Ushering It In

Question:  A couple brings their infant to you after he failed his newborn hearing screen.  You obtain a sedated auditory brainstem response test that demonstrates severe to profound bilateral sensorineural hearing loss.  Genetic testing reveals a mutation consistent with type I Usher syndrome.  You explain to the child's parents that vision impairment occurs with this syndrome and refer them to an ophthalmologist.  What is the etiology of vision loss in this syndrome?  [Answer will be posted with next week's new question]

Answer to last week's question, "Salivary Salvation" (August 5, 2016):