Ocular Blood Flow Research Articles

In vivo photoacoustic imaging of chorioretinal oxygen gradients.

Chorioretinal imaging has a crucial role for the patients with chorioretinal vascular diseases, such as neovascular age-related macular degeneration. Imaging oxygen gradients in the eye could better diagnose and treat ocular diseases. Here, we describe the use of photoacoustic ocular imaging (PAOI) in measuring chorioretinal oxygen saturation (CR - sO2) gradients in New Zealand white rabbits (n = 5) with ocular ischemia. We observed good correlation (R2 = 0.98) between pulse oximetry and PAOI as a function of different oxygen percentages in inhaled air. We then used an established ocular ischemia model in which intraocular pressure is elevated to constrict ocular blood flow, and notice a positive correlation (R2 = 0.92) between the injected volume of phosphate buffered saline (PBS) and intraocular pressure (IOP) as well as a negative correlation (R2 = 0.98) between CR - sO2 and injected volume of PBS. The CR - sO2 was measured before (baseline), during (ischemia), and after the infusion (600-μL PBS). The ischemia-reperfusion model did not affect the measurement of the sO2 using a pulse oximeter on the animal's paw, but the chorioretinal PAOI signal showed a nearly sixfold decrease in CR - sO2 (n = 5, p = 0.00001). We also observe a sixfold decrease in CR - sO2 after significant elevation of IOP during ischemia, with an increase close to baseline during reperfusion. These data suggest that PAOI can detect changes in chorioretinal oxygenation and may be useful for application to imaging oxygen gradients in ocular disease.

Gonadal Hormones and Retinal Disorders: A Review.

Gonadal hormones are essential for reproductive function, but can act on neural and other organ systems, and are probably the cause of the large majority of known sex differences in function and disease. The aim of this review is to provide evidence for this hypothesis in relation to eye disorders and to retinopathies in particular. Epidemiological studies and research articles were reviewed. Analysis of the biological basis for a relationship between eye diseases and hormones showed that estrogen, androgen, and progesterone receptors are present throughout the eye and that these steroids are locally produced in ocular tissues. Sex hormones can have a neuroprotective action on the retina and modulate ocular blood flow. There are differences between the male and the female retina; moreover, sex hormones can influence the development (or not) of certain disorders. For example, exposure to endogenous estrogens, depending on age at menarche and menopause and number of pregnancies, and exposure to exogenous estrogens, as in hormone replacement therapy and use of oral contraceptives, appear to protect against age-related macular degeneration (both drusenoid and neurovascular types), whereas exogenous testosterone therapy is a risk factor for central serous chorioretinopathy. Macular hole is more common among women than men, particularly in postmenopausal women probably owing to the sudden drop in estrogen production in later middle age. Progestin therapy appears to ameliorate the course of retinitis pigmentosa. Diabetic retinopathy, a complication of diabetes, may be more common among men than women. We observed a correlation between many retinopathies and sex, probably as a result of the protective effect some gonadal hormones may exert against the development of certain disorders. This may have ramifications for the use of hormone therapy in the treatment of eye disease and of retinal disorders in particular.

Ginkgo biloba and its potential role in glaucoma.

This study will review the research on the effect of ginkgo biloba extract (GBE) on patients with glaucoma. GBE appears to increase ocular blood flow in those with glaucoma. However, data on visual field outcomes are inconclusive. GBE has been shown to have antioxidant and vascular effects, making it potentially effective in treating glaucoma. Published data are limited but show an increase in ocular blood flow after GBE administration. Conclusive evidence is lacking regarding the effect of GBE on clinical outcomes in glaucoma patients such as visual field performance.

