It is a congenital eye deformation. It may be affecting a single eye or both eyes. The condition is described to be due to a failure in the expression of a transcription factor called microphthalmia-associated transcription factor. Without enough amount of this transcription factor, the choroid fissure does not develop well resulting in the draining of vitreous humor. Without enough vitreous humor the eye(s) fail(s) to develop to the normal size.
Word origin: from micro- (small) + ophthalmos (eye)