Impact Of Intraocular Pressure Research Articles

The impact of intraocular pressure on optical coherence tomography angiography: A review of current evidence.

A scoping review of 45 peer-reviewed manuscripts involving intraocular pressure (IOP) change and concurrent optical coherence tomography angiography (OCTA) assessments was performed to aggregate knowledge, summarize major findings, and identify gaps in literature and methodology relating to the effect of IOP change on OCTA. Articles were identified through PubMed/Medline, Google Scholar, Cochrane, Web of Science, and article reference lists. A total of 838 results were identified, and 45 articles met the inclusion and exclusion criteria for detailed analysis. OCTA metrics including vessel density (VD), perfusion density, and flow density of the superficial capillary plexus and the radial peripapillary capillaries were analyzed in relation to relative temporal IOP changes. Overall, IOP changes were found to affect superficial vascular plexus (VD) measurements on OCTA, especially when IOP elevated above the physiologic normal range (10-21 mmHg). No significant association was found between diurnal IOP variation and OCTA metrics. Cataract surgery improved the whole-image signal strength and VD regardless of changes in IOP. Beta-blockers were associated with paradoxically reduced vessel density in normal tension glaucoma patients in two studies. Although glaucoma surgical intervention studies were inconsistent and limited by scan quality and low sample sizes, patients requiring glaucoma surgery exhibited attenuated postoperative superficial VD recovery despite significant IOP reductions with surgical intervention. In addition to ensuring near-perfect signal strength with minimal media opacities and controlling for high myopia, central corneal thickness, and the presence of retinopathy, clinicians should consider the statistically significant impact of IOP on OCTA metrics when interpreting results.

Corneal Surface Wave Propagation Associated with Intraocular Pressures: OCT Elastography Assessment in a Simplified Eye Model.

Assessing corneal biomechanics in vivo has long been a challenge in the field of ophthalmology. Despite recent advances in optical coherence tomography (OCT)-based elastography (OCE) methods, controversy remains regarding the effect of intraocular pressure (IOP) on mechanical wave propagation speed in the cornea. This could be attributed to the complexity of corneal biomechanics and the difficulties associated with conducting in vivo corneal shear-wave OCE measurements. We constructed a simplified artificial eye model with a silicone cornea and controllable IOPs and performed surface wave OCE measurements in radial directions (54-324°) of the silicone cornea at different IOP levels (10-40 mmHg). The results demonstrated increases in wave propagation speeds (mean ± STD) from 6.55 ± 0.09 m/s (10 mmHg) to 9.82 ± 0.19 m/s (40 mmHg), leading to an estimate of Young's modulus, which increased from 145.23 ± 4.43 kPa to 326.44 ± 13.30 kPa. Our implementation of an artificial eye model highlighted that the impact of IOP on Young's modulus (ΔE = 165.59 kPa, IOP: 10-40 mmHg) was more significant than the effect of stretching of the silicone cornea (ΔE = 15.79 kPa, relative elongation: 0.98-6.49%). Our study sheds light on the potential advantages of using an artificial eye model to represent the response of the human cornea during OCE measurement and provides valuable insights into the impact of IOP on wave-based OCE measurement for future in vivo corneal biomechanics studies.

The impact of horizontal eye movements versus intraocular pressure on optic nerve head biomechanics: A tridimensional finite element analysis study

