Polycythemia vera is commonly known clinical entity resulting from primary hyperplasia of erythroblastic elements of the bone marrow. This disease is seldom detected by the internist, and far more seldom by the ophthalmologist, as vision is occasionally impaired. Nevertheless, the fundus examination is likely to reveal early characteristic lesions of significance in the diagnosis. In view of this, the present study was intended to decode the conundrum regarding PV and the consequent retinal morphological alterations by implementing the novel non-invasive OCTA technique. Increased vascular density was recorded in almost all central retina, in particular foveal region due to PV-related hematic hyperviscosity.
Investigation and comparison of viscosity and coagulation including activated protein C resistance between 87 central retinal vein occlusion patients and the age-matched, population-based control group conducted by Williamson et al [13]., recorded marked reductions in both choroid and retinal blood flow in central retinal vein occlusion patients. Consistently, the present study revealed reductions in flow values and in the FAZ region in PV patients, although the results were not substantial. Ocular symptoms of PV are either due to hyperviscosity or thrombosis [14]. If untreated, PV can be life-threatening due to cardiovascular thrombotic events or PV transition to myelofibrosis, leukemia, or myelodysplastic syndromes [15]. For this reason, PV management is generally designed to prevent thrombotic incidents and to maintain a regular hematocrit level by periodic phlebotomy. In view of this, Dhrami-Gavazi et al [16]., documented a JAK2 mutation patient with central retinal artery occlusion and ipsilateral middle cerebral artery stroke. This also demonstrates the impact of hematic hyperviscosity, as seen in the current study involving PV patients.
Investigation of plasmapheresis effects on hyperviscosity syndrome-related retinopathy and retinal hemodynamic parameters in patients with Waldenström's macroglobulinemia carried out by Menke et al [17]., concluded that hyperviscosity might cause a specific type of retinopathy with retinal vein occlusion-like appearance, although the retinal blood flow remains at normal levels. Following therapy, patients developed reduction in venous diameter, and subsequent increase in the retinal venous blood flow velocity. Despite this, focal vascular constrictions revealed by slit-lamp biomicroscopy and indirect ophthalmoscopy prior to the plasmapheresis were not associated with substantial change following therapy. Likewise, PV patients participating in the present study were associated with reductions in microcirculation parameters and increases in the PERIM and FD-300 parameters with negligible differences contrary to normal subjects, respectively. All these findings indicate sluggishness of the retinal microcirculatory blood flow mainly attributable to hematic hyperviscosity, related to higher hematocrit in PV.
The study reported by Crowe et al [18]., in which the retinal vessel diameter was plotted against relative serum viscosity, showed a consistent relationship between these two parameters. The viscosity decreased directly in relation to the retinal vessel diameter in both arteries and veins. Corresponding findings with which PV patients were associated with significant increase in vascular density in almost all central retina, especially in superficial foveal region relative to normal subjects were revealed in the present study. Optical coherence tomography angiography scanning, as is understood, includes the image acquisition and processing of an erythrocyte motion contrast within the vessel. We proposed that different measurement values could be obtained for hyperviscosity syndrome, including PV, particularly in the foveal region. As revealed in the present study, only superficial foveal vascular density values increased significantly as compared to normal subjects.
The key drawbacks of the present study are the limited sample size and cross-sectional design of the analysis. Further trials with a wider population considering the effects of PV before and after therapy and a longer follow-up duration may also be worthwhile.