It is a defect of the parallelism of eyes. Appeared to the birth or later. Both eyes do not look in the same direction. There is a deviation. * A deviation inside: cross-eye   * A deviation outside: exotropia. * A deviation in height: vertical strabismus   It entails the loss of the vision of the diverted eye; instead of seeing with its two eyes, what we call the binocular vision, the cross-eyed perceives only the image of the not diverted eye, says dominant eye. In the majority of the cases muscles are not paralyzed. They are hypoactive at the most, what is in question it is the nervous system which activates them in a synchronous way. Mostly the strabismuses are accompanied by a farsightedness(hypermetropia): it is the hurt to see so by far that closely, where from tendency to the permanent accommodation. To farsighted not cross-eyed this accommodation is made in well-balanced proportions, between the accommodation and the convergence towards the looked object.   To the cross-eyed the convergence is excessive with regard to the accommodation, where from deviation of an eye. There is a dysfunction.   What can we make?   Not being able to act on the nervous power plant which governs the synchronous movements of eyes, we act on muscles by the surgery, on accommodation by correcting the farsightedness(hypermetropia) by glasses or lenses. Knowing that any accommodation entails a convergence of eyes, the more the correction of the farsightedness(hypermetropia) is complete, the more the deviation of eyes is reduced.   In the optical correction of the farsightedness(hypermetropia), we often resort to sectors, to atropine, and orthoptic reeducation. The surgery turns out necessary at once when the cross-eyed deviation is important, or in front of a residual angle after all therapeutic optical and orthoptic.