theories of strabismus
strabismus, theories of
Many theories have been presented to explain strabismus. They tend to fall into five categories: (1) Theories in which the cause of strabismus is a defect of motor fusion. This view was first developed by Worth who suggested a congenital absence or defect of the fusion faculty. Chavasse did not confine his view to a congenitally defective fusion mechanism, but held that strabismus could be the result of interference with the development of the binocular reflexes. Similarly, Keiner and Zeeman proposed that the causative factor in strabismus was a disturbance of the optomotor reflexes (or psycho-optical reflexes). Keiner believed that this disturbance was due to a delay in the process of myelination of nerve fibres in the visual pathway during the plastic stage of development. (2) Other theories have postulated that strabismus is due to mechanical factors such as anomalies of the ligaments, the muscles (or their insertions), and even of the orbit. Proponents of these theories were Scobee, Nordlow, von Graefe, Landolt, Stilling, etc. (3) The role of accommodation and refraction has also been proposed as a cause of strabismus, especially by Donders. He postulated that esotropia was due to uncorrected hypermetropia, and exotropia to uncorrected myopia. This is the best-substantiated theory of the cause of certain types of strabismus (e.g. accommodative strabismus-refractive type). (4) Other authors suggested that strabismus was due to an anomaly in the brain and nerves (Mackenzie) and particularly to the innervation in the vergence systems (Duane, Parinaud, etc.). (5) Theories in which all the factors cited above contribute in varying degrees to the cause of strabismus (Bielschowsky, van der Hoeve, etc.).