Trabecular Meshwork Thickness Research Articles

In Vivo Assessment of the Pediatric Trabecular Meshwork, Schlemm Canal, and Iridocorneal Angle Using Overhead-Mounted Optical Coherence Tomography

PurposeTo describe the in vivo morphologic characteristics of the trabecular meshwork (TM), Schlemm canal (SC), and iridocorneal angle in pediatric patients with normal eyes, glaucoma and cataract. DesignProspective cohort study Study population70 eyes (41 children) were enrolled. 28 normal eyes, 19 eyes with glaucoma, and 26 eyes with cataract (15 pre-, 11 post-lensectomy). Average age was 2.8±3.0 years at imaging. MethodsPediatric patients undergoing clinically indicated examination under anesthesia underwent overhead-mounted optical coherence tomography (OCT) imaging of the outflow pathway. Images were then evaluated for abnormalities in the outflow pathway. Main outcome measurePresence of thickened TM, SC patency, any iridocorneal angle malformation, and episcleral vessel patency in normal eyes vs. all other eyes. ResultsThickened TM tissue was found in no normal eyes, 47.4% of eyes with glaucoma, and 53.8% of eyes with cataracts. A patent SC was demonstrated in all normal eyes, 32% with glaucoma, and 65.4% with cataracts. Iridocorneal angle abnormality was identified in no normal eyes, 94.7% with glaucoma, and 69.2% with cataracts. Prevalence of iridocorneal angle abnormality was similar in cataract eyes pre- and post-lensectomy. All but one eye with glaucoma secondary to anterior segment dysgenesis had patent episcleral vessels. Intraocular pressure (IOP) at imaging was lower in eyes with than without a patent SC (13.9±3.8mmHg vs. 28.2±11.7mmHg, p<0.001). IOP was lower in eyes with normal iridocorneal angles compared to those with angle malformation (13.9±3.2mmHg vs. 22.6±12.1mmHg, p<0.001). There was no significant difference in IOP between eyes with normal TM thickness compared to those with thickened TM (17.4±8.2mmHg vs.17.4±9.5mmHg, p = 0.943). ConclusionEyes of children with glaucoma demonstrated thickened TM, decreased patency of SC, and abnormalities of the iridocorneal angle on OCT imaging, compared to normal controls. These abnormal findings also appear in many pediatric eyes with cataracts, even prior to lensectomy. Future study is warranted to evaluate the role these structural differences may play in the development of glaucoma following cataract surgery and the significant variation in how individual glaucoma eyes respond to angle surgery.

Evaluation of Anterior Scleral Thickness and Angle Parameters in Eyes with Pseudoexfoliation Syndrome and Glaucoma.

The relationship between anterior scleral thickness (AST) and scleral spur (SS) length was disrupted in eyes with pseudoexfoliation (PX), and SS length was shorter in eyes with pseudoexfoliative glaucoma (PXG). To evaluate AST in eyes with PX and to examine the relationship between AST and Schlemm canal (SC), trabecular meshwork (TM), and SS. Thirty-eight patients with PX syndrome (PXS), 38 patients with PXG, and 38 healthy patients were included in the study. Using sweep source anterior segment optical coherence tomography, AST (0, 1, 2, and 3mm from the SS), SC, and TM were visualized in the nasal and temporal areas, and measurements were compared between groups. The relationships between corneal thickness, TM, SS, SC, and AST were then evaluated. In all groups, the AST, SC, and TM measurements were similar ( P > 0.05). In the PXG group, SS lengths in the temporal area were shorter than those in the control and PXS groups ( P = 0.012). There were significant correlations between TM length and AST in the PXG group ( P < 0.05). The SS length exhibited moderately positive correlations with SC length and mean TM thickness in the PXG ( P < 0.05). There was a significant relationship between AST0 and SS in healthy eyes ( P < 0.05), but not in other eyes. The shorter SS length observed in eyes with PXG may be a sign of structural changes. In addition, disruption of the relationship between AST and SS may be an early sign of pathologic processes, especially in eyes with PXS, and may require closer follow-up of these eyes.

