At least 2.2 billion people worldwide have some form of near or distance vision impairment, according to the World Health Organization (WHO). Of these cases, about half of them could have been prevented, or still need to be properly addressed by a doctor.

That’s why regular eye exams are so important. The American Academy of Ophthalmology (AAO) recommends seeing an ophthalmologist for a complete exam once in your twenties and twice in your thirties, then again at age 40, when early signs of disease or vision changes may occur. If you are 65 or older, you should have your eyes checked every year or two. People with known eye problems, a familial history of certain eye diseases, or systemic diseases such as diabetes or rheumatoid arthritis may need to be seen annually, or even more frequently.

A vision checkup can be particularly helpful in detecting progressive eye conditions, such as glaucoma, a common age-related disease that has no symptoms in its early stages but is a leading cause of blindness for people older than 60, according to the AAO. Blindness from glaucoma can often be prevented with early treatment.

Age-related macular degeneration (AMD), another leading cause of vision loss, can also begin without any symptoms, but can be detected during a routine eye exam.

Still other eye conditions can have symptoms that require immediate medical attention, and shouldn’t wait for a routine checkup. Here are 10 symptoms to be on the lookout for, and how to know when to seek urgent medical attention.

1. Flashing Lights, Floaters, or a Shadow or Curtain in Your Vision

Sudden flashing lights, a noticeable increase in the amount of floaters (small specks, dots, circles, lines, or cobwebs in your field of vision), a shadow in your peripheral vision, or a gray curtain covering part of your field of vision could be symptoms of a tear or detachment of the retina — the light-sensitive nerve layer in the back of the eye that sends images to the brain. Nearsightedness, previous eye surgery, and physical injury to the eye are among the risk factors for detached retina, according to the AAO.

Unless treated quickly, usually with surgery, a detached retina can lead to permanent vision loss or blindness, per the National Eye Institute.

See an ophthalmologist right away if you have any symptoms of a torn or detached retina, because quick treatment can preserve vision that might otherwise be lost.

On the other hand, it's common to see flashes of light occasionally, especially as you get older, and this is usually harmless. Flashes of light that look like shimmering, jagged lines or appear wavy may be due to migraine aura, which is not an emergency, notes the AAO.

In general, brief, single episodes of flashing lights do not require any intervention, and are not usually a sign of retinal disease. But any new visual symptoms should be brought to your ophthalmologist's attention; depending on your description, the doctor may suggest that you be evaluated quickly, or they may say your symptoms are not suggestive of any serious problem and no urgent appointment is necessary.

Floaters are also usually harmless, but call an ophthalmologist right away if you notice new ones, especially if they are associated with persistent flashes of light, a shadow that appears in your peripheral vision, or a curtain that covers part of your vision, notes the AAO.

2. Sudden Vision Loss

Losing vision in one eye may be an early symptom of a stroke.

“Vision loss, especially in one eye, could be a sign that there is a blockage in the small arteries or veins that bring blood to and from the eye,” explains Ashley Brissette, MD, an assistant professor of ophthalmology at Weill Cornell Medicine in New York City and a clinical spokesperson for the American Academy of Ophthalmology. “This may indicate that there are blockages elsewhere, which can lead to a bigger stroke in the future.”

If you experience sudden vision loss you should see your ophthalmologist as soon as possible or visit the emergency room. If your ophthalmologist diagnoses a stroke or ministroke, they will refer you for a full stroke workup with your doctor, says Dr. Brissette.

3. Eye Pain

Many eye diseases are painless, but some conditions or injuries can result in eye pain.

Sometimes eye pain can mean the pressure in the eye is high, which could indicate glaucoma, says Brissette. Glaucoma usually happens when fluid builds up in the front part of your eye, which increases the pressure in your eye, damaging the optic nerve, according to the AAO.

Make sure to have your eye pressure checked when you visit your eye doctor, advises Brissette. More commonly, however, glaucoma causes slow, progressive vision loss, which involves no pain or discomfort.

A rare, serious form of glaucoma, called angle-closure glaucoma (also called closed-angle glaucoma or narrow-angle glaucoma) can produce severe eye pain. While primary open-angle glaucoma, the most common type of glaucoma, is painless and causes no vision changes at first, an acute attack of angle-closure glaucoma may have the following signs:

Sudden blurry vision
Severe eye pain
Headache
Nausea
Vomiting
Seeing rainbow-colored rings or halos around lights

An acute attack of angle-closure glaucoma is an emergency. Call your ophthalmologist immediately to prevent irreversible vision loss.

Eye pain may also be caused by a scratched cornea (corneal abrasion), per the AAO.

If you've scratched or scraped your cornea — the clear, round dome at the front of your eye that covers the iris and pupil — you may also experience blurry vision, sensitivity to light, and headache. Corneal abrasion can permanently affect your vision, so be sure to see an ophthalmologist right away if you have symptoms.

4. Dry Eyes

Occasional eye dryness that responds to over-the-counter eye lubricants is rarely something to worry about.

But chronically dry eyes that cause discomfort and disrupt your daily life shouldn’t be ignored and should be brought to the attention of your doctor or an eye care professional.

Sometimes dry eyes are the result of a problem with the tear-producing glands surrounding the eyes:

In aqueous tear-deficient dry eye, the lacrimal glands, located under the outside edge of the eyebrows, fail to produce enough of the aqueous, or watery, layer of tears, resulting in low tear production.
In evaporative dry eye, the meibomian glands, located along the edges of the eyelids, don’t produce a strong outer lipid, or oily, layer of tears, resulting in tears that evaporate too quickly.

