A developmental abnormality in which there is only one eye WordNet 3.0 & Open English WordNet

Cyclopia, also known as alobar holoprosencephaly, is the most extreme form of holoprosencephaly and is a congenital disorder characterized by the failure of the embryonic prosencephalon to properly divide the orbits of the eye into two cavities. Wikipedia

A congenital disorder Wikipedia Disambiguation

Congenital disorder Wikidata

A congenital abnormality in which the orbits of the eye do not divide to form separate sockets. Wiktionary

Fusion of the eyes, as in cyclopia. Wiktionary