EYE HEMODYNAMICS IN YOUNG AND MIDDLE-AGED PATIENTS WITH RETINAL VEIN OCCLUSION

Actuality. Regional hemodynamics сcontravention is one of the key factors in the development of retinal vein occlusion. The available methods estimating the ocular component of oculoorbital blood flow include opthalmoplethysmography and opthalmorheography. The value of opthalmosphygmography is in question due to the dependence of the results obtained from the orbital component of eye hemodynamics. Assessment of the vascular bed in the fluorescein angiography also gives an indirect assessment of ocular blood flow. The objective is to estimate hemodynamics indices and informativity of used methods in young and middle-aged patients with retinal vein occlusion. Materials and methods. The study included 30 patients with retinal vein occlusion. In all patients, routine ophthalmic examination was performed and ocular blood flow was additionally estimated using ophthalmoplethysmography, ophthalmorheography, ophthalmosphygmography, and fluorescein angiography. Results. Insignificant decrease of ocular blood flow indices was found on the eye with RVO in young and middle-aged patients with retinal vein occlusion. High values of factors weight of opthalmoplethysmography and opthalmorheography was found, which were significantly exceed the contribution of ocular pulse amplitude of pressure. Conclusions. There was a tendency to decrease all hemodynamic parameters on the eye with RVO in young and middle-aged patients with retinal vein occlusion. The received high values of factors weights reflect the comparable informativity of opthalmoplethysmography and opthalmorheography. The researchers are more informative, which results were less affected by the blood flow in the orbital tissues.

Racial differences in the correlations between structural parameters and ocular blood flow in healthy eyes

Purpose: This study aimed to assess differences in the relationship between structural parameters and ocular blood flow between persons of African (AD) and European descent (ED) with healthy eyes.Methods: The relationship between structural and ocular blood flow parameters was assessed in 46 participants (20 AD, 26 ED) with healthy eyes. Disc area (DA), rim area (RA), and retinal nerve fiber layer (RNFL) thickness were measured. Retrobulbar blood flow was assessed in the ophthalmic (OA), central retinal (CRA), nasal (NPCA) and temporal short posterior ciliary arteries (TPCA). Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) were assessed. Retinal capillary blood flow was also evaluated. Differences between the correlations were determined using the Fisher r-to-z transformation.Results: Significant differences in correlations were observed between the AD and ED groups in the CRA, where PSV and DA were positively correlated in AD (r=0.43) and negatively correlated in ED (r=-0.36) (Δr=0.79; P=0.01). A similar finding was observed for PSV and RA (AD: r=0.39; ED: r=-0.23; Δr=0.62; P=0.04). In the inferior hemifield for ED group only, percentage of avascular space and RNFL thickness were positively correlated (r=0.51, P=0.01) and mean retinal flow and RNFL thickness were negatively correlated (r=-0.50, P=0.01).Conclusion: The relationship between structural parameters and the blood supply to the superficial layer of the retina was significantly different in the healthy eyes of AD compared to ED. More research is required to show how these differences may affect glaucomatous risk.

