Spectralis HRA+OCT Imaging of the Retina With Autofluorescence in Sickle Cell Disease

• Patient Care [ Time Frame: 6 months ]
  The use of Spectralis HRA+OCT gives us visualization of the individual layers of the retina to determine if there are underlying changes not seen clinically in the gross ophthalmic posterior segment exam. This knowledge will aid the care of African-Americans with sickle cell disease to enable greater understanding of the ocular disease progression leading to earlier eye screenings, possible novel treatments and ultimately visual loss prevention
  
  

About 10% of African Americans have an abnormal hemoglobin gene. About 8% of African Americans are heterozygous for Hb S. In the United States, sickle cell anemia primarily occurs in the black population, with approximately 0.2% of African American children afflicted by this disease. The prevalence in adults is lower because of the decrease in life expectancy. The Storm Eye Institute at the Medical University of South Carolina (MUSC) is uniquely situated geographically and epidemiologically to study the interaction between sickle cell disease and the retina. The frequency of sickle cell trait (Hb AS) in African-Americans of Charleston County is 16%, twice the national average of 8% in African-Americans. This is thought to be due to the autosomal recessive inheritance of sickle cell disease, and the genetic roots and relative isolation of the Sea Island Gullah population (Pollitzer 1999).

Variations in the alteration of the amino acid sequence on the globin chain produce variations in the disease's expression. The four forms of the disease are often referred to by their genotype: sickle cell trait (AS), sickle cell anemia (SS), sickle cell disease (SC) and sickle cell thalassemia (SThal).

Systemically, the sickle cell anemia variation (SS) produces the most symptoms. With respect to the eye, the sickle cell disease mutation (SC) produces the most effects.

The widely accepted pathogenesis for sickle cell retinopathy is vasoocclusion that leads to retinal hypoxia, ischemia, infarction, neovascularization, and fibrovascularization. In sickle cell anemia, the amino acid substitution valine for glutamate occurs on the beta chain at the sixth position. This substitution, combined with conditions that may promote sickling (ie, acidosis, hypoxia), triggers the deoxygenated Hb S to polymerize, making the erythrocyte rigid. This rigidity is partially responsible for the vasoocclusion.

Vasoocclusion also is in part due to the interaction between sickled cells and the vascular endothelium. The adherence of sickled cells to the endothelium triggers an inflammatory process with the release of inflammatory agents. The result of this cascade is vascular stasis, hemolysis, and vasoocclusion of the capillary beds.

Classically, posterior segment changes are classified by either nonproliferative sickle retinopathy (NPSR) or proliferative sickle retinopathy (PSR). In NPSR, the retinal changes do not involve neovascularization as they do in PSR. The use of Spectralis HRA+OCT gives us visualization of the individual layers of the retina to determine if there are underlying changes not seen clinically in the gross ophthalmic posterior segment exam. This knowledge will aid the care of African-Americans with sickle cell disease to enable greater understanding of the ocular disease progression leading to earlier eye screenings, possible novel treatments and ultimately visual loss prevention.