, previous eye disease or eye surgery, chronic disease, diabetes, and eye injuries can bring on cataracts much earlier.

“Increased difficulty seeing at night or in dim lighting is another easily overlooked symptom. You should consult your eye care professional for an appointment if you have any of these symptoms and, if diagnosed, be sure to have regular check-ups thereafter.”, Dr. Wedeking, Hebron eye doctor.

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Cataract surgery involves the removal of the cloudy natural lens and replacement of the natural lens with an artificial lens made of plastic, silicone or acrylic. The surgery is extremely low risk and is normally done as an outpatient procedure without overnight stay.
Treatment of a cataract varies. In cases in which clouding is minimal, vision is hardly affected and a slight change in eyeglasses prescription may be enough. Alternatively, if all or a large part of the lens is clouded, surgery is required to restore sight.
Proper pre- and post-op care are very important. Proper co-management means your optometrist and eye surgeon are on the same page when it comes to your treatment before, during and and after surgery.” A thorough exam should be conducted by your primary eye doctor to diagnose and decide on treatment of your cataract. After this your doctor should be able to advise about the surgery and refer you to a surgeon, who will answer any questions you have about the surgery. Afterwards, follow ups should take place with both your surgeon and your optometrist to assess your recovery.

Please don’t forget to make an appointment to see our Eye Care Specialist

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