This issue of ACTA, printed and electronic

This issue of <i><scp>ACTA</scp></i>, printed and electronic

VIP changes during daytime in chicken intrinsic choroidal neurons

PurposeOcular autonomic control is mediated by sympathetic and parasympathetic nerve fibres. Their interactions are complemented by primary afferent nerve fibers of and intrinsic choroidal neurons (ICN). As the vasodilatative neuropeptide, vasoactive intestinal peptide (VIP), is expressed in extrinsic and intrinsic ocular neurons, it is of special interest in ophthalmic research. Since circadian changes of ocular blood flow are known in humans and birds, this study aimed at investigating VIP expression at different daytimes in chicken choroid, the preferred model species in ICN research. Methods12 eyes of 12 chickens were retrieved, slaughtered at 8.00–9.30 a.m. (n = 6) and 8.00 p.m. (n = 6), respectively, and choroidal wholemounts were prepared for immunofluorescence of VIP. VIP-positive ICN of both groups were quantified and density of VIP-positive axons assessed semi-quantitatively. In 28 additional eyes retrieved in the morning (n = 14) and evening (n = 14), choroidal VIP content was determined by ELISA. Morning and evening data were analyzed statistically. NADPH-diaphorase (NADPH-d, ICN cell marker) was done at additional 12 whole mount choroids of 12 chicken, retrieved in the morning (n = 6) and evening (n = 6). Results(1) Numbers of VIP positive neurons differed significantly between morning: (239.17 ± 113.9) and evening: (550.83 ± 245.7; p = 0.018). (2) Numbers of VIP-positive perikarya were significantly more accumulated in the temporal part of the choroid in the evening than in the morning (p = 0.026). (3) VIP positive axon density was found to be similar throughout the choroid in the morning and evening. (4) Number of NADPH-d positive neurons was not significantly different between morning (848.8 ± 399.5) and evening (945.8 ± 622.1, p > 0.05). (5) ELISA demonstrated a significant difference of VIP content (p = 0.012) in tissues harvested in the morning (145.41 ± 43.3 pg/ml) compared to evening (221.44 ± 106.3 pg/ml). ConclusionsAs VIP positive axon density was similar in the morning and the evening throughout the choroid, PPG and ICN seemed to contribute equally to the axon network. Yet, changes in the total choroidal VIP content, the numbers of VIP positive perikarya, reflecting the intracellular VIP content, and their topographical distribution at two different days-times argue for a different status of activation of both neuronal sources in contrast to the equal amount of NADPHD-d positive neurons. The higher VIP content in the evening, compared to the morning, correlates with a known circadian rhythm of a lower IOP and a higher choroidal thickness at night. Thus, these changes may argue for a potential role of ICN in the regulation of ocular homeostasis and integrity.

Implication of Intrinsic Intraocular Risk Factors at Ocular Blood Flow to Primary Glaucoma

Implication of Intrinsic Intraocular Risk Factors at Ocular Blood Flow to Primary Glaucoma

Heart rate variability in normal tension glaucoma: A case-control study.

Primary vascular dysregulation (PVD) is believed to be a main cause of local vasospasm and impaired autoregulation as a possible contributing factor in the pathogenesis of normal tension glaucoma (NTG). Subjects with PVD respond stronger to psychological stress. Autonomic dysfunction is another reason of instable ocular blood flow and may be studied by means of assessment of heart rate variability (HRV) especially during a hand-cold provocation test (CPT).To compare the shift of HRV parameters in NTG and healthy subjects after a cold provocation test and to assess the relation between structural damage, circulatory parameters and autonomic dysfunction in NTG.HRV was studied using CPT in 78 NTG patients and 60 health control matches. The ocular blood flow was measured using color Doppler imaging (CDI). The 24 hours blood pressure (BP) monitoring was carried out. The cardiovascular fitness assessment was made to all patients before and after CPT. Mean group difference of HRV parameters was compared between NTG and healthy subjects using the Euclidean metric. The mean ocular perfusion pressure (MOPP) was measured. Optic nerve head and retinal nerve fiber layer (RNFL) were evaluated using spectral-domain optic coherence tomography (SD-OCT). The relation between HRV, CDI, and SD-OCT-parameters was assessed.In contrast to healthy subjects, a predominance of the sympathetic activity after the CPT was revealed in the NTG group. The end diastolic velocity (EDV) in central retinal artery (CRA) and short posterior ciliary artery (SPCA) was significantly reduced in NTG compared to healthy eyes. In NTG, the main HRV parameter characterizing the total effect of autonomic blood circulation regulation (SDNN) correlated with MOPP (0.75, P = .035), SPCA EDV (0.93, P < .001), and CRA EDV (0.9, P < .001). The average daily diastolic BP correlated with RNFL (0.67, P = .009).The NTG patients have the disturbance of the autonomic nervous system, which increases in response to stress provocation and is related to ocular blood flow and structural damage.

