Retinal Morphological Alterations in Polycythemia Vera: An Optical Coherence Tomography Angiography Study

Muberra Akdogan (  makdogan@aku.edu.tr ) Afyon Kocatepe Universitesi https://orcid.org/0000-0003-4846-6312 Mustafa Dogan Afyonkarahisar University of Health Sciences: Afyonkarahisar Saglik Bilimleri Universitesi Anar Alizade Ermenek Public Hospital Mehmet Cem Sabaner Samsun Bafra Public Hospital Hamidu Hamisi Gobeka Agri Ibrahim Cecen University: Agri Ibrahim Cecen Universitesi Filiz Yavasoglu Afyonkarahisar University of Health Sciences: Afyonkarahisar Saglik Bilimleri Universitesi


Introduction
Polycythemia vera (PV) is o cially classi ed by the World Health Organization (WHO) classi cation scheme as a major form of myeloproliferative neoplasms (MPN) [1]. The WHO MPN category has seven sub-categories. However, the term "MPN" typically applies to the three JAK2 mutation-enriched clinicpathological entities, that is, PV, essential thrombocythemia, and primary myelo brosis. Diagnosis of PV also includes existence of the JAK2 mutation, in addition to the increased hemoglobin/hematocrit at the threshold level de ned by the 2016 WHO revised criteria (>16.5 g/dL/49 % for males and >16 g/dL/48 % for females) [1]. Initially, PV presents as isolated erythrocytosis, leukocytosis, thrombocytosis, or some combination thereof, along with splenomegaly or myelo brosis, and it may take years for true panmyelopathy to appear [2]. Primary polycythemia, that is, PV is associated with excessive erythrocytes in the bone marrow independent of another cause [3]. Typically, clinical features of PV include: mild-tomoderate degrees of splenomegaly on and constitutional symptoms such as fatigue and pruritus; symptoms of hyperviscosity, leukocytosis, thrombocytosis, microvascular symptoms such as headache, lightheadedness, visual disturbances, atypical chest pain, erythromelalgia, paresthesia; thrombotic and bleeding complications; and risk of leukemic transformation or brotic progression [3,4].
Ophthalmological manifestations of PV, in particular, vary from monocular vision loss due to retinal ischemia, papilledema to combined retinal vein occlusion and anterior ischemic optic neuropathy [5][6][7].
Preventing thromboembolic complications and alleviating symptoms is the current treatment target in PV The ophthalmological evaluation of PV patients involves uorescein angiography which is used to visualize retinal vessels and thus to measure the vessel ow in relation to hematological diseases.
However, the uorescein angiography is unable to distinguish or quantify capillary networks in different retinal layers, and as an invasive technique, its repeated use is constrained. Contrastingly, optical coherence tomography angiography (OCTA, Optovue, Inc., Fremont, CA) is a novel non-invasive imaging technique that has recently been implemented. This technique visualizes retinal and choroid capillary networks, and foveal avascular zone (FAZ) without exogenous dye. Identi cation of retinal ischemic diseases with clinically undetectable fundus lesions is also possible [9]. Optical coherence tomography angiography can produce three dimensional and en face imaging of retinal capillary networks thanks to its split spectrum amplitude-decorrelation angiography property. Quantitative data of the retinal vasculature and its thickness and foveal avascular zone area can be measured automatically using the AngioAnalytics program. Optical coherence tomography angiography is increasingly widely used in the diagnosis and evaluation of various vascular-associated retinal or choroidal diseases, including diabetic retinopathy, choroidal neovascularization, and retinal vein occlusion [10][11][12].
The present study was designed to quantify the OCTA parameters of retinal morphology, including retinal vascular density, FAZ area and central foveal thickness of PV patients, and to compare the data with normal subjects.

