Chapter 9: Risks, Benefits, Limitations and Alternatives to Surgery
A Patient & Parent Guide to Strabismus Surgery
George R. Beauchamp, M.D.
Risks of Strabismus (Eye Muscle) Surgery:
The most common risk to strabismus surgery is partial or complete failure to correct the condition and/or its effects, including associated symptoms such as double vision. In general, the more complicated the strabismus and its associated conditions, the more difficult it is to completely control the deviation and its effects. Because the visual system is complex, involving much of the brain, repositioning the extraocular muscles cannot be expected to resolve all problems associated with strabismus. In particular, the potential for binocular teaming of the eyes is known to have a significant effect; that is, if binocular vision can be achieved or recaptured, the likelihood of additional surgery diminishes. Decisions as to what and how much to do are based on experience—that experience is on a large number of patients, the effects and benefits of which cannot be known looking forward. How a given patient will respond to the experience of those before is unknowable; and there is a statistical bell shaped curve of effects for the population. In essence, therefore, some patients will be overcorrected, and some under corrected. The net effect is that additional surgery is required in a significant number of cases; the likelihood of more than one surgery, depending on a number of factors, can range from as low as 10% to 50% or more, with an average of between 20 and 25 percent. Most other complications, including anesthetic problems, infection and potential loss of vision are very rare. Working together, the patient, family, doctors and nurses can, and will take steps to assure that these potential complications are minimized. For example, post-operative antibiotics taken by mouth are often used to prevent infection, and careful attention to preoperative instructions, meticulous operating room procedures and prompt notification of any problems will be likely to prevent adverse consequences to these rare events.
Benefits of Strabismus (Eye Muscle) Surgery:
The benefits of surgery are aligned with the goals of surgery, and may vary from person to person. Alignment of the eyes may make amblyopia therapy less intense. Proper alignment may eliminate a range of symptoms such as double vision, eye strain or fatigue, and restore the normal relationships between the eyes themselves and other facial structures. Only the patient and his family, with the advice of their doctor can determine if these benefits warrant undergoing strabismus surgery.
Limitations of Strabismus (Eye Muscle) Surgery:
Because of the complexity of the system, strabismus surgery may solve only a portion of a complex problem. Some forms of strabismus respond better than others. And some problems are not amenable to surgery. Your doctor will be able to explain the application of these generalities to your condition.
Alternatives of Strabismus (Eye Muscle) Surgery:
Non-surgical options in the treatment of strabismus include patching (occlusion) prisms, botulinum toxin injection, monocular occlusion or fogging, and in some cases eye exercises.
Occlusion of one eye (or patching) may be useful in selected circumstances. Its principal use is in the treatment of amblyopia, or decreased vision associated with strabismus or other conditions. It is also somewhat useful in children with intermittent outward deviation of the eyes in infancy (typically under two years of age), called intermittent exotropia.
The use of prisms in adult strabismus is commonly applied. Indications for use are broad and flexible based on the individual patient’s circumstances. Small angle strabismus with diplopia is the most common condition where prisms are effective. For example, a patient with a vertical deviation of five to six diopters (the unit of measurement of angles of deviation; one diopter equals about ½ degree of angle), which is comitant (meaning the same in all directions of gaze), would certainly be a candidate for prisms. Prisms may be useful in those patients that show an early over correction following strabismus surgery, and may be effective in helping to maintain good binocularity. Prisms have also been used in helping the surgeon decide how much surgery to do. The Prism Adaptation Trial showed some effectiveness in the preoperative evaluation in esotropia. Those patients who responded to the prism (binocularly) and whose angle increased showed a greater surgical success. However, it should be mentioned that prisms are not without disadvantages. Primarily, prisms are limited by the fact that it is impractical to correct large deviations due to the thickness and weight of the prism. In addition, those patients whose deviation is incomitant or changes from one gaze position to another may continue to manifest diplopia. In addition, patients who normally do not wear glasses may find difficulty in adjusting to glasses with prisms. When using prisms, there are two options. Ground in (to eye glass lenses) prisms are useful when the patient will be wearing the prisms for an extended period of time. Fresnel or stickon prisms are useful when the prisms will be temporary, although many note degradation in visual acuity with and the unusual appearance of Fresnel prisms.
Botulinum toxin has gained significant popular appeal particularly with its cosmetic indications such as removing unwanted wrinkles. Interestingly, botulinum toxin’s role in medical therapy was discovered by a strabismus surgeon 25 years ago in California. Botulinum toxin is one of the most deadly toxins known to man. However, in microscopic quantities it is effective in temporarily weakening specific muscles for six to twelve weeks. The potential advantages of this option, most commonly used in adults, are: 1) it can be injected in the office without requiring general anesthesia; 2) it can be employed as a temporary treatment, e.g., in patients with acute cranial nerve palsies, and this option may be highly effective in the short term while the surgeon waits to see if the palsy will resolve; and 3) this may be an effective treatment in patients who show early over corrections following strabismus surgery. The chief disadvantage of botulinum toxin is that its effect maybe variable and unpredictable. In addition, it is not useful as a permanent form of treatment as its effect wears off after one to two months. In addition, risks include ptosis which maybe very troubling for the patient.
In patients who manifest intractable diplopia or who are poor surgical candidates occlusion or fogging may be an alternative treatment to avoid diplopia. In some patients who suffer mid-brain injury or disease, motor fusion may be permanently impaired. These individuals may never be able to fuse normally. Patching one eye or fogging one lens with a filter may be the only treatment that relieves them of their diplopic symptoms.
The use of eye exercises in strabismus is only occasionally beneficial in the long term. The best example of their potential usefulness is convergence exercises in persons with convergence insufficiency—a form of exodeviation where there is a tendency of the eyes to drift outwardly apart for near visual tasks. However, exercises may be useful: 1) for selected individuals and mild conditions; 2) when signs and symptoms are mild; 3) when affected persons are motivated, and 4) when expected benefits may be sustained through time.
The Informed Consent Process and Document(s)
Completing the documentation of your informed consent for strabismus surgery is dual—medical information combined with certain legal requirements. You have both legal and moral rights to know what the diagnosis for your condition is, what treatment is being proposed (including surgery), and what are the most likely risks, benefits, limitations and alternatives to the treatment proposed. This booklet, along with your discussions with your doctor, can help with these elements.
The documents that you will be required to sign, consenting to the surgery, are legal documents. They are constructed to fully inform you of the worst thing(s) that could happen, and sometimes the effect is to add to your anxiety about the procedure. While such added anxiety is unfortunate, there is no option to their required use. Please read them with this understanding in mind. Do not consent to the surgery if you have unanswered questions or concerns. Surgery is best deferred until you have the information you need to make an informed decision about your or your child’s care. Examples of informed consent documents for strabismus surgery are found in Appendix C.
Please also see Chapters 15 & 16, which describe what to expect and watch for after surgery. These matters should be considered in the context of the risks and consequences of surgery, as well as understanding what may be of concern.
Read How is Strabismus (Eye Muscle) Surgery Performed?
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