Reduction 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.

The impact of scheduled hemodialysis on clinical-functional and morphometric ophthalmological status of patients with a terminal kidney disease

The literature review discusses the impact of scheduled hemodialysis on the state of the anterior part of the eye, the chorioretinal complex, the central and peripheral vision. The hemodialysis procedure is accompanied by a decrease in basal tear production, quickening of the tear film break-up, and an abnormal ocular surface disease index. Thinning of the corneal center is not accompanied by significant keratometric changes. Intradialytic thinning of the choroid and reduction of ocular perfusion pressure may be involved in the progression of ischemic eye diseases. Lower visual acuity is associated with the instability of the lens and choroid thickness. The impact of hemodialysis on the peripheral vision has not been sufficiently investigated. The correlations of ophthalmic changes with systemic effects of the dialysis are ambiguous. The inconsistency of the research results requires that the research should be continued.

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.

Association between intraocular pressure, mean blood pressure, and mean ocular perfusion pressure among normal healthy adults

Background: On the one hand, hypertension is an independent risk factor for glaucoma; on the other hand, hypertension is protective by increasing mean ocular perfusion pressure (MOPP). Reduction in ocular perfusion pressure results in decreased blood flow to the optic nerve head hence plays a role in the pathogenesis of glaucoma. Low MOPP would result from reduction in mean blood pressure (MBP) and increase in intraocular pressure (IOP). Aim and Objective: The aim of the study was to find out the association between MBP, IOP, and MOPP in normal healthy adults. Materials and Methods: The study included 300 healthy young individuals. The BP was recorded using Mercury Sphygmomanometer and IOP recording was done using Slit lamp mounted Goldman Applanation tonometer. MBP was calculated by the formula MBP = DBP+1/3 pulse pressure. The MOPP was calculated by formula: MOPP=MBP–IOP. The subjects were divided into five groups based on the value of MBP: Group 1: 71–80 mm of Hg, Group 2: 81–90 mm of Hg, Group 3: 91–100 mm of Hg, Group 4: 100–110 mm of Hg, and Group 5: >110 mm of Hg. Results: IOP increased linearly with increase in MBP. (P < 0.001) MOPP was positively correlated with MBP in both males (r = 0.985, P < 0.001) and females (r = 0.986, P < 0.001). The MBP is positively correlated with IOP in both males (r = 0.615, P < 0.001) and females (r = 0.668, P < 0.001). Conclusion: Increased MBP is a risk factor for raised IOP as well as raised MOPP. Whether raised MOPP is protective against primary open angle glaucoma or not is still question of debate and needs further evaluation.

Hypercapnia Impairs Vasoreactivity to Changes in Blood Pressure and Intraocular Pressure in Rat Retina.

The balance between oxygen and carbon dioxide sets the resting tone (or diameter) of retinal blood vessels. Eyes that are hypercapnic use up their "vasodilatory reserve" and therefore fail to respond adequately to changes in intraocular or blood pressure. Retinal vessels are regulated by both myogenic and metabolic mechanisms. We considered whether alteration of metabolic status would modify the vascular response to ocular perfusion pressure (OPP) lowering in rat retina. In pentobarbital anesthetized adult Brown-Norway rats, normocapnia or hypercapnia was achieved by artificially ventilating animals with air or 5% carbon dioxide in ~30% oxygen, respectively. Ocular perfusion pressure was gradually reduced to ~20 mmHg by either lowering blood pressure (slowly drawing blood from a femoral artery/vein) or manometrically increasing intraocular pressure under normocapnic or hypercapnic conditions. In all four groups (n = 7 eyes for each), a confocal scanning laser ophthalmoscope was used to acquire image sequences centered on the optic nerve throughout pressure modification. The diameter of arterioles and venules at various OPP levels was measured and expressed as percentage relative to their own baseline. The response of arterioles and venules to OPP lowering was compared between normocapnic and hypercapnic groups. Average arterial carbon dioxide partial pressures were 36.9 ± 2.6 mmHg in normocapnic and 64.1 ± 5.9 mmHg in hypercapnic (P < .001) animals. In the normocapnic groups, blood pressure lowering and intraocular pressure elevation resulted in significant vasodilation of both arterioles and venules (P < .0001). In the hypercapnic groups, OPP lowering-induced vasodilation was significantly attenuated compared with the corresponding normocapnic groups (P < .0001 for both, two-way analysis of variance). Hypercapnia significantly modified myogenic vascular autoregulation in response to OPP reduction.

