TNN: Double Vision is Not Normal!

Our second article in the “That’s Not Normal!” series is a perfect example of the phenomenon this series addresses, where someone with a disability doesn’t realize it because he/she always had it and thinks his/her experience is “normal”, what everyone experiences.

All her life, B.D. thought episodes of double vision were normal. If she looked at an object steadily for 3-5 seconds, it would split into two images, regardless of how far or near the object was. The double image would generally go away if she blinked or otherwise diverted her eyes from the object, but it would recur if she looked steadily at it again. She knew her vision was splitting, but it was so common for her that she barely noticed, ignoring that she was seeing two images. This was how her vision had always worked; she thought everyone experienced that.

B.D. did recall having problems with driving on a few occasions. Street lights would sometimes appear to move. She recalled one particular incident where down the road from her car was a stoplight, then a flagpole beside the road, then a building beside the road, but instead of the order stoplight, flag, building, she saw them in the order flag, stoplight, building. She nearly ran the light. At the time, she thought this was somehow related to her dyslexia, which she had been diagnosed with in her early twenties.

This vision problem was missed by all school eye tests and by several optometrists over many years. When she was thirty, she went to a new optometrist, one who had worked extensively with military pilots in the past. He finally performed tests that diagnosed the problem. (B.D.’s doctor never explained whether he noticed something during the routine parts of the examination that led him to do further tests, or whether he simply did a more comprehensive exam in general.)

It turns out B.D. has Convergence Insufficiency (CI), a disorder of eye muscle strength and coordination. (The available figures on the frequency of CI in the population were, ironically, wildly divergent, ranging from 0.3% to 13%.) In this disorder, the muscles controlling eye direction must work unusually hard to coordinate them correctly for binocular vision, causing eyestrain, double vision, transient blurred vision, and/or headaches.

Her optometrist prescribed special eyeglasses that included prisms to compensate for the eyes’ coordination problems. While these prisms actually made her a touch nauseous right at first, she then experienced fewer headaches and less eyestrain and found reading was easier.

She was surprised by the doctor’s diagnosis, but had a bigger “wow” moment soon after when she mentioned this to two of her friends, who then told her they had never once experienced double vision, not even when very drunk or after a blow to the head.

(I was one of those friends, and this prompted a revelation for me as well. I’d just had nasal surgery and realized my experience of nasal breathing had been abnormal all my life. My other friend in that conversation wondered how many people dealt with disabilities they didn’t even realize they had, and thus planted the seeds of this thread, and hopefully eventually a website around this theme.)

B.D. was of course frustrated that this had not been discovered years earlier. About half of her previous diagnosis of dyslexia actually stemmed from this vision problem! B.D. does in fact have true dyslexia as well, experiencing the classic “letter swapping within a word” problem, but having lines of text or words split into two was hardly helpful in coping with that!

Unfortunately, Convergence Insufficiency can require more complex treatment than eyeglasses. It turns out CI has different aspects; the alignment can be off vertically or horizontally. Most people with CI have some degree of both. While both can be corrected by appropriate prisms in the eyeglasses, the horizontal muscles are more elastic and will often adapt and “soak up the prism”, requiring an increasingly stronger prism over time to correct. The vertical muscles are more static and don’t adapt this way. Thus prisms are the standard treatment for vertical issues, but vision therapy, special exercises that strengthen the eye muscles, is often needed for horizontal issues.

B.D. started with just eyeglass prisms, but she was directed to vision therapy when the horizontal muscle control was indeed seen to be worsening. Vision therapy was not easy for her, and with it her eyestrain got worse before it got better, but she no longer regularly experiences double vision.

Double vision is neither necessary nor sufficient for diagnosis of Convergence Insufficiency. Double vision can be caused by many problems other than CI, and a person can have CI without experiencing double vision. Our purpose here is not to diagnose the cause of anyone’s double vision. The diagnosis and treatment of that should be done by an optometrist or ophthalmologist. Our purpose is to tell you that frequent double vision is not normal. If it happens to you often, you should see an eye doctor as soon as possible.

It may sound a bit incredible that someone could experience double vision regularly and not realize how unusual that was. Certainly someone who had had normal binocular vision would realize something was wrong if he/she then began seeing double regularly. But anyone experiencing it their entire life will naturally assume that their experience is universal. This is no different from people with normal binocular vision assuming that their experience is universal. In the latter case it nearly is, so they are of course much closer to being correct, but their assumption means that no non-specialist thinks to ask any questions that could challenge this view. Thus the people with frequent double vision never hear anything that contradicts their assumptions; they have little chance to learn that that isn’t normal.

That brings up a second possible benefit of this series. In addition to letting people with these hidden conditions learn that they have them, it could also lead people without them to learn what can happen and what questions might bring these conditions to light in their family and friends. Before hearing B.D.’s story, I doubt it would ever have occurred to me to ask a child how often they see double. Now, if I ever have kids, I’ll be sure to ask them that when they are growing up.