Divergent, non-paralytic squint is less common than esotropia, particularly in infancy and childhood, and increases with age. Amblyopia is rare.
Typically, there is an exophoria which progresses to an intermittent exotropia and finally, to a constant exotropia. In other patients, the divergence starts as an intermittent or constant exotropia and remains stationary. Less commonly, exotropia results from uncorrected myopia. Many patients show a hereditary element with both exophoria and exotropia inherited as an autosomal dominant trait.
The condition may be classified on a descriptive basis:
- basic exotropia - distance and near deviation approximately equal
- divergence excess - deviation is more than 15 dioptres greater for distance than near deviation
- convergence insufficiency - near deviation greater than distance deviation