Retinal oximetry in patients with ischaemic retinal diseases

The retinal oxygen metabolism and hemodynamics as a substitute for biochemical tests to predict nonproliferative diabetic retinopathy

Predicting the occurrence of nonproliferative diabetic retinopathy (NPDR) using biochemical parameters is invasive, which limits large-scale clinical application. Noninvasive retinal oxygen metabolism and hemodynamics of 215 eyes from 73 age-matched healthy subjects, 90 diabetic patients without DR, 40 NPDR, and 12 DR with postpanretinal photocoagulation were measured with a custom-built multimodal retinal imaging device. Diabetic patients underwent biochemical examinations. Two logistic regression models were developed to predict NPDR using retinal and biochemical metrics, respectively. The predictive model 1 using retinal metrics incorporated male gender, insulin treatment condition, diastolic duration, resistance index, and oxygen extraction fraction presented a similar predictive power with model 2 using biochemical metrics incorporated diabetic duration, diastolic blood pressure, and glycated hemoglobin A1c (area under curve: 0.73 vs. 0.70; sensitivity: 76% vs. 68%; specificity: 64% vs. 62%). These results suggest that retinal oxygen metabolic and hemodynamic biomarkers may replace biochemical parameters to predict the occurrence of NPDR .

Laser Treatment Modalities for Diabetic Retinopathy

Diabetes is a chronic progressive metabolic disorder that is caused by the body's inability to regulate blood glucose levels. If uncontrolled, it can lead to various complications. Among its various complications, long-term diabetes leads to diabetic retinopathy (DR). It is a disease involving blood vessels and the destruction of retinal nerves. It is usually classified into two types: proliferative diabetic retinopathy (PDR) and nonproliferative diabetic retinopathy (NPDR). It progresses and causes loss of vision. The leading cause of loss of vision is diabetic macular edema (DME). The argon laser is used as a modality in the management of PDR. There are various types of laser photocoagulation, such as peripheral retinal laser photocoagulation, focal macular laser photocoagulation, and grid photocoagulation. DR results in various adverse consequences such as vitreous hemorrhage, fibrosis, traction, detachment of the retina, and glaucoma. To assess DR, a detailed fundus examination with a slit lamp biomicroscope needs to be done. Seven-standard field stereoscopic-color fundus photography needs to be done for documentation and follow-up. Patients with diabetes mellitus (DM) type 1 have a greater risk of suffering from DR. Another major complication of the condition is DME, which is characterized by an increase in the permeability of vessels and the thickening of the central part of the retina along with the accumulation of hard exudates on the macula. This article discusses various laser therapy modalities for the treatment of DR, their types, mechanisms, and aims. Clinical features of DR include abnormal dilatation of capillaries, and outpouchings in the form of microaneurysm from the capillary wall are one of the earliest and most dangerous changes; later, non-perfusion of the retina occurs, which is associated with cotton wool spots and blot hemorrhages. In patients suffering from PDR and maculopathy, peripheral retinal laser photocoagulation is used as a mode of intervention.

Non-invasive structural and metabolic retinal markers of disease activity in non-proliferative diabetic retinopathy

PURPOSE

Metabolic and structural microvascular retinal alterations are essential components in diabetic retinopathy (DR). The present study aimed to measure changes at different stages of non-proliferative DR (NPDR) and to explore interactions of imaging-based metrics.

METHODS

This cross-sectional, cohort study included 139 eyes from 80 diabetic patients. Each patient underwent dilated fundal examinations including colour fundus photography, retinal oximetry and optical coherence tomography angiography (OCTA), analysed by semi-automated and automated software. Diabetic retinopathy (DR) severity was classified according to the International Clinical Diabetic Retinopathy (ICDR) Severity Scale, ranging from no DR to severe NPDR (level 0-3). Retinal metabolism was evaluated by oximetry as retinal arteriolar (raSatO₂ ) and venular oxygen saturation (rvSatO₂ ), and macular microvascular structure was measured by OCTA as the area of foveal avascular zone (FAZ), vessel density (VD), vessel diameter index (VDI), FAZ circularity and fractal dimension (FD) in the superficial and deep retinal capillary plexus.

RESULTS

A trend for increasing rvSatO₂ was found with increasing DR severity (51.3%, 53.3%, 54.2%, 59.8%, p = 0.02). Increasing severity of DR associated with decreasing FD in the superficial and deep plexus (p < 0.001 and p = 0.014), and in the superficial plexus decreasing VD (p < 0.001), increasing VDI (p = 0.003) and decreasing FAZ circularity (p = 0.006). A few interactions were identified between raSatO₂ , rvSatO₂ and VDI, but only in the deep capillary plexus (p < 0.01 and p < 0.01).

CONCLUSION

Alterations of the venular retinal vascular oxygen saturation and microvascular structural abnormities were found continuously throughout the DR-spectrum. Given the sparse correlations between metabolic and structural abnormalities, it seems that these occur independently in DR.

Retinal vascular oxygen saturation in response to a less extensive laser treatment in proliferative diabetic retinopathy

PURPOSE

The purpose of this study was to evaluate the association between retinal laser burden and vascular oxygen saturation in patients with proliferative diabetic retinopathy (PDR) treated with different extent of retinal laser.

METHODS

The study was a prospective, interventional study of patients with treatment-naïve PDR. Patients were treated with navigated retinal laser (Navilas^® , OD-OS GmbH, Teltow, Germany) in different doses. Retinal oximetry was obtained at baseline (BL) prior to laser and after 6 months (M6). Patients were divided into three groups according to total laser spots applied: <1500 spots (Group 1), 1500-2000 spots (Group 2), and >2000 spots (Group 3).

