Retinal oxygen saturation changes progressively over time in diabetic retinopathy

Effect of panretinal photocoagulation on retinal oxygen metabolism and ocular blood flow in diabetic retinopathy

PURPOSE

To investigate the effects of panretinal photocoagulation (PRP) on retinal oxygen metabolism, calibre of retinal vessels, and blood flow velocity in the optic nerve head (ONH) and choroid in patients with severe nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR).

METHODS

In this retrospective study, 37 patients (37 eyes) were studied. Retinal oximetry and laser speckle flowgraphy measurements were performed at baseline and after PRP.

RESULTS

After PRP, oxygen saturation of retinal arterioles (p = 0.003) and arteriovenous oxygen saturation difference (p = 0.005) significantly increased. On the other hand, the calibre of retinal arterioles significantly decreased (p = 0.016). In the ONH, mean blur rate (MBR)-vessel (p = 0.002), representing blood flow velocity in the retinal vessels, and MBR-tissue (p = 0.002), representing ONH blood flow velocity, and choroidal MBR (p = 0.012) significantly decreased. At baseline, there were significant negative correlations between ONH MBR-overall (r = -0.382, p = 0.026) and ONH MBR-tissue (r = -0.455, p = 0.007) and arteriovenous oxygen saturation difference. After PRP, choroidal MBR had a significant negative correlation with arteriolar oxygen saturation (r = -0.415, p = 0.016).

CONCLUSIONS

The effects of PRP are correlated with increased arteriovenous oxygen saturation difference, reduction in the calibre of retinal arterioles, and reduction of retinal and choroidal blood flow velocities.

Association of Retinal Oximetry with Peripheral Diabetic Retinopathy Lesions and Nonperfusion on Ultra-widefield Angiography

Purpose

To evaluate the association of retinal ischemia measured using retinal oximetry with retinal nonperfusion and predominantly peripheral lesions on ultra-widefield (UWF) fluorescein angiography (FA PPL).

Design

Prospective single-center, image evaluation study.

Participants

Images from 42 eyes from 21 participants with diabetes.

Methods

Ultra-widefield images were evaluated to determine diabetic retinopathy (DR) severity. Ultra-widefield FA images were used to measure nonperfusion area (NPA, mm2) and nonperfusion index (NPI) and FA PPL presence. Retinal oximetry was performed to measure venous oxygen saturation (VO2, %) and arteriovenous difference (A-V, %) within a 2-disc diameter ring centered on the optic disc.

Main Outcome Measures

Nonperfusion area, NPI, and presence of FA PPL.

Results

Mean age was 40.7 ± 10.4 years, diabetes duration 21.4 ± 10.0 years, hemoglobin A1c (HbA1c) 7.7 ± 1.0, 33.3% (14) were female, and 76.2% (32) had type 1. Distribution of DR on UWF color imaging was no-DR 9.5% (4); mild 45.2% (19), moderate 21.4% (9), and severe 9.5% (4) nonproliferative DR; and proliferative DR 14.3 (6) with FA PPL present in 25 (59.5%). Mean NPA/NPI was associated with increasing DR severity (P = 0.0014/0.0018), even after correction for diabetes duration and HbA1c (P = 0.0029/0.0025). In multivariate analysis adjusting for diabetes duration, HbA1c, and DR severity, the presence of FA PPL was associated with increasing VO2 and decreasing A-V (VO2; P = 0.03, A-V; P = 0.009).

Conclusions

Past studies have established an increased risk of DR progression with the presence of FA PPL. These data show that FA PPL presence is associated with retinal oximetry measures consistent with the presence of venous shunting or reduced retinal oxygen consumption, possibly indicative of greater areas of retinal ischemia. These findings highlight the value of retinal oximetry as a noninvasive measure of retinal ischemia and as a potential marker for increased risk of DR worsening.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Retinal oximetry: new insights into ocular and systemic diseases

Retinal oximetry, which refers to the measurement of the oxygen saturation of haemoglobin in retinal blood, has emerged as a promising tool for understanding ocular and systemic diseases over the past few decades. Advances in traditional dual-wavelength measurement techniques, as well as their integration with more advanced technologies, have driven significant progress in the field. Researchers have utilised commercially available devices to explore the applications of retinal oximetry in both healthy individuals and various disease states. To provide a comprehensive overview of the current status and development trends of retinal oximetry in ophthalmology, this review analyses relevant studies on retinal oximetry, including its principles, techniques, instrumentation, and applications in healthy individuals, ocular diseases, and systemic disorders. As a biomarker, retinal oximetry provides reliable insights into the retinal and systemic microcirculation in a noninvasive, rapid, and convenient manner. It has demonstrated potential value in the measurement of standardised data and in contributing to the understanding of disease mechanisms. However, its measurement accuracy is influenced by factors such as vessel diameter, retinal pigmentation, and optical media transparency. Future advancements, including wide-field imaging technology, nonmydriatic technology, integration with blood flow measurement techniques, and artificial intelligence, are expected to further improve the accuracy and clinical application potential of retinal oximetry.

