Reduced metabolic function and structural alterations in inherited retinal dystrophies: investigating the effect of peripapillary vessel oxygen saturation and vascular diameter on the retinal nerve fibre layer thickness

Investigation of Structural Alterations in Inherited Retinal Diseases: A Quantitative SD-OCT-Analysis of Retinal Layer Thicknesses in Light of Underlying Genetic Mutations

Inherited retinal diseases can result from various genetic defects and are one of the leading causes for blindness in the working-age population. The present study aims to provide a comprehensive description of changes in retinal structure associated with phenotypic disease entities and underlying genetic mutations. Full macular spectral domain optical coherence tomography scans were obtained and manually segmented in 16 patients with retinitis pigmentosa, 7 patients with cone−rod dystrophy, and 7 patients with Stargardt disease, as well as 23 age- and sex-matched controls without retinal disease, to assess retinal layer thicknesses. As indicated by generalized least squares models, all IRDs were associated with retinal thinning (p < 0.001), especially of the outer nuclear layer (ONL, p < 0.001). Except for the retinal nerve fiber layer, such thinning was associated with a reduced visual acuity (p < 0.001). These advances in our understanding of ultrastructural retinal changes are important for the development of gene-, cell-, and optogenetic therapy. Longitudinal studies are warranted to describe the temporal component of those changes.

The Presence of Hyperreflective Foci Reflects Vascular, Morphologic and Metabolic Alterations in Retinitis Pigmentosa

Background: The presence of hyperreflective foci (HRF) in retinitis pigmentosa (RP) is a potentially new finding. We investigated the presence of HRF in SD-OCT images in eyes with RP and its relation to vascular, morphologic and metabolic findings in RP. Methods: The study was performed on 42 RP patients and 24 controls. Using SD-OCT, we calculated the amount of HRF within the entire retina (HRF-ER) and the outer nuclear layer (HRF-ONL). Retinal vessel diameters (μm) and oxygen saturation (%) values were measured using Oxymap T1. We evaluated the mean diameter in retinal arterioles (D-A) and venules (D-V), the corresponding oxygen saturation values (A-SO₂, V-SO₂) and the oxygen saturation difference (A-V SO₂). Results: RP differed from controls by HRF-ER, HRF-ON and EZ-length (p < 0.001). D-A and D-V were narrower and A-SO₂ and V-SO₂ were higher in RP (p ≤ 0.001). Within RP, significant interactions were found between the HRF-ER* group and: BCVA, EZ length, D-A, A-SO₂ and A-V SO₂ (p ≤ 0.018). The HRF-ONL* group interactions were significant for: BCVA, EZ length, D-A, A-SO₂ and A-V SO₂ (p ≤ 0.014). Conclusion: The present study highlights the presence of HRF to reflect the vascular, morphologic and metabolic alterations in RP. These biomarkers seem to be associated with remodeling and apoptosis that occur with the progression of degeneration.

Peripapillary Oxygenation and Retinal Vascular Responsiveness to Flicker Light in Primary Open Angle Glaucoma

The aim of our study was to evaluate peripapillary oxygenation and its relationship to retinal vascular responsiveness to flicker light in patients with primary open angle glaucoma (POAG). Retinal vessel oxygen saturation was measured in 46 eyes of 34 Caucasian patients with POAG and in 21 eyes of 17 age-matched controls using the oximetry tool of Retinal Vessel Analyser (RVA: IMEDOS Systems UG, Jena, Germany). The mean oxygen saturation of the major arterioles (A-SO2; %) and venules (V-SO2; %), as well as the corresponding arterio−venular difference (A-V SO2; %), were calculated. We also measured retinal vascular responsiveness (RVR) to flicker light by means of RVA. Glaucoma patients were divided in two subgroups according to their median arteriolar and venular vascular responsiveness to flicker light (AFR and VFR). Glaucomatous damage was assessed by optical coherence tomography (Carl Zeiss Meditec, Dublin, CA, USA) and static automated perimetry (Octopus, program G2/standard strategy: Haag-Streit International, Köniz, Switzerland). In addition, we calculated the mean peripapillary oxygen exposure [ppO2E; %/µm] by dividing the mean A-V SO2 with the mean retinal nerve fibre layer (RNFL) thickness. In glaucoma patients, A-SO2 and V-SO2 values were significantly increased, and their difference decreased when compared to controls (p < 0.017; linear mixed-effects model). Grouped with respect to retinal vascular responsiveness to flicker light, subjects with reduced VFR (≤2.9%) had significantly higher ppO2E (0.49 ± 0.08%/µm, respectively, 0.43 ± 0.06%/µm; p = 0.027). Additionally, higher ppO2E in glaucoma patients correlated negatively with the neuroretinal rim area (p < 0.001) and the RNFL thickness (p = 0.017), and positively with the mean defect of the visual field (p = 0.012). Reduced venular vascular responsiveness in our glaucoma patients was associated with increased peripapillary oxygenation exposure. Thus, ganglion cells and their axons in glaucomatous eyes with reduced retinal vascular responsiveness are prone to be more exposed to higher oxidative stress, probably contributing to the further progression of glaucomatous damage.