Effect of digital ocular massage on intraocular pressure and Schlemm’s canal dimensions

Digital ocular massage has been reported to temporarily lower intraocular pressure (IOP). This could be related to an enhanced aqueous humor outflow; however, the mechanism is not clearly understood. Using anterior segment optical coherence tomography, the Schlemm’s canal (SC) and trabecular meshwork (TM) can be imaged and measured. Here, 66 healthy adults underwent digital ocular massage for 10 min in their right eyes. The IOP and dimensions of the SC and TM were measured before and after ocular massage. All subjects demonstrated IOP reduction from 15.7 ± 2.5 mmHg at baseline to 9.6 ± 2.2 mmHg immediately after, and median of 11.6 mmHg 5-min after ocular massage (Friedman’s test, p < 0.001). There was significant change in SC area (median 10,063.5 μm2 at baseline to median 10,151.0 μm2 after ocular massage, Wilcoxon test, p = 0.02), and TM thickness (median 149.8 μm at baseline to 144.6 ± 25.3 μm after ocular massage, Wilcoxon test, p = 0.036). One-third of the subjects demonstrated collapse of the SC area (−2 to −52%), while two-thirds showed expansion of the SC area (2 to 168%). There were no significant changes in SC diameter (270.4 ± 84.1 μm vs. 276.5 ± 68.7 μm, paired t-test, p = 0.499), and TM width (733.3 ± 110.1 μm vs. 733.5 ± 111.6 μm, paired t-test, p = 0.988). Eyes with a higher baseline IOP demonstrated a greater IOP reduction (Pearson correlation coefficient r = −0.521, p < 0.001). Eyes with smaller SC area at baseline showed greater SC area expansion (Pearson correlation coefficient = −0.389, p < 0.001). Greater IOP reduction appeared in eyes with greater SC area expansion (Pearson correlation coefficient r = −0.306, p = 0.01). Association between change in IOP and change in TM thickness was not significant (Spearman’s ρ = 0.015, p = 0.902). Simple digital ocular massage is an effective method to lower IOP values, and change in the SC area was significantly associated with IOP changes.

The anterior scleral thickness in primary open-angle glaucoma with high myopia.

This study aimed to investigate and compare the anterior scleral thickness (AST) among high myopia (HM), primary open-angle glaucoma (POAG), and POAG with HM (HMPOAG) groups. Thirty-two HM eyes, 30 POAG eyes, and 31 HMPOAG eyes were included. The Schlemm's canal (SC) area, trabecular meshwork (TM) thickness, scleral spur (SS) length, and AST were measured using swept-source optical coherence tomography. AST was measured at 0 mm (AST0), 1 mm (AST1), 2 mm (AST2), and 3 mm (AST3) from SS. The HMPOAG group had significantly thinner AST, SS length, and TM thickness than the HM and POAG groups (all p < 0.05). In addition, the SC area of the HMPOAG group was also significantly smaller than that of the HM group (p < 0.001). The HMPOAG group had the thinnest AST, shortest SS, thinnest TM, and smallest SC. The thinnest AST might contribute to the shortest SS, and further to the thinnest TM and smallest SC in the HMPOAG group. AST might be a novel clinical indicator in the prediction and evaluation of POAG.

The effect of uneventful cataract surgery on Schlemm's canal and the trabecular meshwork in cases with pseudoexfoliation.

To evaluate the effect of uneventful cataract surgery on Schlemm's canal (SC) and the trabecular meshwork (TM) in cases with pseudoexfoliation (PX). In this prospective study, 37 PX and 37 normal eyes, who underwent cataract surgery, were included. The PX group was further divided into two subgroups: PX syndrome (PXS) and PX glaucoma (PXG). Preoperative complete ophthalmologic examination, anterior segment (AS) imaging using a Scheimpflug camera, and measurements of SC length and area and TM thickness and length using AS optical coherence tomography (AS-OCT) were performed in all cases. All measurements were repeated at the first and third months after surgery. Preoperative intraocular pressure (IOP), AS parameters, SC, and TM values showed no significant differences between the groups (p > 0.05). After surgery, there was a significant increase in AS parameter values and a significant decrease in IOP values in both the PX and control groups (p < 0.05). The nasal and temporal SC area showed a significant increase in the PX group after surgery (p = 0.007, p = 0.003, respectively). In the subgroup analysis, the only significant change in the nasal and temporal SC area was in the PXS group (p = 0.006, p = 0.003, respectively). Cataract surgery resulted in an increase in the SC area in patients with PXS. This increase may be due to multiple mechanisms including the IOP-lowering effect of cataract removal, change in AS, and removal of intraocular PX material after surgery.

Changes to Outflow Structures After Pilocarpine in Primary Open Angle Glaucoma Compared With Healthy Individuals Using Optical Coherence Tomography.