The impact of laparoscopic surgery in Trendelenburg position on intraocular pressure

Background Patients′ intraocular pressure (IOP) significantly increase during laparoscopic surgery in Trendelenburg position, and the resulting intraoperative intraocular hypertension may be related to postoperative visual loss (POVL). Objective To review the impact of laparoscopic surgery in Trendelenburg position on IOP to let the practitioners aware of the association between intraocular hypertension and POVL. Content One of the major causes for POVL is ischemia in optic nerve following reduction of ocular perfusion pressure (OPP) because of the increase of IOP. Animal studies prove that persistently increased IOP leads to damages in the retina. Patients often receive the laparoscopic surgery in Trendelenburg position, and low OPP and high IOP are commonly seen in this situation. In addition to the body position, the increase of IOP can also be a consequence of hypercapnia following CO2 inflation in the abdominal cavity, and may be affected by anesthetics, duration of the surgery, blood pressure, obesity and gender, etc. Several procedures have been performed to alleviate the increase of IOP, such as, intermittent shift the Trendelenburg position into supine position and intraoperative pharmacological intervention. Trend POVL is rarely seen in laparoscopic surgery, but severely compromises patient′s life quality if happens. Cautions should be taken to carefully monitor IOP in the patients with risk factors for POVL during laparoscopic surgery in the Trendelenburg position. Key words: Intraocular pressure; Laparoscopic surgery; Trendelenburg position

A comparative analysis of the postural and diurnal ocular perfusion pressure of young healthy individuals of different ethnicities

Purpose: Ocular perfusion pressure (OPP) regulates the flow of blood to the optic nerve and is determined by the interaction between intraocular pressure (IOP) and blood pressure (BP). Low OPP increases the incidence of primary open-angle glaucoma (POAG). The aim is to compare the diurnal (i.e. morning vs. afternoon) and postural (i.e. seated vs. supine) OPP in healthy individuals from different ethnicities aged between 18 and 30 years. Methodology: Averaged IOP and BP measurements were obtained with an ICare rebound tonometer and an automated sphygmomanometer, respectively. Measurements were taken in the morning and afternoon, in the supine and seated positions in healthy young adults: Africans ( n = 10), white people ( n = 10), mixed-race people ( n = 10) and Indians ( n = 10). Results: The whole sample ( N = 40) displayed a statistically significant reduction in postural and diurnal OPP both in the supine position and in the morning, respectively. A comparative analysis revealed that Africans displayed statistically significant reduction in OPP when compared to other ethnicities. Discussion: A change in posture to the supine position has a greater impact on the reduction of OPP when compared to diurnal changes. Africans displayed clinically significant reduction in OPP which may increase the incidence of POAG in this ethnicity at an early age. Conclusion: Our findings question whether OPP should be considered as a biomarker in the dark-skinned individuals. An evaluation of BP and IOP in the supine position is recommended for all patients to obtain more conclusive readings.

Intraocular pressure and glaucoma: Is physical exercise beneficial or a risk?