A Systematic Review of Artificial Intelligence Applications Used for Inherited Retinal Disease Management

Nowadays, Artificial Intelligence (AI) and its subfields, Machine Learning (ML) and Deep Learning (DL), are used for a variety of medical applications. It can help clinicians track the patient’s illness cycle, assist with diagnosis, and offer appropriate therapy alternatives. Each approach employed may address one or more AI problems, such as segmentation, prediction, recognition, classification, and regression. However, the amount of AI-featured research on Inherited Retinal Diseases (IRDs) is currently limited. Thus, this study aims to examine artificial intelligence approaches used in managing Inherited Retinal Disorders, from diagnosis to treatment. A total of 20,906 articles were identified using the Natural Language Processing (NLP) method from the IEEE Xplore, Springer, Elsevier, MDPI, and PubMed databases, and papers submitted from 2010 to 30 October 2021 are included in this systematic review. The resultant study demonstrates the AI approaches utilized on images from different IRD patient categories and the most utilized AI architectures and models with their imaging modalities, identifying the main benefits and challenges of using such methods.

Full-field sensitivity threshold and the relation to the oxygen metabolic retinal function in retinitis pigmentosa

PURPOSE

The aim of our study was to evaluate retinal function with white light dark-adapted full-field sensitivity threshold (FST) and find possible correlations with metabolic function measured with retinal oximetry (RO) in patients with retinitis pigmentosa (RP).

METHODS

In this prospective observational study (BASEC 2020-00,122), FST and RO measurements were performed on 66 RP eyes (33 subjects, 12♀ 21♂) aged between 18 and 80 years (mean 43.2 years); all eyes were graded for disease severity. Main outcome parameters were white FST thresholds using the Diagnosys Espion system with the ColorDomeTM LED full-field stimulator (Diagnosys LLC, Lowell, MA) as well as the main RO parameters: the mean arterial (A-SO₂; %), venular (V-SO₂; %) oxygen saturation, their difference (A-V SO₂; %), and the corresponding mean diameters of the peripapillary retinal arterioles (D-A; μm) and venules (D-V; μm) recorded with the oxygen saturation tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). In addition, semi-automated kinetic perimetry (V4e, III4e, I4e, III3e isopters, Octopus 900®, Haag-Streit AG Bern, Switzerland) was performed and included in the linear mixed-effects models analysis calculated with SPSS®.

RESULTS

Neither the oxygen saturation parameters (p > 0.21) nor the D-A and D-V (p > 0.13) showed significant correlations with the FST. However, when compared systematically with the visual field (VF) areas of the different isopters, RO parameters V-SO₂ (p = 0.024) and A-V SO₂ (p < 0.02) showed significant correlations. Furthermore, both V-SO₂ and A-V SO₂ showed gradual changes with more pronounced impairment in oxygen metabolic function in advanced stages of RP when analyzed in subgroups of disease severity grades.

CONCLUSION

In contrast to standardized VF parameters, white dark-adapted FST appears not to correlate with retinal oxygen metabolic function measured with RO in patients with RP, suggesting that the two examinations may capture unrelated aspects of the retinal pathological process. However, RO showed a significant association with standardized VF testing parameters and may, therefore, offer an alternative outcome measure for interventional trials.

Microvascular and metabolic alterations in retinitis pigmentosa and Stargardt disease

PURPOSE

The aim of our study was to evaluate retinal microvascular changes recorded with optical coherence tomography angiography (OCTA) and the metabolic function measured with retinal oximetry (RO) in patients with retinitis pigmentosa (RP) and Stargardt disease (STGD).

