On the etiology and treatment of convergent squint.

  • Simeon Snell
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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    The absence of diplopia in concomitant squint is made a subject for comment. It appears that it may be undoubtedly present at the outset, and be unobserved or uncotnmented on by the little patients. But a marked difference exists between the gradual onset of concomitant squint and that from paralysis. Schweigger thinks that the habit of binocular vision may not have been learnt or forgotten ; and asks why should tnose who squint from their earliest childhood not see well with both eyes, but yet with each separately, just as is the case with animals with laterally placed eyes ? But then in children, as soon as they at all commence to observe, both eyes move regularly, and appear directed to the same object ; and thus it would seem that fixation does not need much acquiring. He has asserted that diplopia can often be produced by a vertical prism and a red glass before one eye, and this he considers con- clusive evidence against the suppression theory. We are familiar with the fact that in ocular muscular palsy the most distressing diplopia results when the deviation is not great, and the false image is perceived at no great distance from the macula. Images formed more at the periphery are less troublesome, and especially after a time are less regarded by the patient. It is not, I think, difficult to understand in a case of squint, in which it is presumed that imperfect images formed on the less sensitive periphery of the retina and suppressed, should be rendered evident indiplopiaby theimages being brought nearer the more sensitive macula. If the false image were not suppressed, it seems almost evident that, in alternating squint, diplopia would be more common than it is at present. Schweigger, it may be observed, allows the suppression of images, but denies that it ever passes the bounds of incapacity for use ; and he draws a distinction between incapacity for use in these cases and defective vision, the former being due merely to weakness of accommodation ; but I should fancy that very few of those who have written on squint amblyopia have in any way placed such cases in that category. Dr. Mules (Journal, 1886, vol. i, p. 836), representing Schweigger's views, says: Visual acuity, in its relation to squint, is as follows: Equal visual acuity in the two eyes is represented by persistent alternating strabismus. Slight monocular amblyopia causes at first alternating strabismus, but finally determines the amblyopia as the fixed squinting eye. High monocular amblyopia determines the fixed eye from the commencement. Now it is only in the permanent squint that amblyopia is very com- monly met with, while asquint is periodic or alternating, visual acute- ness in the two eyes is equal. This can be verified, and in going over my cases I am satisfied that it is so. If Dr. Mules' way of expiess- ing it were correct, we should certainly find more during the periodic ami alternating stages who were amblyopic. For it seems to me lor a squint to become immediately fixed is very unusual. Dr. Mules' statement is precise and ingenious, but is rather in advance of our present experiences. It appears, also, that it is desirable to have some more exact definition of what is meant by slight and high monocular amblyopia. From my cases it seems that the majority vary in visual acuity, after correction, from £ to 2Vi tne greater number being nearer the former. The question as to why some hypermetropes only are cross-eyed is a very interesting one. It has already been touched upon in referring to amblyopia. Landolt thinks that with the majority of those who tquiut there exists a predisposition to strabismus, with whose exact nature we are not yet entirely acquainted. He, moreover, as others have done, lays stress on one eye being inferior, from higher degree of bypernietiopia, strong astigmatism, etc., in fact, any cause which diminishes visual acuteness, as giving rise to strabismus. He considers this plausible, and that it is otten confirmed by clinical experience.