Arteriolar Oxygen Saturation Research Articles

Retinal oximetry and microvascular assessment after hypertensive pregnancy complications.

Women with hypertensive disorders of pregnancy (HDP) are at increased risk of developing premature cardiovascular disease (CVD). The mechanisms behind this are not fully understood, but microvascular alterations have been documented in retinal arterioles and venules. The aim of this study was to use non-invasive retinal imaging to investigate the structural and functional properties of arterioles, venules and capillaries in this patient group. We examined 27 women with previous HDP and 23 controls at 3 years postpartum. The retinal microvasculature was assessed by vessel calibre measurements, retinal oximetry and optical coherence tomography angiography. Differences were analysed using non-parametric tests and multiple regression analyses, adjusted for age and body mass index. Median arteriolar oxygen saturation (SaO2; 94.2% vs. 93.0%), venular oxygen saturation (SvO2; 60.1% vs. 62.4%) and arteriovenous saturation difference (AV-difference; 32.8% vs. 32.3%) were similar across groups. Capillary vessel density (VD; 46.2% vs. 46.3%), skeletonised VD (VSD; 21.3 vs. 21.1 mm/mm2) and vessel diameter index (21.65 vs. 21.86) were also comparable. In the HDP group, mean arterial pressure (MAP) was positively correlated with AV-difference (R2 = 0.209) and negatively correlated with arteriolar diameter (CRAE; r2 = 0.382). Structural microvascular alterations appear not to be key biomarkers for CVD risk after HDP as early as 3 years postpartum in otherwise healthy women. Further studies are needed to evaluate whether such changes occur later in life. MAP was associated with AV-difference only in the HDP group, suggesting specific mechanisms affecting functional microvascular properties in these women.

Alterations in ocular microcirculation and oxygen metabolism in patients with lipemia retinalis

PurposeThe study aims to assess the alterations in retinal oxygen saturation and retinal and choroidal blood flow in lipemia retinalis.MethodsThis was a cross-sectional study on 10 eyes (5 patients) with history of lipemia retinalis. The study comprised 10 eyes with documented history of lipemia retinalis and 10 participants as healthy controls. Patients with a confirmed history of lipemia retinalis were grouped into two cohorts based on their most recent fundus examination: untreated lipemia retinalis (abnormal fundus) and resolved lipemia retinalis (normal fundus). Both retinal arteriolar and venular oxygen saturation were measured using the non-invasive spectrophotometric retinal oximeter (Oxymap T1). The mean blur rate (MBR) of the optic nerve and choroidal blood flow were analyzed using a laser speckle flowgraph (LSFG).ResultsPatients with untreated lipemia retinalis had a significantly higher retinal arteriolar and venular oxygen saturation than that of the other two groups (p < 0.001). Moreover, patients with untreated lipemia retinalis had significantly smaller retinal arteriolar and venular diameters (p < 0.001). On LSFG, there was a significant difference in the overall MBR (p = 0.007) and vessel MBR of the optic nerve between the groups (p = 0.011). The patients with history of lipemia retinalis (untreated and resolved) exhibited a high overall MBR and vessel MBR of the optic nerve than that of the control group. There was a significant elevation of the optic nerve (p = 0.002) and choroidal blowout score (p < 0.001), while the resistivity index of the optic nerve (p = 0.001) and choroids (p = 0.002) was significantly lower in patients with resolved and untreated lipemia retinalis.ConclusionsThere was a significant alteration in retinal oximetry, in untreated lipemia retinalis, and in retinal blood flow, in both the resolved and untreated groups. The increase in retinal blood flow and oxygen saturation may elucidate the preservation of visual acuity and function despite the fundus changes observed in lipemia retinalis.

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

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. 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 6months (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). 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±15.3μm versus 165.1±28.7μm, p=0.01). 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 6months after treatment. Our results suggest that less extensive laser treatment may be sufficient to improve the retinal metabolic environment conducive to PDR regression.

