Cyclopia is an extremely rare type of congenital malformation & is part of a spectrum of anomalies occurring in holoprosencephaly.

This group of congenital anomalies occurs due to to abnormal differentiation & cleavage of the prosencephalon. There is anomalous formation of the central cavity of the orbit, with absence of the nasal cavity. A rudimentary bony process is formed over the orbital cavity called proboscis.

True cyclopia is an extreme form, where only a single orbit is present. But two globes may be found in different degrees of fusion, called synopthalmos.

Associated mid line facial deformities like midfacial clefts, primitive nasal structures & hypotelorism, may be there.