RESULTS

We included 33 eyes of 28 patients with treatment-naïve PDR. The groups did not differ according in BL characteristics. Between BL and M6, retinal arteriolar oxygen saturation did not change but retinal venular oxygen saturation (median with interquartile range) decreased in Groups 1 and 2 (1: 65.5 ± 8.8% versus 60.5 ± 9.5%, p = 0.04; 2: 65.3 ± 7.3% versus 63.0 ± 13.5%, p = 0.04). Focal retinal venular oxygen saturation, located to quadrants with retinal neovascularization, decreased in Group 2 from BL to M6 (67.5 ± 13.3% versus 61.5 ± 8.8%, p = 0.04). Retinal venular diameter decreased from BL to M6 in Group 1 (174.5 ± 15.3 μm versus 165.1 ± 28.7 μm, p = 0.01).

CONCLUSIONS

In this study of patients with treatment-naïve PDR, we showed that a less extensive laser treatment caused a reduction in retinal venular oxygen saturation and diameter 6 months after treatment. Our results suggest that less extensive laser treatment may be sufficient to improve the retinal metabolic environment conducive to PDR regression.

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.

RETINAL OXIMETRY IS ALTERED IN EYES WITH CHOROIDAL MELANOMA BUT NOT IN EYES WITH CHOROIDAL NEVI

Supplemental Digital Content is Available in the Text.

Noninvasive retinal oximetry demonstrates alterations in eyes with untreated choroidal melanoma, including an increased difference between arterial and venous saturation. These changes were not observed in eyes with choroidal nevi and may be related to the tumour's metabolism or inflammatory changes.

Purpose:

To compare retinal vessel oxygenation in eyes with an untreated choroidal nevus or choroidal melanoma.

Methods:

The affected and fellow eye of patients with an untreated choroidal nevus (n = 42) or choroidal melanoma (n = 45) were investigated using noninvasive retinal oximetry (Oxymap T1). Oxygen saturation of arterioles (ArtSat) and venules (VenSat) was determined, together with the arteriovenous difference (AV-difference).

Results:

In choroidal nevus patients, retinal oximetry did not differ between the affected and fellow eye: the mean ArtSat was 94.5% and 94.2% (P = 0.56), the VenSat was 60.5% and 61.3% (P = 0.35), and the AV-difference was 34.0% and 32.9% (P = 0.18), respectively. In choroidal melanoma patients, alterations were detected: the mean ArtSat was 94.8% and 93.2% (P = 0.006), the VenSat was 58.0% and 60.0% (P = 0.014), and the AV-difference was 36.8% and 33.2% (P < 0.001), respectively. The largest increase in AV-difference was observed between the retinal halves without the lesion in melanoma eyes compared with the corresponding half in the fellow eye (37.5% vs. 32.1%, P < 0.001).

Conclusion:

Although retinal oximetry was not significantly altered in eyes with a choroidal nevus, eyes with choroidal melanoma showed an increased ArtSat and decreased VenSat, leading to an increased AV-difference. These changes may be caused by inflammation and a higher metabolism, with larger oxygen consumption, leading to altered blood flow and intraocular oxygen relocation.

Effect of immunosuppressive therapy on oxygen saturation and diameter of retinal vessels in initial onset acute uveitis associated with Vogt-Koyanagi-Harada disease

PURPOSE

To demonstrate changes in oxygen saturation and calibre of retinal vessels in initial-onset acute uveitis associated with Vogt-Koyanagi-Harada (VKH) disease at baseline and during immunosuppressive therapy.

METHODS

In this prospective study, 22 patients (44 eyes) were studied. Retinal oximetry measurements were performed using the noninvasive spectrophotometric retinal oximeter (Oxymap T1) at baseline and at 1-3 months, 4-6 months, 5-7 months and more than 9 months after treatment.

RESULTS

At baseline, mean logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity (BCVA) was 1.12 ± 0.78 (Snellen equivalent, 20/265). Arteriolar and venular oxygen saturations were 108 ± 7% and 70 ± 9%, respectively and calibres of arterioles and venules were 12.1 ± 1.1 pixels and 16.9 ± 1.4 pixels, respectively. At 4-6 months of follow-up, logMAR BCVA was almost maximum (0.08 ± 0.1, Snellen equivalent 20/24; p < 0.001) and thereafter remained almost unchanged. After immunosuppressive therapy, arteriolar and venular oxygen saturation values continued to decrease up to >9 months of follow-up (92 ± 7% and 56 ± 10%, respectively; p < 0.001 for both arterioles and venules). Similarly, arteriolar and venular calibres continued to decrease up to >9 months of follow-up to 11.4 ± 0.9 pixels (p = 0.006) and 15.6 ± 1.3 pixels (p = 0.001), respectively.

CONCLUSIONS

Eyes with initial-onset acute uveitis associated with VKH disease have increased oxygen saturation and calibres of retinal vessels at baseline. Immunosuppressive therapy normalizes these changes and in a similar pattern improves BCVA.

Retinal vessel oxygen saturation in patients with unilateral internal carotid artery stenosis: a pilot study

PURPOSE

To investigate the retinal vessel oxygen saturation in patients with internal carotid artery stenosis (ICAS).

METHODS

This is a cross-sectional study. Sixteen patients with unilateral moderate or worse ICAS (≥50%) and no fundus diseases were included in the study. Sixteen gender- and age-matched healthy subjects were selected as controls. The mean oxygen saturation and vessel diameters of the retinal arterioles and venules were obtained using a dual-wavelength spectrophotometric retinal oximeter.

RESULTS

In the eye of the stenotic side, the retinal vessel oxygen saturation was 100.14 ± 10.27% in the arterioles and 56.50 ± 10.79% in the venules, and the arteriovenous (A-V) difference was 43.63 ± 7.71%. In the eye of the contralateral side, the oxygen saturation was 96.55 ± 7.50% in the arterioles and 57.42 ± 9.84% in the venules, and the A-V difference was 39.39 ± 6.33%. In healthy subjects, the oxygen saturation was 93.22 ± 5.98% in the arterioles and 56.57 ± 7.05% in the venules, and the A-V difference was 36.65 ± 7.33%. The arteriolar oxygen saturation in the stenotic side was higher than that in the contralateral side (p = 0.025) and that in the healthy subjects (p = 0.027), and the A-V difference in the stenotic side was significantly higher than that in the contralateral side (p = 0.009) and that in the healthy subjects (p = 0.013). The diameters of the arterioles in the stenotic side were smaller than those in the healthy subjects (p = 0.030).

