congenital microcoria (MONDO_0007989, a Monarch Disease Ontology id) is a rare autosomal dominant ophthalmological disease caused by maldevelopment of the dilator muscle of the pupil that is characterized by small pupils (<2 mm in diameter) from birth, peripheral iris hypopigmentation and transillumination defects leading to errors of refraction (myopia, astigmatism) and sometimes juvenile open angle glaucoma. Also known as: congenital miosis.