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Microphthalmia and Anophthalmia

Microphthalmia and Anophthalmia

Definition

Anophthalmia is the complete absence of an eye. Microphthalmia is an eye that has an abnormal smallness.

Description

Anophthalmia is caused by a defect in embryonic development. The total absence of an eye is extremely rare and often a clinical sign associated with a broad range of genetic disorders or, more commonly, a sporadic mutation. Sporadic transmission occurs in the affected individual due to a genetic abnormality. It is not passed on from the parents, but usually due to a combination of environmental and genetic influences. More commonly anophthalmia clinically presents as a small cyst. The defect, which causes anophthalmia, is an absence of the optic vesicle, a structure important for eye development. The genetic abnormality usually occurs during weeks one to three after conception. It is estimated that the incidence of microphthalmia occurs 0.22 times per 1,000 live births. Anophthalmia can occur during adult life but not associated with a genetic cause.

Microphthalmia refers to an abnormally small eye. This clinical sign is often associated with autosomal dominant or recessively transmitted genetic disorders. Most disorders dominantly inherited with microphthalmia are associated with some visual capabilities in infancy and early childhood. Microphthalmia may be isolated (the only presenting sign) or associated with a range of ocular or systemic abnormalities. Isolated cases of microphthalmia may be sporadic or inherited. There is a variable degree of visual impairment. Microphthalmia occurs due to autosomal recessive transmission and is part of a syndrome associated with abnormalities in the retina or systemic lesions. Microphthalmia results from a developmental defect after formation of the optic vesicle. The developmental abnormality causes the optic vesicle to fold inwards, resulting in the formation of a cyst. The cyst will progressively swell from birth, and it may be situated along the optic nerve. The cyst may also be situated along other important eye structures.

Causes and symptoms

Microphthalmia and anophthalmia can be caused by sporadic or genetic mutations. Anophthalmia is characterized by a total absence of an eye. Anophthalmia in an adult is usually caused by trauma, infection, tumor, or advanced eye disease.

Diagnosis

Microscope examination confirms the diagnosis of true anophthalmia. The clinician examines a piece of tissue taken from the eye and notes eviscerated tissue. For microphthalmia the confirmation can be established by eye measurements. Eyes, which have an axial length <21 mm in an adult, or <19 mm in a one-year-old child are described as having microphthalmia.

Treatment

Large cysts causing microphthalmia should be aspirated or removed surgically. There is no known cure for anophthalmia or microphthalmia. For anophthalmia a prosthetic eye can be fitted which may involve surgery. Treatment for microphthalmia depends on the complexity of eye involvement.

Prognosis

For anophthalmia, prosthetic eyes should be seen by a specialist two to three times per year to assess fit, mobility, and smoothness. They are usually well tolerated and have good appearance and mobility. The clinical course for microphthalmia depends on the extent of smallness, but usually patients progress favorably without major treatment. Since the smallness is distinctly noticeable, there may be individual cosmetic considerations.

Prevention

There is no known prevention for either, since these clinical signs are commonly associated with genetic inheritance.

Resources

BOOKS

Yanoff, Myron, et al, editors. Ophthalmology. 1st ed. Mosby International Ltd., 1999.

PERIODICALS

Mills, M. "The Eye in Childhood." American Family Physician 60 (September 1999).

ORGANIZATIONS

American Society of Human Genetics. Administrative Office. 9650 Rockville Pike Bethesda, Maryland 20814-3998. (301) 571-1825. 2001. http://www.faseb.org/genetics/ashg/moreinfo.htm.

KEY TERMS

Axial A straight line passing through a spherical body between its two poles and about which the body may revolve.

Eviserated Removal of eye contents.

Prostheses A synthetic object that resembles a missing anatomical part.

Retina A major portion of the eye responsible for reception of visual light rays.

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