Evaluation of the circadian fluctuations of intraocular pressure and ocular perfusion pressure in different types of glaucoma

Background: Glaucoma is a frequent leading cause of blindness. Objective evidence showed that it can be secondary to optic nerve head hypoperfusion and autonomic dysfunction, not only to ocular hypertension. This makes the assessment of ocular blood flow a crucial step in the management of this disease. Aim: To investigate the circadian fluctuations of the intraocular pressure (IOP) and of the mean ocular perfusion pressure (mOPP) in patients with different types of glaucoma. Materials and methods: Sixty-five eyes of 65 glaucoma patients, managed in the Ophthalmology Department of the Careggi University Hospital, Firenze, Italy (2012-2014). Among these eyes, 22 had normotensive glaucoma (NTG), 21 hypertensive glaucoma (HTG), and 22 exfoliative glaucoma (XTG). The IOP was measured by Goldmann tonometry and the blood pressure, both systolic (sBP) and diastolic (dBP), by Riva-Rocci sphygmomanometry, at three time points (8am, 2pm, 8pm). The mOPP was then calculated according to the formula mOPP = [2/3 (2/3 dBP + 1/3sBP) - IOP]. Results: The fluctuations of IOP and mOPP were statistically significant in all the studied eyes (p&lt;0.001 for all the comparisons). Both IOP and mOPP showed significantly larger fluctuations in the XFG eyes than in the NTG and HTG ones (p&lt;0.001 for IOP and p=0.001 for mOPP). Conclusions: In our study, the mOPP had larger circadian fluctuations in eyes with XFG than in those with NTG and HTG. This parameter deserves to be assessed in all types of glaucoma. Key words: Glaucoma, intraocular pressure, mean ocular perfusion pressure.

Pharmacology of Serotonin Receptors Causing Contraction of Isolated Bovine Posterior Ciliary Arteries: Role in Ocular Blood Flow.

To determine the serotonergic (5HT) receptor subtype mediating the contraction of bovine posterior ciliary arteries (BPCAs) in vitro. Longitudinal isometric tension was measured in BPCA strips (4-5 mm) mounted in 25 mL organ baths containing oxygenated Krebs solution at 37°C. Cumulative contractile concentration-response (C-R) curves were generated for various 5-HT agonists to assess their potencies and maximal degrees of contraction. Multiple agonist C-R curves were also constructed in the presence and absence of receptor-selective antagonists to determine antagonist potencies using Schild plots. Selective and nonselective agonists for 5-HT receptors elicited concentration-dependent contractile responses in BPCAs with the following rank order of potency: MK-212 > BW723C86 > α-methyl-5-HT >5-methoxy-α-5-methyl-5-HT >> R-DO1 > >5-HT >> cabergoline >> 5-methoxy-dimethyl-tryptamine >> 2-methyl-5-HT >> tryptamine. Interestingly, both 8-OH-DPAT (5HT1A agonist) and quipazine (5HT3 agonist) did not elicit contractions in BPCAs. The contractions produced by BW723C86 (5-HT2B agonist) were antagonized by 5-HT receptor blockers, RS-127445 (5-HT2B antagonist), and M-100907 (5-HT2A antagonist), yielding antagonist pA2 values of 7.5 ± 0.12 (n = 4) and 6.2 ± 0.17 (n = 4), respectively. Furthermore, contractions elicited by MK-212 (5-HT2C agonist) was blocked by RS-102221 (5-HT2C antagonist), although noncompetitively. On the basis of the pharmacological profile of selective agonists and antagonists, we conclude that serotonin-induced contractions of the BPCA are mediated primarily by a combination of 5HT2C and/or 5HT2B receptors. It appears that 5-HT1A and 5-HT3 receptors are not involved in the contractile action of BPCAs to serotonin.

Physical exercise and glaucoma: a review on the roles of physical exercise on intraocular pressure control, ocular blood flow regulation, neuroprotection and glaucoma-related mental health.

The benefits of physical exercise on health and well-being have been studied in a wide range of systemic and ocular diseases, including glaucoma, a progressive optic neuropathy characterized by accelerated apoptosis of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) and insufficient ocular perfusion have been postulated to be the two main theories in glaucoma development and progression. The effects of exercise in these two aspects have been demonstrated by numerous researches. A review in 2009 focusing on these two theories concluded that exercise results in transient IOP reduction but an inconsistent elevation in ocular perfusion. However, the majority of the studies had been conducted in healthy subjects. Over the past decade, technological advancement has brought forth new and more detailed evidence regarding the effects of exercise. Moreover, the neuroprotective effect of exercise by upregulation of neurotrophin and enhancement of mitochondrial function has been a focus of interest. Apart from visual impairment, the mental health issues in patients with glaucoma, which include anxiety and depression, should also be addressed. In this review, we mainly focus on publications from the recent years, so as to provide a comprehensive review on the impact of physical exercise on IOP, ocular perfusion, neuroprotection and mental health in patients with glaucoma.

