Intraocular Pressure Fluctuation Research Articles

THE MOMENTARY EFFECT OF XYLOPIA AETHIOPICA ON INTRAOCULAR PRESSURE

Xylopia aethiopica is an important item of local trade throughout Africa as a spice, flavouring for food and for medicine. The aim of this study was to determine the effect of aqueous extract of its fruit on intraocular pressure (IOP) of normotensive subjects. A total of eighty (n=80) ocular normotensives between 18 and 50 years, with mean age of 27.28±7.84years and mean body weight of 64.45±12.70kg consisting of forty (40) (50%) males and forty (40) (50%) females, were recruited for this study. Their baseline intraocular pressure was measured and intraocular pressure was taken for 30, 60 and 90 minutes after ingestion of either distilled water or aqueous extract of Xylopia aethiopica fruit. The mean baseline intraocular pressure was 13.52±1.70mmHg; 30minutes after ingestion of the aqueous extract of Xylopia aethiopica, there was a significant increase in mean intraocular pressure to 15.55±2.00mmHg (p< 0.05); after 60minutes the mean IOP decreased to 14.43±1.62mmHg and then returned close to mean baseline IOP of 13.45±1.80mmHg.There was no significant change in mean IOP (p> 0.05) when males were compared withfemales. Xylopia aethiopica causes a transient fluctuation in IOP which may affect thefindings and analyses of IOP. Eye care providers should be cautious of raised IOP inducedby spices like X. aethiopica; and ask patients about their meals or medications before IOPmeasurements are taken.

Intraocular Pressure Fluctuation in Primary Open-Angle Glaucoma with Canaloplasty and Microcatheter Assisted Trabeculotomy.

Background: Schlemm’s canal (SC) targeted procedures constitute a promising therapy for open angle glaucoma (POAG), safer and less invasive. However, little attention was paid to the intraocular pressure (IOP) variation in patients receiving these procedures, which is the risk factor for POAG progression. This study is to evaluate the IOP variation in eyes with POAG after modified canaloplasty (MC) and microcatheter assisted trabeculotomy (MAT). (2) Methods: POAG with good IOP in office hours after MC or MAT and age-matched normal subjects were recruited in this prospective coherent study. IOP in sitting and supine positions and 24-h IOP was measured. Aqueous vein and blood reflux into the SC were examined. (3) Results: Among 20 normal subjects, 25 eyes with MC eyes and 30 eyes with MAT were recruited in this study. Aqueous veins are frequently located in the inferior nasal quadrants in all groups. No pulsatile signs were observed in an aqueous vein in the MAT group but they were observed in 68% of the MC group. Blood reflux in the SC could be seen in all the operated eyes. The IOP in the sitting position was not significant different among groups (p = 0.419). Compared to normal, the IOP increased dramatically after lying down for 5 min in the MC and MAT groups (PMC vs. normal = 0.003, PMAT vs. normal = 0.004), which is similar for IOP change after lying down for 60 min (PMC vs. normal < 0.001, PMAT vs. normal < 0.001). In terms of diurnal IOP, subjects were stable in the MAT group (p < 0.01), variable in the normal group (p = 0.002), and most fluctuant in MC group (p < 0.001). (4) Conclusions: MC and MAT reduce the IOP but present aberrant short-term IOP regulation, which should be paid attention to in clinical settings.

Clinical Profile and Intraocular Pressure Control of Medically Treated Glaucoma Patients Seen in a Tertiary Hospital in Enugu, Nigeria