Participants
Thirty PV patients (Group 1) who were followed-up at Afyonkarahisar Health Sciences University Hospital, Department of Hematology, and 30 normal subjects (Group 2) who applied to our Ophthalmology Department for routine eye examination were enrolled in this cross-sectional, single-centered study. All procedures were carried out according to the tenets of the Helsinki Declaration. The approval of the board of institutional review was received from the Afyonkarahisar Health Sciences University Ethics Committee. Formal informed consent was obtained prior to the study.
Ophthalmological Examination and Optical coherence Tomography Angiography Acquisition A thorough ophthalmological examination including measurements of the best-corrected visual acuity and Goldmann applanation tonometry intraocular pressure, anterior and posterior segment slit-lamp biomicroscopy were carried out. All participants underwent spectral-domain OCTA scanning in Angio Retina mode (6x6 mm) under normal conditions by the same clinician. Eye movement artefacts were minimized by an eye-tracking mode and eliminated by a motion correction technology. All scans were reviewed to ensure proper segmentation and image quality (Quality Index ≥7) and scans of low quality were omitted. AngioVue Analytics, RTVue-XR version 2017.1.0.155 program automatically quanti ed the vessel density in super cial retinal layer (super cial capillary plexus, SCP) and deep retinal layer (deep capillary plexus, DCP). Central macular thickness-de ned as the average thickness of the central 1 mm 2 fovea region, the parafovea macula thickness, the average retinal thickness of the 6x6 mm region and the superior and inferior hemi elds were also quanti ed automatically by the AngioVue Analytics program.
The ow area of the 3 mm diameter circle was determined. Meanwhile the FAZ, FAZ perimeter (PERIM), and foveal vessel density were also obtained from the software's FAZ mode in 300 μm wide regions around FAZ (FD-300).

Statistical Analysis
The SPSS software (Version 18, SPSS Inc., Chicago, IL, USA) and Microsoft Excel (Microsoft Corp., Redmond, Washington, USA) were used to conduct statistical analysis. All parameters were analyzed for distribution by the Shapiro-Wilk test. And, since the data were identi ed in a normal distribution, an independent sample t-test was used in the data analysis. P-values of less than 0.05 were considered statistically signi cant.

Results
There was a male-to-female ratio of 1:1 among the 60 participants. The mean ages for male and female PV patients were 49±5.15 years and 46.21±2.25 years, respectively. While the mean age of all PV patients was 46.97±3.20 years, normal subjects had 47.42±2.55 years (P: 0.350). The demographic features of the respective study groups are shown in Table 1. Table 2 shows alterations in the retinal vascular density of the respective study groups. Patients with PV had statistically non-signi cant increases in the vascular density in super cial whole, parafoveal, deep foveal, and perifoveal region relative to normal subjects. Statistically non-signi cant decreases in ow values as well as in the FAZ region were also observed in patients with PV relative to normal subjects (Table 3 and 4). Besides, Patients with PV were associated with statistically non-signi cant increases in PERIM and FD-300 parameters (Table 4). Moreover, in comparison to normal subjects, patients with PV were associated with a statistically signi cantly increased vascular density in the super cial foveal area (P: 0.032) (Figure 1).

Discussion
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 signi cance 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 ow in central retinal vein occlusion patients. Consistently, the present study revealed reductions in ow 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 myelo brosis, 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 speci c type of retinopathy with retinal vein occlusionlike appearance, although the retinal blood ow remains at normal levels. Following therapy, patients developed reduction in venous diameter, and subsequent increase in the retinal venous blood ow 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 ndings indicate sluggishness of the retinal microcirculatory blood ow 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 ndings with which PV patients were associated with signi cant increase in vascular density in almost all central retina, especially in super cial 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 super cial foveal vascular density values increased signi cantly 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.

Conclusions
For the rst time, the present study revealed association of PV with substantial increase in the vascular density around the foveal region. These ndings suggest consideration of possible hyperviscosity impact on the vessel density during macular microcirculation assessment in patients with PV.

Declarations
Funding: Authors declare no public or private nancial support or involvement whatsoever in the products, methods or materials referred to in this manuscript.

Con icts of interest/Competing Interests: The authors claim no con ict of interest.
Financial Interest: Both authors certify that they have no association or participation with any organization or individual with any nancial interest or non-nancial interest in the subject matter or materials discussed in this article.
Ethics approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.