The disc sign in sickling hemoglobinopathies.

The disc sign is the presence of dark red spots on the optic disc of patients with a sickling hemoglobinopathy. The dark spots appear to be plugs of deoxygenated erythrocytes in small surface disc vessels. The occlusions, which are transient and do not produce clinically detectable visual impairment, were seen most often in patients with homozygous sickle cell anemia and may be the result of clogging of small vessels by irreversibly sickled erythrocytes.