Fibrosis of Extraocular Muscles, CFEOM2
Patient Information
Characteristics
Background and History
This is one of several hereditary, nonprogressive forms of strabismus (abnormal alignment of the eyes) in which the eye movements are restricted. Although the name implies a disease of the muscles that move the eye, the primary disorder is one of maldevelopment of the nerves that supplies those muscles.
Clinical Correlations
Eyeball movements are severely restricted and they seem to be fixed in their position. In CFEOM2, the eyes are deviated to the side and move little if at all. Patients have to move their heads to look in different directions. The eyelids may droop (ptosis) severely and can cover part of the pupil. Since blinking is abnormal, the corneas (windshield of the eye) can dry out and this may lead to serious complications. Often one eye becomes lazy (amblyopia) and does not see well. The pupils may be abnormally small and react to light poorly. Refractive errors such as astigmatism are common.
There are no consistent systemic abnormalities in the rest of the body.
Genetics
Inheritance
This type of eye movement problem has been found primarily in Middle Eastern families in which the parents are related. Genetic studies have confirmed that the inheritance pattern in CFEOM2 is autosomal recessive in which two mutations are required for the disorder to manifest itself. The parents, who are clinically normal, each carry one copy of the mutation and can expect on average that one in four of their children will have this eye problem.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
The diagnosis is made by an ophthalmologist based on clinical examination of the eyes. Surgery can correct the deviation of the eyes although it is not possible to restore full movement. Surgery can also correct some of the droopy eyelids. It is important to monitor individuals with this problem to ensure that the cornea receives the proper protective lubrication. The lazy eye should be treated appropriately as well to maintain good vision and, of course, the proper glasses or contacts should be worn for the best vision.
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