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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 Troy 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 Troy 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 618-667-2020 or visit us in person at Unger 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.

Are You Susceptible To Vision Loss?

Vision loss is more common than you may think! In fact, it’s among the most prevalent disabilities in adults and children. Knowing what puts you at risk of developing vision loss is important and can help you to be proactive about caring for your eyes.

Below, we’ll explore the most common causes of vision loss and the risk factors associated with each.

Spreading awareness and education about visual health is just one way that our eye doctors near you can help. To schedule your comprehensive eye exam, call us today.

Common Causes of Vision Loss

Glaucoma

Glaucoma is a group of eye diseases caused by a buildup of pressure within the eye. Too much inner-eye pressure can damage the optic nerve and lead to vision loss.

Since symptoms don’t usually manifest in the early stages of glaucoma, getting regular eye exams is all the more crucial. Advanced or rapidly progressing glaucoma can show a variety of symptoms, such as blurred vision, headache, severe eye pain and redness, seeing halos around lights, and nausea.

Risk factors for developing glaucoma include:

  • Being 60 years or older
  • Family history of glaucoma
  • African, Asian, or Hispanic descent
  • High myopia (nearsightedness) or hyperopia (farsightedness)
  • Previous eye injury or certain eye surgeries
  • Certain medications, like corticosteroids
  • Thin corneas
  • Certain medical conditions, like diabetes, hypertension, heart disease, and sickle-cell anemia

Cataracts

Cataracts occur when the eye’s lens becomes cloudy. A healthy lens is clear and allows light to pass through it undisturbed.

Common cataract symptoms include cloudy or blurred vision, difficulty seeing at night, light sensitivity, double vision in the affected eye, and seeing colors as faded or yellowish.

Risk factors for developing cataracts include:

  • Aging
  • Diabetes
  • Hypertension
  • Smoking
  • Previous eye surgery, injury, or inflammation
  • Alcoholism
  • Extended use of corticosteroids

Age-Related Macular Degeneration (AMD)

AMD is the leading cause of severe vision loss in adults over the age of 60. It occurs when the macula (the small central portion of the retina, which is responsible for sharp, colorful, central vision) begins to wear down.

Early stages of AMD usually go unnoticed, but later stages of the disease can produce symptoms like blurred vision, dark or blurry areas in your central vision, and problems with color perception.

There’s not yet a cure for AMD, but certain treatments can help prevent vision loss.

Risk factors for developing AMD include:

  • Smoking
  • Obesity
  • Aging
  • Long-term sun exposure
  • Hypertension
  • Heart disease
  • Family history of AMD
  • Light-colored eyes
  • Farsightedness

Diabetic Retinopathy (DR)

Diabetic retinopathy is a complication of Type 1 or Type 2 diabetes that affects the light-sensitive tissue at the back of the eye called the retina.

Initially, diabetic retinopathy shows no symptoms but can eventually lead to blindness. As it develops, it can cause increased floaters, impaired color vision, dark spots in your visual field, and blurred vision.

Risk factors for developing diabetic retinopathy include:

  • Length of time from diabetes diagnosis — the longer you’ve had it, the higher your chances of developing visual complications
  • Uncontrolled blood sugar
  • Obesity
  • High cholesterol or blood pressure
  • Pregnancy
  • Smoking
  • African American, Hispanic, and Native American ethnicities
  • Family history of DR

So, what’s the bottom line ?

Multiple factors contribute to eye disease and vision loss, and some may even be relevant to you. If you think you may be at risk for vision loss or experience any of the symptoms listed above, speak with your eye doctor in Troy as soon as possible. We also recommend you have your eyes thoroughly examined every 1-2 years, or as often as your eye doctor recommends. To schedule your comprehensive eye exam, call Unger Eye Care today.

 

Frequently Asked Questions With Our Troy Eye Doctors

  1. Can blindness be prevented?

When caught early, many eye diseases can be treated to halt or slow the progression of the disease and potentially prevent vision loss. The best things you can do to preserve your vision for the long term is to lead a healthy lifestyle and make sure you undergo a comprehensive eye exam every 1-2 years.

  1. Which eye diseases are genetically inherited?

More than 350 ocular diseases have some sort of genetic component. Certain diseases, like retinitis pigmentosa and albinism, are directly inherited through chromosomal information. In other cases, a predisposition to the disease is inherited, rather than the disease itself.