Quiz: Nyctalopia in 8-Year-Old Twin Boys

An optometrist has referred two 8-year-old twin boys, initially seen after they failed a vision screening at school. The children were having difficulty seeing small letters on the blackboard and had reduced night vision (nyctalopia). One of the twins had a history of frequent falls and collisions with objects. Otherwise, growth and development were typical for their age and they were healthy. Family history revealed that their maternal uncle had “retinitis pigmentosa” diagnosed in childhood, and their maternal great–grandfather experienced nyctalopia and vision loss in his early years. There is no parental consanguinity and the families do not have any common ancestry. Examination revealed similar and symmetrical findings in both siblings’ retinas.