A concomitant strabismus is a deviation of the eye in which the angle of deviation does not vary with the direction of gaze or the fixating eye.
In paralytic strabismus the deviation of the eye becomes greater as the eye is moved in the direction of function of the paretic muscle.
There are a number of possible causes of a concomitant strabismus. These include defects of innervation, refraction, and accommodation plus a genetic predisposition as well as a large group in which the cause is unknown. Common causes are imbalance of the near reflex (accommodative strabismus) and unilateral reduced vision in an infant or child.
By about age 7 years the accommodative and fusion reflexes are set. Muscle imbalance before this age results in concomitant strabismus. Muscle imbalance after this age is usually paralytic in type. It is not always easy to classify strabismus as concomitant or paralytic.
Concomitant strabismus does not usually produce the complaint of double vision. When a patient has a latent strabismus (phoria) and, because of fatigue or a debilitating illness, presents with a manifest strabismus (tropia), he may complain of the sudden onset of double vision. If the distance between the two images is the same in every direction of gaze, this is not paralytic.
In concomitant strabismus monocular eye movements are full in all directions, the angle of deviation is the same in all directions of gaze, and the primary and secondary deviations are identical irrespective of which eye fixates.
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