Cyclopia is a rare birth condition that occurs when the front portion of the brain does not properly split into two halves, known as the right and left hemispheres.

Cyclopia can lead to structural abnormalities of the head and face. It is also associated with low survival rates. Most infants born with cyclopia are stillborn or die within a few hours of birth.

In this article, we look at cyclopia in more detail, including its causes and diagnosis. We also consider the outlook for people with this condition.

Cyclopia is also known as alobar holoprosencephaly.

Holoprosencephaly refers to a group of rare disorders in which the front portion of the brain does not divide into the right and left hemispheres. There are four types of holoprosencephaly:

  • Alobar holoprosencephaly occurs when the brain does not divide into the right and left hemispheres.
  • Semi-lobar holoprosencephaly occurs when the left hemisphere fuses to the right hemisphere in the frontal and parietal (side) lobes.
  • Lobar holoprosencephaly occurs when the right and left ventricles form, but the hemispheres remain fused.
  • Middle interhemispheric variant (MIHV) holoprosencephaly occurs when the right and left hemispheres form but remain fused in the middle.

Cyclopia is the most severe form of holoprosencephaly. It typically develops between days 18 and 28 of pregnancy.

In people with cyclopia, there is no separation between the right and left hemispheres of the brain.

Cyclopia can also affect the structure of the head and face. The most apparent sign of cyclopia is a single eye or a partially divided eye in a single socket.

Other signs include:

  • the absence of a nose
  • a proboscis, or nose-like structure, above the eye
  • microcephaly, which is an abnormally small head
  • cleft lip or palate
  • tooth abnormalities
  • hormonal abnormalities
  • hypoglycemia, which is low blood sugar
  • low levels of sodium in the blood
  • genital abnormalities

The exact causes of cyclopia remain unknown. However, researchers believe that several factors can increase the risk of cyclopia.

These include:

  • genetic factors
  • gestational diabetes
  • infections during pregnancy
  • exposure to UV light
  • using alcohol and certain medications during pregnancy

According to the National Organization for Rare Disorders (NORD), one-third of infants born with holoprosencephaly have chromosomal abnormalities. The NORD note that the most common of these is having three copies of chromosome 13, which is known as trisomy 13.

Holoprosencephaly can also occur in Smith-Lemli-Opitz syndrome, a rare genetic condition that affects multiple organs and bodily systems.

Cyclopia and other forms of holoprosencephaly develop during the first trimester of pregnancy. A doctor can diagnose cyclopia using ultrasound imaging while the fetus is still developing in the womb.

Brain malformations and other structural abnormalities appear on ultrasounds. A doctor may also use an MRI scan to identify cyclopia.

Cyclopia occurs in about 1 in every 250 embryos and 1 in every 100,000 births, about 50% of which are stillbirths. Infants born with cyclopia survive for only a few hours.

There is no standard treatment for cyclopia or the other forms of holoprosencephaly. Treatment typically focuses on addressing the symptoms and providing life support.

Cyclopia is a rare condition that occurs while an embryo develops in the womb. Most embryos that develop cyclopia do not make it to full term. Babies born with cyclopia usually only survive for a few hours.

Researchers believe that genetic factors contribute to this rare condition. People who carry the genetic trait may have a higher risk of having a child with cyclopia. However, the condition is so rare that even parents with the hereditary trait rarely give birth to a child with cyclopia.