METHODS

In this prospective, noninterventional study, OCTA and RO were performed on 107 eyes (56 subjects): 53 eyes diagnosed with RP without the presence of macular oedema (no-ME-RP), 26 eyes with STGD, and 28 control eyes. Main outcome measures were the mean superficial (FAZ-S; mm² ) and deep foveal avascular zone (FAZ-D; mm² ) measured with OCTA as well as the mean arterial (A-SO₂ ; %), venular (V-SO₂ ; %) oxygen saturation, their difference (A-V SO₂ ; %) and the corresponding mean diameters of the peripapillary retinal arterioles (D-A; μm) and venules (D-V; μm) determined with RO.

RESULTS

Stargardt disease (STGD) patients differed from controls and no-ME-RP by an enlarged FAZ-S and reduced A-SO₂ and V-SO₂ (p ≤ 0.013). No-ME-RP eyes presented with attenuated vessels (p < 0.001) and increased A-SO₂ and V-SO₂ (p ≤ 0.012) compared to controls and STGD. The FAZ-D showed significant interactions with A-SO₂ (p = 0.003) in no-ME-RP while the FAZ-S correlated with visual acuity in no-ME-RP (p = 0.007) and STGD (p = 0.034).

CONCLUSION

Retinitis pigmentosa (RP) and Stargardt disease (STGD) patients suffer from microvascular and metabolic alterations, however, showing a different pattern. A combined microvascular-metabolic model may therefore allow to more precisely characterize RP and STGD as well as presumably other inherited retinal diseases.

Metabolic Long-Term Monitoring of Transcorneal Electrical Stimulation in Retinitis Pigmentosa

INTRODUCTION

Transcorneal electrical stimulation (TES) is a new therapeutical approach for retinitis pigmentosa (RP). With progression of RP, degeneration of photoreceptors results in lower oxygen consumption of the retina. Retinal oximetry (RO) is a noninvasive method to analyze oxygen saturation in retinal vessels and has shown promising short-term results as a therapy monitoring tool for TES. The aim of our study was to measure the long-term effects of TES on RO parameters over a period of 3 years (3Y).

METHODS

A total of 18 eyes of 9 subjects (5♀ 4♂) suffering from RP were examined at baseline (BL), 6 months, and 3Y of TES (OkuStim®) treatment. TES was performed for 30 min once a week at 200% of the individual phosphene threshold simultaneously on both eyes. The oxygen saturation was examined at BL and following TES therapy with the oxygen saturation tool of the Retinal Vessel Analyser (IMEDOS Systems UG, Jena, Germany). The global oxygen saturation parameters (in %), within 1.0-1.5 optic-disc diameters from the disc margin, in retinal arterioles (A-SO2) and venules (V SO2) were measured and their difference (A-V SO2) was calculated. In addition, we recorded the diameters in the main arterioles (D-A) and venules (D-V). ANOVA-based linear mixed-effects models were employed for statistical analysis using SPSS®.

RESULTS

After 3Y of TES treatment both the mean A-SO2 (from 96.35 ± 12.76% to 100.89 ± 5.87%, p = 0.22) and V SO2 (from 62.20 ± 11.55% to 64.55 ± 8.24%, p = 0.77) increased slightly. The A-V SO2, which corresponds to the oxygen consumption of the retina, presented also with a slight increment from 34.15 ± 9.68% at BL to 36.23 ± 7.71% without reaching statistical significance (p = 0.27). TES also did not appear to alter the vascular diameter parameters, D-A and D-V (p > 0.05).

CONCLUSION

Our long-term observations indicate that TES therapy in RP might lead to a slight increment in oxygen consumption of the retina. However, a larger cohort and longer duration may be needed to adequately power a follow-up study and to confirm this trend reflecting a possible benefit of TES for RP.

Variability of Retinal Oxygen Metrics in Healthy and Diabetic Subjects

Purpose

Previous studies have reported alterations in total retinal blood flow (TRBF), oxygen delivery (DO2), oxygen metabolism (MO2), and oxygen extraction fraction (OEF) due to retinal diseases. The purposes of the current study were to determine variabilities and establish normal confidence intervals (CIs) for these metrics.

Methods

A total of 22 healthy and 14 diabetic subjects participated in the study. Retinal vascular oxygen saturation (SO2) and TRBF were measured by oximetry and Doppler optical coherence tomography, respectively. DO2, MO2, and OEF were calculated from SO2 and TRBF measurements. Means, standard deviations (SDs), and CIs of metrics were determined in healthy subjects. Intra-visit variability was determined by the mean SDs of repeated measurements. Inter-visit variability was determined by the difference of measurements between two visits.