It has been proposed that eye movements could be related to glaucoma development. This research aimed to compare the impact of intraocular pressure (IOP) versus horizontal duction on optic nerve head (ONH) strains. Thus, a tridimensional finite element model of the eye including the three tunics of the eye, all of the meninges, and the subarachnoid space (SAS) was developed using a series of medical tests and anatomical data. The ONH was divided into 22 subregions, and the model was subjected to 21 different eye pressures, as well as 24 different degrees of adduction and abduction ranging from 0.5° to 12°. Mean deformations were documented along anatomical axes and in principal directions. Additionally, the impact of tissue stiffness was assessed. The results show no statistically significant differences between the lamina cribrosa (LC) strains due to eye rotation and IOP variation. However, when assessing LC regions some experienced a reduction in principal strains following a 12° duction, while after the IOP reached 12 mmHg, all LC subzones showed an increase in strains. From an anatomical perspective, the effect on the ONH following 12° duction was opposite to that observed after a rise in IOP. Moreover, high strain dispersion inside the ONH subregions was obtained with lateral eye movements, which was not observed with increased IOP and variation. Finally, SAS and orbital fat stiffness strongly influenced ONH strains during eye movements, while SAS stiffness was also influential under ocular hypertension. Even if horizontal eye movements cause large ONH deformations, their biomechanical effect would be markedly distinct from that induced by IOP. It could be predicted that, at least in physiological conditions, their potential to cause axonal injury would not be so relevant. Thus, a causative role in glaucoma does not appear likely. By contrast, an important role of SAS would be expectable.

Impact of Intraocular Pressure Control on Rates of Retinal Nerve Fiber Layer Loss in a Large Clinical Population

To investigate the impact of intraocular pressure (IOP) control on rates of change of spectral-domain OCT (SD-OCT) retinal nerve fiber layer (RNFL) thickness in a large clinical population. Retrospective cohort study. A total of 85 835 IOP measurements and 60 223 SD-OCT tests from 14 790 eyes of 7844 patients. Data were extracted from the Duke Glaucoma Registry, a large database of electronic medical records of patients with glaucoma and suspected disease followed over time at the Duke Eye Center and satellite clinics. All records from patients with a minimum of 6 months of follow-up and at least 2 good-quality SD-OCT scans and 2 clinical visits with Goldmann applanation tonometry were included. Eyes were categorized according to the frequency of visits with IOP below cutoffs of 21 mmHg, 18 mmHg, and 15 mmHg over time. Rates of change for global RNFL thickness were obtained using linear mixed models and classified as slow if change was slower than-1.0 μm/year; moderate if between-1.0 and-2.0 μm/year; and fast if faster than-2.0 μm/year. Multivariable models were adjusted for age, gender, race, diagnosis, central corneal thickness, follow-up time, and baseline disease severity. Rates of change in SD-OCT RNFL thickness according to levels of IOP control. Eyes had a mean follow-up of 3.5±1.9 years. Average rate of change in RNFL thickness was-0.68±0.59 μm/year. Each 1 mmHg higher mean IOP was associated with 0.05 μm/year faster RNFL loss (P < 0.001) after adjustment for potentially confounding variables. For eyes that had fast progression, 41% of them had IOP <21 mmHg in all visits during follow-up, whereas 20% of them had all visits with IOP <18 mmHg, but only 9% of them had all visits with IOP <15 mmHg. Intraocular pressure was significantly associated with rates of progressive RNFL loss in a large clinical population. Eyes with stricter IOP control over follow-up visits had a smaller chance of exhibiting fast deterioration. Our findings may assist clinicians in establishing target pressures in clinical practice.

IS THERE A LINK BETWEEN ABDOMINAL SURGERY AND OCULAR PRESSURE?

The mechanisms of variation of intraocular pressure (IOP) during abdominal surgical interventions it is not completely clear and its result on the recovering patient may vary from benign alterations to disabilities. This review aims to identify the most important triggers and its impact of IOP along with individual risk factors during the perioperative period of abdominal surgeries. International literature is providing limited data on this topic. We reviewed 9 studies using PubMed, Scopus, and Web of Science as database. From the multitude of effects and implications that abdominal surgery has onto the physiology of eyeball, the highest impact was linked to the positioning of the patient, induction of anesthesia, perianesthetic events such as intubation and extubation, type of anesthesia and anesthetic used, pneumoperitoneum induced in laparoscopic surgeries and its contribution to the alterations of ocular parameters which are increasing the risk of ocular events. In addition to this, the association of individual risk factors as well as the pre-existing of ophthalmologic diseases may have severe consequences onto the visual function.