Background: Glaucoma is the second most common cause of blindness and the leading cause of irreversible blindness worldwide. It is a chronic optic neuropathy with characteristic optic disc changes and corresponding visual field defect. Aim: The aim of this study was to determine the clinical profile and intraocular pressure control of Primary Open Angle Glaucoma (POAG) patients on medical treatment at the glaucoma clinic of Enugu State University of Science and Technology Teaching Hospital Parklane (ESUTTHP), Enugu with a view for better patient management. Methods: The study was a hospital based cross sectional study on POAG patients on medical treatment attending the eye clinic of ESUTTHP, Enugu. Patients were selected by simple random sampling. Their eyes were examined which included visual acuity assessment, follow-up clinic intraocular pressure measurement, gonioscopy, anterior and posterior segments examination. Water Drinking Test (WDT) and modified phasing were carried out on them. WDT was done over 2 hours after intake of 1 liter of water with intraocular pressure measured every 15 minutes. Modified phasing was done over 8 hours with intraocular pressure measured at 2 hourly intervals. Data analysis was done using SPSS version 20 (U.S.A). The mean follow-up clinic intraocular pressure (IOP), IOP peak and fluctuation during WDT and phasing were determined and compared using T-test. Results: A total of 130 primary angle glaucoma patients on medical treatment were examined comprising of 43.1% males and 56.9% females with mean age of 62.25±9.002. Few of the patients were blind (3.8%) while 66.2% had normal vision. Their mean vertical cup disc ratio was 0.78±0.13. Majority of the patients had thin central cornea and uncontrolled intraocular pressure. The mean follow-up clinic IOP, mean IOP peaks during WDT and phasing were 16.2±4.3, 22.9±5.7, 18.0±4.4mmHg, respectively. There was a significant correlation between central corneal thickness and IOP peaks in WDT and modified phasing as well as follow-up clinic IOP but there was no significant correlation between central corneal thickness and IOP fluctuations in WDT and modified phasing. There was a significant correlation between vertical cup disc ratio and IOP peaks in WDT as well as vertical cup disc ratio and follow-up clinic IOP (p&lt; 0.01). Conclusion: Few patients are blind from glaucoma but greater percentage still have uncontrolled IOP despite being on medical treatment. Therefore, other treatment options should be explored to bring their IOP under control to avoid further glaucomatous progression and consequent blindness.

Innovative approaches to measuring intraocular pressure

AbstractAlthough different factors have been implicated in the development and progression of glaucoma, intraocular pressure (IOP) remains the main modifiable risk factor. Goldmann applanation tonometer (GAT) considers the “gold standard” for measuring IOP. The main deficiency of GAT, however, is the static nature of its measurements and that it is dependent on corneal biomechanics, central corneal thickness as well as scleral stiffness. The single measurement of IOP for the management of glaucoma provides limited information since it does not take into account the natural fluctuation of IOP, individual ranges, IOP peaks or variations throughout the day. Although the role of IOP fluctuations in glaucoma progression is not clearly defined, there is consensus on the importance of understanding the circadian profiles of IOP in glaucoma patients. Given the limitations of GAT for the actual measurement of IOP, different tonometers have been designed with the aim of advancing in self‐tonometry as Icare HOME, or obtaining independent measurements of corneal biomechanics, as Ocular Response Analyser (ORA), Pascal dynamic contour tonometer or the Corvis ST tonometer. Research to monitor IOP is based on three different strategies: (1) self‐tonometry; (2) permanent monitoring of the IOP; and (3) the temporary monitoring of the IOP. Currently, the sensors in contact lenses allow the IOP profiles to be recorded semi‐continuously for 24 hours with a minimally invasive technique, independent of the patient's position and the activity performed, opening new perspectives in the knowledge and management of glaucoma.

Features of cataract surgery and the postoperative period in patients with glaucoma (part 2)

According to the results of various studies, in up to 50% cases after cataract phacoemulsification patients with glaucoma experience ophthalmic hypertension on the first day. This occurs due to the mechanical retention of aqueous humor in the anterior chamber. Temporary decrease in the function of the eye drainage system is explained by pigment particles, viscoelastic, erythrocytes, protein cells, product of postoperative inflammation and lens particles obstructing the trabecula. In the long-term period after phacoemulsification in glaucoma patients there is a decrease in the intraocular pressure in up to 74% of cases.A decrease in the density of endothelial cells in these patients occurs as a result of fluctuation of intraocular pressure, prolonged application of hypotensive drops, surgical intervention and presence of drainage devices after antiglaucoma surgery. This leads to the increase of inflammatory reaction of the cornea in the form of edema of up to 16.9% after cataract phacoemulsification.Phacoemulsification also provides a significant hypotensive effect (up to 34%) and is a preventive measure for an acute attack in patients with angle-closure glaucoma. However, the state of acute glaucoma attack leads to difficulties in phacoemulsification in the form of high intraocular pressure, corneal edema and small chamber. Cataract extraction under such circumstances causes an increase in postoperative corneal edema and eye inflammation of up to 22.85%.