CONCLUSIONS

Patients with ICAS had decreased retinal arteriole diameters and increased retinal vessel oxygen saturation in the arterioles and A-V differences, suggesting the presence of microcirculation disorder and hyperoxia in the retina.

Coronary artery bypass surgery independently associates with retinal vascular oxygen saturation

PURPOSE

The retinal vasculature is the only part of the microcirculation that can be directly studied by non-invasive imaging. Based on the hypothesis that the systemic circulation is reflected in retinal vessels, we investigated if coronary artery bypass grafting (CABG) is related to changes in retinal vascular oxygen saturation (rSatO₂ ).

METHODS

Retinal metabolism was evaluated by Oxymap T1, which simultaneously captures two retinal images at different wavelengths measuring the retinal arteriolar (raSatO₂ ) and venular (rvSatO₂ ) oxygen saturation. Three to 4 days after surgery, we measured the median rSatO₂ after CABG in 38 patients and in 39 healthy controls (operated for cataract).

RESULTS

Coronary artery bypass grafting patients had higher raSatO₂ (median ± standard deviation 93.1 ± 6.7% versus 90.5 ± 11.2%, p = 0.001) and rvSatO₂ (57.4 ± 8.3% versus 53.5 ± 15.4%, p = 0.048) compared to healthy controls. In multivariable linear regression models, raSatO₂ independently associated with CABG (coefficient + 3.6% in CABG patients, p = 0.007), and rvSatO₂ correlated with gender (coefficient + 9.4% for females, p = 0.001) and CABG (coefficient + 8.2% in patients with CABG, p = 0.001).

CONCLUSIONS

Comparing patients with and without cardiovascular disease, raSatO₂ and rvSatO₂ positively and independently associated with CABG, suggesting their potential as non-invasive markers for coronary large artery disease.

Retinal oximetry in glaucoma: investigations and findings reviewed

Abnormalities of the retinal blood supply have been widely implicated in primary open-angle glaucoma (POAG). Impaired blood supply to the retina and optic nerve head (ONH) may be a primary pathophysiologic mechanism contributing to POAG ('vascular hypothesis'). However, the decreased metabolic activity of atrophic tissue is itself known to induce both vascular changes and decreased blood flow due to reduced oxygen demand. Therefore, primary nonvascular factors could potentially induce glaucomatous atrophy, with subsequent secondary vascular pathology ('mechanical hypothesis'). Retinal oximetry holds great promise in the investigation of glaucoma pathogenesis, as it can provide useful data on retinal metabolic oxygen demand, especially when combined with measurements of retinal blood flow. This review surveys the research on retinal metabolism in POAG using spectroscopic retinal oximetry. The use of mathematical models in combination with oximetric data to investigate the role of retinal metabolism and oxygen supply in POAG is also discussed.

The Various Oximetric Techniques Used for the Evaluation of Blood Oxygenation

Adequate oxygen delivery to a tissue depends on sufficient oxygen content in arterial blood and blood flow to the tissue. Oximetry is a technique for the assessment of blood oxygenation by measurements of light transmission through the blood, which is based on the different absorption spectra of oxygenated and deoxygenated hemoglobin. Oxygen saturation in arterial blood provides information on the adequacy of respiration and is routinely measured in clinical settings, utilizing pulse oximetry. Oxygen saturation, in venous blood (SvO₂) and in the entire blood in a tissue (StO₂), is related to the blood supply to the tissue, and several oximetric techniques have been developed for their assessment. SvO₂ can be measured non-invasively in the fingers, making use of modified pulse oximetry, and in the retina, using the modified Beer–Lambert Law. StO₂ is measured in peripheral muscle and cerebral tissue by means of various modes of near infrared spectroscopy (NIRS), utilizing the relative transparency of infrared light in muscle and cerebral tissue. The primary problem of oximetry is the discrimination between absorption by hemoglobin and scattering by tissue elements in the attenuation measurement, and the various techniques developed for isolating the absorption effect are presented in the current review, with their limitations.

Discovery and clinical translation of novel glaucoma biomarkers

Glaucoma and other optic neuropathies are characterized by progressive dysfunction and loss of retinal ganglion cells and their axons. Given the high prevalence of glaucoma-related blindness and the availability of treatment options, improving the diagnosis and precise monitoring of progression in these conditions is paramount. Here we review recent progress in the development of novel biomarkers for glaucoma in the context of disease pathophysiology and we propose future steps for the field, including integration of exploratory biomarker outcomes into prospective therapeutic trials. We anticipate that, when validated, some of the novel glaucoma biomarkers discussed here will prove useful for clinical diagnosis and prediction of progression, as well as monitoring of clinical responses to standard and investigational therapies.

Retinal blood oxygen saturation and vascular endothelial growth factor-A in early diabetic retinopathy: A protocol for systematic review and meta-analysis

BACKGROUND

Diabetic retinopathy (DR) remains the most common microvascular complication of diabetes; both its high prevalence and associated high risk of vision loss lead it to the major global health burden. Despite significant research efforts, there still remains much of the underlying pathology not fully understand. In the past studies, inner retinal blood flow disturbances are widely assessed as a potential biomarker of DR. However, the results have been variable and even contradictory. Improved methods to figure out the metabolic disturbances associated with DR are essential. Some research showed that both vascular endothelial growth factor-A and blood oxygen saturation are higher in DR patients and correlated with disease severity. Therefore, we decided to conduct a systematic review and meta-analysis to find out the connection of them and provide robust evidence on the mechanism underlying this connection to help us better understand the pathophysiology behind the hypoxic retina and find better ways to treat DR.