Results

TRBF was 44 ± 15 µL/min (95% CI, 37-51) in healthy subjects. Intra-visit variabilities of TRBF were 5 µL/min and 6 µL/min in healthy and diabetic subjects, respectively. Inter-visit variability of TRBF was 3 µL/min in diabetic subjects. DO2, MO2, and OEF were 8.3 ± 2.9 µLO2/min (95% CI, 7.0-9.6), 3.2 ± 0.9 µLO2/min (95% CI, 2.8-3.6), and 0.40 ± 0.08 (95% CI, 0.36-0.43), respectively, in healthy subjects. Inter-visit variabilities of DO2, MO2, and OEF were 0.6 µLO2/min, 0.1 µLO2/min, and 0.03, respectively, in diabetic subjects.

Conclusions

The findings established variabilities and normal baselines for TRBF, DO2, MO2, and OEF measurements in a small cohort of subjects.

Translational Relevance

The variability and normal baselines of retinal oxygen metrics may be useful for diagnosing and monitoring patients with retinal diseases.

Analysis of imaging biomarkers and retinal nerve fiber layer thickness in RPGR-associated retinitis pigmentosa

Purpose

To investigate multimodal retinal imaging characteristics including the retinal nerve fiber layer (RNFL) thickness in patients with RPGR-associated retinitis pigmentosa (RP).

Methods

This cross-sectional case–control study included 17 consecutive patients (median age, 21 years) with RPGR-associated RP who underwent retinal imaging including optical coherence tomography (OCT), short-wavelength fundus autofluorescence (AF) imaging, and RNFL scans centered on the optic disc. RNFL thickness was manually segmented and compared to clinical and imaging parameters including the transfoveal ellipsoid zone (EZ) width, the horizontal diameter of the macular hyperautofluorescent ring. RNFL thickness was compared to 17 age- and sex-matched controls.

Results

In patients with RPGR-associated RP, the EZ width (R² = 0.65), the central hyperautofluorescent ring on AF images (R² = 0.72), and visual acuity (R² = 0.68) were negatively correlated with age. In comparison to controls, a significantly (p < 0.0001) increased global RNFL thickness was identified in RPGR-associated RP, which was, however, less pronounced in progressed disease as indicated by the EZ width or the diameter of the central hyperautofluorescent ring.

Conclusions

This study describes retinal characteristics in patients with RPGR-associated RP including a pronounced peripapillary RNFL thickness compared to healthy controls. These results contribute to the knowledge about imaging biomarkers in RP, which might be of interest for therapeutic approaches such as gene replacement therapies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00417-021-05233-w.

Linking the Presence of Macular Oedema to Structural and Functional Alterations in Retinitis Pigmentosa

OBJECTIVE

To investigate the association between the central retinal thickness (CRT), the retinal nerve fibre layer thickness (RNFL), and the functional alterations in retinitis pigmentosa (RP) patients.

METHODS

Forty-three patients with typical RP and nineteen age-matched controls, who underwent SD-OCT (macular and optic disc OCT protocols) and electrophysiology, were included. The RP group was divided into two subgroups: with clinical appearance of macular oedema (ME-RP; 30 eyes) and without macular oedema (no-ME; 44 eyes). Central retinal thickness OCT data were averaged in three zones (zone 1 [0°-3°], zone 2 [3°-8°], and zone 3 [8°-15°]) and were evaluated in relation to the RNFL thickness and electrophysiological data.

RESULTS

The ME-RP group showed increased CRT (zone 1) and RNFL thickness compared to the controls and no-ME-RP (p ≤ 0.002). The no-ME-RP group had reduced CRT thickness (all zones; p ≤ 0.018) compared to the controls and ME-RP, whereas the RNFL thickness in the no-ME-RP group was reduced only compared to the ME-RP group (p < 0.001). The ME-RP group showed significantly more attenuated functional responses than the no-ME-RP patients. A significant positive interaction was found between the CRT (zones 1 and 2) and the RNFL thickness within ME-RP (p ≤ 0.010). Significant negative interactions were found between CRT, RNFL thickness, and functional findings within ME-RP (p ≤ 0.049).

CONCLUSION

The presence of macular oedema correlated well with increased RNFL thickness and residual function in RP patients. Such association provides evidence of an underlying transneuronal mechanism of retinal degeneration. Simultaneous monitoring of CRT and RNFL thickness may help in the future to evaluate the progression of the disease and the efficacy of treatments in RP patients.

