n. a tendency to squint. Normally both the eyes work together and look at the same point simultaneously, but if one eye is covered it will move out of alignment with the object the other eye is still viewing. When the cover is removed the eye immediately returns to its normal position. Most people have a small degree of heterophoria in which the covered eye turns outwards, away from the nose (exophoria; compare esophoria). Heterophoria may produce eyestrain because of the unconscious effort required to keep the two eyes aligned. See also strabismus.
n. the condition of complete balance between the alignment of the two eyes, such that perfect alignment is maintained even when one eye is covered. This theoretically normal state is in fact rarely seen, since in most people there is a minimal tendency for the eyes to deviate (see heterophoria).... orthophoria
(heterotropia) n. squint: abnormal alignment of the two eyes. The strabismus is most commonly horizontal – convergent strabismus (or esotropia) or divergent strabismus (exotropia) – but it may be vertical (hypertropia, in which the eye looks upwards, or hypotropia, in which it looks downwards). In rare cases both eyes look towards the same point but one is twisted clockwise or anticlockwise in relation to the other (cyclotropia). Usually strabismus is concomitant, i.e. the abnormal alignment of the two eyes remains fairly constant, in whatever direction the person is looking. Strabismus acquired by injury or disease is usually incomitant, i.e. the degree of misalignment varies in different directions of gaze. See also cover test; deviation; divergence; heterophoria.... strabismus
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