METHODS

This study will be conducted according to Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols. We will do electronic searches from PubMed, EMBASE, Web of Science, Cochrane Library, Wanfang database, CNKI, and VIP database. Two reviewers will screen all the references independently and any disagreement will be solved by the third involvement. All data will be extracted by 2 independent reviewers according to a standardized data extraction sheet. Based on the type of studies, 2 reviewers will independently use different scales to assess the risk of bias. Any disagreements and conflicts will be resolved by discussing it with a third reviewer. We will conduct a random-effects meta-analysis. Individual and pooled odds ratios/relative risks and associated 95% confidence intervals will be calculated as well as between-study heterogeneity. The potential for publication bias will also be evaluated. If possible, we will explore reasons for potential between-study heterogeneity.

RESULTS

This study is a protocol for systematic review and meta-analysis without results. Associated data analysis will be carried out after the protocol.

CONCLUSION

The protocol aims to guide a meta-analysis whose purpose is investigating the association between retinal blood oxygen saturation and vascular endothelial growth factors in patients with early DR and trying to find out the mechanism that the changing of retinal oxygen saturation in patients with DR.

INPLASY REGISTRATION NUMBER

INPLASY202040161.

Influence of cataract light scatters on retinal vessel oxygen saturation

BACKGROUND

The aim of our study was to compare metabolic (oxygen saturation; %) and anatomical parameters (retinal vessel diameter; μm) of retinal vessel oximetry (RO) in patients with cataract formation against those of healthy controls with clear lenses.

METHODS

A total of 96 eyes of 62 subjects were examined: 51 eyes from 33 cataract patients (mean age: 64.8y) were compared to 45 eyes from 29 controls with clear lenses (mean age: 61.5y). RO was performed with the oxygen saturation measurement tool from the RVA (IMEDOS Systems UG). The oxygen saturation in all major peripapillary retinal arterioles (A-SO₂ ) and venules (V-SO₂ ) was measured, and their difference (A-V SO₂ ) was calculated. In addition, the corresponding diameter in retinal arterioles (D-A) and venules (D-V) was evaluated. Cataract formation was graded according to the Lens Opacities Classification System III (LOCS III). Oximetry data were compared with the grade of cataract formation within both groups. For statistical evaluation, anova-based linear mixed-effects models were calculated (spss^® , pairwise comparisons: Bonferroni-corrected; p < 0.05).

RESULTS

Cataract eyes showed significantly lower A-SO₂ and A-V SO₂ values (mean ± SD 92.52 ± 9.80% and 28.56 ± 9.80%), when compared to healthy controls (95.47 ± 4.48% and 34.8 ± 7.08%; p = 0.046 and p = 0.001). Within the cataract group, cortical opacities showed significant interactions with the A-SO₂ , V-SO₂ and the A-V SO₂ parameters (p = 0.027; p = 0.002; and p = 0.026, respectively).

CONCLUSIONS

These data indicate that the cataract-induced light scatter influences optical retinal oxygen measurements. Cortical opacities showed the highest influence on RO measurement when compared to nuclear opacification, nuclear colour and posterior cataract formation.

Ranibizumab treatment improves diabetic macular oedema without influencing retinal oximetry parameters

PURPOSE

To evaluate the effect of ranibizumab on retinal oximetry in eyes with diabetic macular oedema (DME).

METHODS

In this prospective interventional study, 30 eyes (30 patients) with DME were treated with three-monthly intravitreal ranibizumab injections, followed by pro re nata administration for 12 months. Retinal oximetry was performed using an Oxymap T1.

RESULTS

The mean number of injections was 6.6 ± 2.5. No adverse event was observed throughout the study period. Ranibizumab treatments for 12 months improved the macular oedema (p = 0.002) and achieved a recovery of visual acuity (VA; p = 0.011). However, oxygen saturation levels in the major retinal blood vessels, either the arteries or the veins, remained unchanged during the observational period. Arterial oxygen saturation was 100.3 ± 9.4% before treatment and 100.9 ± 10.7% (p = 0.698) at 6 months. Venous oxygen saturation was 56.4 ± 8.9% before treatment and 55.6 ± 8.6% (p = 0.529) at 6 months. In addition, there were no significant changes in diameters of the major retinal arteries and veins. Greater improvement of VA at 12 months was correlated with a smaller number of ranibizumab injections (r = 0.459, p = 0.011). The number of ranibizumab injections during these 12 months correlated with an increased baseline central retinal thickness (r = 0.385, p = 0.035).

CONCLUSION

Ranibizumab treatments for DME improved the macular oedema and achieved VA recovery, but no changes were noted in the retinal oxygen saturation.

Correlation between Diabetic Retinopathy Severity and Oxygen Metabolism in Patients with Diabetic Macular Edema during Treatment with Intravitreal Aflibercept

PURPOSE

To attribute data on changes in diabetic retinopathy (DR) severity during treatment of diabetic macular edema (DME) with vascular endothelial growth factor inhibitors (anti-VEGF), this study aimed to (1) examine the correlation between oxygen saturations in retinal vessels and the number of DR lesions on ultra-wide field color fundus photographs prior to anti-VEGF treatment and (2) compare changes in oxygen saturations in retinal vessels with changes in the number of DR lesions after a loading dose of three monthly intravitreal injections of 2.0 mg of aflibercept.

METHODS

This 3-month prospective study included 37 eyes of patients with DME and varying severity of peripheral DR lesions. DR lesions were graded on wide field images and retinal oxygen saturations were evaluated by retinal oximetry. Patients were then treated with three monthly intravitreal injections of 2 mg aflibercept and wide field imaging and retinal oximetry were repeated 4 weeks after the last injection. Patients with proliferative DR or previous panretinal photocoagulation were excluded.

RESULTS

Baseline retinal arteriolar oxygen saturation increased with increasing DR severity and numbers of microaneurysms, hemorrhages, and cotton wool spots (p = 0.03, 0.01, 0.03, and <0.001), while no correlation between the severity of DR lesions and retinal venular oxygen saturation was found. After treatment with intravitreal aflibercept, the severity of DR lesions significantly reduced, while retinal arteriolar and venular oxygen saturation as well as the arteriolar-venular difference remained unchanged (95.5 vs. 95.8%, p = 0.44; 62.9 vs. 64.5%, p = 0.08; 32.5 vs. 31.4%, p = 0.33).

