222 Squint and Amblyopia: Their Cause
the correction of the squint is only approximate, and in many cases the condition has been made worse, while a restoration of binocular vision-the power of fusing the two visual images into one-is scarcely even hoped for.1
The muscle theory fitted the facts so badly that when Donders advanced the idea that squint was a condition growing out of refractive errors-hypermetropia being held responsible for the production of convergent and myopia for divergent squint-it was universally accepted. This theory, too, proved unsatisfactory, and now medical opinion is divided between various theories. Hansen-Grut attributed the condition, in the great majority of cases, to a defect, not of the muscles, but of the nerve supply; and this idea has had many supporters. Worth and his disciples lay stress on the lack of a so-called fusion faculty, and have recommended the use of prisms, or other measures, to develop it. Stevens believes that the anomaly results from a wrong shape of the orbit, and as it is impossible to alter this condition, advocates operations for the purpose of neutralizing its influence.
In order to make any of these theories appear consist ent it is necessary to explain away a great many trouble some facts. The uncertain result of operations upon the eye muscles is sufficient to cast suspicion on the theory that the condition is due to any abnormality of the mus cles, and many cases of marked paralysis of one or more muscles have been observed in which there was no squint. Relief of paralysis, moreover, may not relieve the squint, nor the relief of the squint the paralysis. Worth found
™Th? JeSUr!t °btaine.d .by the operation is, as a rule, simply cosmetic, ine sight of the squinting eye is not influenced by the operation, and in t ^ 1 u7 ^stances is even binocular vision restored.-Fuchs: Text-book of Ophthalmology, p. 795.
The result of even the most successful squint operation, in long-standing strabismus, is merely cosmetic in the vast majority of cases.-Eversbuschl The Diseases of Children, edited by Pfaunder and Schlossman. English translation by Shaw and La Fetra, second edition, 1912-1914, vol. vii. p 316