Skip to main content
Home »

News

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.

Bloodshot Eyes – Should You Be Concerned?

You wake up in the morning ready to start your day, only to discover that your eyes are bloodshot. That might not be surprising if you stayed up late to finish a project, had too many drinks at a party or spent time in a smoke-filled room.

But bloodshot eyes can also signal an underlying eye problem. If your eyes appear red or bloodshot, make an appointment with an eye doctor for a comprehensive eye exam to determine the cause and to receive effective treatment.

Why Do I Have Bloodshot Eyes?

When blood rushes to the front of the eye, the tiny red blood vessels on the white of the eye dilate and become visible. This makes the eyes appear red and irritated.

So why do these blood vessels dilate, causing your eyes to look bloodshot?

Bloodshot eyes tend to be caused by:

  • Dry eyes
  • Irritants such as smoke, pollen and perfume
  • Lack of sleep
  • Excessive alcohol consumption
  • Spending too much time in front of the computer

Bloodshot eyes due to lifestyle and environmental irritants may disappear on their own, or you can try to relieve them with over-the-counter eye drops or liquid tears. Lifestyle changes, such as getting more sleep, cutting down on alcohol intake and limiting screen time can often be helpful. If allergies are the culprit, oral antihistamines and antihistamine eye drops may relieve symptoms.

At other times, underlying problems requiring prompt medical attention can cause your eye’s blood vessels to dilate. The following are some of these medical conditions:

Conjunctivitis

You’ve probably heard of “pink eye.” It’s another name for infectious conjunctivitis – an infection of the conjunctiva, the thin membrane covering the eyelid and the front surface of the eye.

There are two types of infectious conjunctivitis – bacterial and viral.

If your child has conjunctivitis, they’re not alone. About 12% of kids get bacterial conjunctivitis every year. This highly contagious condition affects children and adults. In addition to reddish eyes, the following symptoms are associated with conjunctivitis:

  • Bacterial conjunctivitis – irritated eyes, swollen eyelids, eye discharge, crusty eyelids and excessive tearing
  • Viral conjunctivitis – cold or flu-like symptoms, runny nose, fever, itchy eyes, excessive tearing

If you or your child are experiencing these symptoms, it’s important to schedule a prompt appointment with an eye doctor, who can diagnose whether the conjunctivitis is viral, bacterial or due to allergies.

Depending on the diagnosis, your eye doctor will prescribe antibiotic eye drops or creams to treat bacterial conjunctivitis. The viral form may run its course after a few days, but cold compresses and non-prescription eye drops may provide relief.

Dry Eye Syndrome

If your eyes are chronically bloodshot you may have dry eye syndrome (DES). Signs of DES include:

  • Dry, irritated eyes
  • Burning or stinging eyes
  • Discharge from the eyes
  • Light sensitivity
  • A feeling you have something stuck in your eyes
  • Blurred vision
  • Watery eyes

Dry eye syndrome is most commonly caused by a blockage of the tiny meibomian glands in the eyelids. These glands secrete oil that keeps eye moisture from evaporating too quickly. Without the oil, tears dry fast, leaving your eyes feeling dry, itchy and with a bloodshot appearance.

Too much screen time, aging, certain medications such as antihistamines, and medical conditions such as Sjogren’s syndrome can cause dry eye syndrome.

In addition to any medications or in-office treatments your eye doctor recommends, make sure to get plenty of hydration, take frequent breaks from digital screens and use a humidifier in your home.

Uveitis

In addition to bloodshot eyes, if you also experience blurred vision, see floaters or your eyes feel painful, you may have an eye inflammation called uveitis. The causes of uveitis include:

  • Autoimmune or inflammatory condition
  • Infection
  • Medication side effects
  • Cancer (in rare cases)

Unfortunately, uveitis symptoms can often be mistaken for something less serious. That’s the reason it’s important to get an eye exam if your eyes are bloodshot. Left untreated, uveitis can lead to serious conditions such as retinal scarring, cataracts and vision loss.

Depending on the cause and severity, your eye doctor may treat uveitis with prescription eye drops, steroid pills, injections or eye implants.

Eye Injury

It’s vital that all eye injuries receive immediate eye care from an eye doctor.

Even a minor eye injury can cause a big red blotch to form on the white part of the eye (sclera). The cause is a broken blood vessel or a subconjunctival hemorrhage.

Although the appearance of this blood looks severe, and can make the entire white part of the eye appear bright red, a subconjunctival hemorrhage is usually painless and doesn’t cause vision loss. Any time you notice excessive blood on the eye following an eye injury, schedule an appointment with an eye doctor to assess the health of your eye.

Glaucoma

In rare cases, bloodshot eyes may signal the presence of glaucoma – a leading cause of vision loss and blindness.

While some types of glaucoma don’t show symptoms in the early phases, bloodshot eyes can indicate the type of glaucoma that requires immediate medical care. This disease causes damage to the optic nerve due to excessive pressure within the eye. When this pressure suddenly rises, the eye’s blood vessels become dilated and visible, making the eye appear red.

If you have bloodshot eyes and/or have the following risk factors for glaucoma, immediately schedule an appointment with your eye doctor.

  • Family history of glaucoma
  • Aged 60+
  • African American, Asian or Hispanic
  • Diabetes
  • High blood pressure

Bloodshot Eyes Won’t Go Away?

Talk to Us Any time you notice bloodshot eyes or blood on the front of the eye, don’t wait. Schedule your eye exam with John R. McGough, O.D. at Texas State Optical Tyler in Tyler today.

Q&A With Your Local Optometrist

Can I get bloodshot eyes after LASIK surgery?

LASIK surgery is highly effective minimally invasive laser eye surgery that can correct refractive errors, but like all surgical procedures, it can have side effects. Your eyes may be bloodshot or you could see halos from a few days to three weeks after surgery. Additionally, you may experience other dry eye symptoms. Eye drops and liquid tears can alleviate these symptoms, but if you have any concerns about your eyes following LASIK surgery contact your eye surgeon.

What Should I Expect from a Glaucoma Exam?

If you have a family history and/or other risk factors for glaucoma, and if your eyes look bloodshot, consider scheduling a glaucoma exam. Your eye doctor may perform the following tests:

  • Tonometry – eye pressure test
  • Gonioscopy – to see how fluid is draining out of your eye
  • Vision field test – to examine the functioning of the optic nerve
  • Dilated pupil exam – to detect any damage to the optic nerve
  • Retinal photo or OCT – digital examination of the retina and optic nerve health

Call for an Appointment, We are open!

We are making special arrangements with the current public health concerns. When you call Texas State Optical Tyler, we will space your appointment time to be mindful of social distancing and your personal comfort.

Texas State Optical Tyler is here for your vision care. We are aware of your concerns and are taking extra precautionary action for your protection and safety. We carefully sanitize all surfaces, including equipment, frames and supplies, frame boards, desks, and keyboards.

When you schedule your eye exam appointment, you can have the extra confidence that you will be safe and comfortable at Texas State Optical.

TSO Logo