Changes In Ocular Perfusion Pressure Research Articles

Postural effects on blood pressure, intraocular pressure, and ocular perfusion pressure in patients with spinal cord injury

Background Reduced ocular perfusion pressure (OPP) from hypotension and consistent OPP variability due to blood pressure (BP) fluctuations are predisposing factors for glaucoma. Low resting BP and orthostatic hypotension (OH) in spinal cord injury (SCI) patients may increase the risk of glaucoma post-injury. This study investigated BP, intraocular pressure (IOP), and OPP changes between supine and sitting positions in SCI and normal individuals. Methods Twenty SCI cases (high paraplegia, T1–T6 n = 6; low paraplegia, T7–L3 n = 14) and matched controls (1:1) were included. Systolic and diastolic BP (SBP and DBP) were measured digitally, and IOP with rebound tonometry. Measurements were taken one minute apart in both positions. Mean arterial pressure (MAP) was calculated, and OPP was determined using position-specific formulas. Results No SCI subjects exhibited OH. Both groups experienced significant BP increment (P < 0.05) from supine to sitting. SBP increased by 4.4 ± 8.4 mmHg (SCI) and 3.6 ± 6.2 mmHg (normal), while DBP increased by 4.2 ± 5.1 mmHg (SCI) and 6.7 ± 5.5 mmHg (normal). IOP and OPP decreased significantly (P < 0.05) after postural change in both groups, yet differences between them were not significant. Analysis by injury level revealed lower parameter values in high paraplegia than in low paraplegia, with the latter group showing a more significant reduction in OPP after postural change. Conclusion Postural changes differently affect BP, IOP, and OPP in SCI compared to normal individuals, with variations based on the level of SCI. While not directly assessing glaucoma, the study offers insights into ocular hemodynamics in SCI compared to normals.

Effects of Hemodialysis on Intraocular Pressure and Ocular Perfusion Pressure.

Elevated intraocular pressure (IOP) and reduced ocular perfusion pressure (OPP) related to hemodialysis (HD) are risk factors for the development and progression of glaucoma. The aim of this study was to evaluate the effect of HD on IOP and OPP in our patients. This was a cross-sectional, descriptive, and analytical study conducted between January 2 and February 5, 2024, in the HD and ophthalmology departments of the Heinrich Lübke Regional Hospital in Diourbel. The IOP of both eyes was measured one hour before the start of the HD session and within 30 minutes after the end of the session, by the same ophthalmologist, for all included patients, using a Goldmann applanation tonometer. OPP were calculated and other socio-demographic data collected. Fifty-eight eyes from 29 chronic HD patients were included. The mean age of the patients was 47.58±12.94 years, with a predominance of women (17 women or 58.6%; sex ratio 0.71). In the left eye, mean IOP increased significantly from 12.21±2.96 mmHg before the HD session to 14.10±4.27 mmHg at the end of the session (p=0.04). For the right eye, the IOP also increased with a strong tendency to significance from 12.97±3.79 mmHg before the HD session to 15.03±5.23 mmHg at the end of the session (p=0.05). OPP did not change significantly after the HD session. The HD session significantly increased IOP with no significant change in OPP.

Retinal electrophysiologic response to IOP elevation in living human eyes

PurposeThe relationships between intraocular pressure (IOP), ocular perfusion pressure (OPP), retinal perfusion, and retinal electrophysiologic responses have been explored experimentally across several animal models. These studies have demonstrated that elevated IOP reduces OPP, and when this reduction in OPP exceeds the autoregulatory capacity of the retina vasculature, retinal perfusion and electrophysiologic responses are reduced. This study aimed to evaluate these interactions for the first time in the living human eye. MethodsFive eyes from three research-consented brain-dead organ donors underwent optical coherence tomography with angiographic (OCT/A; Spectralis, Heidelberg Engineering) and electroretinographic (ERG, Diagnosys LLC) measurements while IOP was manometrically-elevated stepwise to pressures of 10, 30 and 50 mmHg. Systemic blood pressure (BP) was monitored continuously during testing. Correlation analysis was applied to assess association between ERG and OPP changes. In a single eye, prolonged IOP elevation was induced with viscoelastic injection and serial ERG measurements were obtained. ResultsReductions in inner retinal function defined by photopic ERG were observed with elevation in IOP and concomitant reduction in OPP. Reductions, especially in b-wave, and photopic negative response (PhNR) amplitudes and implicit times were significantly correlated with elevation in IOP and reduction in OPP. There were more appreciable changes in perfusion and functional responses in eyes tested while systemic blood pressure was lower. With prolonged IOP elevation, selective loss of the PhNR response was observed. ConclusionsIn the living human eye, retinal perfusion and inner retinal function are acutely impacted by elevation of IOP, and this impact is related to systemic BP and OPP. This novel approach provides a viable model to study the autoregulatory responses to IOP elevation in the living human eye.