Retinal Oxygenation in Inherited Diseases of the Retina

(1) Background: The aim of our study was to investigate the relationship between retinal metabolic alterations (retinal vessel oximetry, RO) and structural findings (retinal vessel diameter, central retinal thickness and retinal nerve fiber layer thickness, RNFL) in patients with inherited retinal diseases (IRDs). (2) Methods: A total of 181 eyes of 92 subjects were examined: 121 eyes of 62 patients with IRDs were compared to 60 eyes of 30 healthy age-matched controls. The retinal vessel oximetry was performed with the oxygen saturation measurement tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). The oxygen saturation in all four major peripapillary retinal arterioles (A-SO₂; %) and venules (V-SO₂; %) were measured and their difference (A-V SO₂; %) was calculated. Additionally, retinal vessel diameters of the corresponding arterioles (D-A; µm) and venules (D-V; µm) were determined. The peripapillary central retinal thickness and the RNFL thickness were measured using spectral domain optical coherence tomography (SD-OCT) (Carl Zeiss Meditec, Dublin, CA, USA). Moreover, we calculated the mean central retinal oxygen exposure (cO₂-E; %/µm) and the mean peripapillary oxygen exposure (pO₂-E; %/µm) per micron of central retinal thickness and nerve fiber layer thickness by dividing the mean central retinal thickness (CRT) and the RNFL thickness with the mean A-V SO₂. (3) Results: Rod-cone dystrophy patients had the highest V-SO₂ and A-SO₂, the lowest A-V SO₂, the narrowest D-A and D-V and the thickest RNFL, when compared not only to controls (p ≤ 0.040), but also to patients with other IRDs. Furthermore, in rod-cone dystrophies the cO₂-E and the pO₂-E were higher in comparison to controls and to patients with other IRDs (p ≤ 0.005). Cone-rod dystrophy patients had the lowest cO₂-E compared to controls and patients with other IRDs (p ≤ 0.035). Evaluated in central zones, the cO₂-E was significantly different when comparing cone-rod dystrophy (CRD) against rod-cone dystrophy (RCD) patients in all zones (p < 0.001), whereas compared with controls and patients with inherited macular dystrophy this was observed only in zones 1 and 2 (p ≤ 0.018). The oxygen exposure was also the highest in the RCD group for both the nasal and the temporal peripapillary area, among all the evaluated groups (p ≤ 0.025). (4) Conclusions: The presented metabolic-structural approach enhances our understanding of inherited photoreceptor degenerations. Clearly demonstrated through the O₂-E comparisons, the central and the peripapillary retina in rod-cone dystrophy eyes consume less oxygen than the control-eyes and eyes with other IRDs. Rod-cone dystrophy eyes seem to be proportionally more exposed to oxygen, the later presumably leading to more pronounced oxidative damage-related remodeling.

Retinal vessel oximetry in children with inherited retinal diseases

BACKGROUND

Retinal vessel oximetry (RO) has been used to show altered metabolic function in patients with inherited retinal diseases (IRDs). The aim of this study was to investigate RO parameters of children with IRDs and presumed IRD carriers (pIRDc) and to compare them to controls.

METHODS

In this cross-sectional cohort study, 142 eyes from 71 Caucasian subjects were included: 40 eyes with IRDs, 26 eyes with pIRDc and 76 control eyes. The oxygen saturation was measured with the Retinal Vessel Analyser (IMEDOS Systems UG, Jena, Germany). Mean oxygen saturations in the peripapillary retinal arterioles (A-SO₂ ; %) and venules (V-SO₂ ; %) were estimated, and their difference (A-V SO₂ ; %) was calculated. In addition, we evaluated the mean diameter in all major retinal arterioles (D-A; μm) and venules (D-V; μm). anova-based linear mixed-effects models were calculated with SPSS^® .

RESULTS

In general, children suffering from IRDs differed from controls when the A-SO₂ and A-V SO₂ were taken into account: both the A-SO₂ and the A-V SO₂ were significantly increased (p = 0.012). In subgroup analyses, children suffering from rod-cone dystrophy (RCD) presented an A-SO₂ increase (99.12 ± 8.24%) when compared to controls (91.33 ± 10.34%, p = 0.014) and pIRDc (92.37 ± 6.57%, p = 0.065). For V-SO₂ significant changes in RCD (67.42 ± 9.19%) were found in comparison with controls (58.24 ± 11.74%, p < 0.041), pIRDc (56.67 ± 7.16%, p = 0.007), cone-rod dystrophies (CRD, 52.17 ± 5.32%, p < 0.001) and inherited macular dystrophies (IMD, 55.74 ± 6.96%, p = 0.004), In addition, A-V SO₂ was decreased in RCD (31.69 ± 3.92%) when measured against CRD (41.9 ± 8.87%, p = 0.017) or IMD (39.52 ± 8.95%, p = 0.059).

