Hereditary CFEOM is a congenital, nonprogressive condition. The eyes are usually fixed in the infraducted position about 20-30 degrees below the primary position. Horizontal movement is absent or severely restricted. Blepharoptosis is almost always present and patients exhibit a marked chin-up position of gaze. Binocularity is usually absent. Some patients have large amounts of astigmatism. Amblyopia has been reported to occur on a refractive or strabismic basis. However, careful examination of the optic nerve may reveal anomalies such as increased cupping, asymmetric cupping and hypoplasia and could be responsible for the reduced vision in some patients.
Neuropathologic studies in rare patients have shown defects in brainstem neural development including in one case absence of the superior division of the oculomotor nerve. Fibrosis of extraocular muscles and Tenon's capsule as well as adhesions to the globe and between muscles have been described. Anomalous insertions of EOMs may also occur. An MRI can reveal atrophy of the levator palpebrae and the superior rectus muscles as well as absence or hypoplasia of the oculomotor and sometimes abducens nerves. It is now considered that CFEOM disorders result from primary neuronal disease resulting in secondary myopathy.