Seeing double can cause considerable concern if you or a loved one experience it. Double vision, which is also called diplopia, causes people to see two of the same image—whether horizontal, vertical or diagonal—instead of one. 

Sometimes double vision can just be an irritating but benign problem called strabismus. Other times the condition arises from a serious medical condition.

Specialists at Yale Medicine are experts at evaluating double vision and, if necessary, performing surgery to correct it. They provide compassionate patient-centered care and use the newest diagnostic and therapeutic techniques available to treat patients with a range of disorders including diplopia.

Two main types of double vision exist:

Monocular diplopia occurs when someone sees double vision with only one eye open, a second image usually appearing as “a ghost.” Causes are typically confined to the eye and less likely to be neurological.

Binocular diplopia occurs when someone sees double vision only when both eyes are open. Causes may be serious conditions, neurological or otherwise.

Dozens of medical conditions can lead to double vision.

A common non-serious cause of double vision is a mild form of strabismus, a congenital condition in which someone’s eyes have a misalignment. As people with strabismus reaches adulthood, they may develop double vision.

Serious causes include myasthenia gravis, a weakness in the body’s voluntary muscles, multiple sclerosis, a brain tumor or aneurysm, a stroke and giant cell arteritis.

Sometimes the causes have multiple layers. For example, long-term smoking can lead to a brain aneurysm, which, in turn, can cause double vision. Poorly treated diabetes can lead to cranial nerve palsy, a lack of nerve function due to poor blood flow, which can also cause double vision.

The doctor will perform a general examination, including a full eye exam. This includes a sensorimotor exam, which measures the alignment of the eyes in all types of gazes, and alternate cover testing, which measures eye movement when focused on a target.

If the eye misalignment is atypical, doctors must look deeper. Ocular motility testing, when doctors observe patients as they move their eyes and gaze in different directions, helps professionals discover any limitations in eye movement that could be caused by neurological or other conditions.

Doctors may order brain imaging–usually magnetic resonance imaging (MRI)–or blood testing to find the root cause of the double vision.

For double vision caused by benign medical conditions, special prism lenses can sometimes be quite helpful. Press-on prisms, placed on one or both eyeglasses, help to realign the eyes to reduce temporary double vision. For permanent double vision, prism lenses are ground into the glasses. Yale Medicine physicians provide the measurements for these special lenses.

Some patients will require surgery if doctors conclude that the double vision is permanent. A specialist can fix eye alignment by operating on the eye muscles. Yale Medicine surgeons perform these and other surgeries at Yale New Haven Hospital and at the Yale Eye Center.

If a serious underlying cause is identified, patients may be referred to the appropriate Yale Medicine department, such as neurosurgery or neurology.

Patients are often quite worried about their double vision. Yale Medicine doctors are among the nation’s best at quickly diagnosing the root problems behind the symptom.

“It’s our ability to make the diagnosis fairly quickly, get patients evaluated as soon as possible, and hopefully ease their concerns,” says Hilary Fazzone, MD, a neuro-ophthalmologist for Yale Medicine Ophthalmology. 

“We see many patients with double vision,” Dr. Fazzone says, “especially if they come through the emergency department with acute onset of double vision. It’s the Yale team that sees them first. We order any required testing to be done as soon as possible, and we determine if the problem is urgent or not.”