Medically Reviewed by Whitney Seltman, OD on January 22, 2022

You Need Glasses

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When your eyeball is shaped more like an egg than round, or your cornea or your lens isn't curved just so, light can't focus in the right spot. That can lead to seeing clearly only at certain distances (nearsighted and farsighted) and distorted vision (astigmatism). You can often correct these "refractive errors" with eyeglasses, contact lenses, or minor surgery.

Your Eyes May Be Tired or Dry

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Have you been staring at a screen or page or focusing on a task for a long time? People tend to blink less often when they're concentrating like that. And each time you blink, you're spreading tears across the surface of your eye to keep it lubricated, clean, and refreshed. You may need to remind yourself to blink more often, take breaks, and look around to prevent vision fatigue. It can also be helpful to use artificial tears during the day to help keep your eyes lubricated.

You Have Diabetes

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When your blood sugar isn't well-controlled, fluid may seep into the lens of your eye and make it swell. This can happen before you're diagnosed or if you're changing your treatment, like starting insulin. As your glucose level gets back to normal, the lens should, too. People with diabetes are more likely to get retinopathy, or bleeding in the back of your eye, and other eye problems, which your eye doctor will check for at your yearly exam.

Your Eye Is Inflamed

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Eye tissue may swell because it's been bruised or something bad was splashed in it. The herpes virus from a cold sore could move to your eye. Sleeping in your contacts, not cleaning them correctly, or not throwing them away when you should can also lead to serious infections. Immune system diseases that affect other parts of your body, like psoriasis, IBS, and rheumatoid arthritis, can also cause inflammation in your eye.

Your Blood Pressure Is Low

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Feeling weak and dizzy, too? Your blood pressure might be too low because you're dehydrated -- maybe from too much activity in the hot sun. Things like some medications, heart problems, poor nutrition, and hormone imbalances could also cause low blood pressure and related blurry vision.

Fluid Is Building Up in Your Eye

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That can put pressure on the optic nerve and damage it. If you're also seeing halos around lights, your eyes are very red and hurt a lot, and you feel queasy, you may have a type of glaucoma called acute angle closure glaucoma. It develops very quickly, and you could lose your vision within a day if it's not treated. Open-angle glaucoma is more common, but it doesn't usually affect your vision at first, because it progresses very slowly over time. Once glaucoma affects your vision, there is no way to get that vision back because your optic nerve has been permanently damaged. The best way to prevent damage is to be diagnosed early by seeing your doctor regularly, who will monitor your eye pressure. If it’s too high, they may recommend eye drops or surgery to lower the eye pressure into a safe zone to prevent damage and vision loss. 

A Migraine Is Starting

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About 1/4 of people who have migraines get visual auras, usually before the pain and for less than an hour. These range from shimmering zig-zag lines, sparkles, and flashes to blind spots and tunnel vision. It may seem like you're looking through water or cracked glass. (You could also have vision symptoms without or after the headache.) If it happens only in one eye, does not go away in an hour or less, or causes a total black out of vision even for a few seconds, see your doctor in case it's a serious problem.

You Have a Cataract

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That's a cloudy area in the normally clear lens of the eye. They grow slowly, usually in both eyes, after age 55. But younger people, even kids, can get them, too. Colors may seem faded, it may be harder to see at night, and you may be more sensitive to glare. Special glasses and lens coatings can help you see. Surgery can replace the cloudy lens with a man-made one.

You're Getting Older

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Starting around 40, you'll notice it's harder to focus on up-close tasks like reading. The clear lens inside your eye isn't as flexible as younger people's. This is called presbyopia, it's a normal part of aging, and it happens to everyone. Your eye doctor can help you with reading glasses or contacts. There is no surgery that can reverse the aging effects of the lens of your eye.

You Scratched Your Cornea

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Typically, this feels like you've got a big, rough chunk in your eye. A corneal abrasion might be from an injury, but it's more likely from a bit of dust or sand. Try flushing your eye with non preserved saline solution (artificial tears) or eye wash. You can blink several times to make more tears, but don't rub or touch your eyeball. That could make it worse. See your eye doctor ASAP, because it can turn into an infection.

It's Something in Your Brain

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A concussion or brain injury could disrupt how information from your eyes gets processed. Depending where and how big it is, a brain tumor may affect your sight. Double vision can be one of many symptoms of brain swelling or of the membrane that surrounds it (encephalitis or meningitis), often because of infection. While it's not a symptom people usually think of, sudden blurry vision can be a sign of a stroke or another serious problem

Your Retina Is Damaged

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The retina (which includes your macula) is the back part of your eye where light gets focused, like a movie screen. If something happens to that surface, like swelling or tearing, the picture can be distorted or lost. A family history of retinal disease, poor diet, smoking, previous eye injuries or disease, and health issues such as high blood pressure, high cholesterol, and diabetes can raise the odds of problems like macular edema and a detached retina.

You May Have Multiple Sclerosis

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Signals going from your eye to your brain have a harder time traveling through a swollen or damaged optic nerve. Doctors don't know for sure what causes optic neuritis. But about half of people who have this condition will develop multiple sclerosis within 15 years. Vision trouble or pain with eye movementis often the first symptom of MS.

There's Trouble With Your Pregnancy

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Blurry vision along with headaches, shortness of breath, or feeling like throwing up may signal a serious complication called preeclampsia. It happens when blood vessels in your placenta are too narrow and don't work right. (Higher blood pressure after 20 weeks is usually the first sign.) See your doctor right away. Without treatment, it can cause life-threatening problems. Medications and rest until you deliver can help.  

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SOURCES:

American Optometric Association: "Myopia (Nearsightedness)," "Hyperopia (Farsightedness)," "Astigmatism," "Dry Eye," "Glaucoma," "Cataract."

Victoria State Government, Better Health Channel: "Eyes - common problems."

Joslin Diabetes Center: "Diseases of the Eye."

American Academy of Ophthalmology: "Diabetes and Eye Health," "Herpes Keratitis," "Uveitis," "Presbyopia," "Corneal Abrasion," "Optic Neuritis."

Ophthalmology: "Risk factors for moderate and severe microbial keratitis in daily wear contact lens users."

Mayo Clinic: "Keratitis," "Low blood pressure (hypotension)," "Ocular migraine: When to seek help," "Corneal abrasion (scratch): First aid," "Brain tumor," "Retinal detachment," "Preeclampsia."

National Eye Institute: "Facts About Uveitis," "Facts About Age-Related Macular Degeneration," "Facts About Diabetic Eye Disease."

American Heart Association: "Low Blood Pressure - When Blood Pressure Is Too Low."

American Migraine Foundation: "Visual Disturbances: Related to Migraine or Not?" "Understanding Ocular Migraine."

VisionAware: "I've Had a Concussion or Traumatic Brain Injury: What Do I Ask My Eye Doctor?"

ASCO Cancer.net: "Brain Tumor: Symptoms and Signs."

National Institute of Neurological Disorders: "Meningitis and Encephalitis Fact Sheet."

Harvard Health Publishing: "Recognizing the most common warning signs of a stroke."

Archives of Neurology: " Multiple Sclerosis Risk after Optic Neuritis: Final Optic Neuritis Treatment Trial Follow-Up."

National Multiple Sclerosis Society: "Vision Problems."