During embryological development, the eye sometimes does not develop to its full size, a condition known as microphthalmia. This can occur by itself but is occasionally accompanied by incomplete formation of the eyeball leading to a defect known as a coloboma (from the Greek word meaning unfinished). This malformation may involve various eye structures such as the iris (colored part of the eye), retina, and optic nerve.
In the condition described here, the eyes are abnormally small and the colobomas can be seen as a ‘keyhole’ defect in the iris. The cornea (windshield of the eye) may be small along with other ocular structures and this creates an appearance suggesting the eyelids are not completely open. The retina does not form normally and the iris may not have a pupil. Vision defects are variable depending on what eye structures are involved.
This condition is rare and many reports involve only single generation kinships. In addition, many parents are related to each other, and this pattern is consistent with autosomal recessive inheritance. Thus two mutations are required for the condition to be present. Each normal parent with a single mutation may pass it to a child and when both do the child receives two mutations and has this disorder. Couples like this can expect that one-fourth of their children will inherit microphthalmia with colobomas.
In the disorder described here, only the eye is abnormal. The diagnosis can be suspected from simple inspection when the normally round pupil has a ‘keyhole’ shape or the eye(s) appear small. This may be the only visible abnormality. Vision levels are variable depending upon the eye structures involved. Most patients have a severe vision handicap for which no medical or surgical treatment is available.