Classification of chromosomal eye syndromes.

Human chromosome disease arises from a change in the number or structure of one or more chromosomes. The multiple genes represented in the duplicated or deleted chromosomes are not usually defective and any systemic abnormalities can be attributed to a change in gene dosage. Banding techniques are now commonly used to identify each chromosome and the specific chromosome duplication and deletion and structural rearrangements can now be identified unambiguously. Most ocular abnormalities have occurred in patients with chromosomal defects. Major ocular abnormalities, such as anophthalmia, cyclopia, retinoblastoma, microphthalmia, corneal opacities, coloboma, cataracts, intraocular cartilage, retinal dysplasia and absent optic nerves; and, minor abnormalities, such as ptosis, abnormal eyelid fissures, and Brushfield spots are present in individuals with abnormal chromosomes. The chromosome errors are usually present in all somatic tissues. consequently, multiple tissue abnormalities would be expected in most patients with chromosome abnormalities. Mental retardation is very common in those patients with abnormalities of autosomes. Therefore, it is unlikely that an isolated single clinical or histopathological ocular abnormality will be the result of a chromosome error. However, if the individual has multiple systemic abnormalities, then a chromosome error can be considered reasonably. Any chromosome disorder can be identified correctly by an appropriate banding chromosome determination on the affected individuals. With the possible exception of the association of 13q 14- and retinoblastoma, there does not appear to be any pathognomonic ocular abnormalities that occur in individuals with chromosome errors.