Feasibility of a transmucosal sublingual fentanyl tablet as a procedural pain treatment in colonoscopy patients: a prospective placebo-controlled randomized study

Since patients often experience pain and unpleasantness during a colonoscopy, the present study aimed to evaluate the efficacy and safety of sublingually administered fentanyl tablets for pain treatment. Furthermore, since the use of intravenous drugs significantly increases colonoscopy costs, sublingual tablets could be a cost-effective alternative to intravenous sedation. We conducted a prospective placebo-controlled randomized study of 158 patients to evaluate the analgesic effect of a 100 µg dose of sublingual fentanyl administered before a colonoscopy. Pain, sedation, nausea, and satisfaction were assessed during the colonoscopy by the patients as well as the endoscopists and nurses. Respiratory rate and peripheral arteriolar oxygen saturation were monitored throughout the procedure. There were no differences between the fentanyl and placebo groups in any of the measured variables. The median pain intensity values, as measured using a numerical rating scale, were 4.5 in the fentanyl group and 5 in the placebo group. The sedation and oxygen saturation levels and the respiratory rate did not differ between the groups. The majority of the colonoscopies were completed.Our results indicate that a 100 µg dose of sublingual fentanyl is not beneficial compared to the placebo in the treatment of procedural pain during a colonoscopy.

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

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

Automatic analysis of normative retinal oximetry images

Retinal oximetry is an important screening tool for early detection of retinal pathologies due to changes in the vasculature and also serves as a useful indicator of human-body-wide vascular abnormalities. We present an automatic technique for the measurement of oxygen saturation in retinal arterioles and venules using dual-wavelength retinal oximetry images. The technique is based on segmenting an optic-disc-centered ring-shaped region of interest and subsequent analysis of the oxygen saturation levels. We show that the two dominant peaks in the histogram of the oxygen saturation levels correspond to arteriolar and venular oxygen saturations from which the arterio-venous saturation difference (AVSD) can be calculated. For evaluation, we use a normative database of Asian Indian eyes containing 44 dual-wavelength retinal oximetry images. Validations against expert manual annotations of arterioles and venules show that the proposed technique results in an average arteriolar oxygen saturation (SatO2) of 87.48%, venular SatO2 of 57.41%, and AVSD of 30.07% in comparison with the expert ground-truth average arteriolar SatO2 of 89.41%, venular SatO2 of 56.32%, and AVSD of 33.09%, respectively. The results exhibit high consistency across the dataset indicating that the automated technique is an accurate alternative to the manual procedure.

Retinal arteriolar oxygen saturation predicts the need for intravitreal aflibercept in patients with diabetic macular oedema

ObjectiveGiven the increasing burden of repetitive intravitreal injections in diabetic macular oedema (DMO) treatment, non-invasive markers of treatment outcome are needed. Hence, we aimed to examine retinal oximetry parameters as...

Retinal oximetry as a biomarker in multiple sclerosis

AbstractPurposeStructural and physiological abnormalities have been reported in the retina in patients with multiple sclerosis (MS). Retinal oximetry has recently detected changes in retinal oxygen metabolism in Alzheimer’s disease, mild cognitive impairment and in a small cohort of MS patients with history of optic neuritis. Our goal was to determine whether oxygen saturation in retinal blood vessels of newly diagnosed MS patients is different from that of a healthy population.MethodsOxygen saturation of hemoglobin was measured in retinal blood vessels, using imaging with spectrophotometric non‐invasive retinal oximeter. Six newly diagnosed MS patients were measured and compared to six healthy individuals that were age‐ and gender‐matched with the MS patients.ResultsVenular oxygen saturation was increased in patients with MS compared to healthy individuals (mean: 61.9% versus 56.3%). Retinal venular diameter (138.2 µm versus 160.2 µm: mean) and retinal arteriolar diameter were smaller in MS patients (111.8 µm versus 131.3 µm: mean) when compared to healthy individuals. No big difference could be measured in the oxygen saturation in arterioles when patients with MS (mean: 91.2%) and healthy individuals (mean: 92.3%) were compared.ConclusionIncreased venular oxygen saturation and smaller retinal venular and arteriolar diameter in patients with MS may indicate reduced oxygen uptake in the retina. This may be due to less oxygen demand following axonal loss and may be a useful objective biomarker for MS. Further studies are needed to confirm and expand these findings.

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.

Retinal Vascular Oxygen Saturation and Its Variation With Refractive Error and Axial Length.

