Strabismus

Strabismus, or SQUINT, is the condition in which the visual axes of the two eyes are not both directed to the same point when an object is fixed by the patient. The squint may be convergent or divergent. In the former case, the eye whose visual axis is not directed towards the object is deflected towards the nose; in the latter case it is, on the other hand. deflected outwards. The most common form of squint is the convergent squint which is met with in association with hypermetropia. In this form of strabismus there is no paralysis of any muscle, and it is often the case that either eye is indifferently used by the patient for fixing an object, the squint in that case being termed "alternating" or "concomitant." In most instances, however, after a while the patient acquires the habit of always fixing objects with one eye; the squint is then said to be "fixed" in the other eye. The power of seeing objects with this latter becomes increasingly impaired, and, if the squint remains unrelieved, the eye in which the squint is "fixed" ultimately becomes a blind eye. The cause of the association between hypermetropia and convergent strabismus has already been dealt with. [EYE, ERRORS OF REFRACTION.] Divergent squint is often associated with short sight, and unlike convergent squint there is commonly a serious impairment of the power of vision from the outset; indeed, the eye whose visual axis becomes deflected outwards is an eye, as a rule, which the subject of the squint never uses in fixing objects by reason of its defective vision. Paralytic squint may be met with altogether apart from refraction, as a result of brain disease involving the nerve structures which are concerned with movements of the ocular muscles.

In paralytic squint "diplopia" or double vision is usually present, the images of any object to the patient directs his gaze falling upon the retinae of the two eyes which do not correspond. This diplopia is often very distressing to the patient. It might have been anticipated that double vision would have also been present in the ordinal concomitant squint, but this is not the case as a rule, the subjects of this latter form of squint being rarely troubled with diplopia - a fact which is otherwise expressed by saying they are able to suppress the visual image transmitted from the squinting eye. The operation for squint consists in dividing the tendon of one of the ocular muscles thus, in the case of concomitant squint, the tendon of the internal rectus of one or both eyes is divided with a view to placing the muscle at a disadvantage as compared with the opposing muscles and so obviating its exaggerated action. In some instances in addition to putting back the attachment of the muscle which is too active, it is necessary to advance the attachment of the opposing muscle. The importance of dealing with the common convergent strabismus of children in its early stages cannot be insisted upon too strongly. Indeed, in some instances the use of appropriate glasses from the time of appearance of the squint is effectual in remedying the condition without making it needful to resort to operation at all.