Efficacy of selective laser trabeculoplasty on lowering intraocular pressure fluctuations and nocturnal peak intraocular pressure in treated primary open-angle glaucoma patients

PurposeTo investigate the efficacy of adjunctive selective laser trabeculoplasty (SLT) in reducing 24-h intraocular pressure (IOP) fluctuations and nocturnal IOP peaks.MethodsIn this prospective interventional case series, 157 medically treated eyes of 157 patients with primary open-angle glaucoma (POAG) who were assigned SLT to further reduce IOP were consecutively included. Each patient had a complete glaucoma work-up and 24-h IOP monitoring (6 measurements, including one in the supine position) taken before and on average 6 months after SLT. The main outcome measures were the reduction of 24-h IOP fluctuations and nocturnal peak IOP. Secondary outcome measures were success rates, factors influencing the reduction of high 24-h IOP fluctuations and nocturnal peak IOP, complications, and severe adverse events.ResultsMedicated mean 24-h IOP (mmHg) was statistically significantly reduced from 15.1 ± 2.6 to 13.8 ± 2.4 (P < 0.001) and IOP fluctuations from 6.5 ± 2.7 to 5.4 ± 2.6 (P < 0.001) 6 months after SLT. Ninety-four eyes (59.9%) initially had high IOP fluctuations (more than 5 mmHg). These were reduced from 8.1 ± 2.3 to 5.6 ± 2.7 at 6 months (P < 0.001). Fifty-two eyes (55.3%) had fluctuations below 5 mmHg post-SLT which was defined as success. Fifty-one patients (32.5%) had nocturnal IOP peaks. In these cases, nocturnal IOP was reduced by 19.2% from 20.1 ± 3.4 to 16.2 ± 3.3 mmHg at 6 months (P = 0.001).ConclusionsThe current study demonstrates that adjunctive SLT not only reduces mean 24-h IOP in treated POAG patients, but also has an additional benefit in reducing IOP fluctuations and nocturnal peak IOP.Trial registrationClinical trial registration: NCT02959242.

The Effect of Intraocular Pressure Load Boundary on the Biomechanics of the Human Conventional Aqueous Outflow Pathway.

Aqueous humor outflow resistance in the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway actively contribute to intraocular pressure (IOP) regulation. Outflow resistance is actively affected by the dynamic outflow pressure gradient across the TM, JCT, and SC inner wall tissues. The resistance effect implies the presence of a fluid-structure interaction (FSI) coupling between the outflow tissues and the aqueous humor. However, the biomechanical interactions between viscoelastic outflow tissues and aqueous humor dynamics are largely unknown. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex was constructed with elastic and viscoelastic material properties for the bulk extracellular matrix and embedded elastic cable elements. The FE models were subjected to both idealized and a physiologic IOP load boundary using the FSI method. The elastic material model for both the idealized and physiologic IOP load boundary at equal IOPs showed similar stresses and strains in the outflow tissues as well as pressure in the aqueous humor. However, outflow tissues with viscoelastic material properties were sensitive to the IOP load rate, resulting in different mechanical and hydrodynamic responses in the tissues and aqueous humor. Transient IOP fluctuations may cause a relatively large IOP difference of ~20 mmHg in a very short time frame of ~0.1 s, resulting in a rate stiffening in the outflow tissues. Rate stiffening reduces strains and causes a rate-dependent pressure gradient across the outflow tissues. Thus, the results suggest it is necessary to use a viscoelastic material model in outflow tissues that includes the important role of IOP load rate.

