We previously discussed how it is normal to see double all the time here. However generally when we discuss double vision however it is in non-normal situations.
When someone has a problem with double vision the first thing to do is determine if it goes away after covering either eye. If it does go away then it is binocular (both eyes) diplopia, otherwise it is monocular (one eyed) diplopia. Binocular double vision occurs where there is a new eye alignment problem; one eye is not looking where it should. Monocular diplopia occurs when something is disrupting the light before it reaches the retina, but it is actually quite rare.
Binocular diplopia occurs because something has changed causing the eyes to be misaligned. If the eyes were constantly misaligned from birth the brain would simply turn off (suppress) an eye and double vision would not be a problem. If the eyes are misaligned intermittently that can cause visual strain, poor reading skills and general discomfort but this less obtrusive than constant double vision.
Constant binocular double vision can have several causes:
- An old eye alignment problem may have returned:
- Previous vision therapy may not have been properly maintained causing compensating mechanisms to break down
- Prism changes can cause the same
- Damage within the brain can cause loss of muscle control. Causes can include:
- The eye muscles or bone around the eye may have been damaged from:
Some causes are more apparent than others. If someone was just hit by a baseball in the eye an aneurysm is unlikely. However damage to the bone around the eye entrapping an eye muscle is likely especially if the double vision is vertical.
Any new binocular double vision needs to be evaluated immediately. If someone had an eye turn in the past it is most likely that is the cause again, but the more dangerous causes need to be ruled out.