Evaluation of macular retinal oximetry across different levels of diabetic retinopathy: a cross sectional study

BACKGROUND

This study evaluates retinal oxygen saturation and vessel density within the macula and correlates these measures in controls and subjects with type 2 diabetes (DM) with (DMR) and without (DMnR) retinopathy. Changes in retinal oxygen saturation have not been evaluated regionally in diabetic patients.

METHODS

Data from seventy subjects (28 controls, 26 DMnR, and 16 DMR were analyzed. For those with DMR,8 were mild/moderate diabetic retinopathy (NPDR) and 8 severe NPDR/proliferative (PDR). Subjects were categorized with glycosylated hemoglobin A1c and fundus photography. Retinal oximetry measurements were performed within a 300-400 μm region at four diagonal locations 3.1 degrees from the center of the fovea in the superior nasal, superior temporal, inferior nasal, and inferior temporal locations adjacent to the foveal avascular zone (FAZ). Optical coherence tomography angiography (OCTA) was performed and corrected for refractive error. Photoshop and ImageJ were utilized to calculate the superficial capillary plexus vascular density (SCP). Oximetry and OCTA vessel density were analyzed overall and by region.

RESULTS

Average retinal oxygen saturation was highest in DMR (p = 0.008). Average OCTA density was less in DMR compared to controls (p = 0.01), but not compared to DMnR subjects (p = 0.07). A significant inverse correlation was observed between averaged oxygen saturation and SCP vascular density for all subjects (p = 0.02). Duration of DM was positively associated with oxygen saturation (p = 0.01) and negatively with OCTA SCP vascular density (p = 0.009). There were no differential effects of retinal location.

CONCLUSION

To our knowledge, this study is the first to evaluate the relationship between macular oxygen saturation and SCP vascular density at different levels of retinopathy. This may be useful to track patients with DM as they move through stages of retinopathy.

Test-retest repeatability in macular retinal oximetry

CLINICAL RELEVANCE

Evaluation of retinal macular oxygen saturation in healthy controls can aid in understanding the pathological changes seen in similar locations of those with vascular diseases like diabetes.

BACKGROUND

The aim of this study was to determine the test-retest repeatability of localised retinal oximetry measurements in the macula on the Zilia Oximeter within healthy subjects of different races, 18-40 years old. Oxygen saturation was measured between three time points within the same locations of the right eye.

METHODS

Twenty seven subjects were included (aged 26.3 ± 3.6 years). All were confirmed to have healthy retinas and at least 6/9 vision. Oximetry measurements were taken using the Zilia to acquire local oxygen saturation measurements (300 µm diameter) at four points 3.1 degrees from the fovea in the superior/temporal, superior/nasal, inferior/temporal, and inferior/nasal locations. Oximetry measurements were taken twice on the same day 20 minutes apart and then again 1-2 weeks later. Oximetry data was analysed with intraclass correlation between visits. To assess intrasubject repeatability, the Bland-Altman repeatability coefficient and coefficient of variation were calculated.

RESULTS

Average Intraclass correlation for the three acquisition times of the right eye was 0.78. The averaged intrasubject repeatability coefficient for the three acquisition times was 8.4. The averaged coefficient of variation was 5.4%.

CONCLUSION

The Zilia oximeter has good macular test-retest repeatability; however, multiple measurements may be needed to ensure accuracy.

Effects of high-intensity interval training on retinal vessel diameters and oxygen saturation in patients with hypertension: A cross-sectional and randomized controlled trial

INTRODUCTION

Arterial hypertension is a global healthcare burden that affects macrovascular and microvascular structure and function and can promote vascular end-organ damage. This study aimed 1) to evaluate differences in microvascular health between normotensive individuals and patients with arterial hypertension and 2) to assess the effects of short-term high-intensity interval training (HIIT) on microvascular health in the subgroup with arterial hypertension as add-on treatment to antihypertensive medication.

