Abnormal corneal development resulting in structural or clarity defects. The cornea owes its transparency to the presence of a regular lattice structure of collagen fibres. Anything that affects this regularity results in loss of the transparency, which is essential for good corneal function and health. Corneal dystrophies form a group of rare disorders that usually affect both eyes. Dystrophies may be present at birth, but more frequently develop during adolescence and progress gradually throughout life. Some forms are mild, others severe. (Ref: RNIB website)