On the etiology and treatment of convergent squint.

  • Snell, Simeon, 1851-1909.
Date:
[1887]
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Licence: Public Domain Mark

Credit: On the etiology and treatment of convergent squint. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    There are numerous exceptions, and he admits the fact that strabismus is met with in cases where the eyes are of equal strength. But, ho adds, untilsomebody has proved, by ample statistics, that such cases constitute the majority, we shall hold that the inferiority of a hypermetropic eye may become for it the cause of convergent strabismus. There can be little question tha^ in squint the degree of refraction is often different in the two eyes, and that, as a general rule, the higher degree will be found in the squinting eye. In this way it may often be accepted as conducing to determining which shall be the squinting eye. Another way suggests itself of looking at this subject. It is held now that hypermetropia in many instances becomes loss in degree, and passes on its way towards myopia. In strabismus the full efforts of accommodation will be dirested from the fixing eye, and will be but little exerted in the squinting eye. Does not the hyper- metropia become less in the fixing eye ? The relations of the refrac- tion of each eye in ordinary hypermetropia, and also in squint, might with advantage be statistically worked out, ascertaining the relative condition in each. Ulrich = held that to account for some hypermetropic eyes squinting and others not, something beyond the convergence and accommoda- tion must be found, and he sought for it in the muscles. Schweigger, also, it is well known, has assigned a prominent place in the production of convergent squint to the preponderance of the internal with insufficiency of the external recti. Much has been said of insufficiency of tho internal recti; why not let attention be directed to the condition of the external muscles ? It may, however, be remarked that any marked weakness, though not amounting to paresis of the external recti, would tend greatly to obliterate the distinguishing features between concomitant and paralytic squint, but in the circumstances calling for such an extra use of the convergence as, at all events, Donders taught, a very trifling weakness would suffice to allow of the internal overcoming the external recti. The existence of such a condition seems plausible, and receives support from the little effect division of both internal recti has, in certain cases, towards straightening the eye, the external recti lacking power of abduction. Schneller's3 observations, undertaken to ascertain the normal equilibrium between the two muscles, internal recti and external recti, also lend valuable assistance. He found that in eyes without stra- bismus, the field of action of the internal recti surpassed ordinarily, according to the cases, from 1 to 11 degrees (measured by a perimeter) as much in hypermetropia as in myopia. More rarely the external recti predominated. Normally, the internal recti surpassed the external recti ; more rarely, the external recti, and without the slightest squint. In the cases, so common, of strabismus which disappear with correcting spectacles, the predominance of the internal recti do not exceed the limits laid down. Some of these cases, to see clearly at ordinary vision at 25 to 35 centimetres, found it necessary to employ at least § of accommodation. This is nearly always the case with hypermetropia of 3 5 D. Schneller conceives that it is just a rule that when it is necessary to use as much as f of accommodation, convergent squint will result. In convergent strabismus (muscular), which cannot be corrected by plus glasses, Schneller found that the field of action of the internal recti always surpassed that of the ex- ternal recti beyond the physiological limits before indicated. 2 Klin. M. f. Avgen., October, 1S7S, abstracted in Annates d'Oculistique, vol. ii, 1879, p. 268. 3 Annates d'Oculistiqvc, vol. i, 1SS3, p. 15G (abstract).