The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017

Microphthalmia

Microphthalmia, also known as microphthalmos, is an eye abnormality that arises before birth. This condition can affect one or both eyeballs, causing them to be abnormally small. The eyeball could appear to be completely missing, but eye tissue is still present. This condition is often confused with anophthalmia, in which no eyeball forms at all before birth. Microphthalmia may or may not result in significant vision loss. A condition called coloboma often accompanies microphthalmia. Colobomas are missing pieces of the tissue structures from the eye. There could be an appearance of notches or gaps in the iris (the colored part of the eye), the retina, the choroid (blood vessel under the retina), or the optic nerve. They could be present in one or both eyes and could affect a person’s vision.

Many other eye abnormalities may accompany microphthalmia. These abnormalities include but are not limited to clouding of the lens (cataract), narrowing of the eye opening (narrowed palpebral fissure), and microcornea.

Causes

Microphthalmia occurs in approximately 1 in every 10,000 individuals. It may be caused by changes or mutations in genes involved in early development of the eye. Many of these gene mutations have not yet been identified. It could also result from a chromosomal abnormality (Trisomy 13) that affects one or more genes. Most genetic changes related to microphthalmia have only been identified in a small number of affected individuals. Environmental factors may also cause microphthalmia. Factors affecting the early development of the eye include but are not limited to vitamin deficiency, radiation, infections (rubella, herpes, or cytomegalovirus), or exposure to substances (alcohol or drugs) that cause birth defects (teratogens). Microphthalmia has an autosomal recessive pattern of inheritance. This means that both copies of the mutated gene in each cell must be present, meaning both parents carry one copy of the mutated gene. Parents typically do not show signs or symptoms of the condition. Microphthalmia is often not inherited and only affects one individual in a family.

Fetal Alcohol Syndrome

Microphthalmia is sometimes associated with fetal alcohol syndrome. It is important to understand that there is no safe amount of alcohol to use during pregnancy and as a result, there is a wide range of effects such as microphthalmia based on the dose and timing of the alcohol exposure. The timing of the alcohol exposure will determine the variations of the anatomical effects in the developing fetus. Because the fetal development occurs over the course of several months, critical structures may be affected at various periods. In addition, the dose or amount of alcohol consumed also plays a critical role in the damage that can occur. If you have a critical period of development, timing, and a dose high enough to cause damage, the fetus will be impacted by the prenatal alcohol exposure. One example of this is the facial development of the fetus. This occurs during the embryonic period of gestation or around the third and fourth weeks after conception. Drinking alcohol during this time may result in damage to the face, causing the dysmorphic facial features including short palpebral fissures (small eye opening), microphthalmia, smooth philtrum (area under the nose that typically has a ridge is now smoothed and flattened), and thin upper lip. An individual who has the dysmorphic face will also have some degree of brain injury due to the prenatal alcohol exposure.

Treatment

Treatments of microphthalmia are very limited. Most of the treatments just involve support. A doctor may patch the better eye to encourage the poorer eye to develop better vision. If other issues like glaucoma or cataracts arise, treatment could include using drops or performing operations. Family members and friends can support the affected individual in wearing glasses or contact lenses. The corrective lenses ensure that the vision regions of the brain will grow and develop correctly. Prescription eye drops should also be used regularly.

Renee Johnson

See also: Amblyopia; Anophthalmia; Visual Fields; Visual System

Further Reading

Blaikie, Andrew. (n.d.). Medical information on microphthalmia. Scottish Sensory Centre. Retrieved from http://www.ssc.education.ed.ac.uk/resources/vi&multi/eyeconds/Micro.html

Genetics Home Reference. (2011). Microphthalmia. Retrieved from https://ghr.nlm.nih.gov/condition/microphthalmia

Minnesota Department of Health. (n.d.). Anophthalmia and microphthalmia. Retrieved from http://www.health.state.mn.us/divs/cfh/topic/diseasesconds/anophthalmia.cfm