Definition and classification

By "strabismus" we mean any disorder of the position of the eyes, not looking at the same time the object we want to see.

Normally the visual axes intersect at the fixation point, and if this is too far, then the lines are parallel to each other. In strabismus the axis of one eye is directed towards the object, while the other is deviated in an angle that characterizes the type of strabismus. The terms 'phoria' and 'Tropia' designate correspondingly the latent and permanent derogation axes of vision.

The “phorias” are displayed only when the match is interrupted, i.e when we cover one of the eyes of a child. And with both eyes open the child does not have strabismus. To cover though one eye, while the other is still open and facing the object, the covered eye squints and faces another direction.

 
With “tropias” strabismus is manifest and present even with both eyes open. Depending on the direction that the strabismic eye is looking, we are talking about esophoria or esotropia, or exotropia and exophoria, and vertical heterophoria or heterotropia.

 
The absence of overt derogation of the eyes is called orthotropia and the ideal normal state in which the child does not squint, even if the identification is interrupted, is called orthophoria.

 
Strabismus can be permanent or intermittent, so it appears only in certain times or at a certain distance (long or short).

 
It can be the same eye (left or right) or be alternate and appear one on one eye and one on the other.

If the angle of strabismus remains constant in all gaze positions, then strabismus is called coherent. Non-coherent strabismus (with the angle to varying depending on the eye position) is due to paralysis of one or more of the oculomotor muscles and is called paralytic strabismus.

A specific category of Strabismus is cyclotropia wherein the eye rotates abnormally around the sagittal axis.