The impact of intraocular pressure on elastic wave velocity estimates in the crystalline lens

Intraocular pressure (IOP) is believed to influence the mechanical properties of ocular tissues including cornea and sclera. The elastic properties of the crystalline lens have been mainly investigated with regard to presbyopia, the age-related loss of accommodation power of the eye. However, the relationship between the elastic properties of the lens and IOP remains to be established. The objective of this study is to measure the elastic wave velocity, which represents the mechanical properties of tissue, in the crystalline lens ex vivo in response to changes in IOP. The elastic wave velocities in the cornea and lens from seven enucleated bovine globe samples were estimated using ultrasound shear wave elasticity imaging. To generate and then image the elastic wave propagation, an ultrasound imaging system was used to transmit a 600 µs pushing pulse at 4.5 MHz center frequency and to acquire ultrasound tracking frames at 6 kHz frame rate. The pushing beams were separately applied to the cornea and lens. IOP in the eyeballs was varied from 5 to 50 mmHg. The results indicate that while the elastic wave velocity in the cornea increased from 0.96 ± 0.30 m s−1 to 6.27 ± 0.75 m s−1 as IOP was elevated from 5 to 50 mmHg, there were insignificant changes in the elastic wave velocity in the crystalline lens with the minimum and the maximum speeds of 1.44 ± 0.27 m s−1 and 2.03 ± 0.46 m s−1, respectively. This study shows that ultrasound shear wave elasticity imaging can be used to assess the biomechanical properties of the crystalline lens noninvasively. Also, it was observed that the dependency of the crystalline lens stiffness on the IOP was significantly lower in comparison with that of cornea.

Effects of Chronic and Acute Intraocular Pressure Elevation on Scotopic and Photopic Contrast Sensitivity in Mice.

PurposeTo compare the impact of intraocular pressure (IOP) elevation on scotopic and photopic contrast sensitivity in mice.MethodsWe chronically elevated the IOP of wild-type mice via injection of polystyrene beads or acutely via injection of highly cohesive sodium hyaluronate. Some eyes with chronically elevated IOP were treated with either topical brimonidine tartrate 0.1% or brinzolamide 1%. Scotopic and photopic contrast sensitivity was assessed at peak spatiotemporal frequencies at multiple time points, with an established optokinetic technique. Retinal ganglion cell (RGC) counts were determined with an antibody to class III beta-tubulin. Correlations among IOP level, RGC count, and scotopic or photopic contrast sensitivity were performed.ResultsSix weeks of IOP elevation caused a generalized reduction of photopic contrast sensitivity and a preferential reduction of scotopic contrast sensitivity at peak spatiotemporal frequencies. The administration of brinzolamide but not brimonidine caused a significant reduction in cumulative IOP, whereas brimonidine, but not brinzolamide, prevented RGC loss. Both brimonidine and brinzolamide prevented contrast sensitivity loss, but brimonidine did so at earlier time points and across a wider range of lighting conditions. Following either chronic or acute IOP elevation, scotopic contrast sensitivity was impacted most prominently by IOP level and not by RGC count, while photopic contrast sensitivity was impacted by a combination of factors.ConclusionsIt is possible that scotopic-specific retinal circuitry is altered preferentially by IOP elevation, and that changes in scotopic contrast sensitivity will assist with glaucoma detection. Brimonidine appears to prevent RGC loss via an IOP-independent mechanism.

Impact of intraocular pressure on changes of blood flow in the retina, choroid, and optic nerve head in rats investigated by optical microangiography