PurposeTo evaluate the relationships between refractive error, axial length (AL), and retinal vascular oxygen saturation in an adult population.MethodsThis was a hospital-based, prospective observational study. The left eyes of phakic adult subjects without media opacity were analyzed. Subjective undilated manifest refraction was performed, and refractive errors were defined as myopia (spherical equivalent [SE], <−1 D), emmetropia (SE between −1 D and +1 D) and hyperopia (SE >+1 D). Retinal oximetry was performed using the Oxymap system (Oxymap Inc., Reykjavik, Iceland). Multivariate linear regression models were constructed to assess the relationship between retinal vascular oxygen saturation, SE, and AL obtained with optical biometry, with adjustments for age, sex, race, blood pressure, hyperlipidemia, and diabetes mellitus.ResultsThere were 85 subjects, with mean age of 66.1 ± 11.3 years. The majority were female (60%) and Chinese (84%). A total of 60% were myopic, 28% emmetropic, and 12% hyperopic. Mean SE was −5.29 ± 6.51 D and mean AL was 25.30 ± 2.99 mm. In multivariate analyses, more myopic SE and longer AL were associated with lower retinal arteriolar oxygen saturation (regression coefficient B = 0.61 [95% confidence interval, 0.28, 0.95], P = 0.001; and B = −1.13 [95% confidence interval, −1.71, −0.56], P < 0.001, respectively). Subjects with myopic SE and AL also had lower retinal arteriolar oxygen saturation than emmetropes and hyperopes (P = 0.03 and P = 0.02, respectively).ConclusionsEyes with more myopic SE and longer AL have lower retinal arteriolar oxygen saturation.Translational RelevanceThis study provides direct evidence of a link between retinal oxygenation and hypoxia and myopia by using a novel device that quantifies retinal vascular oxygenation in vivo.

This issue of Acta

This issue of Acta

Retinal vessel oxygen saturation is affected in uveitis associated with Vogt-Koyanagi-Harada disease

AimsTo discover whether retinal vessel oxygen metabolism is affected in uveitis associated with Vogt-Koyanagi-Harada (VKH) disease.Methods41 patients with VKH disease (82 eyes) and 12 healthy subjects (24 eyes) matched in...

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

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. 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 2.0mg 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 1month after the third injection. 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 114.3μm, 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). 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.

ARTERIAL OXYGEN SATURATION IN NEOVASCULARIZATIONS IN PROLIFERATIVE DIABETIC RETINOPATHY.

Retinal neovascularizations in proliferative diabetic retinopathy have been proposed to develop from larger retinal venules. However, angiographic evidence suggests that the new vessels may originate from both arterioles and venules, and the vitreous oxygen tension near retinal neovascularizations is similar to that of retinal arterioles. An assessment of the oxygen saturation in neovascularizations may help characterizing the vascular origin of these vessels in proliferative diabetic retinopathy. Dual wavelength oximetry was used to study the oxygen saturation in arterioles, venules, and retinal neovascularizations in 40 eyes from 40 patients with proliferative diabetic retinopathy. The oxygen saturation was significantly lower in retinal venules than in arterioles and neovascularizations (P < 0.0001), and after a correction for the influence of vessel diameter, there was no significant difference between the oxygen saturation in retinal arterioles and neovascularizations (P = 0.71). Age at onset and duration of diabetes mellitus contributed significantly to the variation in oxygen saturation of the venules, whereas none of the clinical background parameters contributed to the variation in oxygen saturation in arterioles and neovascularizations. The oxygen saturation in retinal neovascularizations in proliferative diabetic retinopathy is similar to that of the arterioles. Neovascularizations may act as shunts to bypass areas of capillary occlusion.

Retinal perfusion changes in radiation retinopathy.

To investigate retinal blood flow and oxygen saturation changes in patients diagnosed with retinopathy following plaque radiation treatment to treat choroidal melanoma. Eight patients (mean age 55.75years, SD 12.58years) 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. The average TRBF in the retinopathy eye was significantly lower compared to the fellow eye (33.48±12.73μl/min versus 50.37±15.26μl/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. 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.