A cross-sectional study of association between ocular pressures and different grades of myopia in young adults

Introduction and Aim: My­opia is one of the most common refractive errors causing visual disability worldwide. Uncorrected refractive error poses a public health challenge especially in young adults who have to spend most of their time in literary works. Intra ocular pressure (IOP) is one of the crucial factors intertwined in the pathophysiology of myopia. Ocular perfusion pressure (OPP) determines ocular blood flow. Studies done on association between IOP and refractive errors are contradictory. There is paucity of literature on relationship between OPP and myopia. Hence this original article aimed to assess the association of IOP and OPP changes with myopia and to analyze the relationship between ocular pressures with severity of myopia. Materials and Methods: Hundred normal adults in the age group of 18-24 years of either gender were recruited for the present study. Voluntary written and informed consent was sought from all participants and the refractive power of their eyes was noted. They were categorised into three groups based on the severity of myopia. Controls were the emmetropes. All participants were asked to relax for 5-10 minutes and the resting BP and IOP were recorded using sphygmomanometer and rebound tonometer respectively. OPP was calculated. Results: IOP values were comparatively higher in myopes than emmetropes. A significant reduction in OPP values were observed in moderate myopes. Conclusion: Myopes have a higher IOP suggesting myopia is one of the major risk factor for ocular hypertension. Low OPP values in moderate myopes indicate reduced ocular perfusion, making the progressive myopes highly susceptible to glaucoma.

Effect of adding clonidine to lidocaine on ocular hemodynamics during sub-Tenon’s anesthesia: randomized double-blind study

Introduction and objectivesDifferent regional anesthesia techniques for ophthalmology can have hemodynamic effects on the eye. We assessed the effects of adding clonidine to lidocaine on Intraocular Pressure (IOP), Ocular Pulse Amplitude (OPA), and Ocular Perfusion Pressure (OPP) after the sub-Tenon’s technique for cataract surgery. MethodsThe study included 40 patients randomly allocated into two groups: sub-Tenon’s blockade with Lidocaine plus Saline Solution (LS) or Lidocaine plus Clonidine (LC). IOP, OPA and OPP were measured before anesthesia, and 1, 5 and 10 minutes after the injection of anesthetic solution. ResultsThere was no difference between the groups in IOP, OPA, and OPP baseline values. After the injection of the anesthetic solution, the IOP increased in both groups at minute one, with a mean difference of +4.67 mmHg (p = 0.001) and +2.15 mmHg (p = 0.013) at 5 minutes. The increase was lower in the LC group when compared to LS (p = 0.027). OPA decreased in both groups, with a baseline difference, after 1 minute, of -0.85 mmHg (p = -0.85 mmHg (p = 0.001), and at 5 and 10 minutes with differences of -1.17 (p = 0.001) and -0.89 mmHg (p = 0.001), respectively. The highest decrease was observed in group LC in relation to group LS (p = 0.03). There was no difference in OPP in relation to baseline measurements. ConclusionsAdding clonidine to lidocaine for sub-Tenon’s anesthesia reduced IOP and OPA without significant changes in OPP.

