Microcoria, Congenital

Background and History: 

This is a rare inherited condition in which the pupils are abnormally small and fail to dilate, even with the usual eye drops.  The condition is present at birth.

Clinical Correlations: 

The pupils are only 2 mm or less from birth and do not change in size throughout life.  Studies have shown that the muscle fibers that normally dilate the pupil in dim light are underdeveloped as is the iris (colored part of the eye) generally.  Even eye drops used by eye doctors to dilate pupils for examination of the eye have little effect.  The colored portion of the eye is normally opaque but in this condition tissue defects (small holes) may transmit light.  Glaucoma is often present as well.  The glaucoma (due to elevated pressure inside the eye) may be detected during teenage years or early adulthood.  It is difficult to treat with the usual eye drops and surgery may be required to lower the pressure.

Many but not all patients are very nearsighted.

There are no abnormalities outside the eye. 


This is an autosomal dominant condition as evidenced by family patterns but the causative gene mutation has not been identified.  However, we know that adults with this disorder can expect that each of their children have a 50% chance of inheriting congenital microcoria.

Diagnosis and Prognosis: 

This disorder only causes ocular problems and affected individuals can expect to live normal lives with good eye care.  All children of parents with congenital microcoria should be regularly checked for glaucoma beginning in childhood.  If the eye pressure cannot be controlled with medicine, surgery may be necessary and usually is effective.  Corrective lenses (contacts or glasses) to correct the nearsightedness enable many individuals to have normal vision.

Additional Information
Autosomal dominant