This article includes discussion of lazy eye, esotropia, exotropia, nonparalytic horizontal strabismus, acquired esotropia, esodeviations, and exodeviations. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
The author reviews the different forms of nonparalytic horizontal strabismus. This article presents the various types of in-turning (esotropia) and out-turning (exotropia) strabismus, explaining why certain patients will be prescribed glasses for correction of their deviation whereas other patients with a similar-appearing deviation will be offered surgery. The multiple references give a balanced view of contentious issues such as when to offer surgery for infantile esotropia and underline that for some types of strabismus like intermittent exotropia there is no clear-cut ideal form of treatment. An extensive list of references supporting why adults benefit from strabismus correction is included.
Historical note and terminology
In primitive folklore and mythology, strabismus was considered an affliction sent by a malignant spirit or evil god. The bad luck brought from the look of cross-eyed person forms the basis for the legends based on “the evil eye." Maya, the Egyptian goddess, squinted; and the statue of King Djoser (2600 BC), for whom the first pyramid was erected, depicts him as having a large internal ocular deviation. Hippocrates first differentiated between paralytic and nonparalytic type of squint and correctly stressed the hereditary aspect of the latter.
Ocular deviations are described as a phoria or a tropia. A phoria is a misalignment of the visual axis kept in check by fusion. Fusion is an innate drive to keep each fovea directed to the object of regard, thus, allowing stereopsis and single binocular vision. A tropia is a manifest misalignment of the visual axis not controlled by fusion. The visual axis of an eye joins the fovea with the object of regard and passes through the nodal point of the eye.
Nonparalytic strabismus can best be considered under several large, sometimes overlapping categories.
• Esotropia, or internal strabismus (eyes crossed inward toward the nose), may be infantile (congenital) or acquired, which may be accommodative, partly accommodative, or nonaccommodative.
• Exotropia, or out-turning strabismus, may be infantile (congenital) or acquired. The latter is subdivided into intermittent, constant, or consecutive.
Vertical deviations are termed "hypertropias." The measurement of an ocular misalignment is of paramount importance, not only to assess the necessity for active intervention to correct strabismus, but also to follow the deterioration of a squint or the success of treatment.
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