OCT Angiography ‐ A new tool to assess vascular autoregulation in the retina

AbstractVascular autoregulation is defined as the ability of a vascular bed to keep blood flow constant despite changes in ocular perfusion pressure. In the eye, the retinal circulation and also to a certain degree the choroidal circulation exhibit autoregulatory properties in response to changes in blood or intraocular pressure. Interestingly, it has been shown that these autoregulatory properties are compromised in ocular diseases such as glaucoma or diabetic retinopathy. New tools such as OCT angiography allow now for the investigation of vascular changes up to the microvascular level. The current talk will summaries how these new technologies can be used to get more insight in the complex regulation of blood flow in the eye.

Regulation of Choroidal Blood Flow During Isometric Exercise at Different Levels of Intraocular Pressure.

There is evidence that choroidal blood flow (ChBF) is regulated in a complex way during changes in ocular perfusion pressure (OPP). We hypothesized that ChBF regulates better in response to changes in mean arterial pressure (MAP) than in intraocular pressure (IOP). Eighteen volunteers (mean age, 26 years) were recruited for a randomized, three-way crossover design. MAP was varied via isometric exercise. IOP was either kept normal or elevated by 10 or 20 mm Hg by using a suction cup. Subfoveal ChBF was measured continuously for 8 minutes with laser Doppler flowmetry and OPP was calculated as 2/3*MAP-IOP. For data analysis, values from all subjects were pooled according to either IOP or MAP values, and correlation analyses were done. When data were grouped according to IOP, no correlation was observed between ChBF and MAP, but ChBF was lower the higher the IOP (P < 0.001). When data were grouped according to MAP, a significant correlation was found between ChBF and IOP (P < 0.001). When data were pooled according to IOP, the correlation between ChBF and OPP was weaker (P < 0.05). The OPP at which ChBF significantly increased from baseline was 61.3% ± 4.9% without suction cup, 65.2% ± 3.5% when IOP was increased by 10 mm Hg, and slightly lower when IOP was increased by 20 mm Hg (56.3% ± 4.8%, P = 0.07), but this effect did not reach the level of significance. The present study provides further evidence that the regulation of ChBF during changes in OPP is controlled by complex mechanisms in humans and has less capacity to adapt to IOP elevation than to MAP increase.

Evaluation of optic nerve head blood flow in response to increase of intraocular pressure

The time course of the changes in the optic nerve head (ONH) blood flow in response to changes in the ocular perfusion pressure (OPP) induced by an artificial elevation of the intraocular pressure (IOP) has not been determined. We measured the blood flow, represented by the mean blur rate (MBR), on the ONH determined by laser speckle flowgraphy. The MBR was determined before, during, and after the IOP was elevated by 20 or 30 mmHg by pressure applied on the eye by an ophthalmodynamometer in a total of 27 healthy eyes. For an IOP elevation of 20 mmHg, the percentage reduction in the MBR-vessel was −24.7%, and in the MBR-tissue was −16.0% (P < 0.001). For an IOP elevation of 30 mmHg, the percentage reduction of the MBR-vessel was −35.3% and the MBR-tissue was −24.7% (P < 0.001). During the 30 mmHg IOP elevation for 10 minutes, both the MBR-vessel and MBR-tissue began returning to the baseline level from 1 minute after the beginning of the IOP elevation (P < 0.01, P < 0.05, respectively) and continued returning during the 10 minutes IOP elevation (P < 0.001, P < 0.01, respectively). We conclude that the ONH can autoregulate its blood flow in response to experimental changes in OPP induced by IOP elevations.

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.

Factors Associated With Choroidal Blood Flow Regulation in Healthy Young Subjects.

To analyze regulation of subfoveal choroidal blood flow (FLOW) during isometric exercise in healthy subjects in dependence of intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP), age, sex, fasting glucose, cholesterol, triglycerides, creatinine, and C-reactive protein levels and hematocrit. We retrospectively analyzed results obtained in 261 healthy subjects who underwent a period of 6 minutes of isometric exercise during which FLOW was measured continuously and MAP was measured every minute. From these data, OPP and choroidal pressure/flow curves were calculated. Subjects were grouped into tertiles with regard to the dependent variables, and pressure/flow relationships were compared. Choroidal blood flow started to increase at OPP values of approximately 65% dependent on the MAP/IOP tertile. A significant increase of FLOW from baseline was noted at 67.7 ± 2.1% in the lowest MAP tertile, at 67.7 ± 2.0% in the second MAP tertile, and at 61.8 ± 2.0% in the highest MAP tertile (P = 0.01). At the three IOP levels, FLOW started to increase at an OPP increase of 69.8 ± 2.1%, 70.1 ± 2.2%, and 65.4 ± 1.9% above baseline, respectively (P = 0.03). Choroidal pressure/flow curves were independent of the other variables. The present analysis indicates that FLOW regulation during isometric exercise is dependent on absolute MAP as well as IOP levels. This indicates that regulation depends on pressure levels at both the arterial and the venous side of the choroidal circulation and highlights the complexity of FLOW regulation during changes in OPP that cannot be simply characterized by classical autoregulation models.

