Cyclopia

Overview
Cyclopia (also cyclocephaly or synophthalmia) is a rare form of holoprosencephaly and is a congenital disorder (birth defect) characterized by the failure of the embryonic prosencephalon to properly divide the orbits of the eye into two cavities. Its incidence is 1 in 16,000 in born animals, and 1 in 250 in embryos.

Presentation
Typically, the nose is either missing or replaced with a non-functioning nose in the form of a proboscis. Although cyclopia is very rare, several cyclopic human babies are preserved in medical museums (e.g The Vrolik Museum, Amsterdam). There are also two known cases of children with Down Syndrome being born with one eye.

Some extreme cases of cyclopia have been documented in cats. In such cases, the nose and mouth fail to form, resulting in suffocation shortly after birth.

Causes
Genetic problems or toxins can cause problems in the embryonic forebrain-dividing process.

One highly teratogenic alkaloid toxin that can cause cyclopia is cyclopamine or 2-deoxyjervine, found in the plant Veratrum californicum (also known as corn lily or vetch weed). The mistake of ingesting Veratrum californicum while pregnant is often due to the fact that hellebore, a plant with which it is easily confused, is recommended as a natural treatment for vomiting, cramps, and poor circulation, three conditions that are quite common in pregnant women.

Notable cases
An old description of a colt apparently suffering from cyclopia reads:

First, That it had no sign of any Nose in the usual place, nor had it any, in any other place of the Head, unless the double Bagg CC that grew out of the midst of the forehead, were some rudiment of it. Next, That the two Eyes were united into one Double Eye which was placed just in the middle of the Brow.

In 2005, a kitten with cyclopia, "Cy", was born in the United States and died about one day after birth.