Author: Beyza Yavuzer (Turkey)
Co-authors: Kamil Yavuzer, Mehmet Citirik
Retinitis pigmentosa (RP) is the most common form of hereditary retinal dystrophy characterized by progressive impairment and death of the retinal photoreceptors. Previous RP studies have reported that the earliest histopathological change is a shortening of the photoreceptor outer segments. This change begins in the mid-periphery and progresses to the central retina; therefore, morphological and functional assessments of retinal changes may be useful in predicting disease progression and remaining retinal function in RP patients. Optical coherence tomography (OCT) in vivo quantitatively tracks these morphological changes in retinal tissue by in vivo segmentation. The new OCT device software enables easier and more accurate automatic differentiation and thickness measurement for each retinal layer. The information provided by optical OCT-angiography (OCT-A) about the vascular densities of retinal vessels has been a guide for researchers especially about RP patients. Evaluating the retinal layers one by one and obtaining information about vascular densities in RP can help us to understand the course of the disease and its clinical reflections. This study analyzes the retinal layers in macular regions of RP eyes one by one to examine their retinal vascular plexus densities and to evaluate the effect of the pathophysiological process on the retina.
University of Health Sciences, Ankara Ulucanlar Eye Training and Research Hospital, Ankara/TURKEY
Thirty-six eyes from 20 patients showing the classic triad for RP who had undergone retinal segment analysis and OCT-A were included; a control group of 36 eyes from 18 patients was also included in the study. Patients with systemic diseases such as diabetes mellitus or hypertension; ocular diseases that require chronic medication use such as uveitis, glaucoma, dry eye; an ocular history of intraocular surgery or trauma; and patients with additional findings affecting the macular area, such as cystoid macular edema, vitreomacular adhesion/traction, epiretinal membrane, or macular atrophy, were excluded from the study. The eyes of RP patients with additional pathology affecting the macular region were not included in the study. Besides, cases with artifacts in measurements and those whose retinal segmentation analysis could not be performed were also excluded from the study. Total retinal thickness and retinal layer thickness in the macular region were measured using spectral domain OCT (HRA2-Heidelberg Retina Angiography, Optical Coherence Tomography, Heidelberg Engineering, Heidelberg, Germany). OCT-A imaging of the cases was performed using AngioVue OCT-A (RTVue XR Avanti, version 2017.1.0.151; Optovue, Inc., Fremont, CA, USA). Radial peripapillary capillary plexus (RPCP), superficial capillary plexus (SCP), and deep capillary plexus (DCP) density values were obtained.
RP and control groups had similar characteristics in terms of age and gender (p= 0.323 and p= 0.092, respectively) (Table 1). Analyzes were performed in the central 1 mm foveal area and 4 regions (superior, inferior, temporal, nasal) in the parafoveal and perifoveal region. Retinal layers were evaluated with retinal segmentation analysis and the results are shown in Tables 2 and 3. The density of RPCP detected by OCT-A was 45.57 ± 1.82% in the RP group and 49.46 ± 2.78% in the control group. SCP density was 42.62 ± 3.18%, DCP density was 41.33 ± 1.33% in the RP group, while SCP density was 48.02% ± 1.34% and DCP density was 49.34 ± 2.51% in the control group. The density of RPCP, SCP, and DCP were less in the RP group (P: 0.044, P: <0.001, and P: 0.016, respectively).
The weakening of the retinal vessels occurs long before the bone specular pigment formation in RP. The migration of RPE cells around the inner retinal vessels stimulates the accumulation of extracellular matrix (ECM) which is similar to the ectopic Bruch membrane, and this perivascular ECM gradually thickness and occludes the lumen of the vessels. Inner and outer retinal segments feed from different vascular structures, so different retinal segments may be affected in circulatory disorders. Since retina is rich in terms of vascular tissues, there are vascular pathologies in many retinal diseases. In this study we examined how much retinal perfusion and retinal layers are affected in patients with RP, which may have a complex genetic structure. According to this study, while there was no significant difference in retinal layer thickness in RP patients in the central fovea, RNFL, GCL, IPL, and ONL were thinner in both parafoveal and perifoveal regions. As an OCT-A finding, patients with RP had less vascular densities in the RCP, SCP, and DCP layers. When the retinal layers are examined, it is revealed that in addition to the genetic pathophysiological process of RP, retinal vascular perfusion is also affected by this process and/or affects the process.
The authors received no grants and funds in support of the study.