Ocular Blood Flow Autoregulation Mechanisms and Methods.

The main function of ocular blood flow is to supply sufficient oxygen and nutrients to the eye. Local blood vessels resistance regulates overall blood distribution to the eye and can vary rapidly over time depending on ocular need. Under normal conditions, the relation between blood flow and perfusion pressure in the eye is autoregulated. Basically, autoregulation is a capacity to maintain a relatively constant level of blood flow in the presence of changes in ocular perfusion pressure and varied metabolic demand. In addition, ocular blood flow dysregulation has been demonstrated as an independent risk factor to many ocular diseases. For instance, ocular perfusion pressure plays key role in the progression of retinopathy such as glaucoma and diabetic retinopathy. In this review, different direct and indirect techniques to measure ocular blood flow and the effect of myogenic and neurogenic mechanisms on ocular blood flow are discussed. Moreover, ocular blood flow regulation in ocular disease will be described.

Systemic and Ocular Hemodynamic Risk Factors in Glaucoma.

Primary open angle glaucoma (POAG) is a multifactorial disease characterized by progressive retinal ganglion cell death and visual field loss. It is known that alterations in intraocular pressure (IOP), blood pressure (BP), and ocular perfusion pressure (OPP) can play a significant role in the pathogenesis of the disease. Impaired autoregulatory capacity of ocular blood vessels may render tissues vulnerable to OPP changes and potentially harmful tissue ischemia-reperfusion damage. Vascular risk factors should be considered more important in a subgroup of patients with POAG, and especially in patients with normal tension glaucoma (NTG) with evidence of unphysiological BP response. For example, reduction of BP during the nighttime has an influence on OPP, and increased circadian OPP fluctuation, which might stand for unstable ocular blood flow, has been found to be the consistent risk factor for NTG development and progression. Central visual field may be affected more severely than peripheral visual field in NTG patients with higher 24-hour fluctuation of OPP. This review will discuss the current understanding of allegedly major systemic and ocular hemodynamic risk factors for glaucoma including systemic hypertension, arterial stiffness, antihypertensive medication, exaggerated nocturnal hypotension, OPP, and autonomic dysregulation.

Long term effect of trabeculectomy on retrobulbar haemodynamics in glaucoma.

Previous reports showed increased flow velocities in retrobulbar vessels after glaucoma surgery in the first weeks. Colour Doppler imaging was performed to investigate the long-term effects of trabeculectomy on retrobulbar haemodynamics in patients with primary open-angle glaucoma (POAG). In a prospective study 30 patients (mean age 63.2±15.4years) with POAG were included. Colour Doppler imaging was performed before 1-2weeks, after 2months, after 4-6months, and up to 3years after trabeculectomy to determine the peak systolic and end-diastolic velocities in the ophthalmic artery, central retinal artery, and the short nasal and temporal posterior ciliary arteries. Mean follow-up was 416±246days. In the first postsurgical period mean intraocular pressure (IOP) decreased after trabeculectomy from 25±6mmHg to 9±4mm Hg (p<0.0001) and then increased in the further follow-up to 13±3mmHg (p<0.05) without any anti-glaucomatous medication. Colour Doppler imaging revealed a significant increase of the end-diastolic velocities of the central retinal artery at all postoperative visits compared to pre-surgery (p<0.003) and of the end-diastolic velocities in the temporal posterior ciliary arteries (p<0.003). The change of blood flow parameters that increased during follow-up was significantly correlated to the change in ocular perfusion pressure and IOP. End-diastolic velocities of the central retinal artery and of the temporal posterior ciliary arteries increased after successful trabeculectomy and remained stable in a longer period - even if IOP rose significantly in the follow-up.

