A 2-year-old boy has bilateral ptosis, both eyes fixed in a downward position below the horizontal, and an inability to elevate either eye above the midline, forcing him to hold his chin elevated. Forced duction testing is positive. His father has identical findings. The fundamental defect underlying congenital fibrosis of the extraocular muscles type 1 is:
- A Primary myopathic degeneration of all six extraocular muscles
- B Aplasia of the abducens nuclei bilaterally
- C Aberrant innervation of the superior rectus and levator palpebrae by the oculomotor nerve ✓
- D Orbital fibrosis secondary to intrauterine inflammation
Explanation
CFEOM type 1 is an autosomal dominant developmental disorder of cranial motor neuron axon guidance in which oculomotor neurons misroute and innervate the superior rectus and levator palpebrae abnormally. The muscles become fibrotic and restrictive, producing bilateral ptosis, infraducted globes, inability to elevate above the midline, a compensatory chin-up posture, and positive forced ductions. Abducens nuclear aplasia causes horizontal gaze failure as in Duane or Mobius syndromes, not isolated vertical restriction, and the disorder is neurogenic rather than a primary myopathy.
Reference: American Academy of Ophthalmology BCSC Section 6: Pediatric Ophthalmology and Strabismus, 2022-2023 ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.