When One Eye Sees Clearly And The Other Doesn't: Causes Of Blurry Vision In One Eye

Blurry vision is a common eye condition often associated with near-sightedness, far-sightedness, and astigmatism. However, in certain cases patients may experience blurry vision exclusively in one of their eyes, in a condition known as unilateral blurry vision.

This condition can be alarming to patients, as their vision may appear uneven or skewed. Learning the potential causes of blurry vision in one eye can help patients understand the condition, select an appropriate treatment option, and maintain their eye health.

Blurred vision is when the eyes have difficulty seeing clearly or sharply. It is the most common sight-related symptom reported to doctors and healthcare providers. Blurred vision can happen concurrently in both eyes, or exclusively in a single eye in a condition called unilateral blurry vision.

Blurred vision is associated with a variety of eye and overall health issues that range in severity. Even in non-serious cases, blurred vision typically gets worse over time. No matter the severity or circumstances, patients should see their eye doctor when they begin to experience unexpected or sudden blurry vision.

The appearance of blurry vision in one eye may appear jarring and even frightening to patients. In most cases, blurred vision in one eye is not serious or life threatening. However, it may be a sign of a larger health condition.

These conditions differ in causes and severity—ranging from relatively benign (myopia) to potentially life threatening (stroke or TIA). This means patients should always see an eye doctor if they experience sudden blurry vision in one eye in order to get an accurate diagnosis.

The most common, and least severe, cause of blurred vision in one eye are refractive errors. Refractive errors occur when the shape of the eye prevents light from focusing directly on the cornea—resulting in cloudy or blurred vision.

Common refractive errors include: nearsightedness (myopia), farsightedness (hyperopia), and astigmatism.

Refractive errors can be treated using corrective lenses such as eyeglasses or contact lenses. They can also be corrected by refractive surgeries such as LASIK, Refractive Lens Exchange (RLE), and PRK.

A cataract is an ocular condition where the lens inside of the eye becomes cloudy and hardened over time, allowing less and less light to enter. This can cause sudden blurry vision in one or both eyes.

Cataracts are the most common age-related eye condition. Unlike refractive errors, serious cataracts cannot be treated with glasses or contacts. Patients with visually disruptive cataracts can manage the condition with cataract surgery, where an eye doctor replaces the patient's cloudy lens with an artificial intraocular lens.

Related: Cataracts Awareness Month

A range of eye infections may also be responsible for blurred vision in one eye. Some of these include:

Keratitis: A serious bacterial infection of the cornea which can cause blurred vision and, in severe cases, loss of vision.

Conjunctivitis (pink eye): When the conjunctiva (a membrane that covers the front of the eye) becomes inflamed, causing the eye to become pink, swollen, and irritated

Orbital cellulitis: A bacterial infection in the deeper layers of skin surrounding the eye socket.

Many of these infections and their associated symptoms can be treated with prescription medications and eye drops.

A torn retina occurs when the retina or thin tissue at the back of the eye begins to tear away from its normal position. Retinal tears can lead to a retinal detachment, which requires immediate attention. Both conditions can cause blurry vision in one eye, along with other symptoms such as floaters, flashes, and reduced peripheral vision.

Retinal tears can be treated by creating scar tissue around the tear to prevent fluid from entering through the tear. This can be done through laser surgery or a procedure called cryopexy, where a doctor applies a freezing probe to the outer eye over the tear to secure the retina to the surrounding tissue.

Migraines are severe headaches that can cause throbbing, pulsing, and intense pain.

Visually disruptive migraines, also called retinal migraines, can lead to sudden blurry vision and temporary blindness in one eye. Though painful, these symptoms typically last less than an hour and may be relieved with over-the-counter pain medication.

Patients with frequent and severe migraines may be put on prescription medications such as triptans to control the condition.

In rare cases, a stroke or a TIA—often called a mini-stroke—can lead to blurred vision in one eye. In these severe cases the stroke may affect the patient's visual field, causing blurry vision in one or both eyes.

Other stroke-related symptoms can include headache, disorientation, difficulty speaking, and numbness (often on one side of the face).

Strokes are considered a medical emergency. If patients experience stroke symptoms, they should immediately see their doctor.

Glaucoma is a progressive eye disease that targets the optic nerve, usually associated with high pressure inside the eye. There are two principle types of glaucoma:

Open-angle glaucoma: Occurs without noticeable symptoms appearing. It can often go undiagnosed without proper checkups and worsen over time without treatment.

Closed-angle glaucoma: Less common but more damaging. It is marked with a rapid rise in eye pressure.

Glaucoma often affects one eye more than the other, leading to blurry vision in one eye.

As open-angle glaucoma (the most common type of glaucoma) occurs gradually and often undetected, patients’ best defense against the condition is regular comprehensive eye exams.

Dry eye syndrome is a condition in which the eye is not able to produce enough tears to sufficiently lubricate the eye.

These tears are in charge of a variety of important eye functions such as lubricating the eye, sweeping away foreign objects, and reducing the risk of infections.

Without the tears performing these important functions, conditions such as sudden blurred vision become more common.

Dry-eye-related blurred vision can be treated with over-the-counter artificial tears and prescription drops which can increase tear production.

Macular degeneration is an eye condition where the cells in a patient’s macula (an oval area in the central portion of the retina) deteriorate. This can cause a range of symptoms including sudden blurred vision in one eye.

There are two forms of macular degeneration:

Dry macular degeneration: Progresses slowly over many years, leading to the gradual loss of central vision.

Wet macular degeneration: One eye experiences leakage or bleeding, causing rapid loss of vision in that eye. This is an eye emergency, so if patients experience sudden blurry vision they should immediately see their doctor.

Related: Emergency Eye Care: When You Should See Your Doctor ASAP

Diabetes is a systemic disease in which abnormal levels of sugar (glucose) build up in the bloodstream. Diabetic retinopathy occurs when the retina’s blood vessels swell, leak, or close off. This leakage is often accompanied by swelling or sudden blurred vision.

Treatment will depend on the severity of the disease and the areas affected. Some treatment options include:

• Argon laser photocoagulation

• Intraocular injections

• Surgical intervention

Lifestyle changes such as a healthy diet and physical activity can also reduce the risk of diabetes.

Related: Diagnosed With Diabetes? See an Ophthalmologist

Diagnosis and treatment options will vary depending on the source and severity of the condition. If a patient is experiencing blurred vision in one eye their first course of action should be to receive a comprehensive eye examination.

The exam will allow the doctor to examine the patient’s eyes, assess any damage, and recommend an appropriate treatment.

Treatment varies widely based on the underlying condition and may range from prescription glasses to medical management for conditions like glaucoma or diabetic retinopathy.