Physiologic Diplopia in Adults

Normal Double Vision

Did you know that everyone sees a form of double vision all the time but they 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. You can see this for yourself with a simple demonstration: 

  1. Pick a target in the distance in front of you, perhaps a clock or a similarly sized object. 
  2. Now, hold up your thumb in front of you at arm's length between you and the target. You will notice that if you are looking at the distant object, your thumb will be doubled. 
  3. Move your focus to the thumb and the distant object will become doubled. This is 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.

Occasionally, we will have a very astute patient notice this phenomenon and come to the eye clinic for evaluation. First we need to investigate if what they are actually noticing and describing is physiologic diplopia. If so, and if the rest of the eye exam is normal, we can be reassured this is normal.

Double vision is more worrisome when what you are trying to focus on goes double. This could be a sign of strabismus (eye misalignment). It is important to get a full evaluation if you notice double vision so we can make sure there is nothing more serious going on.

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