Why is Strabismus Surgery Performed?
General Comments About Strabismus Treatment
Many forms of strabismus can be managed with non-surgical treatment, including eyeglasses, prisms in eyeglasses, patching, and in certain circumstances, exercises. In general, each of these approaches has limitations. Eyeglasses may completely control strabismus, as in accommodative esotropia. In other cases, eye glasses may have no effect at all. Prisms are useful for relatively small, stable angles of deviation (strabismus); yet they may need to be made progressively stronger, are expensive, and there are practical limits to the power that may be applied (strong prisms turn light into rainbows!). In children, patching of a dominant eye to improve vision will sometimes, in conjunction with other treatment such as eyeglasses, facilitate improved eye alignment. In certain forms of early childhood strabismus, patching will improve alignment, although sometimes only for a period of time. Exercises may completely control some forms of strabismus and have no effect on others. Your doctor will try all appropriate non-surgical methods of treatment prior to recommending surgery. And many mild forms of strabismus—those with no or very mild symptoms—may require no treatment at all. Overall, only about 25% of strabismus warrants surgery.
Some forms of strabismus require surgery, and non-surgical methods may only temporize and delay a recommendation for surgery. In other cases, non-surgical means may work for a period of time (even for several years), and then cease to be effective. Generally, deviations of a significant degree (usually 5 degrees of deviation or more, with or without symptomes) and smaller deviations (where symptoms cannot be controlled otherwise) are appropriate to consider surgery. Of course, all factors that are appropriate to a given individual’s needs should be considered in the context of the patient’s desires and best interests. A decision to proceed with surgery should make sense to all parties to the decision!
Indications for Surgery
Surgery is recommended when strabismus and its effects are “clinically significant”, meaning the angle of deviation is large enough, the condition is amenable, and the adaptations or consequences significant enough to promise improvements in alignment and function. These potential benefits are correlated to the particulars of a given person’s circumstances, be they a child or adult.
A person’s visual system develops and functions in a complex interplay between and among the vision in each eye, alignment of the eyes, the field of vision, fusion of the images from each eye, plus the affected person’s experience and perception of strabismus and its consequences. Early visual development occurs rapidly, and when strabismus occurs, adaptations—including decreased vision (amblyopia) and loss of binocular function (stereopsis or depth perception)—occur equally swiftly. The keys to successful treatment are: prevention if possible, early detection and prompt treatment.
In some individuals, strabismus can be overcome with a compensatory head posture, such as tilting or turning the head. In some of these cases, there may be long-term adverse consequences in the bones and muscles of the head and neck (please see following sections and appendix for examples of when surgery may be appropriate to align the head position).
In adults, the conditions either are “held over” from childhood strabismus, or acquired later in life, generally spoken of as onset “after visual maturation” (generally after nine years of age). In either children or adults, the benefits of strabismus treatment may be multiple, depending on the type, severity and individual effects of the condition. Treatment is therefore promptly directed to:
- Improve Vision—The earliest adaptation to strabismus in a child is often the development of amblyopia, or decreased vision secondary to suppression of the image from the misaligned eye. Glasses and patching are often required to treat amblyopia. Elimination of the misalignment (strabismus) often will make the task of visual rehabilitation easier. Amblyopia does not occur in adults.
- Align the Eyes—Good alignment facilitates both good vision and binocular vision. As above, eyes that are out of alignment present a significant risk to the vision of young children and their developing sight. Moreover, misalignment precludes the development or maintenance of good binocular vision, including stereovision; persistent misalignment, for as short as three continuous months, may also cause adults to lose (irretrievably) their stereopsis (three dimensional vision). Establishing or reestablishing good alignment can improve binocular visual outcomes; in certain circumstances (not always predictable) binocular vision is completely normalized.
- Align the Head—Abnormal or compensatory head positions may occur with certain strabismus syndromes (for example, Duane’s syndrome, IV cranial nerve palsy, thyroid eye disease) or nystagmus. The long-term consequences may be orthopedic (arthritis, etc.), appearance (asymmetry of the face), social challenges (e.g., teasing), or practical (e.g., wearing glasses effectively). Such problems may be avoided by straightening the head—by moving the eye muscles—and in some instances of nystagmus, vision may be slightly improved.
- Improve Binocular Vision—Binocular vision refers to simultaneous teaming of the eyes and includes the functions of stereovision and depth perception. These functions occur in the brain; having good alignment is necessary (although not necessarily sufficient) for improving the quality of binocular vision. In general, the younger the child, both the risk and the opportunity for binocularity are increased.
- Eliminate Diplopia When Present—Diplopia, or double vision, occurs when eyes have previously been aligned and good binocular function obtained. When the eyes become subsequently misaligned, double vision occurs. This is relatively uncommon in very young children, but may be present in older children. It is common in acquired strabismus in adults.
- Improve the Field of Vision—Crossed eyes, technically called esotropia, will diminish the total field of vision by decreasing side or temporal vision in amounts that are directly related to the degree or amount of crossing of the eyes. Elimination of the misalignment will therefore increase the field of vision for these persons (and will decrease in exotropia).
- Improve Self Image—Persons with misaligned eyes of almost any age above three to four years will develop a sense of difference related to the significance of their strabismus. This awareness will often affect a child’s self-concept (image) and confidence, and may be reflected in shyness or withdrawal.
- Improve Social Interaction—Strabismus may affect the ways in which a family, friends and others will interact with a child, and thereby affect all of their relationships. Older children and adults may experience difficulty in communication related to difficulties in maintaining eye contact. Others may be distracted and behave differently towards persons with strabismus, and this may be hurtful to them.
- Improve Employment Opportunities—Children with strabismus may experience, perhaps in part related to the above, some perceived and actual limits to career options and advancement. Strabismus is a disqualifier for certain occupations. Other persons will occasionally and quite inappropriately question the intellectual capacity of those with strabismus.
Strabismus at any age has multiple and complex effects. The sooner strabismus and its associated problems are identified, the longer and more profoundly the benefits may be enjoyed!
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