Diplopia aka "Double Vision"

We get a few patients/referrals a month complaining of "double vision". Things that cause double vision and their solutions are not easily understood by even medical professionals.

Far and away the most common cause of "double vision" is ASTIGMATISM. Uncorrected astigmatism (or any corneal distortion) causes what I call "ghosting', which is 2 images nearly superimposed, but slightly displaced. I consider it a form of blur, not TRUE "double vision" or diplopia". This is an easy fix - glasses/contacts/lasik. If the corneal distortion is from keratoconus or trauma, obviously a special contact lens or possibly even a surgical procedure may be indicated. But *most* people who complain about seeing "two of everything"...they're not talking about true diplopia. They're talking about ghosting. They just don't know what to call it.

True diplopia is: one eye sees one image, the other eye sees a totally different image at a different point in space. You must have 2 working/non-suppressed eyes to experience true diplopia, that's why when anyone asks me about double vision or tells me they think they might have double vision, I ask them "one eye or both eyes?" If you shut one eye and the double vision is still present, that's not diplopia. That's "monocular diplopia", or GHOSTING from astigmatism or corneal distortion (or rarely retinal distortion or "metamorphopsia" like in macular degeneration).

I had a patient tell me they only "see double" when they look closely in a mirror. That's not diplopia...that's not any eye problem at all. That patient just noted (correctly) that there are 2 reflected images from a mirror- one from the mirrored back side of the glass, and another, fainter reflection from the ANTERIOR surface.

I also have parents of strabismus children worried about their children seeing double. That almost never happens. The brain greatly dislikes diplopia (because its fairly disconcerting) and children with "crossed" eyes instead experience SUPPRESSION, not double vision. Suppression is when the brain "ignores" one of the images in order to avoid diplopia. Suppression is a big problem because it usually leads to permanent vision loss in children (amblyopia).

True diplopia usually occurs in adults with a new-onset eye or brain condition. That's why its so interesting in medicine. True double vision implies a new problem that needs to be investigated. Cranial nerve palsies & trauma are the most common causes of true diplopia, and both require a neurological work-up. It's not really usually from any "eye" problem - the eyes themselves are usually fine. Its the muscles/nerves that control them (or not) that are the problem.

The treatment for true diplopia is treatment of the underlying cause of the diplopia - many nerve palsies are self-resolving, but obviously must be monitored by a neurologist or neuro-ophthalmologist. If there is trauma and muscle-entrapment, surgery is indicated to correct that. Some patients can end up with permanent diplopia because their traumatic condition or nerve palsy never really resolves. For those patients we can usually prescribe glasses with PRISM in them to account for the eye/eyes that don't track/move/aim properly. The prism doesn't treat the diplopia, it just accounts for it by bending light to "aim" it in a way where the patient doesn't see double.

A quick note about prism: I could blog all day about it because there are so many misconceptions, but prisms do not "move" your EYE. A prism moves the IMAGE. Even some eye care professionals are confused on this point. I've heard eye care professionals tell patients that the prism glasses "move the eyes so they're aligned" - no, that's absolutely incorrect. Prism glasses move the IMAGE to account for an eye pointing the wrong way. Prism doesn't "treat" diplopia, it just accounts for it.

In short & the main message of this blog post is: MOST people who think they have "double vision", don't. They have ghosting from a corneal problem. Maybe if someone is Googling "double vision" they'll find this post and be a little less anxious about it! It still warrants a visit to an eye doc, tho ;)

Edit: a fellow O.D. emailed me and brought up the topic of binocular vision & vision therapy. While I do not discount the existence of convergence insufficiency (my wife is CI) nor the validity of vision therapy, I do not consider it a "common" cause of diplopia. A "common" cause of headaches, eyestrain, asthenopia - YES. But not diplopia...IMO, anyway. Maybe I'm wrong. But he's right in one aspect - it does deserve a mention in this post.

I'm admittedly a little biased against VT and binocular vision disorders. Here goes my feather-ruffling, but hey! It's my blog! :D I attended SUNY College of Optometry where I received an excellent education. Top notch ocular disease & contact lens training especially. However IMO we spent way, way too much time diagnosing and treating vision therapy problems. My "pediatrics" internship was quite literally all VT. I was...uh...not happy. This was after I had already completed a separate entire VT internship that was all VT. Then I went & did an externship at a VA hospital where I saw a lot of eye disease and learned a lot...but also did a lot of VT. No joke. SUNY was a little bit VT-overboard IMO. Maybe its changed now, I don't know. I haven't been back in 10 years. But they burned me out on VT. I don't practice VT, and I don't diagnose a lot of binocular vision disorders like CI. I do *some*, but its a minute part of our practice. Maybe if I was more interested in it...?

But again, IMO binocular vision problems are probably not a major cause of diplopia.