CONCLUSION

In general, we found that children with IRDs presented early metabolic changes. Within IRDs, children with RCD showed more affected metabolic changes. Thus, RO may support early screening to rule out IRDs in children, and more precisely may help to differentiate those suffering from RCD.

Optical coherence tomography angiography findings in patients undergoing transcorneal electrical stimulation for treating retinitis pigmentosa

Purpose

Transcorneal electrical stimulation (TES) is a novel treatment approach for patients with retinitis pigmentosa (RP). The aim of our study was to observe changes in optical coherence tomography angiography (OCTA) that would be attributed to TES treatment.

Methods

A total of 73 eyes were included: 43 eyes of 22 subjects (11 ♀, 11 ♂) suffering from RP were examined at baseline (BL), after first stimulation (TS), 1 week (1W), and 6 months (6M) after treatment initiation and were compared with 30 control eyes of 15 subjects (8 ♀, 7 ♂). TES was performed simultaneously on both eyes for 30 min weekly. OCTA scans of 9 × 15 mm were recorded with a PLEX Elite 9000 swept-source OCTA device (Carl Zeiss Meditec AG, Jena). Vascular density metrics such as perfusion density (PD) and vessel density (VD) were calculated automatically for the macular area by using standardised extended early treatment diabetic retinopathy study (ETDRS) grids centred around the fovea. In addition, the capillary perfusion density (CPD) and the capillary flux index (CFI) of the peripapillary nerve fibre layer microvasculature in all four quadrants of an annulus centred at the optic disc were measured. All parameters were determined over all retinal layers and separately for the superficial (SCP) and deep capillary plexus (DCP). ANOVA-based linear mixed-effects models were calculated with SPSS®.

Results

Throughout the course of TES treatment, the macular VD and PD of all retinal layers in all subsections showed a slight decrement without reaching statistical significance, also when analysed separately in the SCP and DCP (p > 0.08). In analogy, the average CPD and CFI also presented with a slight decrement (p > 0.20). However, when compared with controls, most OCTA parameters showed a significant decrement (p < 0.05). When analysed systematically in all subsections of the extended ETDRS grid, the temporal macular subsections within the outer ring (radius 1.5–3 mm) and also of the peripheral C1, C2, and C3 rings (radius 3–7.5 mm) showed lower VD and PD values when compared with the other subsections (p < 0.05).

Conclusion

Vascular density metrics in the macular region and the peripapillary microvasculature appear to remain unaffected by continuous TES treatment within a period of 6 months.

Electronic supplementary material

The online version of this article (10.1007/s00417-020-04963-7) contains supplementary material, which is available to authorized users.

Identification of PROS1 as a Novel Candidate Gene for Juvenile Retinitis Pigmentosa

Homozygous mutations of PROS1, encoding vitamin K-dependent protein S (PS), have been reported so far to be associated with purpura fulminans, a characteristic fatal venous thromboembolic disorder. The current work for the first time reports the clinical phenotype in patients with juvenile retinitis pigmentosa harboring a novel likely pathogenic variant in thePROS1 gene. Whole-exome sequencing was performed on probands of a cohort with inherited retinal disease. Detailed phenotyping was performed, including clinical evaluation, electroretinography, fundus photography and spectral-domain optical coherence tomography. Analysis of whole-exome and Sanger sequencing led to the identification of a homozygous missense substitution (c.G122C:p.R41P) in PROS1 in affected individuals from two unrelated consanguineous families of Persian origin which had classic retinitis pigmentosa with no history of venous thromboembolic disorder. This variant was segregated, fully congruous with the phenotype in all family members. Consistently, none of 1000 unrelated healthy individuals from the same population carried the mentioned variant, according to Iranian national genome database (Iranome) and additional in-house exome control data. This study provides inaugural clinical traces for different role of PS as a ligand for TAM receptor-mediated efferocytosis at the retinal pigmented epithelium; the R41P variant may affect proper folding of PS needed for γ-carboxylation and extra-cellular secretion. That conformational change may also lead to defective apoptotic cell phagocytosis resulting in postnatal degeneration of photoreceptors.

