The Most Important Causes of Sudden Blurry Vision In One Eye

The Most Important Causes of Sudden Blurry Vision In One Eye

Having blurry vision in one eye definitely can ring some alarm bells. This is especially the case if this vision loss happens all of a sudden. Should you be worried?

There are some less serious causes of sudden blurry vision in one eye. Dry eye may be one of the most common causes. However, there are some very serious causes such as a retinal detachment or acute angle closure glaucoma which are true emergencies and require treatment.

Sudden blurry vision in one eye requires further investigation by an optometrist and / or ophthalmologist. Some causes of sudden blurry vision require treatment in order for the vision to be restored or prevent further vision loss. There aren’t a ton of eye emergencies, but a lot of them involve sudden blurry vision in one eye.

The “Less Serious” Causes

While these may not be true emergencies, these causes still may require treatment in order to prevent or treat the blurry vision.

Dry Eye

Dryness is a very common reason why one eye can become more blurred than the other.

Signs that vision is blurred from dry eye:

  • Vision becomes blurred but you don’t lose vision
  • The blurry vision comes and goes or fluctuates
  • You may notice the blurred vision more when working on computers or reading
  • You have other symptoms of dry eye such as burning or watering (yes, watery eyes can be a sign of dry eye)

On the surface of the eye is a tear film. This tear film protects our eye and provides a nice clear surface for our vision to pass through. When the eye drys out, this tear film becomes unstable and breaks up. This causes the tear film to become irregular and the vision blurry.

Fortunately, there are many treatments to treat dry eye. The first line is often starting with frequent artificial tear use as well as adding a fish oil or omega-3 supplement. All of these have the goal of providing a stable tear film to prevent the vision from fluctuating.

Severe Conjunctivitis

While many cases of conjunctivitis involve both eyes, viral conjunctivitis (also known as pink eye) often can start off only affecting one eye. Typically this doesn't cause much blurred vision but in severe cases the vision can become blurred.

Most often conjunctivitis causes redness and irritation to the eye and cases of viral conjunctivitis will resolve on their own. To help with the discomfort, artificial tears are used and frequent hand washing is done to avoid spreading the infection. Viral conjunctivitis is highly contagious.

If the conjunctivitis has a thick discharge, this can be a sign of bacterial conjunctivitis which requires antibiotics to resolve.


Migraines can cause a short-term alteration of vision and blurred vision. This is called the aura of the migraine. But migraines can even occur without getting a headache afterwards. These types of migraines are called ocular migraines.

During these migraine attacks, sudden geometrical shapes and patterns of flashing light can appear in the vision. One can instead experience loss of parts or all of their vision during these migraine attacks.

These symptoms last around 5 to 20 minutes and typically recur in a standard pattern and can occur more in one eye.

The treatment for ocular migraines is mostly preventative: identify and eliminate migraine triggers such as caffeine or alcohol or potentially start a medication for prophylaxis against migraines.


A cataract is a clouding in the natural lens inside your eye. Cataracts can cause loss of vision in one eye. Technically cataracts aren’t all that “sudden”, but what can happen though is the sudden realization that the cataract is present. You may wonder how someone can have a cataract for a long time without realizing it, but we often don’t walk around constantly covering and comparing our eyes.

Typically cataracts occur in both eyes and take a long time to develop. This is the reason why most cataract surgery is performed on individuals in their 60s, 70, and 80s - cataracts simply take a long time to develop.

But cataracts can happen to anyone at any age. Cataracts can even effect one eye much more than the other and develop very quickly. These types of cataracts are sometimes caused by a known cause such as diabetes or steroid medication use, but more often than not there is no known reason as to why the cataract developed.

Fortunately, cataracts are treated very successfully with cataract surgery - the cataract is removed and replaced with an artificial lens restoring all vision.

Also check out Your Comprehensive Handbook To Learn What Are Cataracts

Severe Causes of Sudden Vision Loss

The severe causes of blurry vision in one eye often has certain “red flag” signs that the less-severe causes don’t have:

  • More severe loss of vision
  • Longer duration of loss of vision
  • Other symptoms such as pain

These all need to be seen by an eye specialist and frequently as quickly as possible.

Retinal Detachment

A retinal tear can develop in the far periphery of the retina. This can happen with any impact to the eye or the head or can just happen naturally on it's own. If a retina tear develops, this can cause flashing lights and new floaters to develop.

However, a retinal tear on its own won't blur the vision. But if left untreated, fluid can get underneath a retinal tear and cause the retina to detach - leading to a retina detachment. Retinal detachments are an emergency!

Retinal detachments can cause a shade or curtain of vision loss or if caught too late can cause permanent loss of vision or blindness. These symptoms are important to be recognized so that tears and retinal detachments are treated.

A retinal tear is treated by using a laser to create a "barrier" around the tear. A retinal detachment is frequently treated with a surgery called a vitrectomy to replace the retina back in position with laser to seal everything in place.

Angle Closure Glaucoma

If the sudden blurred vision comes with pain, it's possible that glaucoma is the cause.