Changes in retinal arteriolar oxygen saturation predict disease activity in patients treated with aflibercept for neovascular age‐related macular degeneration

PurposeIn order to individualize treatment, it is important to identify non‐invasive markers for disease activity in patients with neovascular age‐related macular degeneration (nAMD). In this prospective study we aimed to investigate changes in retinal oxygen saturation in patients with nAMD before and after initial aflibercept therapy.MethodsSixty‐six eyes diagnosed with nAMD were included. All patients received three monthly injections with 2.0 mg aflibercept and were then divided into responders and non‐responders according to post‐treatment disease activity. Non‐responders by definition had loss of ≥5 ETDRS letters or residual retinal edema (based on spectral domain‐OCT) or macular hemorrhage. Retinal oximetry (Oxymap T1, Oxymap, Reykjavik, Iceland) was performed at baseline and follow‐up, and images were graded by a trained grader.ResultsAt baseline, mean age was 80.0 years and 62.1% were women. Thirty‐six of 66 patients (54.5%) were non‐responders, and these were younger (77.8 vs. 82.8 years, p=0.01) and trended towards a higher increase in retinal arteriolar oxygen saturation from baseline to follow‐up (+1.0% vs. +0.1%, p=0.06). In a multiple logistic regression model, adjusted for sex, age, diabetes and smoking, each 1%‐point increment in retinal arteriolar oxygen saturation from baseline to follow‐up was independently associated with a lower chance of full treatment response (odds ratio 0.78, 95% confidence interval 0.62‐0.98, p=0.036). Retinal venular oxygen saturation did not associate with pre‐ or post‐treatment disease activity.ConclusionsRetinal oxygen saturation may be a promising marker for disease activity in nAMD. Increasing retinal arteriolar oxygen saturation in response to initial intravitreal aflibercept therapy associates with a 22% lower chance of full treatment response after initial aflibercept therapy.

Development and Validation of Non simultaneous Retinal Image Acquisition\u2013Based Retinal Oximeter

The purpose of this study was to develop and validate a tool for the measurement of retinal oxygen saturation using a conventional fundus camera–based nonsimultaneous imaging technique. Retinal oximetry setup comprising a conventional Zeiss FF450IR fundus camera, dual wavelength band-pass filters of wavelengths 570 and 600 nm were used. Image analysis was performed using MATLAB R2013b. All the study participants underwent comprehensive eye examination, fundus examination, complete hemogram analysis, and evaluation of systemic hemodynamics. Fundus images were captured by a nonsimultaneous retinal oximetry. A total of 45 subjects were included in the analysis. Median age of the subjects was 21 years ranging from 19 to 34 years. The median retinal arteriolar and venular oxygen saturation was 94.7% and 55.8%. Comparison of retinal oxygen saturation between three visits showed no statistically significant difference for both arteriolar (p = 0.33)and venular oxygen saturation (p = 0.79). Intraclass correlation coefficients for test–retest, short-term, and day-to-day repeatability were 0.84, 0.90, and 0.86 for arteriolar oxygen saturation and 0.92, 0.98, and 0.98 for retinal venular oxygen saturation. Oxygen saturation in retinal arteriolar and venular blood vessels can be measured by nonsimultaneous image acquisition technique using a conventional fundus camera with good repeatability.

Oxygen saturation in the retinal vessels of glaucoma and normal eyes

Objective To observe the difference of retinal vessel oxygen saturation in glaucoma and normal eyes. Methods A cross sectional study design was performed. Fifty eyes of 30 glaucoma patients (glaucoma group) and 41 eyes of 27 age- and sex-matched healthy subjects (control group) were included. Retinal vessel oxygen saturation was measured with a spectrophotometric retinal oximeter in darkness and visual fields were obtained by Humphrey filed analyzer. The glaucoma eyes were divided into two groups: mean defect (MD) <6 dB (28 eyes) and MD≥6 dB (22 eyes) according to mean defect of visual field. Results Retinal arteriolar oxygen saturation values in glaucoma group and control group were (94.52±6.51)% and (93.47±6.30)% respectively. No statistical difference was found in retinal oxygen saturation in arterioles (H=-0.949, P=0.343). Retinal venous oxygen saturation values in glaucoma group and control group were (57.57±7.96)% and (52.60±7.70)% respectively. The retinal venous oxygen saturation values in glaucoma group was higher than that in control group (H=-3.318, P=0.001). The retinal arteriovenous difference in glaucoma group and control group were (36.59±4.69)% and (42.41±6.73)% respectively. The retinal arteriovenous difference in glaucoma group was lower than that in control group (H=-4.148, P<0.01). The retinal arteriolar oxygen saturation values in glaucoma eyes with MD<6 dB and MD≥6 dB were (93.38±6.33)% and (95.71±6.54)% respectively, with no statistical difference (H=-1.857, P=0.063). Retinal venous oxygen saturation values in glaucoma eyes with MD<6 dB and MD≥6 dB were (54.83±6.10)% and (61.07±8.79)% respectively. The retinal venous oxygen saturation values in MD≥6 dB glaucoma eyes was higher than that in MD<6 dB glaucoma eyes (H=-2.599, P=0.009). The retinal arteriovenous difference in glaucoma eyes with MD<6 dB and MD≥6 dB were (38.12±4.34)% and (34.64±4.49)% respectively. The retinal arteriovenous difference in MD≥6 dB glaucoma eyes was lower than that in MD<6 dB glaucoma eyes (H=-2.463, P<0.05). Conclusions Compared with healthy eyes, there is no change in the retinal arteriolar oxygen saturation, but the retinal venous oxygen saturation is higher and the retinal arteriovenous difference is lower. This feature is more obvious in MD≥6 dB glaucoma eyes. Key words: Glaucoma/etiology; Oximetry

