DEAR MAYO CLINIC: I have double vision in my right eye and can read with glasses, but distance is not very clear. What causes double vision? Is there a procedure to correct it?
ANSWER: A number of conditions can lead to double vision. Treatment typically depends on the underlying cause. With a careful evaluation and accurate diagnosis, double vision can often be effectively treated.
Double vision, also called diplopia, is either monocular or binocular. Monocular double vision is present in each eye separately. Binocular double vision is only present with both eyes open. This distinction is very important because monocular double vision is never dangerous, while binocular double vision can be caused by some serious neurologic conditions.
If you have new symptoms of double vision, a quick way to assess which type you have is to close each eye separately. Using your question as an example, “I have double vision in my right eye,” suggests that you have monocular, or “one-eyed,” diplopia. This means that when you close your left eye, you see images as double out of your right eye. But when you close your right eye, the double vision goes away. If you have binocular double vision, when you close either your right eye or left eye, the double vision goes away.
Monocular double vision in one eye often appears as a ghosting or shadow that overlaps with the primary image. It can affect the right eye, the left eye, or both eyes at the same time. The most common cause of this type of double vision is dry eye syndrome.
Dry eye syndrome causes double vision and blurred vision because the tear film along the surface of your eye becomes uneven due to the dryness. People who have dry eye syndrome often complain that their eyes burn or feel scratchy and itchy. It also can feel like something is caught in the eye. Symptoms of dry eye are often made worse by reading or by doing computer work because you unconsciously blink less while concentrating on reading. Treatment of dry eye syndrome usually begins with the use of artificial tears.
Other causes of monocular double vision include an irregular cornea, a cataract or retinal disease. With these causes, symptoms of double vision do not tend to fluctuate as much as double vision associated with dry eye syndrome.
It’s possible that the source of the problem could also be your glasses. Prescription glasses can contribute to poor vision and monocular double vision if they are out-of-date, the frames are bent or the lenses are scratched.
Binocular double vision, or binocular diplopia, is caused by misalignment of the eyes. This causes the images from each eye to be off a bit, making you see two images. With this type of double vision, the images often are completely distinct with space between them.
Conditions that may cause binocular double vision include previous trauma, stroke, systemic disorders and other diseases. If you develop symptoms of binocular diplopia suddenly, seek medical care right away. Some of the causes of binocular double vision can be neurologically dangerous.
Treatment of binocular double vision usually begins with the use of prisms in your glasses to realign the two images into a single image. Covering one eye with a patch is another option. Once the double vision is stable, then referral to a surgeon may be appropriate to correct the misalignment of the eyes.
Make an appointment to have your double vision evaluated by your eye provider. He or she can determine the exact cause of your symptoms, rule out other problems that may require regular monitoring — such as corneal, lens or retinal diseases — and help you decide on a treatment plan that fits your needs. — John J. Chen, M.D., Ph.D., Ophthalmology, Mayo Clinic, Rochester, Minn.