A detailed in vivo analysis of the retinal nerve fibre layer in choroideremia

PURPOSE

Choroideremia is a currently incurable X-linked recessive retinal degeneration that leads to blindness. Gene therapy approaches to date target the outer retinal layers. However, the choroideremia (CHM) gene is expressed in all retinal layers, and a previous study on a small cohort of choroideremia patients suggested possible thinning of the retinal nerve fibre layer (RNFL). The purpose of the study was to examine the RNFL in detail using advanced imaging techniques in a larger cohort of choroideremia patients.

METHODS

Spectral domain optical coherence tomography of the peripapillary RNFL acquired with the Heidelberg Spectralis HRA circular scan mode were analysed retrospectively in 41 eyes of 21 choroideremia patients aged 39.6 years (±3.7 SEM). As age-matched controls, 20 eyes from 10 patients with retinitis pigmentosa and 56 eyes from 28 healthy individuals were also assessed. Automated RNFL segmentation was adjusted manually to precisely delineate the RNFL. The data were also compared against an external normative database.

RESULTS

Mean peripapillary RNFL thickness in choroideremia was 130 ± 3 μm in the right eye (OD) and 133 ± 3 μm in the left eye (OS). This was 24% and 27% thicker than RNFL thickness in the controls (p < 0.001 for both). Patients with retinitis pigmentosa also showed an increase in RNFL thickness, which was no different to the choroideremia cohort (p > 0.05). Compared with manual analysis, the automated function of the inbuilt software was consistently inaccurate in segmenting the RNFL in choroideremia.

CONCLUSION

The RNFL is significantly thicker in choroideremia compared with age-matched normal controls, which was similar to what was seen in retinitis pigmentosa.

Choroidal structural analysis and vascularity index in retinal dystrophies

PURPOSE

To assess choroidal structural changes in patients with retinal dystrophies using choroidal vascularity index (CVI), a novel optical coherence tomography (OCT) based tool.

METHODS

This retrospective study included 26 patients with retinal dystrophies (17 with retinitis pigmentosa, four with Stargardt disease, three with cone-rod dystrophy, one each with Best disease and Bietti crystalline dystrophy) and 32 healthy controls. Subfoveal OCT images were used for analysis. Mean CVI was compared between retinal dystrophy and control group, as well as among the retinal dystrophy subgroups.

RESULTS

Mean CVI in eyes with retinal dystrophies was 52 ± 9% and it was significantly lower compared to that in normal eyes (70 ± 3%, p < 0.001). The differences among subgroups of retinal dystrophy were not statistically significant (p = 0.084). All types of retinal dystrophy were associated with lower CVI (all p < 0.001), after adjusting for age, gender, visual acuity and duration of symptoms. Older age was also shown to be independently associated with lower CVI (p = 0.012). Gender, visual acuity (VA) and duration of symptoms did not significantly affect CVI.

CONCLUSION

Decreased choroidal vascularity was seen in eyes with retinal dystrophies. (CVI) may be a helpful tool in monitoring choroidal involvement in retinal dystrophies.

Normative values of retinal vessel oximetry in healthy children against adults

BACKGROUND

Retinal oximetry (RO) has been established as a non-invasive method to analyse oxygen saturation in retinal vessels. The aim of our study was to compare the RO parameters of healthy children to those in adults.

METHODS

A total of 200 eyes of 104 healthy subjects were examined: 20 eyes of children aged <10 years and 62 eyes of children aged 10-19 years were compared to the eyes of adult controls from five different age groups (20-29 years:n = 24; 30-39 years:n = 32; 40-49 years:n = 15; 50-59 years:n = 20, 60-80 years:n = 27; n indicates the number of analysed eyes). The oxygen saturation was estimated with the oxygen saturation measurement tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). The global oxygen saturations, within 1.0-1.5 optic disc diameters from the disc margin, in the peripapillary retinal arterioles (A-SO₂ ; %) and venules (V-SO₂ ; %) were estimated and their difference (A-V SO₂ ; %) was calculated. In addition, we evaluated the mean diameter in all four major retinal arterioles (D-A; μm) and venules (D-V; μm). The ratio between venular and arterial vessel diameter (D-V/A; μm) was calculated thereafter. For statistical evaluation, anova-based linear mixed-effects models were calculated with spss^® .

