To explore the ultrastructural alteration of extraocular muscle proprioceptor in congenital idiopathic nystagmus (CIN).

Case-control study. Ten extraocular muscle samples were collected from five CIN children who underwent nystagmus surgeries in Beijing Children's Hospital from March 2015 to March 2016. Another ten extraocular muscle specimens were collected from five strabismus children in surgery at the same period as normal contrast. There were 3 male patients and 2 female patients of CIN with age of 61—147 months (median age: 91 months). The ultrastructure of extraocular muscle proprioceptors was compared between these two groups by transmission electron microscope.

Twenty-three proprioceptors were found in extraocular muscle specimens of CIN children, whereas thirty-three proprioceptors were detected in strabismus children. The ultrastructure of extraocular muscle proprioceptor of CIN altered greatly comparing with that of the control. Fourteen extraocular muscle proprioceptors of CIN were discovered much smaller and vacuolated not only at inner capsules but also at the space between inner and outer capsules with lipofuscins and myeloid bodies in the intrafusal muscle fibers. Sensory nerve fibers degenerated greatly with a lot of lipofuscins and myeloid bodies in these sensory nerve fibers. Demyelination also appeared in some severe cases. Nine extraocular muscle proprioceptors of CIN showed significant dissolving degeneration of myofibrils and proliferation of collagen fibrils. The normal structures could not be distinguished in these proprioceptors. And these structural disorders also appeared in extrafusal muscle fibers and nerve endings.

The ultrastructure of extraocular muscle proprioceptor in CIN turned much smaller and had significantly structural disorder.(Chin J Ophthalmol, 2017, 53: 136-139)

Nystagmus, congenital; Oculomotor muscles; Proprioception; Child