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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 Port Elgin 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 Port Elgin 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 888-389-5511 or visit us in person at Saugeen Shores Family Eye Care, 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.

The Causes and Treatment of Dry Eyes, Dr. Carr – Saugeen Shores Family Eye Care, Port Elgin, ON

This can cause a consistent lack of sufficient lubrication and moisture on the surface of the eye, known as dry eyes.

Normally, the eye constantly lubricates itself with tears by producing them at a slow and steady rate, keeping itself moist and comfortable. Usually these tears consist of three layers, an oily, a watery, and a mucus layer. Each layer has a specific role in lubricating your eyes. The oily layer is outermost. It’s main purpose is to slow evaporation of the tear. The watery layer is in the middle. This makes up the majority of what a person normally thinks of as tears. This layer cleans the eye and helps to wash away small foreign objects and particles. The inner layer consists of mucus. This mucus allows the watery layer to stick to the eye and spread evenly over the eye in order to keep it lubricated. In a person with dry eyes, either hormonal changes, side effects from medication or some other factor causes the eye to either not produce enough tears, or leave out parts of the tear that make proper lubrication possible.

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Although dry eyes are not always curable, your optometrist may prescribe artificial tears to help with some of the symptoms. Artificial tears are lubricating eye drops that may help with dry, scratchy feeling eyes. Different artificial tears work in different ways. Some help replenish parts of the tear that your eyes are not producing on its own, others help to produce more tears overall. Your eye doctor will assist you to choose which will help you most.



Dr. Carr

Dr. Carr

“Symptoms of dry eyes include stinging or burning in the eyes, scratchiness, and excessive irritation from smoke or wind. Although it may sound counter-intuitive, the eyes’ response to the consistent irritation caused by dry eyes may also cause a person to experience excessive tearing. In this case, the eye is attempting to flush and lubricate itself by producing more tears, but is unable to do so successfully due to the rate of evaporation or inability to spread the tears properly.”, , Port Elgin eye doctor.





Some cases of dry eyes are seasonal, such as those which occur as a result of cold, dry winter air. In this case, your eye doctor may recommend wearing sunglasses or goggles when outdoors to reduce your eyes’ exposure to the sun, wind and dust. For indoors, your optometrist may recommend an air cleaner and humidifier to take dust out of the air and add moisture to air which is too dry.

“These artificial tears should not be confused with eye drops that are advertised to ‘get the red out.’ These eye drops may indeed reduce the appearance of redness in your eyes, but this is accomplished by making the blood vessels in your eyes smaller rather than actually lubricating your eyes. As such, these drops can sometimes actually make your symptoms worse. One should also be aware that if you wear contacts, some eye drops require you to take them out before using the drops and wait 15 minutes or more before reinserting your contact lenses.”

Studies have also shown that nutrition may have a part in helping to relieve some symptoms of dry eyes. Your eye doctor may recommend nutritional supplements such as omega-3. Good sources of omega-3 fatty acids are cold-water fish, cod, herring and salmon, as well as flaxseed oil. Mild dehydration can make symptoms worse too, so be sure to drink plenty of water, 100 percent fruit and vegetable juices and milk.

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


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