METHODS

In the cross-sectional part, central retinal arteriolar (CRAE) and venular diameter equivalent (CRVE), arteriolar-to-venular diameter ratio (AVR), and retinal oxygen saturation (O2-saturation) were investigated in 19 normotensive healthy controls (mean age 56 ± 7 years) and 41 patients with arterial hypertension (mean age 59 ± 7 years). In the subsequent randomized controlled trial (RCT), patients with arterial hypertension were randomized to an intervention group (HIIT 3×/week) or a control group that received standard physical activity recommendations after baseline assessment. Assessments of retinal vessel biomarkers and patients` characteristics were repeated after the intervention period of 8 weeks.

RESULTS

In the cross-sectional part, individuals with normal blood pressure (BP) showed lower body mass index (BMI), body fat, 24 h systolic and diastolic BP, higher peak oxygen uptake, wider CRAE (174 ± 17 μm vs. 161 ± 17 μm, p = 0.009), and higher AVR (0.84 ± 0.05 vs. 0.79 ± 0.05, p = 0.003) compared to patients with hypertension. In the RCT, patients with arterial hypertension showed reduced BMI and fasting glucose levels after HIIT and control condition. In addition, the intervention group reduced body fat percentage (27.0 ± 5.5 vs. 25.8 ± 6.1, p = 0.023) and increased peak oxygen uptake (33.3 ± 5.7 vs. 36.7 ± 5.1, p < 0.001). No changes in BP were found in either group. The intervention group showed narrower CRVE (β -4.8 [95 % CI, -8.85, -0.81] p = 0.020) and higher AVR (0.03 [0.01, 0.04] p < 0.001) after eight weeks of HIIT compared to the control group. No statistically significant changes in retinal O2-saturation were found in either group.

CONCLUSION

Short-term HIIT proved to be an effective treatment to ameliorate hypertension-induced retinal microvascular abnormalities in patients with hypertension. Retinal vessel diameters may prove to be a sensitive biomarker to quantify treatment efficacy at the microvascular level, at the earliest possible stage in patients with hypertension.

Variability in Capillary Perfusion Is Increased in Regions of Retinal Ischemia Due to Branch Retinal Vein Occlusion

Purpose

To investigate alterations in macular perfusion variability due to branch retinal vein occlusion (BRVO) using a novel approach based on optical coherence tomography angiography (OCTA) coefficient of variation (CoV) analysis.

Methods

Thirteen eyes of 13 patients with macular ischemia due to BRVO were studied. Multiple consecutive en face OCTA images were acquired. Bias field correction, spatial alignment, and normalization of intensities across the images were performed followed by pixelwise computation of standard deviation divided by the mean to generate a CoV map. Region of interest-based CoV values, derived from this map, for arterioles, venules, and the microvasculature were compared between regions with macular ischemia and control areas of the same eye. Control areas were regions of the same macula that were not affected by the BRVO and had normal retinal vascular structure as seen on multimodal imaging and normal retinal vascular density measurements as quantified using OCTA.

Results

CoV increased by a mean value of 17.6% within the microvasculature of ischemic regions compared to the control microvasculature (P < 0.0001). CoV measurements of microvasculature were consistently greater in the ischemic area of all 13 eyes compared to control. There were no differences in CoV measurements between ischemic and control areas for arterioles (P = 0.13) and venules (P = 1.0).

Conclusions

Greater variability in microvasculature perfusion occurs at sites of macular ischemia due to BRVO. We report a novel way for quantifying macular perfusion variability using OCTA. This technique may have applicability for studying the pathophysiology of other retinal vascular diseases.

Retinal Oxygen Metabolism in Patients With Type 2 Diabetes and Different Stages of Diabetic Retinopathy

