Squinting (Lat. strabismus), a deformity consisting in a want of parallelism between the visual axes of the eyes. Except in cases where it is caused by paralysis, spasmodic or hydrop-ical affections, or irritation of the brain, it is not a disease, and is not accompanied with pain. Ophthalmic surgeons notice three degrees of squinting: 1, where there is but a slight convergence or divergence from the normal axis, such as is ordinarily called a "cast of the eye;" 2, where the inclination is strongly marked, but less than half the cornea is thrown under the eyelid or within the orbit, which is the most frequent variety; 3, where the cornea is nearly or quite thrown under the eyelid or within the orbit, common among those who are born blind, but rare in the case of those who can see. The surgeons also distinguish it according to the departure from the normal axis; as convergent, where the pupil is drawn toward the nose; divergent, where it is drawn toward the outer corner of the eye; ascendent, where it is drawn upward; and descendent, where it is drawn downward. Of these, the convergent form is by far the most frequent, and next in order the divergent and ascendent. The descendent is the rarest of all.
Squinting may also be double or single as one or both eyes are aftected; it may be congenital, i. e., existing from birth, or accidental, occurring from accident or improper treatment of the eye; the former is rare. It may be also continuous, or rarely intermittent. When not due to one of the causes mentioned above, it depends in a large majority of cases on parallel rays of light not focusing on the retina. To correct this the eye turns in, as in so doing the power of accommodation is increased, because the same nerve which supplies the internal rectus also supplies the muscle of accommodation. (See Eye.) - The treatment prior to 1839 consisted in attempting by various methods to strengthen the weaker muscles, bandaging the normal eye, and compelling the constant use of the other; or by the use of goggles, spectacles, etc, in which all except the centre was opaque. In 1838 Stromeyer described the operation of dividing one of the recti muscles, but without having tried it on the living subject. In 1839 Dieffenbach, an eminent surgeon of Berlin, performed it successfully, and was followed by many English and French surgeons.
The operation has now become very common, though the best surgeons admit that there are three classes of cases in which it should not be performed, viz.: those in which the position of the eye is fixed, those which result from the paralysis of the antagonist muscle, and those occurring in infants before dentition. The operation is not difficult nor particularly dangerous, and is generally successful. There are two methods of performing it, the ordinary or that of Dieffenbach, where the conjunctiva is divided and the muscle to be severed is laid bare, and the subconjunctival, where the conjunctiva is divided to a much less extent. The latter is generally preferred.