Nanophthalmos, or small eye, is a disorder limited to the eye in which it is significantly smaller than normal. It has long been known as one of several conditions that carry a risk for a rare type of glaucoma known as angle closure glaucoma. The term microphthalmus is sometimes applied to small eyes as well but generally refers to a different condition in which there are other associated abnormalities.
This is a rare eye malformation in which the eyeball does not grow to a normal size. While the size of the eye varies to some extent among different people, this inherited disorder results in an extremely small globe that is outside of normal limits. As a result the eye is very farsighted. However, even though glasses can correct this, the vision may still be not be normal for this abnormal development is associated with other changes in the eye including the retina and its supporting tissues. The lens is of normal size and in a small eyeball this causes crowding of other structures which may interfere with the dynamics of the fluid in the eye sometimes resulting in acute and painful glaucoma attacks. Fluid may also accumulate beneath the retina leading to retinal detachments. As a result of multiple abnormalities throughout the eye, surgery, while sometimes necessary, carries serious risks.
This is not a progressive disorder and many individuals have useful vision throughout their lives.
Nanophthalmos is caused by several mutations. Certain ones require that both parents contribute a mutation to their offspring and the disorder is only evident therefore when two mutant genes are present (autosomal recessive pattern). Since this is an uncommon event, most examples of this condition occur sporadically without a family history of this disease. Other gene mutations cause nanophthalmos in a single dose, and the family tree may contain several affected individuals with evident transmission through several generations (autosomal dominant pattern). Genetic counseling can be helpful in determining the type of inheritance and assessing the risk of recurrence.
This condition can only be diagnosed by an eye doctor. However, because the globe is so small, simple inspection can give useful clues since the eyelids do appear as widely open as in other people. An ultrasonic test can be used to accurately measure the size of the eyeball and is required to make the diagnosis. The retina, while abnormal in many cases, has no characteristics that definitively separate it from other retinal conditions. Because many individuals have few symptoms, the first suggestion of this condition may occur when acute glaucoma occurs. This is a painful condition that must be treated quickly to prevent serious damage to the optic nerve but fortunately results are generally good. Likewise sudden loss of vision should be evaluated immediately so that retinal detachments can be detected and treated early.
Anyone with this condition needs to have frequent eye examinations throughout their life. This condition is not associated with other problems in the body although somewhat small eyes are sometimes found in other developmental disorders.