Congenital microphthalmia describes an abnormally small globe, generally noted in combination with a smaller palpebral fissure and orbit. The degree of microphthalmia varies considerably, extending from only a mild decrease in size of a functional globe, to rare cases of anophthalmos, in which there is a complete absence of ocular tissue. Changes are generally bilateral. Commonly affected breeds include the collie breeds, notably the Rough Collie.