Impact of antiangiogenic therapy on ocular blood flow and microcirculation in diabetic macular edema

To identify changes in the ocular blood flow and microvascular network of the macular zone in patients with DME after antiangiogenic therapy. In the course of the study, 25 patients (50 eyes) with monolateral clinically significant DME aged 67.5±3.85 years were examined. Control group consisted of 75 healthy subjects (150 eyes). All patients underwent ultrasound examination of the eyes and orbits (in Color Doppler Imaging (CDI) and Pulse-Doppler modes) and OCT-angiography (OCT-A) before the intravitreal injection of ranibizumab, as well as 3 days, 2 weeks, and 1 month after the treatment. According to OCT-A, the initial values of microvascular network parameters were significantly below the norm (p<0.05). After intravitreal ranibizumab injection (IRI), no significant changes in the density of microcapillaries or in the parameters of foveal avascular zone (FAZ) were recorded. However, a transient increase of the FAZ area was revealed 2 weeks after the injection, as well as an increase of microcapillaries density in the central quadrant together with a decrease of density in the peripheral quadrants 1 month after IRI. By the end of the follow-up period, a decrease in the initially raised maximum systolic velocity (Vsyst) and resistance index (RI) in the ophthalmic artery (OA) of the affected eye were documented. Additionally, an increase in Vsyst and 2-fold increase in end-diastolic velocity (Vdiast), as well as a decrease in RI in the central retinal artery (CRA) on the affected and paired eyes were detected. The study revealed no negative effects of the angiogenesis inhibitor ranibizumab on retinal microcirculation or ocular blood flow. The registered changes in blood flow may indicate improvement of hemodynamic parameters after resorption of macular edema.

Modern Diagnostic Techniques for the Assessment of Ocular Blood Flow in Myopia: Current State of Knowledge.

Myopia is the most common refractive error and the subject of interest of various studies assessing ocular blood flow. Increasing refractive error and axial elongation of the eye result in the stretching and thinning of the scleral, choroid, and retinal tissues and the decrease in retinal vessel diameter, disturbing ocular blood flow. Local and systemic factors known to change ocular blood flow include glaucoma, medications and fluctuations in intraocular pressure, and metabolic parameters. Techniques and tools assessing ocular blood flow include, among others, laser Doppler flowmetry (LDF), retinal function imager (RFI), laser speckle contrast imaging (LSCI), magnetic resonance imaging (MRI), optical coherence tomography angiography (OCTA), pulsatile ocular blood flowmeter (POBF), fundus pulsation amplitude (FPA), colour Doppler imaging (CDI), and Doppler optical coherence tomography (DOCT). Many researchers consistently reported lower blood flow parameters in myopic eyes regardless of the used diagnostic method. It is unclear whether this is a primary change that causes secondary thinning of ocular tissues or quite the opposite; that is, the mechanical stretching of the eye wall reduces its thickness and causes a secondary lower demand of tissues for oxygen. This paper presents a review of studies assessing ocular blood flow in myopes.

