Isolated absence of the optic chiasm: a rare cause of congenital nystagmus.

The cases presented are rare examples of congenital nystagmus associated with isolated absence of the optic chiasm. MR imaging in both patients demonstrated unremarkable anterior optic pathways and optic tracts. No additional midline central nervous system abnormalities, migrational anomalies, space-occupying lesions, or destructive processes were noted. These cases demonstrate that the achiasmatic syndrome should be included in the differential diagnosis of congenital nystagmus and may be overlooked without careful MR imaging evaluation.