Congenital cranial dysinnervation disorders (CCDD) are a heterogeneous group of disorders affecting the development and function of the extraocular muscles due to failure of normal innervation of the target muscle. The surgical management of these disorders can be complex requiring combinations of supramaximal recessions, muscle transpositions, and botulinum toxin (BT). We report an unusual case of large-angle exotropia due to absent medial recti, the subsequent surgical management, and outcome.

Agenesis or hypoplasia of individual or combinations of extraocular muscles has been reported since the eighteenth century.1 The extraocular muscles derive from superior and three inferior complexes of orbital mesodermal tissue. The ocular motor nerves originate from mesencephalic and rhombencephalic structures and migrate to their target muscles. Cranial nerve motoneuron aplasia or failed extraocular muscle innervation may cause aberrant ocular motor patterns, ptosis, and secondary structural muscular abnormalities. The aetiology is frequently genetic.2 These non-progressive developmental disorders are known as CCDD, and among them are Duane retraction syndrome, congenital fibrosis of extraocular muscles, and Möbius syndrome.2, 3 There are numerous associated non-ocular defects, and clinical heterogeneity is common. MRI may show affected muscles and cranial nerves to be normal, hypoplastic, or absent.4 We believe this case to be part of the CCDD spectrum. Ideally, in this case, the MRI should have shown more detail. We would advocate high-resolution MRI before surgery for large-angle congenital exotropia with adduction deficits to facilitate diagnosis and surgical plan.

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