Lower response of aqueous outflow pathway structures after pilocarpine could be observed in primary open angle glaucoma (POAG) patients, which is likely to be helpful for understanding intraocular pressure (IOP) evaluation in glaucoma. To evaluate the morphologic changes in the trabecular meshwork (TM), Schlemm canal (SC), scleral spur (SS), and ciliary muscle after miosis in patients with POAG and healthy individuals. A total of 30 patients with POAG and 26 healthy controls were recruited. All participants underwent complete ophthalmologic examinations, including IOP and swept-source optical coherence tomography (OCT), before and 1 hour after the local administration of pilocarpine (2%). OCT measurements included TM thickness and width, SC diameter and area, SS length, ciliary muscle thickness, and ciliary muscle angle (CMA). Pilocarpine administration induced a decline in IOP (15.6±2.3-14.6±2.2mmHg), decrease in nasal SS length (196.31±47.75-171.52±33.93μm), decrease in TM thickness (90.18±16.43-83.02±13.74μm), and increase in SC diameter (134.84±32.28-162.08±48.67μm) and SC area (3851.37±1455.07-4801.39±1762.37μm 2 ) among healthy controls. In contrast, no significant changes in IOP and OCT measurements were found in patients with POAG. At baseline, CMA was independently correlated with IOP in normal eyes. After miosis, the change in TM thickness was independently correlated with changes in IOP in normal eyes; in eyes with POAG, changes in SS length and CMA were independently associated with changes in IOP. Topical pilocarpine-induced morphologic changes to outflow pathway structures in healthy individuals without significant changes in POAG. The lower response observed in patients with glaucoma may be relevant to understanding IOP changes.

The Anterior Segment Biometrics in High Myopia Eyes

Introduction: The aim of this study was to investigate and compare the anterior segment biometrics in high myopia and control groups. Methods: Thirty-four eyes of 34 high myopia patients and 42 eyes of 42 control subjects were included. Schlemm’s canal (SC) area, trabecular meshwork (TM) thickness and length, scleral spur (SS) length, and anterior scleral thickness (AST) were measured using swept-source optical coherence tomography. Associations between SC area, TM thickness, TM length, SS length, and AST were also estimated. Results: SC area, TM thickness, and SS length were significantly associated with AST0 (AST at 0 mm from SS) in both high myopia and control groups. AST0 (702.61 ± 78.05 vs. 729.12 ± 95.87 μm, p = 0.085) and SS length (206.25 ± 52.25 vs. 212.09 ± 51.86 μm, p = 0.556) were not significantly different between high myopia and control groups, whereas SC area (6,622.68 ± 1,130.06 vs. 6,105.85 ± 1,297.84 μm2, p = 0.015) was significantly greater and TM thickness (96.15 ± 34.40 vs. 107.93 ± 29.97 μm, p = 0.048) was significantly thinner in high myopia group than in control group. Conclusion: SC area and TM thickness were significantly associated with AST0, while AST0 and SS length were not significantly different between high myopia and control groups. The changes in SC and TM dimensions in high myopia eyes might be caused by factors other than AST0 and SS length.

Changes in Schlemm's canal, trabecular meshwork, and relevant parameters in the early stage after SMILE of myopia patients.

To observe the changes in Schlemm's canal (SC), trabecular meshwork (TM), and anterior chamber relevant parameters after small incision lenticule extraction (SMILE) of myopia patients. A total of 58 eyes from 30 patients who underwent SMILE were divided into a low and moderate myopia group (group A, 32 eyes) and a high myopia group (group B, 26 eyes). The diameter and area of the SC, the width and thickness of TM obtained by CIRRUS HD-OCT5000, and the related anterior chamber parameters obtained by Pentacam anterior segment analysis system, accommodation amplitude (AMP) were observed pre- and postoperatively. The preoperative intraocular pressure (IOP) and postoperative correction of intraocular pressure (IOPcc) were measured. The diameter and area of the SC in the two groups were significantly increased postoperatively (all P<0.01). The TM width of the patients in the two groups were increased at 1mo after surgery (both P<0.01), but the TM thickness did not change (P>0.05). The corneal curvature, central anterior chamber depth, and anterior chamber volume decreased after SMILE surgery (all P<0.01). There was a weak negative correlation between the SC area change and AMP change in group A (r=-0.362, P<0.01). The postoperative IOP decreased after correction by Shah formula (P<0.05). SC and TM in myopia patients change in the early postoperative stage of SMILE and the IOP is decline.

