Refractive Errors 101: Why You’re Not Seeing Clearly

More than 150 million Americans have refractive errors, and many don’t even know that they could be seeing more clearly. Learn about myopia, hyperopia, astigmatism, presbyopia and how they are diagnosed and treated.

By

Sally Wadyka

| Reviewed by

Cindy Cork, OD

In order to see clearly, light rays entering your eyes must focus directly on the retina.  When this happens without the aid of prescription lenses, this condition is called emmetropia. When glasses or contact lenses are required to focus correctly, you have what’s called a refractive error. Refractive errors include common vision issues, like nearsightedness, farsightedness and astigmatism. 

How the eye works

Different parts of your eye work together to take in light, process images, deliver messages to your brain and ultimately, help you see clearly. If any of those parts aren’t functioning properly, your vision may suffer. 

The cornea and the lens work together to bend (refract) the light that comes into your eyes so that it focuses on the retina. The retina is the paper-thin layer of light-sensing tissue that lines the back of the eye. It processes signals, sends them along to the optic nerve, then onto the brain—which turns them into the images you see. 

The shape of the cornea and the flexibility of the lens affects how well you see. When your cornea and lens don’t properly refract light, the result is a refractive error. 


Refractive Errors Explained
Refractive errors can impact anyone’s vision at any age. Many refractive errors begin in childhood, while others are more common as your eyes age.  

  • Myopia (nearsightedness): Myopia occurs when the eyeball is too long (front to back) or the shape of the cornea is too steeply curved. Instead of light focusing on the retina, it focuses in front of the retina. This makes objects that are far away look blurry. 
  • Hyperopia (farsightedness): This condition is the opposite of myopia. People with hyperopia have either an eyeball that’s too short or a cornea that is too flat. This results in light focusing behind the retina, which makes nearby objects appear blurry. Children with hyperopia are often born with the condition, and may still be able to see faraway images clearly. With age, people with hyperopia often have difficulty seeing both close up and far away. 
  • Astigmatism: A cornea or lens that is not perfectly spherical results in astigmatism. When you have astigmatism, it causes light to bend and focus differently, leading to blurry vision both close up and far away. 
  • Presbyopia: This difficulty seeing close up occurs with age. Typically in one’s 40s, the lens in the eye loses its flexibility. Since it is too stiff to bend and change shape as needed to focus light, nearby items start to look blurry. 

How refractive errors are diagnosed

Your eyecare professional can diagnose refractive errors during an eye exam or vision check. During a vision check, your provider uses a Snellen chart and other tools to assess your ability to see at all distances. A comprehensive eye exam includes a vision check as well as other tests that examine the health of your eyes and look for signs of eye disease. 

How refractive errors are treated

Glasses and contact lenses are the easiest and most common ways to treat refractive errors and correct vision. Your provider will prescribe glasses or lenses with the right shape and power to refocus light onto your retina and allow you to see clearly. 

Laser surgery is also an option for correction of myopia, hyperopia and astigmatism. The procedure works by reshaping the cornea and allowing the light rays to focus on the retina. Because presbyopia involves the inability of the lens to focus and not issues with the cornea, laser vision correction is not an option for presbyopia.     

The two most common types of laser surgery used to fix refractive errors are:

  • Laser in situ keratomileusis (LASIK): During LASIK surgery, your provider makes a small incision in your cornea, folds back the flap then uses the laser to correct the cornea’s shape. 
  • Photorefractive keratectomy (PRK): This type of refractive surgery uses a laser to resurface and reshape the cornea without cutting a flap. It can be a better option for people with thin corneas, dry eyes or who are very active. 

QE Perspective

Uncorrected refractive errors are the most common type of vision impairment globally, and many people don’t realize that they have the ability to see better.  Comprehensive eye exams are important for diagnosing and correcting refractive errors, in addition to assessing the health of the eyes and function of the entire visual system.  

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Taking good care of your eyes and your overall health can go a long way toward preventing age-related eye conditions. Eating an eye-healthy diet that includes lots of antioxidant-rich fruits and vegetables slows down the formation of cataracts and reduces your risk of macular degeneration. Getting plenty of exercise and maintaining a healthy weight can prevent diseases like diabetes and high blood pressure--both of which affect vision and eye health. And while you may not be able to prevent the presbyopia (and need for reading glasses) that comes with getting older, your eyecare professional can make sure you get the correct vision correction to see clearly.