Intraocular pressure may become elevated with muscle exertion, changes in body position and increased respiratory volumes, especially when Valsalva manoeuver mechanisms are involved. All of these factors may be present during physical exercise, especially if hydration levels are increased. This review examines the evidence for intraocular pressure changes during and after physical exercise. Intraocular pressure elevation may result in a reduction in ocular perfusion pressure with the associated possibility of mechanical and/or ischaemic damage to the optic nerve head. A key consideration is the possibility that, rather than being beneficial for patients who are susceptible to glaucomatous pathology, any intraocular pressure elevation could be detrimental. Lower intraocular pressure after exercise may result from its elevation causing accelerated aqueous outflow during exercise. Also examined is the possibility that people who have lower frailty are more likely to exercise as well as less likely to have or develop glaucoma. Consequently, lower prevalence of glaucoma would be expected among people who exercise. The evidence base for this topic is deficient and would be greatly improved by the availability of tonometry assessment during dynamic exercise, more studies which control for hydration levels, and methods for assessing the potential general health benefits of exercise against any possibility of exacerbated glaucomatous pathology for individual patients who are susceptible to such changes.

Provocative intraocular pressure challenge preferentially decreases venous oxygen saturation despite no reduction in blood flow.

Ocular disease can both alter the retina's oxygen requirements, and decrease its ability to cope with changes in metabolic demand. We examined the influence of a moderate intraocular pressure (IOP) elevation on three outcome measures: arterial and venous oxygen saturation, blood flow, and the pattern electroretinogram (PERG). We increased IOP to ˜30mmHg in 23 healthy participants (22-39years) using a mechanical probe applied to the eyelid, thereby lowering ocular perfusion pressure (OPP) by ~30%. The Oxymap retinal oximeter was used to measure oxygen saturation for arteries and veins. Blood flow, volume and velocity were measured using the Heidelberg retinal flowmeter and steady-state PERG waveforms (8.34Hz) were recorded bilaterally (200 sweeps). For each outcome measure, data was obtained three times: at baseline, 1min into sustained IOP elevation, and 1min after the probe was removed. During IOP elevation, changes in oxygen saturation of retinal arteries failed to reach statistical significance [F(1,30)=3.69, p=0.05], whereas venous oxygen saturation was significantly reduced [F(1,21)=27.43, p<0.01]. Blood flow increased slightly [F(2,40)=6.28, p<0.0001], PERG amplitude significantly reduced [F(2,44)=24.24, p<0.0001] and PERG phase was significantly delayed [F(2,44)=17.00, p<0.0001]. Contralateral eyes were unchanged. OPP reduction correlated little with PERG amplitude, PERG phase or venous oxygen saturation. Mild, acute IOP elevation increases arterio-venous oxygen saturation differences primarily through lowering venous oxygen saturation, suggesting increased oxygen consumption by healthy neurons when physiologically stressed.

Twenty‐four‐hour rhythm of ocular perfusion pressure in non‐arteritic anterior ischaemic optic neuropathy

In non-arteritic anterior ischaemic optic neuropathy (NAAION) patients, circulatory insufficiency within the optic nerve has previously been hypothesized to be related to nocturnal systemic hypotension. The main objective of this prospective cohort study was to investigate the nyctohemeral variations in ocular perfusion pressure (OPP) in NAAION patients. In 20 patients with NAAION, the intraocular pressure (IOP) was measured using the Tono-Pen XL(™) electronic tonometer every hour for 24 hr. Blood pressure (BP) was evaluated over 24 hr. Mean OPP was calculated with the following formula: OPP sitting position = (0.74 × mean BP) - IOP and OPP lying position = (0.84 × mean BP) - IOP. A nonlinear least squares dual-harmonic regression analysis approach was used to model the 24-hr rhythms of OPP data. On average, a 24-hr amplitude of 4.7 ± 2.6 mmHg was found for OPP. The patients were classified as either having a diurnal OPP rhythm (i.e. with a diurnal acrophase, 10% of the cases), a nocturnal OPP rhythm (45%) or absence of OPP rhythm (45%). Four patients had a nocturnal reduction in OPP (mean, -11%). The physiological nocturnal rhythm of OPP was maintained in 45% of the NAAION patients. The nocturnal reduction in OPP seen in 20% of the patients was within the range of OPP where optic nerve blood flow autoregulation is still fully operative. A high prevalence of obstructive sleep apnoea syndrome in our population (71%) may explain the low frequency of systemic nocturnal hypotension.

