Have fun with strabismus!

What is strabismus, anyway?

Normally, when you look at something, the image of the thing you're looking at, falls simultaneously on the foveas (the fovea is the middle of the macula, the small spot with the highest resolution - and what then, is a macula; it is a small avascular area, often yellowish in color, therefore it is also named the "yellow spot". (By the way, for a great collection of medical jargon see Glossary of medical terms).

If both eyes do not align, only one is actually looking at this object you're watching, and the other will look at something else, which is the basis for some interesting phenomena like diplopia and confusion (more about this on the amblyopia page). Any deviation from perfect ocular alignment is called "strabismus". Misalignment may be in any direction - inward, outward, up, or down, or any combination of these.

Inward deviation (esotropia)	Outward deviation (exotropia)

Note: Above images are not actual photographs. They are artificially altered pictures intended to illustrate the general idea.

The amount of deviation is the angle by which the deviating eye is misaligned. Strabismus present under binocular viewing conditions is manifest strabismus (or heterotropia). A deviation present only after binocular vision has been interrupted (ie, by occlusion of one eye) is called latent strabismus (or heterophoria). Strabismus is present in about 2% of children.

Convergence insufficiency is an exodeviation that is present only at near or is greater at near than at distance fixation. It is said to interfere with near work in most unpleasant ways;  headaches, blurred vision, and other asthenopic symptoms can occur. The good news is that this is one of the few cases of ocular misalignment problems for which orthoptic excercises work really well.

The following pages contain good basic information about strabismus:

Pediatric Ophthalmology at The Children's Hospital of Buffalo
American Academy of Ophthalmology