Overview
Strabismus is misalignment of the eyes, either medially (esotropia) or laterally (exotropia).
Strabismus is often quite subtle and difficult to detect; slight angulation of the head to either side may be a sign of compensation for a subtle strabismus.
Causes of Strabismus
- Structural - intraocular or orbital mass
- Ocular muscle weakness
- Trauma
- Neurological - oculomotor (III), trochlear (IV), abducens (VI) or upper motor neuron lesion
- Fatigue / stress
Cover Test
The cover test is a useful test for determining the presence of a tropia (constant, or manifest strabismus).
In strabismus, there is a normal eye that tends to fixate on objects, an an affected eye that is deviated slightly outward, inward, upward or downward.
How to Perform
- Ask the patient to look at an object such as the wall in front of them. Cover one eye using a hand or an opaque cover for a few seconds, and look for movement of the non-covered eye.
Interpretation
- Non-covered eye does not move - means that no strabismus is present, or the non-covered eye is the normal eye
- Non-covered eye moves inward - suggests an exotropia of the non-covered eye (i.e. that it is angulated outward)
- Non-covered eye moves outward - suggests an esotropia of the non-covered eye (i.e. that it is angulated inward)
Uncover Test
The uncover test is a useful test for determining the presence of a phoria (intermittent, or latent strabismus).
How to Perform
- Ask the patient to look at an object such as the wall in front of them. Cover one eye using a hand or an opaque cover for a few seconds, and then remove it quickly. Look for movement in the now uncovered eye.
Interpretation
- The uncovered eye moves inward - suggests an exophoria (i.e. the covered eye transiently moves outward when covered then corrects inward on uncovering)
- The uncovered eye moves outward - suggests an esophoria (i.e. the covered eye transiently moves inward when covered then corrects outward on uncovering)
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