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The sun’s rays contain damaging ultraviolet (UV) light. The same UV rays that burn your skin and lead to skin cancer also affect your eyes. Staring directly into strong sunlight can damage the retina. And repeated sun exposure over time can lead to cataracts, benign growths on the eyes and even eye cancer. Protect your eyes anytime you’re in the sun by wearing sunglasses that block both UVA and UVB rays.

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Some people claim that by correcting your vision with prescription glasses or contacts, you’re weakening your eyes—which then leads to worse vision. Their “proof” is that after wearing your corrective prescription for a while, your vision appears blurrier when you’re not wearing it. But that’s likely because you’re now used to seeing the world in clear, crisp detail—and in contrast, your uncorrected vision appears fuzzier. Getting the proper vision correction for your eyes is essential for your eye health. Don’t try to tough it out if you can’t see clearly. Visit your eyecare professional for an in-person or virtual vision screening.


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Not having a bright enough light may make it harder to clearly see the words on the page, but it won’t damage your eyes or permanently impact your vision. Because you’re straining to see, you might get a headache or other symptoms of eyestrain. If you want to read in bed without illuminating the entire bedroom, get a reading light that provides just enough brightness to see your book clearly. 


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LASIK surgery corrects your distance vision only, so people who are nearsighted benefit most from it. But LASIK doesn’t affect the lens of the eye, the part that helps you focus up close. As you get older, changes to the lens impact your ability to see close up. So even if you have LASIK in your 20s or 30s, you’ll most likely still need reading glasses by the time you hit your 40s or 50s.

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Having your face right up next to the bright screen may give you a headache or even cause some temporary eyestrain or fatigue, but it won’t damage your vision. Children are more prone to this behavior than adults—which may be because children can focus close up better than adults can. But if your child can only see the television clearly when sitting close (and has to hold other things close to see them clearly), they may be nearsighted. Taking your child to an eyecare professional for a vision exam will help determine if they need glasses to see clearly.

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Most eyecare professionals recommend removing—and thoroughly cleaning—your contacts every night. Even if you use extend-wear lenses that are approved for use a week or month at a time, it’s always safer to give your eyes a nightly break. Your contacts are more likely to accumulate bacteria when you leave them in 24/7, and that can lead to eye infections. Sleeping in your contacts also prevents essential oxygen from getting to your corneas. If you must sleep in your contacts, make it a once-in-a-while event and ask your eyecare provider about contacts that are specially formulated to let more oxygen through. 


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Carrots (along with other vegetables like sweet potatoes and dark leafy greens) contain high amounts of beta-carotene, which the body converts to vitamin A. Vitamin A is essential for eye health, and a deficiency of the nutrient is the leading cause of childhood blindness in developing countries. In the U.S., vitamin A deficiency is rare, and few people get so little it could impact their eyesight. Also, there’s no evidence that beta-carotene affects the sharpness of your vision or can prevent near or farsightedness. So while getting lots of beta-carotene in your diet may help keep your eyes healthy, no amount of carrots is going to actually improve your vision and allow you to toss out your glasses or contacts. 


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The jury is still out on how effective blue light glasses are for eyestrain. One recent study found they made no difference in eyestrain symptoms during a two-hour-long computer task. But some experts feel they may help alleviate eyestrain and fatigue during prolonged, cumulative screen time. Either way, blue glasses alone won’t solve the problem of too much screen time. The best way to reduce eyestrain is to limit screen time and take frequent breaks when you do need to spend several hours at your computer.

True
False

The jury is still out on how effective blue light glasses are for eyestrain. One recent study found they made no difference in eyestrain symptoms during a two-hour-long computer task. But some experts feel they may help alleviate eyestrain and fatigue during prolonged, cumulative screen time. Either way, blue glasses alone won’t solve the problem of too much screen time. The best way to reduce eyestrain is to limit screen time and take frequent breaks when you do need to spend several hours at your computer. 


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