Acute effects of yoga on ocular perfusion pressure in adult yoga practitioners

Background: Ocular perfusion pressure (OPP) is an important determinant of ocular blood flow. Reduced OPP could be a risk factor for glaucoma. According to the WHO, glaucoma is the second leading cause of blindness in the world. Yoga harmonizes the body with the mind. Studies have demonstrated that yogic exercises affect blood pressure (BP) as well as intraocular pressure (IOP). Although OPP depends on BP and IOP, not much of research has been done to analyze the impact of yoga on OPP. Aims and Objectives: The aim of the study is to analyse the immediate and composite effects of yoga on OPP in adult yoga practitioners. Materials and Methods: 32 healthy adult yoga practitioners in the age group of 18-25 years, were selected. Basal IOP and BP were recorded in sitting position using rebound tonometer and sphygmomanometer, respectively. The second recording was done immediately after 45 min of yoga practice. Mean OPP (MOPP) was calculated. Results: There was no significant difference in the IOP of both eyes before and after yoga. Statistically significant fall in the mean arterial pressure (MAP) and OPP of both eyes was observed immediately after yogic exercises (P < 0.001). Conclusion: In this study, MAP was reduced and IOP remained unchanged following yoga. This implies that simple yoga exercises may be useful as supplementary antihypertensive therapy. Although OPP was reduced in our study, autoregulation might maintain blood flow despite changes in perfusion pressure. More insight into ocular blood flow regulation can be studied using optical coherence tomography.

Factors Related to a Right-Left Difference in Visual Field Defect in the Eyes with Untreated Normal Tension Glaucoma.

Purpose To investigate factors related to a right-left difference in visual field defect in untreated normal tension glaucoma (NTG). Methods The medical records of 92 patients with untreated NTG were reviewed. Ocular blood flow was evaluated with laser speckle flowgraphy, and the mean blur rate (MBR) at the optic nerve head was analyzed. Relationships between right-left differences in mean deviation (MD), intraocular pressure, MBR, spherical equivalent, central corneal thickness, and mean ocular perfusion pressure were evaluated using Spearman's rank correlation coefficient. Multiple regression analysis was used to detect factors contributing to a right-left difference in MD. Results The right-left difference in MD was correlated with differences in intraocular pressure (r = −0.263, P = 0.011), MBR (r = 0.417, P < 0.001), and spherical equivalent (r = 0.213, P = 0.042), but not with central corneal thickness or mean ocular perfusion pressure. Multiple regression analysis showed that a difference in MBR was the only significant contributor to a right-left difference in MD (slope 0.047, 95% confidence interval 0.025–0.069; P < 0.001). Conclusion In untreated NTG, a difference in blood flow at the optic nerve head was a significant contributor to a right-left difference in visual field defect.

Evaluation of choroidal perfusion changes in obese patients: ocular effects of insulin resistance

We aimed to evaluate choroidal per-fusion changes in obese patients using optical coherence tomography and dynamic contour tonometry, to determine whether these changes are associated with body mass index, and to assess the ocular effects of insulin resistance. We retrospectively evaluated the data of 32 obese patients with body mass index >30 kg/m2 and 45 healthy control individuals. Intraocular pressure and ocular pulse amplitude values of the patients were measured using dynamic contour tonometry, and the mean choroidal thickness was measured using enhanced depth imaging optical coherence tomography. Insulin resistance was assessed using the homeostasis model assessment-estimated insulin resistance index. The mean choroidal thickness (294.30 ± 60.87 μm) and ocular pulse amplitude (2.10 ± 0.74) were lower, whereas the mean intraocular pressure (16.61 ± 2.35 mmHg) was higher in obese patients than in controls. There was a significant negative correlation between body mass index and ocular pulse amplitude (r=-0.274; p=0.029) and an insignificant negative correlation between mean choroidal thickness, intraocular pressure, and body mass index. There was an insignificant negative correlation between homeostasis model assessment-estimated insulin resistance index, mean choroidal thickness, and intraocular pressure and significant ne-gative correlation between homeostasis model assessment-estimated insulin resistance index and ocular pulse amplitude (r=-0.317; p=0.022). We found reduced mean choroidal thickness and ocular pulse amplitude and increased mean intraocular pressure in obese patients. These changes indicated a decrease in choroidal perfusion and ocular blood flow. It may be possible to detect ocular blood flow changes in obese patients through noninvasive assessment using the choroid. The negative correlation between insulin resistance and ocular pulse amplitude may be associated with intracellular fat accumulation in obese patients.