Flow of Aqueous Humor within the eye

Flow of Aqueous Humor within the eye;, Public domain, via Wikimedia Commons

The front of the eye is filled with a liquid called aqueous humor. This aqueous humor is produced in a structure called the ciliary body and flows around the iris and drains out through the angle of the cornea.

In acute angle closure glaucoma, the iris or the colored part of the eye covers up the angle and prevents the aqueous from draining out. With nowhere to go, this aqueous causes the pressure of the eye to increase to very very painful levels. This high pressure causes the cornea to swell up and cause a sudden blurred vision in that eye.

Angle closure glaucoma is an emergency. If the pressure remains high for too long, irreversible damage occurs and the eye will go blind. Angle closure glaucoma is treated by using a laser to open up a pathway through the iris for the aqueous to flow around and allowing for the pressure in the eye to drop.

Optic Neuritis

Optic neuritis is inflammation of the optic nerve that can occur in young individuals. This condition causes a sudden decrease in the vision in one eye. With optic neuritis, you can also find the loss of color, brightness or contrast perception and pain when moving the eye around.

Treatment with IV steroids can help resolve the symptoms of optic neuritis quicker. However, optic neuritis can recur and can be an initial sign of multiple sclerosis.

Stroke in the Retina or Optic Nerve

There are various ways in which the retina or optic nerve can receive a lack of blood flow or ischemia. All of these conditions will cause sudden loss of vision in the eye.

  • Amaurosis Fugax (or Transient Vision loss). This is a temporary loss of vision and can occur in one eye. The vision can dim and last for minutes before resolving. The most common cause of this is actually not due to the eyes but due to the build-up of plaques on the walls of the carotid arteries in the neck. These plaques can break away from the wall, travel through the blood-stream and cause a short-term blockage in the vessels of the eyes. Amaurosis Fugax thus is a condition which warns about future problems. The carotid disease must be treated to prevent future issues such as a stroke.
  • Retinal artery occlusion. This is a true stroke of the eye. Either a blockage from an embolus or closure of the blood vessel due to atherosclerosis causes the retina to receive a lack of blood flow. This causes severe vision loss. While not much can be done for the eye, individuals with this need to be evaluated for stroke risk factors to prevent future strokes in the brain.
  • Retinal vein occlusion. The veins returning blood away from the retina can become blocked. With no way to flow out, this causes the blood to leak out resulting in lots of bleeding and swelling of the retina. This leakage can interfere with the retina’s ability to get normal blood flow and cause ischemia and further vision loss. This condition needs to followed closely and treated with injections or laser treatments if a significant amount of swelling or ischemia develops.
  • Optic nerve ischemia. This will cause loss of vision and similar to optic neuritis will also cause impairment of color perception. While the loss of the center of the vision can occur, this can also cause impairment of just one field of vision - such as the bottom half or top half of your vision. But unlike optic neuritis, there is no pain and most cases occur after the age of 50 with an average age in the 70s. Unfortunately there isn’t any effective treatment.
  • Temporal Arteritis. This is a condition with inflammation of medium sized arteries that can cause a headache, scalp tenderness and vision loss in an older population. If detected, steroids can be started to prevent vision loss in the other eye.

Sudden blurry vision related to another eye conditions

Macular Degeneration

Macular condition occurs when there is a breakdown in the layers below the retina. Most patients with early macular degeneration will not have a large degree of vision trouble. However, vision loss can occur suddenly if the macular degeneration gets worse.

Abnormal blood vessel growth and bleeding beneath the retina can cause the sudden loss of vision. This is called wet macular degeneration and can cause permanent vision loss.

There are treatments, however. Injections can be used to stop the abnormal blood vessel growth to prevent further loss or in some cases even improve the vision.

It’s difficult to fully restore the vision in macular degeneration. The best outcomes come with the earliest detection. For this reason, patients with macular degeneration should monitor their vision with a special grid called an Amsler’s chart in order to detect the earliest signs of vision loss and follow-up routinely with their eye doctor for evaluation and treatment.

Diabetic Eye Disease

Diabetic patients can have sudden loss of vision in their eyes.

In uncontrolled diabetes, the retina in the back of the eye develops abnormal blood vessel growth. This abnormal growth is called diabetic retinopathy. These abnormal blood vessels aren't as strong as normal blood vessels. As a result, these blood vessels can leak and cause swelling in the back of the eye leading to a slower onset of blurred vision in one or both eyes.

But these blood vessels can suddenly bleed into the eye - called a vitreous hemorrhage. This creates a very rapid loss of vision in that eye. These cases may require injections into the eye, laser or observation in order to allow for the bleeding to break-up and the vision to be restored.


The list of conditions causing blurry vision in one eye is quite large. While this list covers many of the top and most important one, this list isn’t exhaustive. There can be rare conditions that need the expertise of an eye doctor to diagnose. Whenever you have any blurry vision, it is important to seek out medical care to make sure you are properly diagnosed and treated.

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