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) is small along with other ocular structures and this creates an appearance suggesting the eyelids are not completely open. The pressure inside the eye may be too high, a condition often leading to glaucoma. Vision defects are variable depending on what eye structures are involved.
Isolated microphthalmos with colobomas described here is due to an as yet unknown gene mutation on the X chromosome. Thus, males are affected because they inherit the mutant X chromosome from their unaffected carrier mothers. Affected males cannot pass the disorder to their sons since they only pass their Y chromosome to them, but all of their daughters will be carriers like their paternal grandmother.
The diagnosis is usually evident by simple observation in someone whose pupils resemble keyholes. Of course, this may also be present in individuals with normally-sized eyes. However, it is important that children with this defect have complete physical evaluations since this eye condition is often associated with other abnormalities. No treatment is available for the malformations but low vision aids can be helpful in some individuals. An elevated pressure in the eyes needs to be treated to prevent glaucoma.