The IOP lowering effects of "planning" selective laser trabeculoplasty in open angle glaucoma.

PurposeTo investigate whether the planning of selective laser trabeculoplasty (SLT) influences the intraocular pressure (IOP) in patients with open angle glaucoma (OAG).MethodsIn this retrospective case-control study conducted on patients with OAG who planned to undergo SLT treatment (SLT group) or a visual field examination (VF group), we collected the demographic data, IOP on the planning day and on the scheduled day of the SLT treatment or VF examination. ΔIOP was defined as the IOP change between the planning day and the scheduled day. We used multivariable regression analyses and linear mixed model to evaluate the association between the abovementioned factors and ΔIOP in the VF group and the treatment eye (SLTt) and fellow eye (SLTf) of the SLT group.ResultsOne hundred and fifty-three eyes of 102 patients with OAG were included, of which 51 patients in the SLT group and 51 patients in the VF group. The ΔIOP was −1.92 ± 2.77 mmHg in the SLTt, −0.65 ± 2.47 mmHg in the SLTf and −0.08 ± 1.73 mmHg in the VF group (P < 0.05). Both multivariable regression analysis between the VF and SLTt group and linear mixed model in the SLT group showed significant negative association between the ΔIOP and SLT arrangement (P < 0.05). There was no significant association between ΔIOP and age, gender, baseline IOP, IOP fluctuation, nor SE.ConclusionsThe IOP was significantly reduced in patients with OAG after “planning” of SLT treatment, even without actual performing the laser treatment in our retrospective case-control study.

Evaluation of visual field changes with retinal nerve fiber layer thickness in primary congenital glaucoma.

To evaluate visual field changes in primary congenital glaucoma (PCG) with retinal nerve fiber layer thickness on optical coherence tomography. In this cross-sectional, observational study, consecutive PCG children who underwent combined trabeculotomy with trabeculectomy and on regular follow-up were enrolled. All patients were aged over four years and co-operative for RNFL OCT and visual field examination. Perimetry was done on Humphrey visual field (HVF) analyzer using 30-2 and 10-2 SITA standard algorithms as appropriate. If a reliable automated perimetry was not feasible, kinetic perimetry was done. The following were noted at baseline and every follow-up: age, sex, visual acuity, intraocular pressure (IOP), cup-disc ratio (CDR), corneal diameters, refraction, any topical antiglaucoma medications, surgeries underwent, age at surgery and duration between surgery and final examination. Forty-eight eyes of 34 children operated for PCG and 19 eyes of 17 controls were analyzed. A statistically significant thinner average RNFL thickness of 87.2 ± 28 μm was noted in PCG eyes as compared to controls with 100.6 ± 7.2 μm (P = 0.04). The mean cup-disc area ratio on OCT in PCG eyes was 0.43 ± 0.2 (0.02-0.93) and in control eyes was 0.23 ± 0.07 (0.1-0.4) (P < 0.001). On RNFL OCT, there was significant focal RNFL loss in temporal superior (P = 0.003), nasal inferior (P = 0.037) and temporal inferior (P < 0.001) quadrants compared to controls. Among PCG eyes, 20/48 eyes (41.7%), had definitive, reproducible glaucomatous VF defects. Mean baseline IOP in PCG eyes with VF defect was 28.7 ± 5.7 mmHg and in eyes with normal VF was 24.6 ± 5.9 mmHg (P = 0.03). On univariate regression analysis, higher baseline IOP was significantly associated with both RNFL loss (odds ratio (OR): -2.17) and VF defects (OR: 3.35). Fluctuation in follow-up IOP (OR: 3.33) was also significantly associated with the presence of VF defects. On multivariable regression analysis maximum, IOP was significantly associated with RNFL loss and VF defects. Peripapillary RNFL thickness could be used to identify PCG eyes having visual field loss and possibly poor visual function from PCG eyes without visual field defects. Baseline and follow-up IOP, significantly correlated with RNFL thickness in PCG eyes.

