Novel Method Evaluates Progression of Sickle Cell Retinopathy
The clinicians used optical coherence tomography angiography (OCT-A) to assess the motion of blood flow in sequence in contrast to past research that relied on static images to characterize the disease state. The results of the study showed significant dynamic variation of capillary blood flow in sickle cell disease (SCD) patients compared with controls.
“We have added a new dimension to ocular imaging technology that no one has thought of before,” lead investigator Toco Chui, PhD, director of the Marrus Adaptive Optics Laboratory at New York Eye and Ear Infirmary, said.
“For the first time, we have shown that by doing rapid, repeated retinal imaging of sickle cell patients, you can see microscopic changes in blood vessels and blood flow. The more the blood flow fluctuates across images, the more at-risk patients are for a permanent blockage, which severely damage their eyesight. Using this approach, we can noninvasively monitor the retina over time and see how a patient is doing before or after initiation of therapy.”
SCD is a group of gene mutations that alter the folds of hemoglobin, leading to a cascade of events that result in cells clumping together and clotting. Such vaso-occlusion, the hallmark of SCD, is more likely to occur during cellular hypoxia and metabolic stress. Vaso-occlusive events lead to chronic inflammation, changes in blood vessel structure, and ultimately affect vision.
Intermittent blood-flow measurement and mapping enables quantifying and quickly identifying events of intermittent capillary perfusion events in patients with SCD, the authors said. Such events were significantly more frequent in SCD than in controls and could be seen in intervals of minutes as well as hours. The technique shows promise of evaluating treatment effect, the authors said, given that it can detect the response to standard therapy.
The researchers analyzed 27 participants. Thirteen had SCD with retinopathy of varying severity levels; some were on hydroxyurea therapy and others were untreated. The remaining 14 were unaffected controls, with no SCD or retinopathy. The team used OCT-A to image all subjects 10 times in a row over a 10-minute span. An hour later they repeated the imaging procedure.
On all scans, the untreated patients with SCD had substantially more flickering in their images, indicating intermittent blood flow, than patients on treatment, pointing to treatment being effective. Patients with no SCD had no or very minimal blood flow fluctuations.
Assessing retinal blood vessels provides an indirect way to assess microvascular status of other organ systems, the authors noted. There are correlations between retinal pathology and manifestations of diabetes, hypertension, and high cholesterol. For example, correlations of hemoglobin A1c levels and degree of diabetic retinopathy has led to diabetes treatment protocols for primary care physicians and endocrinologists.
Classification of sickle cell retinopathy has generally focused on the peripheral retina and later microvascular complications, as well as sight-threatening vitreous hemorrhage and retinal detachment. OCT provides axial and transverse resolution and is noninvasive. OCT-A builds upon OCT to visualize the microvasculature.
Zhou DB, Castanos MV, Pinhas A, et al. Quantification of intermittent retinal capillary perfusion in sickle cell disease. Biomed. Opt. Express. 2021;12:2825-2840. doi:10.1364/BOE.418874