Posted on November 27, 2017
By: Jeffrey Colburn, MD
Did you know that you see a form of double vision all the time and are not aware of it? Physiologic diplopia, or “normal double vision”, is a phenomenon where objects are doubled either in front of or behind whatever target you are focusing on with your eyes. You can see this for yourself with a simple demonstration. Pick a target in the distance in front of you, perhaps a clock or a similarly sized object. Now hold up your thumb in front of you at arms length between you and the target. You will notice that if you are looking at the distance object, your thumb will be doubled. On the other hand, if you move your focus to the thumb the distance object will become doubled. This is completely normal and our brains do not consciously think about that doubling. On the sub-conscious level, the brain actually uses the difference in the double vision in front of and behind the target object to help with determining depth perception.
On occasion we will have a very astute child notice this phenomenon and be brought to the eye clinic for evaluation because everyone is worried that he/she is suddenly seeing double vision. One of the things that we want to do first is see if they are actually noticing and describing this physiologic diplopia phenomenon. If so, and if the rest of the eye exam is normal, we can reassure everyone that they are okay. Double vision is more worrisome when it is what you are trying to focus on that goes double. This could be a sign of strabismus (eye misalignment). For this reason, it is important to get a full evaluation if a child, or an adult for that matter, starts noticing double vision so that we can make sure there is nothing more serious going on.