RESULTS

Based on our results, younger children (<10 years) present a statistically significant lower A-SO₂ and A-V SO₂ when compared to adult subgroups. The D-A values revealed to be significantly lower in 10 + children when compared to the other groups, while the D-V values did not show significant differences.

CONCLUSION

These data indicate that the retinal oxygen metabolism changes throughout lifetime. Therefore, normative data for different age groups are mandatory.

The effect of autoimmune retinopathy on retinal vessel oxygen saturation

PURPOSE

To study the retinal vessel oxygen saturation alterations in patients with autoimmune retinopathy (AIR) and patients with autoimmune retinopathy associated with retinitis pigmentosa (AIR-RP) in comparison with healthy controls and patients with isolated retinitis pigmentosa (RP).

DESIGN

Prospective, cross-sectional, and non-interventional study.

SUBJECTS

Retinal vessel oximetry (RO) was performed on a total of 139 eyes: six eyes suffering from AIR and four eyes with AIR-RP were compared to 59 healthy control eyes and to 70 eyes with RP.

METHODS

A computer-based program of the retinal vessel analyser unit (IMEDOS Systems UG, Jena, Germany) was used to evaluate retinal vessel oxygen saturation. The mean oxygen saturation in the first and second branch retinal arterioles (A-SO₂) and venules (V-SO₂) were measured and their difference (A-V SO₂) was calculated. In addition, we measured the diameter of the retinal arterioles (D-A) and venules (D-V).

MAIN OUTCOME MEASURES

Oxygen metabolism is altered in patients with isolated AIR and AIR-RP.

RESULTS

Both, AIR and AIR-RP groups, differed from healthy controls showing significantly higher V-SO₂ values and significantly lower A-V SO₂ values (p < 0.025). In addition, the AIR-RP group could be differentiated from eyes suffering from isolated RP by means of significantly higher V-SO₂ values. Comparing retinal vessel diameters, both, the AIR and AIR-RP groups, presented with significant arterial (p = 0.05) and venular (p < 0.03) vessel attenuation than the healthy control group.

CONCLUSIONS

Based on our results, in analogy to patients suffering from RP, oxygen metabolism seems to be altered in AIR patients.

Higher retinal vessel oxygen saturation: investigating its relationship with macular oedema in retinitis pigmentosa patients

PURPOSE

Primary objective-to investigate the effect of retinal vessel oxygen saturation (SO₂) on macular oedema (ME) in retinitis pigmentosa (RP) patients. Secondary objective-to link the presence of ME to metabolic (oxygen saturation of retinal vessels, SO₂), functional (multifocal electroretinography, mfERG) and structural (Spectral Domain Optical Coherent Tomography, SD-OCT) alterations in RP.

DESIGN

Prospective, cross-sectional, non-interventional study.

SUBJECTS

Patients with typical RP (N = 37) and controls (N = 19), who underwent retinal vessel Oximetry (RO), SD-OCT and mfERG, were included.

METHODS

A computer-based program of the retinal vessel analyser unit (IMEDOS Systems UG, Jena, Germany) was used to measure SO₂. We evaluated the mean SO₂, in all major retinal arterioles (oxygen saturation in retinal arterioles, A-SO₂, %) and venules (oxygen saturation in retinal venules, V-SO₂, %). MfERG responses were averaged in zones (zone 1 (0-3°), zone 2 (3-8°) and zone 3 (8-15°)) and compared to corresponding areas of the OCT. The effect of ME on SO₂ was evaluated dividing the RP in two subgroups: with clinical appearance of ME (ME-RP) and without it (no-ME-RP).

MAIN OUTCOME MEASURES

Parallel recording and juxtaposition of metabolic (SO₂) to structural (OCT) and functional-(mfERG) measures. Mean ( ± SD) A-SO₂ and V-SO₂ were higher in no-ME-RP (96.77% (±6.31) and 59.93% (±7.76)) and even higher in the ME-RP (99.82% (±6.21) and 65.63% (±7.63)), compared to controls (93.15% (±3.76) and 53.77% (±3.70), p ≤ 0.006).

RESULTS

The subgroup ME-RP differed significantly from the subgroup no-ME-RP by increased A-SO₂ and V-SO₂, p ≤ 0.026. The presence of ME confirmed a different relationship between the altered SO₂ and the vessel diameters, against the functional and structural parameters.

CONCLUSION

Based on our results, the presence of macular oedema indicates a tendency toward greater alteration of the metabolic function in RP patients.