Monocular vs. Binocular Diplopia

on




Diplopia means double vision.

 This is the very first thing that I need know when I see someone with double vision. Is the problem coming from one eye, is it both eyes or is it the two eyes not working together?


Monocular diplopia is due to some problem in the focusing of an eye. The cornea and the lens are in the front of the eye and together, they take all the light rays coming into the eye and focus the image into a clear and single image to project onto the retina.



If there is any irregularity in the surface of the eye (dry eyes or corneal dystrophy) or lens (cataract) then that perfect beam of light might get split into a double beam and cause double vision. Often times the patient sees the second image like a ghost or shadow version of the main image. Sometimes it is even split into three or more images.

I like to test for this with a pinhole occluder. 


If the images sharpen up by looking through a tiny hole, then I confirm that it is a focusing problem in that eye.

This situation is called monocular diplopia. It is a problem with the focusing in that eye and needs to be addressed as an eye problem. 

The terminology starts to sound a bit confusing, but it makes sense that if one eye could have that problem, then both eyes could have a similar problem. If it shows up in both eyes it is called bilateral monocular diplopia. In other words, both eyes create double vision independently.

This is completely different from binocular diplopia.

Binocular diplopia means two eyes that both independently see well, but when you put the eyes together they don't seem to work together.

This is where we start to get to the neurology. The brain, the nerves and the muscles control the eyes and yoke the two eyes together so that they are always pointed at the same target. If there is some defect in the control from the brain, the nerves or the muscles, then the eyes go out of alignment and point in different directions and patients see double. This is called binocular diplopia. It only occurs with the two eyes together. If you cover the right eye, the left eye sees fine. If you cover the left eye, the right eye sees fine, but when you uncover both eyes simultaneously, they are not working together and images are double. 

At that point we will look into the pattern of misalignment and try to understand the cause, but the very first step is to determine if double vision is monocular or binocular.