Humans have two eyes and yet see a single image, this happens because of both eyes coordination. This effortless clear single vision is the outcome of several mechanisms that involve the eye lens focusing, eye muscle movements, integration of all the sensory and motor input signals in the brain and execution of output signal in the eye.
The assessment of the sensory and motor input and output signals requires a comprehensive binocular vision examination. Within this examination there can be sub-specialty like orthoptics, vision therapy etc. Orthoptics is a discipline that assesses if the eyes are straight, predominantly examining the eye muscles.