0.26 Images of memorable cases: case 26

26. sickle cell disease

Inspection of the conjunctiva with the +40 lens of the ordinary ophthalmoscope can be a useful adjunct to the diagnosis of certaintypes of sickle cell disease, particularly the homozygous form. The characteristic sign consists of sharply defined, dark-red, comma-shaped orcorkscrew-shaped vessel fragments that appear isolated from the rest of the conjunctival circulation. These anomalous segments are visible primarily in thatpart of the lower bulbar conjunctiva covered by the lid.

The pathogenesis of this conjunctival sign remains speculative. There is evidence, however, that endothelial proliferation withtrapping of erythrocytes occurs in the distal portion of some capillaries; immediately proximal to such involvement, the vessels are dilated and thin-walled. Infusion of blood or inhalation of oxygen can modify, if not temporarily eliminate, the sign. Conversely, eye drops that contain vasoconstricting agentscan render the sign more conspicuous.