Ocular Motility and Strabismus
Strabismus is defined as deviation of an eye’s visual axis from its normal posi-tion.
There are two major types of manifest strabismus or heterotropia:
1. Concomitant strabismus (from the Latin “comitare”,accompany). Thedeviating eye accompanies the leading eye in every direction of movement. The angle of deviation remains the same in all directions of gaze. This form of strabismus may occur as monocular strabismus, in which only one eye deviates, or as alternating strabismus, in which both eyes deviate alter-nately.
2. Paralytic strabismus results from paralysis of one or more eye muscles.This form differs from concomitant strabismus in that the angle of devia-tion does not remain constant in every direction of gaze. For this reason, this form is also referred to as incomitant strabismus.
The incidence of strabismus is about 5 – 7%.Esotropia(con-vergent strabismus) occurs far more frequently than exotropia (divergent strabismus) in Europe and North America. Concomitant strabismus usuallyoccurs in children, whereas paralytic strabismus primarily affects adults. This is because concomitant strabismus is generally congenital or acquired within the first few years of life, whereas paralytic strabismus is usually acquired, for example as a post-traumatic condition.