Dear Doctors: I am 88 and have had double vision for 10 years. A prescription for glasses with prism lenses corrected the problem. I recently had cataract surgery, and my distance vision improved, but I still see two images. What causes double vision? What else can be done to correct it?
Dear Reader: When someone has double vision, it means the information collected by the two eyes does not come together into a single image. (For fellow science nerds, the medical term for the condition is “diplopia.”) Although the term “double vision” suggests that someone is seeing two complete sets of each thing, the condition actually exists on a spectrum. It ranges from a slight overlapping of images to distinct duplicates.
The variations of double vision don’t end there. The images themselves may be side by side, known as horizontal diplopia. They can also be one above the other, which is vertical diplopia. For some people, double vision involves a kind of halo effect that is most noticeable when looking at objects lit in the dark.
The condition can also affect one or both eyes. When it’s in one eye, it’s known as monocular diplopia. This indicates a problem with how the visual structures of that eye receive and process light. This can be due to cataracts, astigmatism, dry eye or other abnormalities of the cornea or lens. Monocular diplopia may be caused by certain neurological conditions, but this is rare.
When both eyes are involved, as is happening to you, it is known as binocular diplopia. It is the most common form of this condition. Binocular diplopia is often caused by faulty alignment. For the brain to process the two sets of visual data into a single image, both eyes must focus precisely on the same target. A problem with the ocular muscles or the nerves that animate them can interfere with that precision. Binocular diplopia most often results from damage to the nerves or muscles that control eye movement. This can be due to a stroke, a blow to the head or other head injuries.
The prism lenses you have been prescribed work by compensating for the misalignment that causes double vision. They do this by redirecting the light that the eyes are receiving. This allows the eyes to deliver visual information that the brain can turn into a single image. When prism lenses can’t correct double vision, other treatments may be considered. These can include a specialized type of physical therapy that retrains the eye muscles. Treatments also include surgery to improve eye alignment. If someone has a neurological condition or muscle disorder that affects the eyes, such as myasthenia gravis or Graves’ disease, it should be treated.
In your case, we think it would be a good idea to see an ophthalmologist to have your vision rechecked. A vision test will be able to flag any changes that resulted from your recent cataract surgery. If any changes have occurred, the doctor can write you a prescription for prism lenses that would fit your current needs.
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(Eve Glazier, M.D., MBA, is an internist and professor of medicine at UCLA Health Sciences. She hosts the “Medically Speaking” podcast for UCLA Health. Elizabeth Ko, M.D., is an internist and associate professor of medicine at UCLA Health.)
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(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)