pediatrics
Strabismus
Classification of Strabismus
Several varieties of strabismus have been described, based on direction of deviation, specific conditions under which deviation occurs, and whether deviation is constant or intermittent. Description of these varieties requires the definition of several terms: Eso: Nasal deviation Exo: Temporal deviation Hyper: Upward deviation Hypo: Downward deviation (See figure Ocular deviations in strabismus .) Atropiais a manifest deviation, detectable with both eyes open (so that vision is binocular). A tropia can be constant or intermittent and may involve one eye or both eyes. Aphoriais a latent deviation, detectable only when one eye is covered so that vision is monocular. The deviation in a phoria is latent because the brain, using the extraocular muscles, corrects the minor misalignment. Acomitant deviationhas the same amplitude or degree of misalignment in all gaze directions. Anincomitant deviationvaries in amplitude or degree of misalignment depending on gaze direction. Strabismus involves both eyes; the left eye is shown here. The direction of the deviation is designated by the prefixes eso-, exo-, hyper-, and hypo-. When the deviation is visible, it is indicated by the suffixes -tropia and -phoria. 