Anophthalmia/Microphthalmia/Coloboma (MAC)


Microphthalmia/anophthalmia/coloboma (MAC) are congenital anomalies of the eye that form a continuum from coloboma at the mild end to anophthalmia at the severe end. When we refer to anophthalmia, usually we mean clinical anophthalmia where there is so little eye tissue that it is not visible, but it is in fact severe microphthalmia. On magnetic resonance imaging (MRI) of the orbit, rudimentary tissue might be visible and in some cases, you can see a hypoplastic optic nerve. There may be eye adnexa present like tear ducts. Microphthalmia can be very variable from clinical anophthalmia to slightly small eye. Ultrasound of the orbit can help determine the actual size and structure of the eye.

MAC is genetically heterogeneous. This means that there are many different causes. MAC may be associated with other anomalies (syndromal) or alone (nonsyndromal). There are many developmental genes that can be implicated in these eye anomalies.

Key Concepts

  • Anophthalmia is a very small, abnormal eye and often has no useful vision.
  • Microphthalmia is more variable and can even be a small and normal looking eye.
  • Coloboma develops when the optic fissure does not close fully as the eye develops in the embryo, vision loss is variable.
  • Genetic causes of MAC can be due to mutations in many genes or chromosomal trisomies, deletions/duplications that include eye development genes.
  • Some teratogens such as alcohol can cause MAC.
  • MAC can occur in one eye or both the eyes and each eye can have a different problem.

Keywords: anophthalmia; microphthalmia; coloboma; genes; mutations; variability; penetrance

Figure 1. Embryology of the eye.
Figure 2. Coloboma of the iris.
Figure 3. The nucleus of the cell contains chromosomes made up of strands of DNA. Reproduced with permission (2013) © Encyclopaedia Britannica Inc.
Figure 4. (a) Autosomal dominant inheritance. (b) Autosomal recessive inheritance.
Figure 5. (a) Patient has unilateral microphthalmia. (b) Patient has bilateral anophthalmia. Reproduced from


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Further Reading

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Schneider, Adele, and Kopinsky, Sarina(Mar 2017) Anophthalmia/Microphthalmia/Coloboma (MAC). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0026852]