Ocular Misalignment (Strabismus)
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Ocular Misalignment Assessment:
Misalignment of the eyes is called strabismus (or squint). Assess the patient for manifest eye deviations, which are deviations that occur when both eyes are fixed on a target, and latent deviations, which are eye deviations that occur when only one of the patient’s eyes is allowed to fixate on a target.
1. Manifest deviation. Ask the patient to look at a target with both eyes and assess the patient’s ocular alignment. Normal eye alignment with binocular vision is called orthotropia. If misalignment is observed in this condition, it is considered to be a manifest misalignment and is called a heterotropia (or simply, “tropia”). Orthotropia most commonly occurs because of motor fusion, which is a mechanism that allows the eyes to lock onto a target not because of perfect, natural eye alignment.
2. Latent deviation. When motor fusion is removed, through the covering of an eye, most patients will demonstrate a latent misalignment, called a heterophoria (or simply, “phoria”). Perfect ocular alignment in the setting of monocular vision is rare, and is called orthophoria. The cover/uncover test is commonly performed to assess for latent misalignment.
Ocular Misalignment Terminology:
- Ocular misalignment (again, called strabismus) may be vertical, horizontal, torsional, or some combination of these. The following terminology is used to describe various forms of ocular misalignment: