The etiology of strabismus is a still much-mooted question, and each ophthalmic surgeon follows out a routine of treatment with his cases according to the theory which seems to him most rational. As the title indicates, defective development of the fusion center will be considered the essential etiologic factor in this paper, according to Worth's1 theory.
De Schweinitz's2 new book gives the following factors as causative:
1. Disturbance of the relation between accommodation and convergence by errors of refraction.
2. Disparity in the length, thickness and tension of opposing muscles.
3. Inequality in the vision of the two eyes or amblyopia of one eye, which removes the natural stimulus of diplopia to exact convergence.
4. Disturbances of innervation and defective development of the fusion faculty.
Savage3 says, under the etiology of comitant esotropia : "The conditions causing the error exist from birth, and only one out of several natural causes undergoes any change