Effect of Hemodialysis on Intraocular Pressure and Ocular Perfusion Pressure

Elevated intraocular pressure (IOP) and decreased ocular perfusion pressure (OPP) are risk factors for glaucoma development and progression. Unrecognized significant IOP elevation or OPP reduction during hemodialysis (HD) could lead to glaucomatous optic nerve damage and subsequent visual loss. To evaluate changes in IOP and OPP during HD. A cross-sectional observational study was conducted in patients undergoing HD at an ambulatory care clinic at the University of Illinois at Chicago. Forty-nine patients (97 eyes) undergoing HD were enrolled. Exclusion criteria included preexisting corneal abnormalities, history of corneal surgery, allergy to topical anesthetic agents, and current eye infection. Nine patients had previous diagnoses of open-angle glaucoma (OAG) or suspected glaucoma. At 3 time points, IOP was measured using a pneumatonometer and blood pressure was recorded. Measurements were made with the patient in a seated position approximately 15 minutes before starting HD (T1), approximately 2 hours after starting HD (T2), and approximately 15 minutes after ending HD (T3). Mean arterial pressure (MAP) and OPP (systolic, diastolic, and mean OPP) were calculated. Intraocular pressure and OPP. From T1 to T3, IOP significantly increased by 3.1 mm Hg (both eyes, P < .001), MAP significantly decreased by 5.8 mm Hg (P = .05), and all OPP measures significantly decreased from baseline (all P ≤ .02). Using previously reported thresholds of increased glaucoma development and progression risk, 53% of the right eyes (26 of 49) and 46% of the left eyes (22 of 48) had a systolic OPP of 101 mm Hg or less, 71% of the right eyes (35 of 49) and 73% of the left eyes (35 of 48) had a diastolic OPP of 55 mm Hg or less, and 63% of the right eyes (31 of 49) and 65% of the left eyes (31 of 48) had a mean OPP of 42 mm Hg or less. Significantly increased IOP and decreased OPP occur during HD, bringing both to levels that increase the risk of glaucoma development and progression. Clinicians should consider HD history in patients who have glaucoma progression, even when IOP has been well controlled. Such patients may benefit from IOP and blood pressure monitoring during HD sessions to minimize OPP changes resulting from IOP spikes and/or suboptimal blood pressure.

Optic nerve head autoregulation during changes in arterial blood pressure

AbstractPurpose Previous studies in our laboratory have shown that an increase in blood pressure during isometric exercise leads to an increase in optic nerve head blood flow (ONHBF). An interesting phenomenon was found in some subjects when they were exhausted from isometric exercise and blood pressure decreased slightly. These periods were sometimes associated with a pronounced decrease in ONHBF even though ocular perfusion pressure (OPP) was still much higher than at baseline. The present study aimed to investigate this phenomenon in more detail and to gain insight in the regulatory mechanisms of ONHBF during short‐term fluctuations in OPP.Methods 40 healthy subjects aged between 18 and 35 years were included in this study. Three periods of baseline measurements at rest and 3 periods of measurements during isometric exercise with a handgrip were alternated while ONHBF was measured continuously using laser Doppler flowmetry. Mean arterial blood pressure (MAP) was measured every minute and OPP was calculated as 2/3 MAP – intraocular pressure (IOP).Results OPP significantly increased during handgripping compared to the resting periods (p&lt;0.001), whereas ONHBF was not significantly altered during these changes in OPP indicating for autoregulation. Three subjects showed a decrease of more than 10% in ONHBF during recovery at all 3 periods of isometric exercise. Unexpectedly, however, 3 other subjects consistently showed an ONHBF reduction of more than 10% during isometric exercise.Conclusion The present study indicates a complex regulation of ONHBF. Six subjects (15%) showed an abnormal ONHBF response during handgripping. This is most likely caused by an exaggerated vasoconstrictor response in order to counteract the increase in OPP.