CONCLUSION

This study demonstrated that structural DR lesions correlate with retinal arteriolar oxygen saturation in patients with DME prior to anti-VEGF treatment and that improvement in the severity of DR lesions can occur without corresponding changes in retinal oxygen metabolism during intravitreal therapy. Our results suggest that DR severity on color fundus photographs should be interpreted with caution once intravitreal therapy is initiated.

Resistive index of central retinal artery is a bioimaging biomarker for severity of diabetic retinopathy

BACKGROUND

The present study was undertaken to assess the resistive index (RI) of central retinal artery (CRA) as a bioimaging biomarker for the severity of diabetic retinopathy (DR), for the first time.

METHODS

Eighty-one consecutive patients of type 2 diabetes mellitus between the ages of 40 and 70 years were included in a tertiary care center-based cross sectional study. Severity of retinopathy was assessed according to Early Treatment Diabetic Retinopathy Study (ETDRS) classification: diabetes mellitus with no retinopathy (No DR) (n = 26); non-proliferative diabetic retinopathy (NPDR) (n = 29); and proliferative diabetic retinopathy (PDR) (n = 26). Twenty-six healthy controls of similar age were also included. Resistive index of CRA was studied using color Doppler and gray scale sonography. Central subfield thickness (CST), cube average thickness (CAT), retinal photoreceptor ellipsoid zone (EZ) disruption, and retinal nerve fiber layer (RNFL) thickness were evaluated using spectral domain optical coherence tomography. Sensitivity and specificity were assessed by receiver operating characteristic (ROC) curve.

RESULTS

Mean RI of CRA for the study groups revealed significant increase with severity of diabetic retinopathy (F = 10.24, P < 0.001). The ROC curve analysis showed diagnostic accuracy of RI of CRA (area under curve = 0.841-0.999; sensitivity = 76-100%, specificity = 95.45-100%, P < 0.001) in discriminating controls and patients. Univariate regression analysis revealed significant association between the study groups and RI of CRA (P < 0.001). RI of CRA correlated positively with CST (r = 0.37), CAT (r = 0.45), EZ disruption (r = 0.43) and negatively with RNFL thickness (r = - 0.35) (P < 0.001).

CONCLUSIONS

Resistive index of CRA is a reliable bioimaging biomarker for the severity of DR.

Astragalus root extract inhibits retinal cell apoptosis and repairs damaged retinal neovascularization in retinopathy of prematurity

Since the functions of Astragalus root extract in retinopathy remain to be unraveled, this study is performed to elucidate whether Astragalus root extract functions in retinal cell apoptosis and angiogenesis in retinopathy of prematurity (ROP). Newborn mice were selected for establishing mice models of oxygen-induced retinopathy (OIR), which were treated with high-, medium- or low-Astragalus root extract. Evans Blue (EB) was perfused to detect the blood retinal barrier. Additionally, the vascular morphology, number of endothelial cell nuclei of neovascularization, proliferation of blood vessels, ultrastructural changes were determined via a series of assays. Moreover, levels of reactive oxygen species (ROS), expression of other factors such as VEGF, PEDF, IGF-1, HIF-1α, Bax, Bcl-2, eNOS, nNOS, and iNOS were detected. Astragalus root extract was found to protect blood-retinal barrier in the OIR model mice through repairing the structure and morphology of retina, inhibiting ROS production, retinal cell apoptosis, as well as improving retinal vascular angiogenesis. Astragalus root extract was also found to decrease VEGF and HIF-1α expression, but enhance PEDF and IGF-1 expression in the OIR model mice, thereby protecting retinas in ROP. This study highlights that Astragalus root extract is able to suppress retinal cell apoptosis and repair damaged retinal neovascularization in ROP, which provides basis for ROP therapy.

Retinal oximetry in branch retinal vein occlusion

PURPOSE

To measure retinal oxygen saturation (SO₂ ) in eyes with branch retinal vein occlusion (BRVO).

METHODS

Retinal oximetry was performed using the Oxymap T1 retinal oximeter in 50 eyes (50 patients) with resolved BRVO. SO₂ was calculated in each major retinal artery and vein in four quadrants. The superior or inferior hemisphere with BRVO was categorized as the affected hemisphere and the other as the unaffected hemisphere.

RESULTS

Oxymap T1 allowed us to measure SO₂ in major retinal vessels. Both arterial and venous SO₂ in the affected hemisphere were significantly higher than those in the unaffected hemisphere. However, there was no significant difference in arteriovenous (A-V) difference in SO₂ between the affected and unaffected hemispheres. Of the 50 included eyes, 32 had non-ischemic BRVO and 18 had ischemic BRVO. In the affected hemisphere, arterial SO₂ was significantly higher in ischemic BRVO (106.9 ± 8.8%) than in non-ischemic BRVO (101.3 ± 9.2%, p = 0.044). There were no significant differences in venous SO₂ between non-ischemic and ischemic BRVO. Consequently, the A-V difference in SO₂ was significantly higher in ischemic BRVO (51.9 ± 13.9%) than in non-ischemic BRVO (43.4 ± 11.5%, p = 0.028). In multiple regression analysis, the type of perfusion (non-ischemic or ischemic) had associations with arterial SO₂ (β = 0.365, p = 0.013) and with A-V differences in SO₂ in the affected hemisphere (β = 0.406, p = 0.006).

CONCLUSION

In ischemic BRVO, arterial SO₂ and the A-V difference in SO₂ in the affected hemisphere were significantly higher than in non-ischemic BRVO.

