Divergence excess is the tendency for one eye to drift outwards intermittently. When the two eyes are struggling to work together as a team, the visual system will often compensate by either (1) the eye muscles working harder to pull the eyes together to maintain single vision causing fatigue or (2) the brain only selectively using one eye to see; the other being ignored relaxes and turns out (either by a small, subtle degree or a much larger, more noticeable degree).
The signs of divergence excess are more noticeable when you are tired or in bright light. It is important to monitor a person with divergence excess closely, to ensure that the non-dominant eye that turns out doesn't come 'lazy'. This is known as amblyopia. It is not actually the eye that has become lazy, but rather the special vision parts of the brain that are becoming lazy.
The brain can only learn to see as the picture given to it by the eyes. If the brain has not been given a constant picture by the eye because of an eye turn then it cannot learn to see properly. If spectacles are worn, or eye exercises are used to help the eyes work together as a team, then amblyopia may be prevented.
If the divergence excess is not improving as a child grows, or if it is affecting a child's ability to learn and interact with their environment, the divergence excess then requires treatment.
Treatment involves special prisms and powers in glasses to realign the eyes and to relax the focusing system. As the eye's alignment is different when looking far away compared to looking up close, often different powers and prisms are needed for different viewing distances. In this instance, a bifocal lens is prescribed. This treatment provides clear, single and comfortable vision with the aim to have the two eyes working together as a team to resolve vision-related symptoms and support the vision-based learning systems.