Changes in choroidal thickness, axial length, and ocular perfusion pressure accompanying successful glaucoma filtration surgery

To investigate the changes in choroidal thickness (CT), axial length (AL), and ocular perfusion pressure (OPP) accompanying intraocular pressure (IOP) reduction after trabeculectomy. methods: Thirty-nine eyes of 39 patients with primary open-angle glaucoma uncontrolled by medical therapy were included in this prospective and interventional study. All patients underwent a fornix-based trabeculectomy. The CT was measured by enhanced depth imaging-optical coherence tomography. IOP, AL, and systolic/diastolic blood pressure were also measured, and OPP was calculated. All measurements were performed at baseline and 1 month after surgery. The mean IOP was 25.0 ± 5.8 mm Hg at baseline and 11.7 ± 2.6 mm Hg after trabeculectomy (P<0.001), and the mean subfoveal CT was 295 ± 84 mm Hg at baseline and 331 ± 82 mm Hg after trabeculectomy (P<0.001). The mean AL was 23.64 ± 0.98 mm at baseline and 23.54 ± 0.96 mm after trabeculectomy (P<0.001), whereas the mean OPP was 38.8 ± 6.2 mm Hg preoperatively, and 51.1 ± 7.3 mm Hg postoperatively (P<0.001). The change in CT negatively correlated with the change in IOP (r=-0.785, P<0.001) and AL (r=-0.693, P<0.001), whereas it positively correlated with the change in OPP (r=0.418, P=0.008). These results suggest that the large IOP decrease following trabeculectomy causes choroidal thickening. In addition, CT changes are associated with IOP and AL reduction as well as OPP increase.

Role of nitric oxide in optic nerve head blood flow regulation during experimental increase of intraocular pressure in healthy humans

AbstractPurpose Several studies have indicated that the choroid shows some regulatory potential during changes in ocular perfusion pressure (OPP). For the optic nerve head (ONH) only few data are available. The present study set out to investigate the behavior of ONH blood flow (ONHBF) during an experimental decrease in OPP and to explore whether inhibition of Nitric Oxide Synthase (NOS) alters this response.Methods Twelve healthy subjects participated in this randomized, double‐masked, placebo‐controlled three‐way crossover study. For each subject, three study days were scheduled, on which they either received intravenous infusions of NG‐monomethyl‐ L‐arginine (L‐NMMA), phenylephrine, or placebo. OPP was increased stepwise by the suction cup method. ONHBF was assessed continuously with laser Doppler flowmetry and OPP was calculated as 2/3*mean arterial pressure‐intraocular pressure.Results Administration of L‐NMMA and phenylephrine significantly increased resting OPP compared to placebo (p&lt;0.001 and p=0.016, respectively). As expected, L‐NMMA decreased resting ONHBF compared to phenylephrine (p=0.04). The relative decrease in OPP during suction cup application was comparable with all drugs administered (between ‐69% and ‐72%, p=0.19). In all three groups, the decrease in ONHBF was less pronounced than the decrease in OPP, but not significantly different between groups.Conclusion The present data indicate that NO plays an important role in the regulation of basal ONHBF, but not in ONHBF autoregulation.

Vasomotor reaction of retinal arterioles in hypoxic and ischemic conditions

AbstractPurpose Retinal blood flow is autoregulated by the adaptation of the vascular tone of resistance vessels (arterioles, capillaries) to changes in the perfusion pressure (PP) or metabolic needs of the tissue. The purpose of this study was to evaluate the disturbance of arteriolar reactivity, and thus of blood flow regulation, during the evolution of ischemic retinal microangiopathies.Methods Much of our basic knowledge of retinal arteriolar reactivity is based on data obtained from animal experiments through the use of invasive techniques. However, a variety of non‐invasive techniques has been applied to the human eye for the investigation of retinal hemo‐dynamics and, more specifically, the reactivity of the retinal arterioles in response to a number of physiologic and pharmacologic stimuli, under normal, hypoxic and ischemic conditions.Results In patients with non‐proliferative diabetic retinopathy (DR), isocapnic hypoxia induces a significant increase in Vleuk in the perifoveal circulation, whereas in patients with proliferative DR, the diameter of the retinal vessels remains unchanged, indicating that blood flow regulation in response to a hypoxic challenge is blunted,consequent to the hypoxic retinal conditions. In those patients a hyperoxia‐induced blunted vasoconstriction of the retinal arterioles is also observed. The ability of the retinal arterioles to respond to changes in ocular PP is altered in diabetes, while the response of retinal vessels to diffuse luminance flicker is blunted, particularly in patients suffering from insulin‐dependent diabetes.Conclusion During the evolution of retinal ischemic microangiopathies, impairment of various mechanisms of retinal arteriolar reactivity leads to disturbed retinal blood flow regulation.

