Volume 40, December 2022, 103181AbstractObjective

To evaluate and compare the vessel density (VD) using swept-source optical coherence tomography angiography (OCT-A) and the choroidal vascularity index (CVI) using spectral-domain optical coherence tomography (SD-OCT) in patients with Bietti crystalline dystrophy (BCD) and retinitis pigmentosa (RP).

Materials and methods

A cross-sectional retrospective study was conducted on 26 eyes of 13 BCD patients, 26 eyes of 13 RP patients, and 26 eyes of 13 age- and gender-matched healthy individuals. BCD patients were further staged as having early, intermediate, and advanced disease. VD was assessed in five quadrants of the macula (superior, temporal, inferior, nasal, and center) using a modified ETDRS technique with OCT-A. SD-OCT scans were binarized using Niblack's autolocal threshold, and CVI was determined as the ratio of the luminal area to the total choroidal area.

Results

A significant difference was found in VD in all quadrants of the superficial capillary plexus (SCP) and the deep capillary plexus (DCP) slabs among the three groups (p < 0.001). A statistically significant difference was noted in the mean VD of temporal and inferior quadrants of the SCP and between the BCD and RP groups (p = 0.005, p = 0.015, respectively). A statistically significant difference was observed in the mean VD of the temporal, inferior, and nasal quadrants between the BCD and RP groups on DCP slabs (p = 0.002, p = 0.003, p = 0.003, respectively). The mean central choroidal thickness was 214.65±87.10 μm in the BCD group, 351.69±67.94 μm in the RP group, and 320.92±59.26 μm in the control group (p < 0.001). We found that CVI was significantly higher in the control group than BCD group (p < 0.001), and it was significantly lower in the BCD group when compared to the RP group (p < 0.001).There was no difference in CVI between RP and control groups (p = 0.948). Furthermore, the CVI was significantly lower in the intermediate and advanced disease stages than the early disease stage in the subgroup analysis of BCD patients (p < 0.001, p < 0.001, respectively).

Conclusion

CVI is a novel investigative tool to monitor disease progression. The CVI value was lower in BCD and RP patients than in the healthy subjects, and lower CVI values seem to be related to the disease severity in BCD patients. VD was also significantly lower in BCD patients when compared to RP patients, and VD analysis may help clinicians better understand the disease pathophysiology.

Introduction

Bietti crystalline dystrophy (BCD) is a rare genetically determined retinochoroidal dystrophy characterized by scattered yellow-white glistening crystalline deposits in the retina and less frequently in the corneal limbus, with the progressive chorioretinal atrophy commencing mainly at the posterior pole [1]. While the BCD prevalence is estimated to be 1 in 67,000, the disease seems to be more prevalent in Eastern Asia [2], [3], [4].

BCD is caused by the mutations in the CYP4V2 gene, which encodes a member of the cytochrome P450 protein superfamily involved in oxidation of the substrates in fatty acid oxidation process [5]. We previously investigated the optical coherence tomography (OCT) changes in patients with BCD [6], [7], [8]. Recent optical coherence tomography angiography (OCT-A) studies found that the residual subfoveal choriocapillaris area in BCD patients was in accordance with the good visual outcomes in BCD eyes [9], and macular structural and perfusion parameters were more affected in patients with BCD patients when compared to retinitis pigmentosa (RP) patients [10]. In contrast to BCD, RP is mostly characterized with the photoreceptor cell degeneration, and the mechanism of choroidal thinning is still unknown in RP patients [11].

In this study, we investigated the retinal and choroidal vasculature using swept-source (SS) OCT-A and choroidal vascularity index (CVI) using spectral-domain OCT (SD-OCT) by quantifying the luminal area (LA) and stromal area (SA) of choroidal vessels in BCD and RP patients and healthy subjects.

Section snippetsMaterials and methods

This cross-sectional retrospective study was performed under the tenets of the Declaration of Helsinki and current Turkish legislation after obtaining the approval of the local ethics committee of Dokuz Eylul University (Approval ID: 2021/30-04). Twenty-six eyes of 13 BCD patients, 26 eyes of 13 RP patients, and 26 eyes of 13 age- and gender-matched healthy individuals who had adequate quality of OCT-A examination between November 2018 and October 2022 at the Department of Ophthalmology of

Patient demographics

A total of 13 BCD patients (nine females, four males), 13 RP patients (eight females, five males), and 13 healthy individuals (seven females, six males) were enrolled in this study. Both eyes were analyzed in all subjects. The mean age of BCD patients, RP patients, and control group subjects were 32.92±11.02 years (range: 16–52 years), 35.92±16.08 (range: 14–64 years) years, 33.77±13.93 years (range: 15–62 years), respectively (ANOVA test; p = 0.718). The percentages of female patients were

Discussion

BCD is recognized as a systemic disorder of lipid metabolism, and RPE is one of the targets of the disease [18], [19], [20]. Several recent studies have analyzed the choroidal changes by using OCT-A in BCD patients [9,10]. Miyata et al. [9] investigated the blood flow in the choriocapillaris of the 13 eyes of 13 consecutive BCD patients and 20 healthy eyes in a prospective case-series study involving manual processing of the OCT-A images and reported that choriocapillaris blood flow deficit was

Funding

The authors declared that this study received no financial support.

CRediT authorship contribution statement

Ferdane Ataş: Writing – original draft, Visualization, Software, Project administration, Methodology, Investigation, Formal analysis, Conceptualization. Mustafa Kayabaşı: Data curation. Ali Osman Saatci: Writing – review & editing, Writing – original draft, Supervision, Project administration, Methodology.

Declaration of Competing Interest

The authors report no conflicts of interest.

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