Management of strabismus

The management of strabismus may include the use of drugs or surgery to correct the strabismus. Strabismus is a misalignment of the eyes and may also result in amblyopia (lazy eye) or impairments of binocular vision.

Agents used include paralytic agents such as botox used on extraocular muscles, topical autonomic nervous system agents to alter the refractive index in the eyes, and agents that act in the central nervous system to correct amblyopia.

Treatment is usually surgical, performed at the insertional ends of extraocular muscles (where they attach to the globe). Resection surgery removes tissue in order to stretch a muscle, increasing its elastic force; recession moves an insertion so as to reduce stretch, and so reduce elastic force; transposition moves an insertion “sideways”, sacrificing one direction of muscle action for another; posterior fixation relocates a muscle’s effective insertion to a mechanically disadvantageous position. All are kinds of compensatory impairment. Pharmacologic injection treatments, in contrast, offer the possibility of directly increasing or decreasing contractile muscle strength and elastic stiffness, as well as changing muscle length, without removing tissue or otherwise compromising orbital mechanics.

Spherical lenses and miotic eye drops can provide relief in some types of horizontal strabismus by biasing the neural link between convergence (orienting the lines of sight for near objects) and accommodation (focusing), and prism lenses can relieve diplopia (double vision) by refracting the visual axis, but these treatments don’t address the underlying muscular imbalance, and are not further considered here.

Pharmacologic injection treatments can be given to cooperative adults under local anesthesia in an outpatient setting, and for some agents, under light general anesthesia. In the former case, it is possible to bring the injection needle to an optimal location in the desired muscle using EMG guidance as the alert patient looks in diagnostic directions, the needle is advanced until the electromyogram (the electrical signal from an activated skeletal muscle) indicates it is optimally positioned, whereupon the injection is completed. Some agents (e.g., botulinum toxin) can be injected at the insertional end of a muscle under visual guidance, using special forceps and allowed to diffuse posteriorly, whereas others (e.g., bupivacaine) must be distributed throughout the body of the muscle, which requires non-visual guidance. EMG guidance generally provides more effective injections, but is only suitable for alert, cooperative adults. Because injection treatment does not result in the scaring that is often a troublesome consequence of conventional strabismus surgery, if therapeutic goals are not achieved with one injection, additional injections or surgical treatments can readily be given.

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Wikipedia