Retinal metabolic and structural alterations in response to aflibercept treatment in neovascular age-related macular degeneration

PURPOSE

Non-invasive retinal markers of disease activity could pave the way for individualized treatment in neovascular age-related macular degeneration (nAMD). We aimed to evaluate if retinal vascular oxygen saturation and calibres could predict the initial treatment response after a loading phase of intravitreal aflibercept in nAMD.

METHOD

A total of 149 eyes were included (nAMD, n = 76; dry AMD, n = 30; normal eyes n = 43). Of these, 57 treatment-naïve eyes with nAMD received three monthly injections with 2.0 mg aflibercept and were subsequently stratified according to functional and structural response according to development in best-corrected visual acuity and macular retinal thickness. The retinal vascular oxygen saturation and calibres were measured prior to treatment and 1 month after the third injection.

RESULTS

Patients with nAMD and dry AMD had higher retinal arteriolar oxygen saturation as compared to normal eyes (94.3% versus 95.2% versus 92.6%, p = 0.04). Thirty-nine (68.4%) and 12 (21.1%) eyes with nAMD were functional and structural responders. After the loading phase, structural nonresponders developed a higher retinal arteriolar (95.3% versus 93.3%, p = 0.03) and venular (64.7% versus 59.4%, p = 0.02) oxygen saturation, and responders developed a lower retinal arteriolar calibre (118.0 versus 114.3 μm, p < 0.01). In a multiple logistic regression model, increasing retinal venular oxygen saturation associated with a negative structural treatment outcome (odds ratio 1.17 for each 1% increment after the loading phase, 95% confidence interval 1.01-1.36, p = 0.03).

CONCLUSION

Changes in the retinal venular oxygen saturation associate independently with initial treatment response in nAMD, but functional and structural retinal measurements prior to treatment could not predict the treatment response.

Retinal blood oxygen saturation and aqueous humour biomarkers in early diabetic retinopathy

PURPOSE

The aim of this study was to assess the relationship between retinal blood oxygen saturation (SO₂ ) and specific aqueous humour (AH) concentrations of proangiogenic biomarkers in diabetic patients with nonproliferative diabetic retinopathy (NPDR) and to compare them with those of matched control subjects.

METHODS

The sample comprised 14 participants with mild-to-moderate NPDR (69.1 ± 6.6 years) and 17 age-matched healthy controls (69.7 ± 6.3 years); all participants were previously scheduled for routine cataract extraction with intraocular lens implantation. Multiplex cytokine analyses of specific biomarkers, including vascular endothelial growth factor A (VEGF-A), angiopoietin2 (Ang2), epidermal growth factor (EGF), hepatocyte growth factor (HGF) and interleukin-8 (IL-8) were performed by BioPlex 200 system. Six non-invasive hyperspectral retinal images were acquired.

RESULTS

Mean SO₂ was significantly higher in both arterioles (94.4 ± 1.9 versus 93.0 ± 1.6) and venules (64.4 ± 5.6 versus 55.9 ± 4.8) of NPDR than in the healthy controls (p < 0.001). AH levels of HGF (p = 0.018), Ang2 (p = 0.005) and IL-8 (p = 0.034) were significantly higher, and EGF (p = 0.030) was significantly lower in NPDR subjects. The study demonstrated a correlation between venular retinal blood oxygen saturation and proangiogenic factors HGF (r = 0.558, p = 0.038), Ang2 (r = 0.556, p = 0.039) and EGF (r = -0.554, p = 0.040), but did not find any correlation for IL-8 (r = 0.330, p = 0.249) even though this biomarker was significantly higher in the diabetic group.

CONCLUSION

To our knowledge, the present study is the first report considering the association between SO₂ and AH concentrations of protein biomarkers in diabetic retinopathy. The biomarkers of interest have been shown to participate in cell death, which may explain higher oxygen saturation in NPDR.

Retinal vessel oxygen saturation and vessel diameter in healthy individuals during high-altitude exposure

PURPOSE

To assess changes of retinal vessel oxygen saturation and vessel diameter in healthy individuals during high-altitude exposure.

METHODS

Retinal oxygen saturation and vessel diameter were obtained at sea level (SL, 40 m) and high altitude (HA, 3681 m) on 17 healthy individuals from Beijing (six males, 28.06 ± 8.06 years) using Oxymap T1 and then compared with 21 residents from Yushu (10 males, 28.63 ± 6.00 years). Systemic and ocular parameters were also measured before and after high-altitude exposure. Data were presented as mean ± SD and analysed using paired and independent Student t-test with significance accepted at p < 0.05.

RESULTS

Short-term high-altitude exposure of Beijing Group significantly affected all the systemic and ocular parameters, as well as retinal oxygen saturation and vessel diameter ranging from overall quadrant to different quadrants, other than retinal venous oxygen saturation and retinal arterial diameter. However, these changes were not evident in those permanently living at HA. Pearson's correlation analysis revealed correlations between retinal oxygen saturation and systemic and ocular parameters (all p < 0.05). The multivariate linear regression analysis indicated that retinal arterial oxygen saturation was significantly associated with arterial peripheral arterial oxygen saturation (SpO₂ ) and subfoveal choroidal thickness.

CONCLUSION

Short-term exposure to HA induces retinal microcirculation disturbance and auto-regulatory response in healthy individuals, which is probably attributed to arterial SpO₂ and endothelial dysfunction under hypoxic conditions.

Retinal Oxygen Delivery and Metabolism in Healthy and Sickle Cell Retinopathy Subjects

Purpose

Reduction in inner retinal oxygen delivery (DO2) can cause retinal hypoxia and impair inner retinal oxygen metabolism (MO2), leading to vision loss. The purpose of the current study was to establish measurements of DO2 and MO2 in healthy subjects and test the hypothesis that DO2 and MO2 are reduced in sickle cell retinopathy (SCR) subjects.

