Blue sclera: a bluish coloration of the whites of the eyes. The blue color is caused by thinness and transparency of the collagen fibers of the sclera, allowing the veins in the underlying tissue to show through. Blue sclerae are characteristic of a number of conditions, particularly connective tissue disorders. These include osteogenesis imperfecta, Marfan's syndrome, Ehlers-Danlos syndrome, pseudoxanthoma elasticum, and Willems De Vries syndrome, among others.
REFERENCE: Walsh, S. "The Eyes Have It." Medscape.