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.

Coupling blood flow and neural function in the retina: a model for homeostatic responses to ocular perfusion pressure challenge

Retinal function is known to be more resistant than blood flow to acute reduction of ocular perfusion pressure (OPP). To understand the mechanisms underlying the disconnect between blood flow and neural function, a mathematical model is developed in this study, which proposes that increased oxygen extraction ratio compensates for relative ischemia to sustain retinal function. In addition, the model incorporates a term to account for a pressure-related mechanical stress on neurons when OPP reduction is achieved by intraocular pressure (IOP) elevation. We show that this model, combining ocular blood flow, oxygen extraction ratio, and IOP mechanical stress on neurons, accounts for retinal function over a wide range of OPP manipulations. The robustness of the model is tested against experimental data where ocular blood flow, oxygen tension, and retinal function were simultaneously measured during acute OPP manipulation. The model provides a basis for understanding the retinal hemodynamic responses to short-term OPP challenge.

Individual ONH blood flow patterns during changes in perfusion pressure

AbstractPurpose Abnormal optic nerve head (ONH) blood flow autoregulation has been implemented in the pathogenesis of glaucoma since decades. In fact, however, the regulation of ONH blood flow is poorly characterized and the mechanisms of autoregulation remain obscure.Methods Several studies were performed to investigate the behavior of ONH blood flow during changes in perfusion pressure in healthy subjects. In all these studies laser Doppler flowmetry was used to measure ONH blood flow. Interventions included squatting and handgripping to increase ocular perfusion pressure and use of a sclera suction cup to reduce ocular perfusion pressure.Results During both an increase and a decrease in perfusion pressure the ONH shows some autoregulatory capacity. Data during combined change in arterial pressure and venous pressure indicate that ONH blood flow is not only dependent on the level of perfusion pressure but also on the absolute levels of pressures in the arterial and venous tree. In addition, there is a wide inter‐individual variability in the responses. In some subjects a temporal reduction in ocular perfusion pressure is associated with a pronounced decrease in ONH blood flow.Conclusion Regulation of ONH blood flow is more complex than previously thought. Some subjects show pronounced ischemia during fluctuations in ocular perfusion pressure. Whether this pre‐disposes to ONH disease remains unclear.

Involvement of Glial Cells in the Autoregulation of Optic Nerve Head Blood Flow in Rabbits

To investigate the involvement of glial cells in the autoregulation of optic nerve head (ONH) blood flow in response to elevated intraocular pressure (IOP). Rabbit eyes were treated with an intravitreal injection of l-2-aminoadipic acid (LAA), a gliotoxic compound. Twenty-four hours after the injection IOP was artificially elevated from a baseline of 20 to 50 or 70 mm Hg and maintained at each IOP level for 30 minutes. ONH blood flow was measured by laser speckle flowgraphy every 10 minutes. Ocular perfusion pressure (OPP) was calculated to investigate the relationship between ONH blood flow and OPP. To evaluate the effects of LAA on the function and morphology of retinal neurons and glial cells, electroretinogram (ERG) was monitored after injections of LAA (2.0 and 6.0 mM) or saline as a control. Histologic and immunohistochemical examinations were then performed. In the LAA-treated eyes, histologic changes selectively occurred in the retinal Müller cells and ONH astrocytes. There was not any significant reduction of amplitude or elongation of implicit time of each parameter in the ERG after LAA injection compared with control. ONH blood flow in LAA-treated eyes was significantly decreased with a reduction of OPP during IOP elevation to 50 and 70 mm Hg, whereas blood flow was maintained in control eyes during IOP elevation to 50 mm Hg. These results indicate the involvement of glial ells in the autoregulation of ONH blood flow during IOP elevation.