Methods

Dual wavelength retinal oximetry and Doppler optical coherence tomography were performed in 12 healthy control and 12 SCR subjects. Images were analyzed to measure retinal arterial and venous oxygen content (O2A and O2V), venous diameter (DV), and total retinal blood flow (TRBF). Retinal arteriovenous oxygen content difference (O2AV), DO2, MO2, and oxygen extraction fraction (OEF) were calculated according to the following equations: O2AV = O2A - O2V; DO2 = TRBF * O2A; MO2 = TRBF * O2AV; OEF = MO2/DO2.

Results

Retinal DV and TRBF were higher in the SCR group as compared to the control group, whereas, O2A, O2V, and O2AV were lower in SCR group as compared to the control group. DO2, MO2, and OEF were not significantly different between control and SCR groups. MO2 and DO2 were linearly related, such that higher MO2 was associated with higher DO2. There was an inverse relationship between TRBF and OEF, such that lower TRBF was associated with higher OEF.

Conclusions

Increased blood flow compensated for decreased oxygen content, thereby maintaining DO2, MO2, and OEF at predominately lower stages of SCR. Quantitative assessment of these parameters has the potential to advance knowledge and improve diagnostic evaluation of retinal ischemic conditions.

Retinal vein occlusion and obstructive sleep apnea: a series of 114 patients

PURPOSE

Evaluate the prevalence of obstructive sleep apnea (OSA) in patients with retinal vein occlusion (RVO).

METHODS

A prospective and controlled study including 114 patients from January to September 2016, who were divided into two groups: 69 patients with RVO (RVO+) and 45 controls (RVO-), matched for age, sex and disease. All the patients completed a simple questionnaire and the Epworth Sleepiness Scale and underwent a RUSleeping^® (portable monitoring device and then continuously monitored the subject's respiration to detect respiratory events). In addition, all patients with RVO were administered OSA screening with a polysomnography (PSG) during an overnight stay in the hospital, which was analysed by a single sleep apnea specialist.

RESULTS

Sleep apnea was suspected in 73.9% in the RVO group and 63% in the control group based on the simple questionnaire; 22% in the RVO group and 4.3% in the control group according to the Epworth Sleepiness Scale; 82.6% in the RVO group and 55.6% in the control group (p = 0.005) according to RUSleeping^® . Multivariate logistic regression analysis (based on RUsleeping^® ) confirmed that RVO was associated with OSA (adjusted odds ratio, 5.65, [1.60-19.92], p = 0.007). All patients in the RVO group were confirmed by PSG, and finally, 91.5% were diagnosed with moderate-to-severe OSA. Among the RVO+ patients, the mean apnea-hypopnoea index (AHI) was 42.2 events per hour (7.7-96.5). OSA was moderate in 22% patients and severe in 69.5% patients. There was no significant relationship between RVO severity and the PSG data variables.

CONCLUSION

The systematic screening of OSA with the gold standard PSG found a high prevalence of OSA in patients with RVO. The OSA is probably a risk factor associated with RVO. Polysomnography remains the gold standard method; nevertheless, the RUsleeping^® RTS portable monitoring device can assess the presence and severity of sleep apnea with a low failure rate and a single use, prior to PSG, which is less available in clinical practice. Further studies with larger samples are needed to clarify the association.

Retinal perfusion changes in radiation retinopathy

PURPOSE

To investigate retinal blood flow and oxygen saturation changes in patients diagnosed with retinopathy following plaque radiation treatment to treat choroidal melanoma.

METHODS

Eight patients (mean age 55.75 years, SD 12.58 years) who have developed unilateral ischaemic radiation-related retinopathy as confirmed by wide-field fluorescein angiography were recruited for the study. The fellow eye with no other ocular or retinal pathology was used as control. Both eyes underwent measurement of total retinal blood flow (TRBF) and retinal blood oxygen saturation using prototype methodologies of Doppler Spectral Domain Optical Coherence Tomography (OCT) and Hyperspectral Retinal Camera, respectively.

RESULTS

The average TRBF in the retinopathy eye was significantly lower compared to the fellow eye (33.48 ± 12.73 μl/min versus 50.37 ± 15.26 μl/min; p = 0.013). The arteriolar oxygen saturation (SaO₂ ) and venular oxygen saturation (SvO₂ ) were higher in the retinopathy eye compared to the fellow eye (101.11 ± 4.26%, versus 94.45 ± 5.79%; p = 0.008) and (62.96 ± 11.05% versus 51.24 ± 6.88%, p = 0.051), respectively.

CONCLUSION

The ionizing radiation seems to have an impact on the TRBF, SaO₂ and SvO₂ , clinically presenting similar to a rapidly developing diabetic retinopathy. The results show an altered retinal vascular physiology in patients with radiation-related retinopathy.

Peripheral capillary non-perfusion in treatment-naïve proliferative diabetic retinopathy associates with postoperative disease activity 6 months after panretinal photocoagulation

Background/aims

With the perspective to provide individualised panretinal laser photocoagulation (PRP) for proliferative diabetic retinopathy (PDR), we evaluated if retinal peripheral capillary non-perfusion (PCNP) and oximetry, as non-invasive markers of retinal metabolism and function, could predict disease activity 6 months after PRP.

Methods

We performed a prospective, interventional study of patients with treatment-naïve PDR. Retinal oximetry and ultra-widefield fluorescein angiography were performed at baseline (BL) and three (3M) and 6 months (6M) after PRP by a navigated laser system. At 6M follow-up, patients were divided according to disease activity: active or inactive.

Results

We included 33 eyes, and 69.6% were men. At BL, the median age and duration of diabetes (with IQRs) were 51.6±23.4 and 20.0±15.0 years. Haemoglobin A_1c was 63.0±17.0 mmol/mol and blood pressure was 152±37/82±24 mm Hg. At BL and M6, patients with postoperative disease activity (30.3.%, n=10) had a larger area with PCNP than those with inactive PDR (BL: 51%–75% vs 26%–50%, p=0.03; 6M: 51%–75% vs 26%–50%, p=0.03). The area of PCNP did not change from BL to 6M in either group (inactive PDR: p=0.38, active PDR: p=0.87). Changes in retinal oxygen saturation were not found to be clinical relevant.