In this paper, we demonstrate the use of optical coherence tomography/optical microangiography (OCT/OMAG) to image and measure the effects of acute intraocular pressure (IOP) elevation on retinal, choroidal and optic nerve head (ONH) perfusion in the rat eye. In the experiments, IOP was elevated from 10 to 100 mmHg in 10 mmHg increments. At each IOP level, three-dimensional data volumes were captured using an ultrahigh sensitive (UHS) OMAG scanning protocol for 3D volumetric perfusion imaging, followed by repeated B-scans for Doppler OMAG analysis to determine blood flow velocity. Velocity and vessel diameter measurements were used to calculate blood flow in selected retinal blood vessels. Choroidal perfusion was calculated by determining the peripapillary choroidal filling at each pressure level and calculating this as a percentage of area filling at baseline (10 mmHg). ONH blood perfusion was calculated as the percentage of blood flow area over a segmented ONH area to a depth 150 microns posterior to the choroidal opening. We show that volumetric blood flow reconstructions revealed detailed 3D maps, to the capillary level, of the retinal, choroidal and ONH microvasculature, revealing retinal arterioles, capillaries and veins, the choroidal opening and a consistent presence of the central retinal artery inferior to the ONH. While OCT structural images revealed a reversible compression of the ONH and vasculature with elevated IOP, OMAG successfully documented changes in retinal, choroidal and ONH blood perfusion and allowed quantitative measurements of these changes. Starting from 30 mm Hg, retinal blood flow (RBF) diminished linearly with increasing IOP and was nearly extinguished at 100 mm Hg, with full recovery after return of IOP to baseline. Choroidal filling was unaffected until IOP reached 60 mmHg, then decreased to 20% of baseline at IOP 100 mmHg, and normalized when IOP returned to baseline. A reduction in ONH blood perfusion at higher IOP’s was also observed, but shadow from overlying retinal vessels at lower IOP’s limited precise measurements of changes in ONH capillary perfusion compared to baseline. Therefore, OCT/OMAG can be a useful tool to image and measure blood flow in the retina, choroidal and ONH of the rat eye as well as document the effects of elevated IOP on blood flow in these vascular beds.

Impact of Intraocular Pressure after Filtration Surgery on Visual Field Progression in Primary Open-Angle Glaucoma

To compare visual field progression after trabeculectomy in eyes showing a postoperative intraocular pressure (IOP) less than or equal to 16 mmHg and eyes with an IOP of 17 to 21 mmHg. A retrospective cohort study design was used. A total of 101 eyes of 101 consecutive patients undergoing trabeculectomy for primary open-angle glaucoma (POAG) with a postoperative IOP less than or equal to 21 mmHg were divided into two groups: Group 1 included eyes showing a postoperative IOP less than or equal to 16 mmHg at all visits and Group 2 included eyes with a postoperative IOP between 17 and 21 mmHg. In turn, each of these groups was divided into two subgroups according to whether treatment was required for IOP control. Glaucomatous visual field control during follow-up was compared between the subject groups. Kaplan-Meier analysis revealed glaucomatous visual field control in 98.53% of the eyes in Group 1 and 89.06% of those in Group 2 at 5 years, the difference between the groups being significant. Glaucomatous disease progression is less frequent when IOP is less than or equal to 16 mmHg in all the follow-up visits after trabeculectomy. The results indicate a definite benefit of low IOP in visual field control.

Impact of Intraocular Pressure on Venous Outflow from the Globe

Increasing focus on so-called normal-tension glaucoma has raised questions concerning the mechanism by which intraocular pressure (IOP) may play a role in the pathophysiology of glaucomatous optic neuropathy. However, examination of pressure-relationships suggests that an increase of a few mm Hg in IOP within the normal-tension range may double the magnitude of one important physiologic parameter, the magnitude of the intravascular waterfall effect at the exit of the central retinal vein (CRV) from the globe. This, in turn, increases the pulsatility or the velocity and turbulence of blood flow, depending on the extent of the restriction to venous outflow at the passage of the CRV through the lamina cribrosa. In the absence of such restriction, increased CRV pulsatility, especially in combination with brief IOP spikes, can be expected to cause foci of microvascular collapse in the optic nerve head. These foci can be converted to permanent vascular defects depending on additional risk factors, such as abnormal blood rheology ro platelet aggregation. Greater than normal laminal restrictions can, on the other hand, reduce perfusion pressure and can cause turbulence-induced endothelial damage and thickening of the CRV wall, ultimately further reducing perfusion pressure. These considerations suggest the hypothesis that the size and configuration of the venous outflow channel through the lamina cribrosa is a primary determinant of the extent of vascular and ultimately neuronal damage that occurs at a given IOP level in normal-tension and hypertensive primary open-angle glaucoma.