Congenital rubella cataract. Close-up of the left eye of a patient during a slip lamp examination, with a cataract caused by congenital rubella syndrome (CRS). Cataracts are a clouding of the lens of the eye caused by the gradual denaturation of the proteins that make up the eyes lens. CRS is a condition that can occur in a developing foetus of a woman who has contracted rubella (German measles). It can cause numerous congenital problems, including eye defects (as here), deafness, heart disease and low birth weight.