Just like strabismus (or tropia) intermittent (or transient) strabismus is a condition in which the eyes are not properly aligned with each other. However, unlike constant strabismus, the condition is only evident intermittently (not all the time). Sometimes intermittent strabismus is missed in an eye exam if the patient doesn't report symptoms or the eyes are aligned during the visit and the clinician cannot induce the eye turn.
Intermittent strabismus is often traceable to a problem with binocular vision. A patient may have a natural inward or outward eye posture (called a phoria). Occasionally difficulties with the focusing ability of the eye can lead to intermittent strabismus.
Patients with intermittent strabismus have a slight advance over constant strabismus in that they use both eyes at least SOME of the time. However, a patient that suffers from intermittent strabismus has a risk of progressing to constant strabismus and developing compensatory mechanisms such as suppression to alleviate double vision.
Most cases of intermittent strabismus are horizontal - the eye turns out (exo) or in (eso). In many cases, the patient has a somewhat fragile binocular vision system, and additional stressors cause the eye to deviate.
The eye occasionally turns inwards. Many times intermittent esotropia is associated with excessive focusing (called accommodation). Excessive convergence and esophoria may also cause one of the eyes to turn inwards.
The eye occasionally turns outwards. Intermittent exotropia is more common, in fact, more patients have intermittent exotropia than constant exotropia. Inability to maintain convergence and exophoria cause one of the eyes to turn outwards.
Since intermittent strabismus is associated with at least occasional binocularity, vision training is often helpful for patient to improve their ability to keep the eye straight.