Clinical observations of EVO-ICL implantation and changes in corneal astigmatism using a modified technique

BackgroundImplantable collamer lens (ICL) surgery techniques are constantly progressing. The purpose of this study was to investigate the application effect of the modified technique and its impact on the change in corneal astigmatism in EVO-ICL surgery.MethodsThe analysis of retrospective cohort data included 153 eyes of 81 patients with myopia from July 2018 to May 2020. An EVO-ICL was inserted by modified surgical skills, including a single 3.0 mm corneal incision and no ophthalmic viscosurgical device (OVD) before the insertion of the ICL (modified technique group: 41 cases, 80 eyes) and standard procedure (standard technique group: 40 cases, 73 eyes). Early postoperative intraocular pressure (IOP) was monitored at 2 and 24 h. IOP, corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), vault, and anterior chamber depth (ACD) were measured 1, 6, and 12 months following the initial examination. The corneal endothelial cell density (ECD) was monitored at 6 and 12 months after the operation. Surgically induced astigmatism (SIA) in the total, anterior, and posterior corneal surfaces was analysed 1 month after the operation.ResultsNo serious complications were detected. The two groups had no difference in visual outcomes, ICL vaults, or ACD at any time point (P > 0.05). Two hours postoperatively, IOP was significantly lower in the modified technique group (16.22 ± 2.22 vs. 18.37 ± 1.92 mmHg, P < 0.05) than in the standard technique group. IOP decreased gradually after 24 h to preoperative levels. The postoperative IOP remained stable over a 12-month period. The ECD at 6 and 12 months was not significantly different between the groups (P > 0.05). SIA in the total, anterior, and posterior corneal surfaces were assumed to have no clinically meaningful differences between groups at one month after operation (P > 0.05).ConclusionsThe modified technique is efficient and safe, producing comparable visual and structural outcomes without adversely affecting ECD, and reduces fluctuations in IOP at the early postoperative stages. The auxiliary incision in the standard technique does not increase corneal SIA, which is also a factor to consider for inexperienced surgeons.

Association of Ultra-Short-Term Intraocular Pressure Fluctuation With Disease Progression in Primary Angle Closure Glaucoma: The CUPAL Study.

This study demonstrated significant differences in ultra-short-term IOP fluctuations, measured by a contact lens sensor between progressive and stable PACG eyes, during the first one hour after falling asleep. To identify the most sensitive period for detecting significant ultra-short-term intraocular pressure (IOP) fluctuation associated with disease progression in primary angle closure glaucoma (PACG). PACG eyes, which had been followed up for over 2 years under the CUHK PACG Longitudinal (CUPAL) Study, were recruited. Eyes with or without functional or structural glaucomatous progression were classified into 'progressive' or 'stable' groups on the basis of serial visual field and retinal nerve fiber layer (RNFL) thickness documentations, respectively. Ultra-short-term IOP fluctuations were recorded by Sensimed Triggerfish sensors (Sensimed AG, Lausanne, Switzerland) with 288 readings over 30 seconds, at 5-minute intervals, over a 24-hour period. In each of 7 activity-related 1-hour periods during the examining day, the mean value of the amplitude-frequency profiles of the signal fluctuations in twelve 30-second intervals was calculated by semivariogram/semi-variance. The 'progressive' and 'stable' groups were compared by permutation tests on functional t-statistics. Among the 25 recruited PACG eyes, 16 eyes were classified as RNFL 'progressive' group (the mean rate of change in global RNFL thickness: -0.199 ±0.128μm/mo). Higher signal fluctuations, in terms of amplitude-frequency, were found during the first 1-hour period of sleeping in the RNFL 'progressive' group compared with the RNFL 'stable' group ( P =0.028). Between RNFL 'progressive' and 'stable' PACG eyes, significant differences in ultra-short-term IOP fluctuation at the 1-hour period after falling asleep were identified. The first hour of sleeping may be the most sensitive period for detecting significant ultra-short-term IOP fluctuation in PACG eyes.