Disruption of Gap Junctions May Be Involved in Impairment of Autoregulation in Optic Nerve Head Blood Flow of Diabetic Rabbits

To determine whether an impairment of the autoregulatory mechanism of blood flow in the optic nerve head (ONH) is present in diabetic rabbits and whether the impairment results from the uncoupling of gap junctions. Experiments were performed on six alloxan-induced diabetic rabbits and six healthy control animals. In a test of the integrity of the autoregulatory mechanism, the intraocular pressure (IOP) was elevated from the 20-mm Hg baseline to 50 and then to 70 mm Hg. The capillary blood flow in the ONH was measured every 10 minutes by the laser speckle method, with simultaneous measurements of blood pressure. Ocular perfusion pressure (OPP) was calculated at each step, and the relationship between blood flow and OPP was analyzed. In addition, octanol, gap27 (gap junction uncouplers), or balanced saline solution was injected into the vitreous of healthy rabbits, with the balanced saline solution-injected eyes serving as the control. Changes in the ONH blood flow in response to the IOP elevation were determined in the same way. Diabetic rabbits had a significant decrease in ONH blood flow when the OPP was reduced by an elevation of the IOP to 50 or to 70 mm Hg, whereas the ONH blood flow was well maintained in healthy rabbits. After injection of octanol (10.0 mM) or gap27 (10 μM), a reduction of OPP resulted in a significant decrease in ONH blood flow in the healthy rabbits. These results indicate that autoregulation is disrupted in diabetic animals, and uncoupling the gap junctions in healthy rabbits also disrupts the autoregulation.

Non-contact, two-dimensional measurement of tissue circulation in choroid and optic nerve head using laser speckle phenomenon

A new apparatus has been developed using the laser speckle phenomenon for non-contact, two-dimensional analysis of tissue circulation in the choroid and optic nerve head (ONH). The fundus was illuminated by a diode laser spot and its image speckle was detected by an image sensor. The difference between the average of the speckle intensity (Imean) and the speckle intensity for successive scannings was calculated, and the ratio of Imean to this difference was defined as normalized blur (NB), which is a quantitative index of blood velocity. The results were displayed on color graphic monitors showing the two-dimensional variation of the NB level in the measurement field. In the rabbit, this apparatus was used to study the relationship between the results of NB measurement and the choroidal blood flow determined by the microsphere technique, the relationship between NB obtained from the ONH tissue free of visible surface vessels and the ocular perfusion pressure (OPP) after a lethal injection of pentobarital, and the effect of intraocular pressure (IOP) on the NB in the choroid or in the ONH. A stepwise reduction in the OPP was introduced by elevating the IOP manometrically. The relative decrease in the average NB over the field measured, NBav, in the choroid with the reduction in OPP showed a significant correlation with the relative change in the blood flow rate determined using the microsphere technique (r = 0.60, P < 0.001). NBav in the ONH had a good correlation with the OPP after a lethal injection of pentobarbital (r = 0.98, P < 0.001). NBav in the choroid decreased with reduction in the OPP. Although NBav in the ONH was little affected by OPP change when OPP was above 40 mmHg, at OPP levels below 40 mmHg, NBav in the ONH decreased along with a reduction in the OPP. These results suggest that by using the present apparatus, the blood velocity in the choroid or ONH under various conditions can be studied non-invasively in the living eye.

Ophthalmic artery pressure during retrobulbar anaesthesia.

Ophthalmic artery pressure recordings were performed before and after retrobulbar injection of 4.5 ml Xylocain-Exadrin by the use of Stepanik Arteriotonography. A 50% reduction in ophthalmic artery pulse pressure was found, which correlates well with the corresponding reduction in corneal indentation pulse amplitudes demonstrated by dynamic tonometry. The results demonstrate a shift from pulsatile towards non-pulsatile ocular blood flow. In two of the eight patients a pronounced reduction was also found in ocular perfusion pressure, indicating that retrobulbar anaesthesia may be hazardous in certain cases by initiating a major reduction in ocular blood supply. In order to minimize this hazard in eyes especially vulnerable to a reduction in ocular perfusion pressure, such as glaucomatous eyes, it is probably safest to perform retrobulbar anaesthesia with 2-3 ml of Xylocain 1% without the use of Exadrin (epinephrine).