Dry eyes can also be a symptom of an underlying autoimmune disorder, such as Sjögren’s syndrome, rheumatoid arthritis, lupus, and thyroid eye disease. Eye allergies can also cause dry eyes, as can a variety of medications, as well as environmental conditions such as wind, smoke, and dry air.

Failing to treat chronically dry eyes can lead to inflammation of the conjunctiva, abrasions or ulcers of the cornea, and eye infections, particularly if the cornea is damaged.

And not treating an underlying disorder that’s causing dry eyes can similarly have serious downstream effects.

If you’re regularly bothered by eye irritation, a feeling of grittiness, burning, or sensitivity to light, or excessive eye watering, get it checked out, and let your doctor know about any other symptoms you may be having, whether or not they involve your eyes.

5. Pain or Vision Changes Following an Eye Injury

Any significant injury to the eye should be evaluated by a doctor, particularly if the pain gets worse over time or there is a significant change in your vision, says Brissette.

Eye injuries can cause vision loss or blindness, so be sure to have a doctor look at your eye as soon as possible, even if the injury initially seems minor, says the AAO.

Signs of a possibly serious eye injury include:

You have persistent pain in the eye.
Your vision is reduced.
You have a cut or torn eye or eyelid.
One eye does not move as well as the other or you experience double vision or pain with eye movements.
One eye sticks out of the eye socket, or appears sunken inward or downward compared with the other eye.
The eye has an unusual pupil size or shape.
Blood is visible in the eye, either in the clear central portion, or over the white part of the eye.
You have something in the eye or under the eyelid that doesn't go away with tears or blinking.
You have had chemical burns or splashes in your eye (which requires immediate, copious flushing with water, even before contacting medical personnel or going to the emergency room).

It’s important to be on the lookout for specific symptoms if you get hit in the eye. If you experience a black eye, pain, or visual disturbance even after a light blow, immediately contact your ophthalmologist or visit the emergency room to avoid potentially serious complications.

6. Discomfort Caused by Particles in the Eye

In most cases, sand, dirt, dust, or other small natural particles in your eye aren't cause for alarm, per the AAO.

Your eyes will probably flush out these particles naturally with tears and blinking.

But metal, glass, or other man-made materials in your eye can be more serious, warns the AAO. It’s important that you not try to "fish out" foreign bodies that are not dislodged with normal tears and blinking. Doing so can produce greater damage than was initially present. See a doctor as soon as possible or go to the emergency room if you can't get the particles out of your eye with tears and blinking, or if it still feels like there’s something in your eye after you've gotten the particle out.

7. Red Eye

Having two red eyes is probably not as serious as one red eye. When both eyes are red at the same time, it could be a sign of a cold or allergies.

Conjunctivitis (pink eye) can occur in one eye or two. Pink eye can be caused by a virus or bacteria — see your eye doctor if it doesn’t resolve, says Brissette.

Scleritis, which is inflammation of the white part of the eye (sclera), can occur in one or both eyes, and some forms can be serious. The signs and symptoms of scleritis include severe pain, tenderness of the eye to touch, swelling of the white part of the eye, blurred vision, tearing, and extreme sensitivity to light, per the AAO.

There also can be pain in the jaw, face, or head. If you have symptoms of scleritis, you should see an ophthalmologist as soon as possible to avoid vision loss.

Uveitis, or inflammation inside the eyeball, can also affect one or both eyes. The condition can damage vital eye tissue, leading to vision changes and eye pain, explains Brissette.

Uveitis can develop suddenly. Signs and symptoms can include having a red eye with or without pain, being very sensitive to bright light, having blurry vision, and new worsening floaters, according to the AAO.

People with a history of autoimmune conditions or inflammation elsewhere in the body are prone to developing inflammation in the eye, adds Brissette, and people who have a history of uveitis are also more likely to have subsequent episodes. Contact your ophthalmologist right away if you notice any symptoms of uveitis, in order to prevent complications.

8. Eye Discomfort if You Wear Contact Lenses

While most people who use contact lenses don’t experience problems when they follow the rules of proper contact lens care and use, serious infections can occasionally occur. Symptoms of contact lens–related infections include blurry vision, unusual redness of the eye, pain in the eye, tearing or discharge from the eye, light sensitivity, and feeling like there is something in your eye, according to the AAO.

In some cases, contact lens-related eye infections can cause serious vision loss or even blindness, so see your eye doctor as soon as possible if you have symptoms of an infection.

9. Blurred Vision

Even if it clears up, blurred vision can be a sign of a number of eye problems, such as angle-closure glaucoma, uveitis, detached and torn retina, optic neuritis, or AMD. Since these conditions can be serious, make an appointment to see your doctor right away if you experience blurry vision.

However, the number one cause of blurry vision is refractive, meaning needing glasses, which can happen as people get older, says Brissette. Another more common nonserious cause of blurry vision is dry eyes — the eye needs to be well hydrated for us to see clearly through it, explains Brissette. When dry spots develop, vision can be blurry and can fluctuate. This is not an emergency and can often be treated with over-the-counter eye drops or prescription therapies.

A build-up of bacteria is also common around the eyelids and can lead to blepharitis or inflammation of the eyelids, which is also a common cause of dry eyes and sometimes blurry vision, adds Brissette. It’s important to clean around your eyelids and eyelashes daily to avoid these conditions and keep your eyes healthy, she advises.

The Takeaway

Certain eye symptoms, particularly sudden vision changes and pain, can be signs of serious eye conditions or even systemic illnesses such as stroke, and they should prompt you to seek immediate medical attention. Other symptoms may not seem as urgent, but any persistent discomfort, changes in vision, or changes in your eyes’ appearance merits a visit with an eye doctor to check out what’s going on. Addressing eye problems quickly is your best bet for preserving your vision for the long term.

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