About MACS Conditions

Introduction to MAC conditions

We support children and adults who have one of, or sometimes a combination of, three eye conditions: Microphthalmia (small eye), Anophthalmia (no eye) and Coloboma (gap in the structure of the eye). Around 80-90 children are born with a MACS condition in the UK every year.

Some people with a MACS condition are blind, others have a degree of light perception, and some may be blind in one eye with some, or even good, sight in the other eye. The conditions develop during pregnancy and are often associated with other congenital (present at birth) disorders such as endocrine or heart problems. Some people with a MACS condition also have learning and developmental difficulties and behavioural problems.

What are Microphthalmia, Anophthalmia and Coloboma?

About MAC conditions

About the MAC conditions


Microphthalmia means 'small eye'. Children may be born with one, or both eyes, small and underdeveloped. Some children may be blind, but others may have some residual sight or light perception.


Anophthalmia means an absence of the eye. As with Microphthalmia, a child may be born with one, or both eyes, missing from the eye socket.


Coloboma means that there is a gap or cleft in one or more structures of the eye. Vision may or may not be affected depending on the part of the eye that is involved. The severity of visual impairment depends on the structures affected and size of the cleft.

Information on prosthetic eyes

If you would like information on prosthetic eyes please click here.


It is not yet known exactly why Microphthalmia and Anophthalmia occur, but they are likely due to a disruption in the sequence of developmental steps that take place when the eye is forming during pregnancy. This could be as a result of an error within specific genes affecting eye development and increasingly, more genes are being identified as important in the development of these conditions.

External factors may influence the function of those genes and the conditions have been related to illness experienced during pregnancy such as chicken pox and rubella, or drugs such as thalidomide. Environmental factors such as insecticides and fungicides have also been linked to the development of the conditions.

Coloboma occurs as a result of congenital malformation, with a portion of the eye failing to complete its growth very early in pregnancy.


There is no treatment that will restore vision in children affected by Anophthalmia or severe Microphthalmia.  The management of the condition is mainly focused on changing facial appearance, maximising remaining vision and looking after the child’s general wellbeing. This often requires a team consisting of specialists from different areas. Children with MAC conditions often need to undergo repeated hospital visits and many have prosthetic eyes to ensure that the bone and soft tissue around the eye socket grows properly and to improve appearance.


So far, more than 90 different genes have been identified which may cause various forms of MAC. Human eye development during pregnancy is a complex process not all genes and their roles have been identified yet. Current research focuses on understanding the causes and mechanisms which result in MAC. MACS works closely with research teams, and has funded projects to understand more about the conditions.

Image shows child with bilateral anophthalmia

Child with bilateral anophthalmia

Image shows child with unilateral microphthalmia

Child with unilateral microphthalmia

Image shows child with unilateral coloboma

Child with unilateral coloboma

Gene.Vision Resource


If you would like to learn more about the conditions, Gene.Vision is a great resource for both patients and professionals. The resource provides information on the conditions, treatments and research and much more.

Here is the resource for parents and MACS adults.

Here is the resource for professionals.

Gene Vision website
Gene Vision website