The aim of this cross-sectional study was to assess retinal oxygen metabolism in patients with type 2 diabetes and different stages of nonproliferative diabetic retinopathy (DR) (n = 67) compared with healthy control subjects (n = 20). Thirty-four patients had no DR, 15 had mild DR, and 18 had moderate to severe DR. Retinal oxygen saturation in arteries and veins was measured using the oxygen module of a retinal vessel analyzer. Total retinal blood flow (TRBF) was measured using a custom-built Doppler optical coherence tomography system. Retinal oxygen extraction was calculated from retinal oxygen saturation and TRBF. Arteriovenous difference in oxygen saturation was highest in healthy subjects (34.9 ± 7.5%), followed by patients with no DR (32.5 ± 6.3%) and moderate to severe DR (30.3 ± 6.5%). The lowest values were found in patients with mild DR (27.3 ± 8.0%, P = 0.010 vs. healthy subjects). TRBF tended to be higher in patients with no DR (40.1 ± 9.2 μL/min) and mild DR (41.8 ± 15.0 μL/min) than in healthy subjects (37.2 ± 5.7 μL/min) and patients with moderate to severe DR (34.6 ± 10.4 μL/min). Retinal oxygen extraction was the highest in healthy subjects (2.24 ± 0.57 μL O2/min), followed by patients with no DR (2.14 ± 0.6 μL O2/min), mild DR (1.90 ± 0.77 μL O2/min), and moderate to severe DR (1.78 ± 0.57 μL O2/min, P = 0.040 vs. healthy subjects). These results indicate that retinal oxygen metabolism is altered in patients with type 2 diabetes. Furthermore, retinal oxygen extraction decreases with increasing severity of DR.

Studies of the retinal microcirculation using human donor eyes and high-resolution clinical imaging: Insights gained to guide future research in diabetic retinopathy

The microcirculation plays a key role in delivering oxygen to and removing metabolic wastes from energy-intensive retinal neurons. Microvascular changes are a hallmark feature of diabetic retinopathy (DR), a major cause of irreversible vision loss globally. Early investigators have performed landmark studies characterising the pathologic manifestations of DR. Previous works have collectively informed us of the clinical stages of DR and the retinal manifestations associated with devastating vision loss. Since these reports, major advancements in histologic techniques coupled with three-dimensional image processing has facilitated a deeper understanding of the structural characteristics in the healthy and diseased retinal circulation. Furthermore, breakthroughs in high-resolution retinal imaging have facilitated clinical translation of histologic knowledge to detect and monitor progression of microcirculatory disturbances with greater precision. Isolated perfusion techniques have been applied to human donor eyes to further our understanding of the cytoarchitectural characteristics of the normal human retinal circulation as well as provide novel insights into the pathophysiology of DR. Histology has been used to validate emerging in vivo retinal imaging techniques such as optical coherence tomography angiography. This report provides an overview of our research on the human retinal microcirculation in the context of the current ophthalmic literature. We commence by proposing a standardised histologic lexicon for characterising the human retinal microcirculation and subsequently discuss the pathophysiologic mechanisms underlying key manifestations of DR, with a focus on microaneurysms and retinal ischaemia. The advantages and limitations of current retinal imaging modalities as determined using histologic validation are also presented. We conclude with an overview of the implications of our research and provide a perspective on future directions in DR research.

An analysis of the correlation between diabetic retinopathy and preretinal oxygen tension using three-dimensional spoiled gradient-recalled echo sequence imaging

BACKGROUND

The aims of this study were to evaluate the levels of preretinal oxygen tension in patients with diabetes who did not have hypertension by using three-dimensional spoiled gradient-recalled (3D-SPGR) echo sequence imaging and to explore the correlation between diabetic retinopathy (DR) and changes in preretinal oxygen tension.

METHOD

This study involved 15 patients with type 2 diabetes without hypertension, who were divided into a diabetic retinopathy (DR) group (n = 10 eyes) and a diabetic non-retinopathy (NDR) group (n = 20 eyes), according to the results of a fundus photography test. Another healthy control group (n = 14 eyes) also participated in the study. The preretinal vitreous optic disc area, nasal side, and temporal side signal intensity of the eyes was assessed before and after oxygen inhalation with the use of 3D-SPGR echo magnetic resonance imaging (MRI). The signal acquisition time was 10, 20, 30, 40, and 50 min after oxygen inhalation.

RESULTS

The results showed that, in the DR and NDR groups, the preretinal vitreous oxygen tension increased rapidly at 10 min after oxygen inhalation and peaked at 30-40 min, and the increased slope of the DR group was higher than that of the NDR group. The oxygen tension of the preretinal vitreous gradually increased after oxygen inhalation, and the difference between the DR and NDR groups and the control group was statistically significant (P < 0.05). The preretinal vitreous oxygen tension was higher in the optic disc, temporal side, and nasal side in the NDR group than in the control group, and the difference was statistically significant (P < 0.05). The maximum slope ratios of the optic disc and the temporal side of the DR group were greater than those of the control group, and the difference was statistically significant (P < 0.05).

CONCLUSION

Three-dimensional-SPGR echo MRI sequencing technology is useful for detecting preretinal oxygen tension levels in patients with diabetes. It can be used as one of the functional and imaging observation indicators for the early diagnosis of DR.