Diplopia

The eye is shaped as a slightly irregular, hollow sphere that receives light and converts it into images. Light first passes through the cornea, the clear, front “window” of the eye. The cornea’s refractive power bends (refracts) the light rays that move freely through the pupil, the opening in the center of the iris through which light enters the eye. The iris (the colored part of the eye) works like the shutter of a camera, by opening and closing. It has the ability to control the diameter and size of the pupil, thus controlling the amount of light entering the eye. After passing through the iris, the light rays pass through the natural crystalline lens. This clear, flexible structure operates like a camera lens, shortening and lengthening its width . Light rays pass through a dense, transparent gel-like substance, called the vitreous, that fills the globe of the eyeball and helps the eye maintain its spherical shape. In a normal eye, the light rays come to a sharp focusing point on the retina. The retina functions much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses, then sending them to the optic nerve. 

The movements of the eyes are controlled by six pairs of muscles located on the outer part of each eye. Under normal circumstances, where both eyes look towards the same direction, one pair of muscles contracts while another relaxes. These pairs of muscles function separately with the intention to keep the eyes in parallel positions and to allow them to move towards all directions.

Stereoscopic vision can be defined as the visual ability to distinguish depth; good stereoscopic vision implies that both eyes coordinate and function properly making it unlikely for strabismus or amblyopia to develop. In general, the stereoscopic vision exam is the way to diagnose and medicate visual impairment in children.