An eye on sickle cell retinopathy

Sickle cell disease (SCD) is caused by a single point mutation at the sixth position in the -globin chain that substitutes the amino acid valine for glutamic acid resulting in sickle hemoglobin (Hb S). Despite being characterized by the same point mutation, the clinical course of SCD is extremely variable, ranging from mild to very severe depending on the different genotypes.1–4 Patients with sickle cell anemia (SCA), the most common and most severe form of SCD, have two copies of the altered gene, a genotype referred to as Hb SS. Hemoglobin C (Hb C) occurs frequently in compound heterozygosity with Hb S with the resulting SC disease (Hb SC) being relatively more benign than homozygous Hb SS. However, for reasons not well understood, these patients are more likely to be affected by thromboembolic complications, renal papillary necrosis and retinopathy.5,6 Both the anterior and posterior segments of the eye can be compromised due to the pathological processes of SCD but ocular manifestations in the retina are considered the most important in terms of frequency and visual impairment.7 Sickle cell retinopathy develops in up to 42% of individuals during the second decade of life.8 It is triggered by vaso-occlusion of the ocular microvasculature, as opposed to diabetic retinopathy which is associated with overexposure of