Comparison of Choroidal and Optic Nerve Head Blood Flow Regulation during Changes in Ocular Perfusion Pressure

We compared the response of choroidal and optic nerve head blood flow (ChBF, ONHBF) in response to an increase in ocular perfusion pressure (OPP) during isometric exercise and during a decrease in OPP during an artificial increase in intraocular pressure (IOP). We included 96 healthy subjects in our study. In 48 subjects OPP was increased by 6 minutes of squatting, and either ONHBF (n = 24) or ChBF (n = 24) was measured continuously. In 48 other healthy subjects either ONHBF (n = 24) or ChBF (n = 24) was measured continuously during a period of artificial increase in IOP using a suction cup. All blood flow measurements were done using laser Doppler flowmetry. During all experiments the response in blood flow was less pronounced than the response in OPP, indicating for flow regulation. During isometric exercise ChBF regulated better than ONHBF (P = 0.023). During artificial IOP increase ONHBF regulated better than ChBF (P = 0.001). Inter-individual variability in blood flow responses was high. During squatting ONHBF decreased considerably below baseline ONHBF when OPP fluctuated in 3 subjects, although OPP still was much higher than at baseline. This phenomenon was not observed in the choroid. Our data indicate that regulation of ChBF and ONHBF during changes in OPP is different and complex. In some subjects performing squatting, considerable ONHBF reductions were observed during OPP fluctuations, although OPP still was high. Whether this predisposes to ocular disease remains unclear.

Should Men and Women be Managed Differently in Glaucoma?

IntroductionTo assess differences in associations of ocular perfusion pressure (OPP) as well as retinal and retrobulbar blood flow between men and women with primary open angle glaucoma (OAG).MethodsA total of 116 patients with OAG (age 66.9 ± 10.9 years, 70 females) participating in the Indianapolis Glaucoma Progression Study were assessed for OPP, retinal microcirculation, and retrobulbar blood flow. Confocal scanning laser Doppler flowmetry measured peripapillary retinal capillary blood flow. Color Doppler imaging measured peak systolic (PSV) and diastolic blood flow velocities and vascular resistance in the ophthalmic (OA), central retinal (CRA), and nasal and temporal short posterior ciliary arteries (N/T PCA). Bivariate Spearman correlation and multivariate linear regression analyses were performed.ResultsIn female patients with OAG, inferior retinal capillary flow was associated with OPP (r = 0.246, P = 0.044). In men, superior and inferior sector retinal blood flow was associated with OPP (r = −0.402, P = 0.006 and r = −0.357, P = 0.016, respectively). There was no statistically significant association between OPP and retrobulbar blood vessel flow velocities in male patients with OAG but there was an association between OA and TPCA PSV and OPP in female patients with OAG (r = 0.290, P = 0.015 and r = 0.357, P = 0.002, respectively). In female patients with OAG, multivariate regression showed no statistically significant effect of any variable on the superior retinal capillary blood flow, with CRA PSV as a sole predictor to the inferior retinal sector (partial rho = 0.302, P = 0.015) and in male patients with OAG, superior sector retinal capillary blood flow was independently associated with intraocular pressure (partial rho = −0.371, P = 0.016) and OPP (partial rho = −0.456, P = 0.002) with a trend of association with OPP in the inferior retina (partial rho = −0.301, P = 0.053).ConclusionsThere was a positive linear association between retinal microcirculation and OPP in females and a negative association in males. Male and female patients with OAG may differ in their vascular autoregulation in response to changes in OPP.