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Double vision in one eye is known as monocular diplopia. While there are many reasons why you may have double vision in one eye, not all of them are causes for concern.
Various conditions can cause double vision, such as eye problems that relate to your eye’s cornea or lens.5 The muscles and nerves that control your overall eye function can also cause double vision, as well as brain injuries.
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Monocular diplopia is different from binocular diplopia. They main difference refers to the persistence when the eye is shut.1
Monocular diplopia happens in one eye even if you cover the other eye. You can typically correct it using a pinhole. But binocular diplopia usually happens when both eyes are open, and you can typically correct it by covering either eye.
Monocular diplopia may be caused by a refractive error, early stages of cataracts, clouding of your eye’s lens, and other eye conditions.
Binocular diplopia may be caused by a misalignment of the eyes, known as strabismus. Damage of your cranial nerves that supply the muscles that control your eyes can also be the culprit.
A few common eye and health problems can lead to double vision in one eye. If you see a double image in either eye, any of the following could be the culprit:
Keratoconus refers to an eye condition in which the cornea thins out and gradually starts to bulge outward in a cone-like shape.9 Keratoconus typically affects both eyes, but it can also happen in one eye. The condition may progress and get worse for a decade or more.
A cataract refers to an eye problem that is characterized by a cloudy lens.4 Clouded vision that is caused by cataracts may make it difficult to see, giving you what appears to be double vision. Cataracts can be an underlying cause of monocular diplopia, as it can also occur in just one eye.
Pterygium refers to a growth of fleshy tissue in the eye that can start out as pinguecula, which is a yellow and raised growth on the eye’s conjunctiva.3 Pterygium can grow big enough to cover part of the cornea, which can affect how a person sees. It may only affect the vision in one eye.
Astigmatism refers to an imperfection in the curvature of your eye that causes symptoms like blurry vision.2 You may have blurry distance and near vision if you have astigmatism. Your eye doctor can perform an eye exam to determine a diagnosis.
Dry eye syndrome is a common condition that occurs when your eyes cannot produce enough lubrication to keep them wet.8 Dry eyes can cause discomfort, and you may feel like you are seeing two images at once. Because your eyes are dry, the surface can also become inflamed.
Other health conditions that can cause double vision include myasthenia gravis, multiple sclerosis, hyperthyroidism (Grave’s disease), and more.6 All of these can cause weak eye muscles, eye movement difficulties, the effect of seeing two images, and more.
Yes, it can be. One common symptom of a stroke is a change in vision, which means you can lose vision in one of your eyes.11
The symptoms of monocular diplopia include, but are not limited to, the following:
Speak with your eye doctor to determine the root cause of your double vision. If you have an eye problem like astigmatism, the solution may be as simple as contact lenses or glasses. If you have a more serious reason, like a cataract, you may explore other treatment options like surgery.
If you have had brain tumors, a stroke, or another life-threatening condition, you will need to seek immediate medical attention.
You should see a doctor if you notice that vision in one of your eyes is poor or getting poorer. While the causes of double vision may be nothing serious, like a refractive error, they can also be life threatening, like a brain aneurysm.12
There are a few ways your regular healthcare doctor or eye doctor can diagnose you with monocular diplopia. You may need an eye test and a neurological test, an MRI scan, and/or blood testing to determine the cause of your vision problem.6
If you have binocular double vision or monocular double vision, talk to your doctor about your treatment options.
Alves, Mariana, et al. “Diplopia: a Diagnostic Challenge with Common and Rare Etiologies.” The American Journal of Case Reports, International Scientific Literature, Inc., 13 Apr. 2015.
“Astigmatism.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 4 Sept. 2019.
Boyd, Kierstan. “What Is a Pinguecula and a Pterygium (Surfer's Eye)?” American Academy of Ophthalmology, 29 Oct. 2020.
“Cataracts.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 23 June 2018.
“Causes.” Stanford Health Care (SHC) - Stanford Medical Center.
“Diagnosing Double Vision in Adults.” Patient Care at NYU Langone Health.
“Double Vision (Diplopia).” Harvard Health, 1 July 2019.
“Dry Eyes.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 24 Sept. 2020.
“Keratoconus.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 9 Mar. 2021.
“Mayo Clinic Q and A: Double Vision Can Often Be Effectively Treated.” Mayo Clinic, Mayo Foundation for Medical Education and Research.
“Ministroke: A Warning Sign of a Major Problem.” Harvard Health, 1 June 2019.
Tan, Ak, and Ha Faridah. “The Two-Minute Approach to Monocular Diplopia.” Malaysian Family Physician : the Official Journal of the Academy of Family Physicians of Malaysia, Academy of Family Physician of Malaysia, 31 Dec. 2010.