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What Is Myogenic Strabismus?

Myogenic strabismus is eye misalignment caused by primary disease of one or more extraocular muscles. The muscle itself is weak, stiff, or fibrotic, so the eye cannot move normally even though the nerve supply is intact. Examples include congenital fibrosis syndromes, chronic progressive external ophthalmoplegia, and some muscular dystrophies. Deviation size often changes less with gaze than in purely neurogenic palsies. Recognizing a myogenic pattern guides systemic workup and surgical planning.

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What Is Myogenic Strabismus?

Myogenic strabismus is eye misalignment caused by primary disease of one or more extraocular muscles. The muscle itself is weak, stiff, or fibrotic, so the eye cannot move normally even though the nerve supply is intact. Examples include congenital fibrosis syndromes, chronic progressive external ophthalmoplegia, and some muscular dystrophies. Deviation size often changes less with gaze than in purely neurogenic palsies. Recognizing a myogenic pattern guides systemic workup and surgical planning.

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Causes and Associated Conditions

Congenital myogenic strabismus can arise from maldeveloped or fibrotic muscles present at birth. Acquired forms appear in mitochondrial disease, chronic progressive external ophthalmoplegia, and muscular dystrophies. Long standing thyroid eye disease eventually can lead to marked muscle fibrosis, which behaves in a myogenic way. Inflammatory myopathies and trauma also injure muscle fibers and limit movement. Systemic history, including exercise intolerance or ptosis, gives clues to a broader myopathy.

Clinical Features and Examination

Patients present with ocular misalignment, abnormal head posture, and sometimes diplopia. On examination, there is mechanical restriction in the field of action of the affected muscle, with reduced excursion on versions. Forced duction testing can show resistance to passive movement when fibrosis is present. Saccades may have normal speed in directions where the nerve input is intact but movement is blocked by the muscle. Lid retraction, ptosis, and other motility signs are recorded to build the pattern.

Diagnosis and Imaging

Diagnosis combines motility testing with systemic and imaging data. The clinician measures deviations in different gaze positions and compares findings with patterns expected from nerve palsies. Orbital imaging with MRI or CT can show enlarged, fibrotic, or atrophic muscles. Blood tests, electromyography, and genetic studies are considered when a generalized myopathy is suspected. Distinguishing myogenic from neurogenic strabismus helps set realistic expectations for surgery.

Treatment and Long-Term Management

Treatment aims to improve alignment and comfort while also addressing the underlying muscle disease. Prism glasses can help with small residual deviations and double vision. Strabismus surgery often involves recessing tight muscles or resecting weak ones, tailored to the restriction pattern. In progressive systemic myopathies, alignment can shift over time and repeat surgery can be needed. Regular follow up tracks ocular motility, fusion, and systemic status.

FAQs About Myogenic Strabismus

How is myogenic strabismus different from a nerve palsy?

In myogenic strabismus, the muscle is the main problem, while in a palsy the nerve signal is weak or absent. Patterns of restriction and imaging help separate the two.

Can myogenic strabismus be cured with surgery?

Surgery often improves alignment and head posture, but underlying muscle disease can limit perfect correction and can change over time.

Do all patients with myogenic strabismus have a systemic muscle disease?

Some have isolated ocular involvement, but others have broader myopathy. History and testing help identify those with systemic conditions.

Will prism glasses fix myogenic strabismus completely?

Prisms can ease double vision in certain gaze positions but do not change the muscle problem. They are one part of an overall management plan.

References

NCBI Bookshelf. ?Strabismus.? https://www.ncbi.nlm.nih.gov/books/NBK560782/

EyeWiki. ?Strabismus in Thyroid Eye Disease.? https://eyewiki.org/Strabismus_in_Thyroid_Eye_Disease

NCBI Bookshelf. ?Thyroid Eye Disease.? https://www.ncbi.nlm.nih.gov/books/NBK582134/

EyeWiki. ?Congenital Fibrosis of the Extraocular Muscles (CFEOM).? https://eyewiki.org/Congenital_Fibrosis_of_the_Extraocular_Muscles_%28CFEOM%29

EyeWiki. ?Chronic Progressive External Ophthalmoplegia (CPEO).? https://eyewiki.org/Chronic_Progressive_External_Ophthalmoplegia_%28CPEO%29