Structural damage to the rat eye following long-term simulated weightlessness

To better perform space missions and develop human spaceflights, the eye health of astronauts is receiving increasing attention from researchers. In this study, we used prolonged tail suspension to simulate microgravity cephalad fluid shift in space to observe intraocular pressure (IOP) changes, retinal structure, and optic nerve damage in rats.We observed significant choroidal thickening and optic nerve demyelination lesions in the rats in each experimental group. At the cellular level, retinal ganglion cells (RGCs) survival was significantly reduced, optic nerve oligodendrocytes were reduced, and apoptotic factors and microglia-mediated inflammation-related factors were detected in both the retina and optic nerve. The severity of these changes increased with increasing tails suspension time. In conclusion, simulated long-term microgravity can lead to slight intraocular pressure fluctuations, choroidal thickening, reduced RGCs survival, and optic nerve demyelination in rats.

SALUS—a non-inferiority trial to compare self-tonometry in glaucoma patients with regular inpatient intraocular pressure controls: study design and set-up

PurposeThe SALUS study aims to improve the healthcare situation for glaucoma patients in Germany. In order to detect diurnal intraocular pressure (IOP) fluctuations, inpatient monitoring of IOP in an eye hospital for a minimum of 24 h is the current standard. SALUS assesses the benefits of a new form of outpatient care, where IOP can be measured by the patients themselves at home using a self-tonometer. This approach should promote the patient’s health competence and empowerment within the healthcare system while reducing treatment costs.MethodsThe SALUS study is a randomized controlled, open non-inferiority trial, alongside an economic analysis, determining whether outpatient monitoring of IOP with self-tonometry is at least as effective as current standard care and would reduce treatment costs. Participants (n = 1980) will be recruited by local ophthalmologists in the area of Westphalia-Lippe, Germany, and randomized to receive 7-day outpatient or 24-h inpatient monitoring. Participants in both study arms will also receive 24-h blood pressure monitoring. Furthermore, patient data from both study groups will be collected in an electronic case file (ECF), accessible to practitioners, hospitals, and the study participants. The primary endpoint is the percentage of patients with IOP peaks, defined as levels 30% above the patient-specific target pressure. Data will also be collected during initial and final examinations, and at 3, 6, and 9 months after the initial examination.ResultsThe study implementation and trial management are represented below.ConclusionSALUS is a pioneering prospective clinical trial focused on the care of glaucoma patients in Germany. If SALUS is successful, it could improve the healthcare situation and health literacy of the patients through the introduction of various telemedical components. Furthermore, the approach would almost certainly reduce the treatment costs of glaucoma care.Trial registrationClinicalTrials.gov ID: NCT04698876, registration date: 11/25/2020.DRKS-ID: DRKS00023676, registration date: 11/26/2020.

Cationic Mechanosensitive Channels Mediate Trabecular Meshwork Responses to Cyclic Mechanical Stretch.

The trabecular meshwork (TM) is responsible for intraocular pressure (IOP) homeostasis in the eye. The tissue senses IOP fluctuations and dynamically adapts to the mechanical changes to either increase or decrease aqueous humor outflow. Cationic mechanosensitive channels (CMCs) have been reported to play critical roles in mediating the TM responses to mechanical forces. However, how CMCs influence TM cellular function affect aqueous humor drainage is still elusive. In this study, human TM (HTM) cells were collected from a Chinese donor and subjected to cyclically equiaxial stretching with an amplitude of 20% at 1 Hz GsMTx4, a non-selective inhibitor for CMCs, was added to investigate the proteomic changes induced by CMCs in response to mechanical stretch of HTM. Gene ontology enrichment analysis demonstrated that inhibition of CMCs significantly influenced several biochemical pathways, including store-operated calcium channel activity, microtubule cytoskeleton polarity, toll-like receptor signaling pathway, and neuron cell fate specification. Through heatmap analysis, we grouped 148 differentially expressed proteins (DEPs) into 21 clusters and focused on four specific patterns associated with Ca2+ homeostasis, autophagy, cell cycle, and cell fate. Our results indicated that they might be the critical downstream signals of CMCs adapting to mechanical forces and mediating AH outflow.