A comparative study of intraocular pressure and ocular perfusion pressure changes in prehypertensive individuals

Background: According to the WHO, glaucoma is the second leading cause of blindness in the world. Ocular perfusion pressure (OPP), an important determinant of ocular blood flow, represents the balance between the opposing forces of blood pressure (BP) and intraocular pressure (IOP). Alterations in OPP play a significant role in pathogenesis of glaucoma. Although systemic hypertension has been proved to be a potential risk factor for glaucoma, there is a paucity of literature regarding the vascular effects of prehypertension on optic disc. Aims and Objectives: This study aims to study the effects of prehypertension on IOP and OPP. Materials and Methods: A total of 102 voluntary participants in the age group of 20–50 years were selected. The study group comprised 51 subjects with prehypertension and control group included 51 age and sex-matched normotensives. Basal IOP and BP were recorded in sitting position using rebound tonometer and sphygmomanometer, respectively. Mean OPP was calculated. Results: There was significant increase in the IOP and OPP of both the eyes in prehypertensives when compared with normotensives. Conclusion: Elevated IOP levels in prehypertensive individuals are deleterious to optic disc. Raised OPP observed in prehypertensives could be due to effective autoregulation, which could be compromised if there is further increase in BP. Hence, early detection of prehypertension and measures to reduce the BP must be taken to prevent the development of glaucoma.

Glaucoma related retinal oximetry: a technology update

There are two long-standing theories about the pathogenesis of glaucoma – barotrauma and the effect of vascular hypoxia. Currently, it is still unknown whether diminished blood flow is the cause or result of glaucomatous atrophy of ganglion cells and the optic nerve. Though many other imaging techniques used to directly assess ocular blood flow have been well studied, they are limited by their inability to directly assess metabolism in the ocular tissues or measure the oxygen carrying capacity in the vessels. Retinal oximetry is a relatively novel, noninvasive imaging technique that reliably measures oxygen saturation levels in the retinal vessels, offering surrogate markers for the metabolic demands of the eye. The clinical significance of these measurements has not been well established. Thus, this review gives an overview of ocular imaging and current retinal oximetry techniques, while contextualizing the important oximetry studies that have investigated the vascular theory behind glaucoma.

Optical Coherence Tomography-Based Scattering Properties of Retinal Vessels in Glaucoma Patients

ABSTRACTPurpose: Clinical trials have demonstrated that retinal blood flow deficiencies are present in patients with open-angle glaucoma (OAG). We introduce a method for facilitating retinal vessel analysis: The intensity of the distal shadow of vessels in optical coherence tomography (OCT) caused by the scattered signal is analyzed, compared between healthy subjects and OAG patients and correlated with OCT angiography (OCT-A) flow density.Patients and Methods: We recruited 80 patients with diagnosed OAG (mean age 63.4 ± 13.2 years) and 80 healthy age-matched control subjects for comparison, and 20 patients for the correlation with OCT-A flow density. Patients received perimetry, peripapillary OCT measurements, and selected patients OCT-A of the papillary area. The vessel shadow intensity (VSI) is based on peripapillary OCT scans: the intensity of the distal vessel shadow was automatically compared to its surroundings, separated by arteries and veins. Flow density of the OCT-A scan was calculated by binarization and quantification of the pixel density.Results: The VSI for arteries was in OAG patients with 7.52 ± 2.62 [%] significantly lower compared to healthy subjects (9.03 ± 3.38 [%], p = 0.0029). In veins, the VSI was as well significantly lower for OAG patients (14.9 ± 3.59 [%]) compared to healthy subjects (17.46 ± 4.45 [%], p < 0.0001). Furthermore, in OAG patients there was a significant correlation of mean deviation of the visual field results with the veins’ VSI (p = 0.0006; r = −0,454). There was no significant correlation of scattering properties with OCT-A flow density (p > 0.05).Conclusions: We conclude that the OCT-based analysis of the scattering properties of retinal vessels differs significantly between patients with OAG and healthy subjects. Furthermore, changes in the scattering properties of veins correlated with the stage of the disease in terms of visual field deficits. These properties might complement existing measurements of ocular blood flow including OCT-A flow density.