Inter-eye comparison of retinal oximetry and vessel caliber between eyes with asymmetrical glaucoma severity in different glaucoma subtypes.

BackgroundTo compare retinal vessel oxygenation and vessel caliber in primary angle-closure glaucoma (PACG), primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG), and normal controls, as well as between eyes of asymmetrical glaucoma severity.MethodsThis was a prospective, cross-sectional study. The 159 subjects (PACG, n=39; POAG, n=41; NTG, n=41; normal controls, n=38) underwent retinal oxygen saturation measurements using the Oxymap T1 Retinal Oximeter, optical coherence tomography, and Humphrey visual field testing. Retinal oxygen saturation and vessel diameter were compared between the glaucoma groups and normal controls, as well as between eyes of asymmetrical glaucoma severity. Kruskal–Wallis test was performed for comparison among different subtypes of glaucoma. Wilcoxon signed-rank test was used to compare the inter-eye differences.ResultsCompared to normal controls, arteriolar oxygen saturation was increased in PACG eyes (P=0.048) but not in POAG or NTG eyes. There were no significant differences in oxygen saturation in venules or arteriovenous (AV) difference in all three glaucoma groups. Venular diameter was significantly reduced in all glaucoma groups compared to normal controls (P<0.001), but no such change was observed in arteriolar diameter (P=0.10). When comparing between eyes of asymmetrical glaucoma severity, arteriolar oxygen saturation (P=0.03) and AV difference (P=0.04) were significantly higher, while arteriolar diameter was significantly lower (P=0.001) in the worse eye in PACG group. There were no significant differences in oximetric parameters or vessel calibers between the worse and the better eyes in POAG and NTG groups.ConclusionEyes with PACG showed increased arteriolar oxygen saturation and increased AV difference. This was not observed in POAG and NTG eyes. Arteriolar diameter in PACG and venular diameter in all three glaucoma groups were reduced. The difference observed in PACG eyes may be due to an increased metabolic demand in the disease process compared to open-angle glaucoma.

Retinal oximetry imaging in Alzheimer's disease.

Structural and physiological abnormalities have been reported in the retina in Alzheimer's disease (AD). Retinal oximetry detects changes in retinal oxygen metabolism in many eye diseases, where structural changes are seen. To compare oxygen saturation in retinal blood vessels in patients with AD and a healthy cohort. Oxygen saturation of hemoglobin was measured in retinal blood vessels, using imaging with spectrophotometric noninvasive retinal oximeter. 18 individuals with mild to moderate dementia of the Alzheimer-type (stage 3-5 according to the Global Deterioration Scale) and 18 healthy subjects underwent retinal oximetry in a case control study. Retinal oxygen saturation in arterioles and venules in patients with moderate AD was significantly elevated compared to healthy individuals. Retinal arterioles have 94.2 ± 5.4% oxygen saturation in moderate AD compared with 90.5 ± 3.1% in healthy subjects (mean ± SD, n = 10, p = 0.028). Retinal venules were 51.9 ± 6.0% saturated in moderate AD compared with 49.7 ± 7.0% in healthy subjects (mean ± SD, n = 10, p = 0.02). This is the first study of retinal oxygen metabolism in any central nervous system disease. It discovers abnormalities in retinal oxygen metabolism in AD. The findings are similar to those seen in age-related macular degeneration and diabetic retinopathy. Noninvasive retinal oximetry may offer new insights into pathophysiology of AD. Further studies are needed to confirm and expand these findings.