A Review of Intraocular Pressure (IOP) and Axial Myopia

The pathogenesis of myopia is driven by genetic and environmental risk factors. Accommodation not only alters the curvature and shape of the lens but also involves contraction of the ciliary and extraocular muscles, which influences intraocular pressure (IOP). Scleral matrix remodeling has been shown to contribute to the biomechanical susceptibility of the sclera to accommodation-induced IOP fluctuations, resulting in reduced scleral thickness, axial length (AL) elongation, and axial myopia. The rise in IOP can increase the burden of scleral stretching and cause axial lengthening. Although the accommodation and IOP hypotheses were proposed long ago, they have not been validated. This review provides a brief and updated overview on studies investigating the potential role of accommodation and IOP in myopia progression.

Factors associated with choroidal microvascular dropout change

Background/aimsTo investigate the factors associated with choroidal microvasculature drop-out (MvD) enlargement detected by optical coherence tomography angiography (OCT-A) in glaucomatous eyes.MethodsNinety-one eyes of 68 primary open-angle glaucoma patients were enrolled....

Intracorneal Ring Segment Implantation Results in Corneal Mechanical Strengthening Visualized With Optical Coherence Elastography.

To quantify the mechanical impact of intracorneal ring segment (ICRS) implantation of different dimensions in an ex vivo eye model. A total of 30 enucleated porcine eyes were assigned to ICRS implantation (thickness: 300 µm, angle: 120°, 210°, or 325°), tunnel creation only, or virgin control groups. For mechanical evaluation, each globe was mounted on a customized holder and intraocular pressure (IOP) was increased in steps of 0.5 mm Hg from 15 to 17 mm Hg, simulating physiologic diurnal IOP fluctuations. At each step, an optical coherence tomography volume scan was recorded. Deformations between subsequent scans and the locally induced axial strains were analyzed using a vector-based phase difference method. The effective E-modulus was derived from the overall induced strain as a measure of global mechanical impact. ICRS implantation increased the effective E-modulus from 146 and 163 kPa in virgin and tunnel-only eyes to 149, 192, and 330 kPa in eyes that received a 5-mm optical zone ICRS with 120°, 210°, and 325° arc length, respectively; and to 209 kPa in a 6-mm optical zone ICRS with 325° arc length. The most consistent effect was a shift toward positive strains in the posterior stroma by 0.1% to 0.46% (factor 1.15 to 2.15) after ICRS surgery. ICRS implantation reduces the overall tissue strain under the load of the IOP and provokes posterior tissue relaxation. This effect is more prominent the longer the arc length and the smaller the optical zone of the ICRS is. ICRS have not only a geometrical, but also a mechanical impact on corneal tissue. This behavior might have clinical implications when ICRS implantation is performed in biomechanically weakened keratoconic corneas. [J Refract Surg. 2022;38(7):459-464.].

Twenty-Four-Hour Intraocular Pressure Indicators Distinguish Normal Tension Glaucoma From Healthy Eyes Measured With a Contact Lens Sensor.