Conclusion

We found the area of PCNP at all timepoints to be statistically larger in patients with active PDR 6 months after PRP treatment. Therefore, the area of PCNP, at baseline, may serve as a potential predictive marker for PDR activity after treatment.

Method comparison of two non-invasive dual-wavelength spectrophotometric retinal oximeters in healthy young subjects during normoxia

PURPOSE

Spectrophotometric retinal oximetry is a non-invasive technology for measuring oxygen saturation in arterioles and venules (SaO₂ , SvO₂ ). We compared two commercially available systems: the Oxymap T1 (Oxymap ehf., Reykjavik, Iceland) and the Dynamic Vessel Analyzer (DVA, Imedos, Jena, Germany).

METHODS

Twenty healthy adults were included after giving informed consent. Two measurement cycles 30 min apart, including Oxymap T1, DVA, arterialized capillary blood draw of the earlobe (ScO₂ ) and peripheral oxygen saturation using finger pulse oximetry (SpO₂ ) were scheduled.

RESULTS

SaO₂ (p > 0.0004) but not SvO₂ (p < 0.05) was statistically significantly different between the retinal oximeters used. Agreement between devices using repeated SO₂ measurements resulted in a standard deviation (SD) of differences of 3.5% in retinal arterioles and 4.8% in venules. Bland-Altman plot using the mean of a participant's two measurements from each device showed an average mean difference of 4.4% (95% confidence limits of agreement: -8.6 to 17.4) and -3.3% (95% confidence limits of agreement: -28.8 to 22.2) for SaO₂ and SvO₂ , respectively. Comparison of mean SaO₂ and SvO₂ with mean ScO₂ and SpO₂ indicated that SO₂ measurements were generally higher in ScO₂ and SpO₂ .

CONCLUSION

This study shows very good repeatability for both devices, which is consistent with the literature. However, it does not show sufficient concordance between SaO₂ measurements from both devices, indicating that patients should be followed by one device only. Differences in absorbance wavelengths used and image post-processing may explain the differences.

Nitric oxide in the pathophysiology of retinopathy: evidences from preclinical and clinical researches

Retinopathy is the leading cause of blindness and visual disability in working-aged people. The pathogenesis of retinopathy is an actual and still open query. Alterations contributing to oxidative and nitrosative stress, including elevated nitric oxide and superoxide production, changes in the expression of different isoforms of nitric oxide synthase or endogenous antioxidant system, have been implicated in the mechanisms how this ocular disease develops. In addition, it was documented that renin-angiotensin system has been implicated in the progression of retinopathy. Based on comprehensive preclinical and clinical researches in this area, the role of above-mentioned factors in the pathogenesis of diabetic retinopathy, hypertensive retinopathy and ischaemic proliferative retinopathy is reviewed in this study. Moreover, the genetic susceptibility factors involved in the development of the retinopathy and possible strategies that utilize antioxidants as additive therapy are also highlighted here.

Changes in retinal venular oxygen saturation predict activity of proliferative diabetic retinopathy 3 months after panretinal photocoagulation

BACKGROUND/AIMS

Proliferative diabetic retinopathy (PDR) is a severe blinding condition. We investigated whether retinal metabolism, measured by retinal oximetry, may predict PDR activity after panretinal laser photocoagulation (PRP).

METHODS

We performed a prospective, interventional, clinical study of patients with treatment-naive PDR. Wide-field fluorescein angiography (OPTOS, Optomap) and global and focal retinal oximetry (Oxymap T1) were performed at baseline (BL), and 3 months (3M) after PRP. Angiographic findings were used to divide patients according to progression or non-progression of PDR after PRP. We evaluated differences in global and focal retinal oxygen saturation between patients with and without progression of PDR after PRP treatment.

RESULTS

We included 45 eyes of 37 patients (median age and duration of diabetes were 51.6 and 20 years). Eyes with progression of PDR developed a higher retinal venous oxygen saturation than eyes with non-progression at 3M (global: +5.9% (95% CI -1.5 to 12.9), focal: +5.4%, (95% CI -4.1 to 14.8)). Likewise, progression of PDR was associated with a lower arteriovenular (AV) oxygen difference between BL and 3M (global: -6.1%, (95% CI -13.4 to -1.4), focal: -4.5% (95% CI -12.1 to 3.2)). In a multiple logistic regression model, increment in global retinal venular oxygen saturation (OR 1.30 per 1%-point increment, p=0.017) and decrement in AV oxygen saturation difference (OR 0.72 per 1%-point increment, p=0.016) at 3M independently predicted progression of PDR.

CONCLUSION

Development of higher retinal venular and lower AV global oxygen saturation independently predicts progression of PDR despite standard PRP and might be a potential non-invasive marker of angiogenic disease activity.

Noninvasive Retinal Markers in Diabetic Retinopathy: Advancing from Bench towards Bedside

The retinal vascular system is the only part of the human body available for direct, in vivo inspection. Noninvasive retinal markers are important to identity patients in risk of sight-threatening diabetic retinopathy. Studies have correlated structural features like retinal vascular caliber and fractals with micro- and macrovascular dysfunction in diabetes. Likewise, the retinal metabolism can be evaluated by retinal oximetry, and higher retinal venular oxygen saturation has been demonstrated in patients with diabetic retinopathy. So far, most studies have been cross-sectional, but these can only disclose associations and are not able to separate cause from effect or to establish the predictive value of retinal vascular dysfunction with respect to long-term complications. Likewise, retinal markers have not been investigated as markers of treatment outcome in patients with proliferative diabetic retinopathy and diabetic macular edema. The Department of Ophthalmology at Odense University Hospital, Denmark, has a strong tradition of studying the retinal microvasculature in diabetic retinopathy. In the present paper, we demonstrate the importance of the retinal vasculature not only as predictors of long-term microvasculopathy but also as markers of treatment outcome in sight-threatening diabetic retinopathy in well-established population-based cohorts of patients with diabetes.