Twenty-four-hour IOP measurements with a CLS showed that among IOP indicators studied, the range of IOP fluctuation was most important and significantly larger in NTG eyes compared with nonglaucoma eyes. We conducted the present study to determine (1) the best factor for distinguishing normal tension glaucoma (NTG) and nonglaucoma subjects based on the intraocular pressure (IOP) values measured by a CLS and (2) the optimal cutoff values of that factor. The eyes of 18 nonglaucoma subjects and 26 NTG patients were examined. We evaluated 5 indicators: maximum IOP value, SD, IOP fluctuation range, the cosine-fit curve amplitude, and the amplitude of dual-harmonic regression values. We determined the indicators' cutoff values to distinguish between nonglaucoma subjects and NTG patients with the area under the curve. The mean IOP values were 12.3±2.7mmHg in the nonglaucoma eyes and 12.5±3.1mmHg in the NTG eyes ( P =0.824). All 5 indicators were significantly higher in the NTG group. The best factor to distinguish the nonglaucoma subjects and NTG patients was the IOP fluctuation range ( P <0.0001, area under the curve=0.844); the cutoff level value was 436.5 millivolt equivalents. Twenty-four-hour IOP measurements with a CLS showed that among IOP indicators studied, the range of IOP fluctuation was most important and significantly larger in NTG eyes compared with nonglaucoma eyes.

Intraocular Pressure Fluctuation during Aerobic Exercise at Different Exercise Intensities.

Few studies have examined the effects of different aerobic-exercise intensities on intraocular-pressure (IOP) changes. This may be important for eye diseases that are impacted by IOP or its fluctuation, including glaucoma, and diabetes that is complicated by diabetic retinopathy. We investigated the effects of low-, moderate-, and high-intensity exercise on IOP in healthy subjects. A submaximal cardiopulmonary exercise test was performed in 18 healthy male subjects, and the maximal oxygen uptake was calculated. The subjects then exercised for 20 min at 30%, 50%, and 70% ·VO2 of maximal oxygen uptake, and their IOP was measured at rest and every 5 min during exercise. Oxygen uptake was monitored using an expiratory gas analyzer during exercise to maintain accurate exercise intensity and adjust exercise load. Oxygen uptake during exercise was significantly higher at all intensities from 5 to 20 min than at rest. IOP was significantly lower at 70% exercise intensity from 5 to 20 min than at rest. A negative correlation existed between IOP and ·VO2. IOP remained unchanged during low- and moderate-intensity exercise but significantly declined during high-intensity exercise compared with that at rest. Although various factors, such as β-blockers, are involved in IOP decline at rest, a different mechanism is involved in IOP decline during exercise.

Biomechanics of human trabecular meshwork in healthy and glaucoma eyes via dynamic Schlemm's canal pressurization

Background and objectiveThe trabecular meshwork (TM) consists of extracellular matrix (ECM) with embedded collagen and elastin fibers providing its mechanical support. TM stiffness is considerably higher in glaucoma eyes. Emerging data indicates that the TM moves dynamically with transient intraocular pressure (IOP) fluctuations, implying the viscoelastic mechanical behavior of the TM. However, little is known about TM viscoelastic behavior. We calculated the viscoelastic mechanical properties of the TM in n = 2 healthy and n = 2 glaucoma eyes. MethodsA quadrant of the anterior segment was submerged in a saline bath, and a cannula connected to an adjustable saline reservoir was inserted into Schlemm's canal (SC). A spectral domain-OCT (SD-OCT) provided continuous cross-sectional B-scans of the TM/JCT/SC complex during pressure oscillation from 0 to 30 mmHg at two locations. The TM/JCT/SC complex boundaries were delineated to construct a 20-µm-thick volume finite element (FE) mesh. Pre-tensioned collagen and elastin fibrils were embedded in the model using a mesh-free penalty-based cable-in-solid algorithm. SC pressure was represented by a position- and time-dependent pressure boundary; floating boundary conditions were applied to the other cut edges of the model. An FE-optimization algorithm was used to adjust the ECM/fiber mechanical properties such that the TM/JCT/SC model and SD-OCT imaging data best matched over time. ResultsSignificantly larger short- and long-time ECM shear moduli (p = 0.0032), and collagen (1.82x) and elastin (2.72x) fibril elastic moduli (p = 0.0001), were found in the TM of glaucoma eyes compared to healthy controls. ConclusionsThese findings provide additional clarity on the mechanical property differences in healthy and glaucomatous outflow pathway under dynamic loading. Understanding the viscoelastic properties of the TM may serve as a new biomarker in early diagnosis of glaucoma.