The anterior scleral thickness in eyes with primary open-angle glaucoma

PurposeTo investigate the anterior scleral thickness (AST) and its associations with Schlemm’s canal (SC) area, trabecular meshwork (TM) thickness and length, and scleral spur (SS) length in healthy and primary open-angle glaucoma (POAG) groups.MethodsThirty-five eyes of 35 healthy subjects and 23 eyes of 23 patients with POAG were included. The AST, SC area, TM thickness and length, and SS length were measured using swept-source optical coherence tomography. AST was measured at 0 mm (AST0), 1 mm (AST1), 2 mm (AST2), and 3 mm (AST3) from SS. Associations between AST and SC area, TM thickness and length, and SS length were also estimated.ResultsAST0 (728.84 ± 99.33 vs. 657.39 ± 67.02 μm, p < 0.001), AST1 (537.79 ± 79.55 vs. 506.83 ± 57.37 μm, p = 0.038), AST3 (571.09 ± 79.15 vs. 532.13 ± 59.84 μm, p = 0.009), SC area (6304.26 ± 1238.72 vs. 4755.64 ± 1122.71 μm2, p < 0.001), TM thickness (107.21 ± 31.26 vs. 94.51 ± 24.18 μm, p = 0.035), TM length (736.20 ± 141.85 vs. 656.43 ± 127.03 μm, p = 0.004), and SS length (219.89 ± 50.29 vs. 174.54 ± 35.58 μm, p < 0.001) were significantly greater in healthy group than in POAG group. In addition, SC area, TM thickness, and SS length were significantly and positively associated with AST0 in the healthy group, whereas no similar associations were observed in the POAG group.ConclusionsCompared with the healthy group, AST was significantly thinner in the POAG group, which also had smaller SC and TM dimensions. Moreover, the SC area, TM thickness, and SS length were significantly and positively associated with AST in the healthy group. Thus, AST might play an important role in maintaining TM and SC morphology and further in the pathogenesis of POAG.

Morphological changes in the trabecular meshwork and Schlemm\u2019s canal after treatment with topical intraocular pressure-lowering agents

Glaucoma treatment is usually initiated with topical medication that lowers the intraocular pressure (IOP) by reducing the aqueous production, enhancing the aqueous outflow, or both. However, the effect of topical IOP-lowering medications on the microstructures of the aqueous outflow pathway are relatively unknown. In this retrospective, observational study, 56 treatment-naïve patients with primary open-angle glaucoma were enrolled. Images of the nasal and temporal corneoscleral limbus were obtained using anterior segment optical coherence tomography (AS-OCT). The conjunctival vessels and iris anatomy were used as landmarks to select the same limbal area scan, and the trabecular meshwork (TM) width, TM thickness, and Schlemm’s canal (SC) area were measured before and after using the IOP-lowering agents for 3 months. Among the 56 patients enrolled, 33 patients used prostaglandin (PG) analogues, and 23 patients used dorzolamide/timolol fixed combination (DTFC). After 3 months of DTFC usage, the TM width, TM thickness, and SC area did not show significant changes in either the nasal or temporal sectors. Conversely, after prostaglandin analog usage, the TM thickness significantly increased, and the SC area significantly decreased (all P < 0.01). These findings warrant a deeper investigation into their relationship to aqueous outflow through the conventional and unconventional outflow pathways after treatment with PG analogues.

Effect of iStent Trabecular Micro-Bypass device on outflow system morphology

Purpose: Rigorous clinical testing has established that Schlemm’s canal cross-sectional area (SC-CSA) is reduced in glaucomatous eyes. However, to date, it is unclear whether trabecular bypass procedures impact the morphology of the proximal aqueous outflow tract, or if the introduction of a local region of low outflow resistance adversely affects SC-CSA elsewhere, specifically presenting as SC diminution. This study quantifies changes in the morphology of the distal outflow pathway after iStent Trabecular Micro-Bypass stent (Glaukos Corp, Laguna Hills, CA, USA) implantation in living eyes by anterior segment optical coherence tomography (OCT).&#x0D; Design: This was a prospective observational study.&#x0D; Subjects: This study included six patients (eight eyes) with primary-open angle glaucoma.&#x0D; Methods: Patients underwent iStent placement in the nasal anterior chamber angle quadrant. OCT imaging was obtained of both nasal and temporal eye quadrants before and after surgery. For each SC parameter, an average of ten consecutive, evenly spaced measurements were manually obtained over a 1 mm segment of SC on FIJI ImageJ. Linear mixed effects modeling quantified the effect of the iStent on these parameters.&#x0D; Main outcome measures: Main outcome measures were changes in SC-CSA, inner-to-outer wall distance (IOD), and trabecular meshwork (TM) thickness following iStent placement.&#x0D; Results: Following iStent placement, total SC-CSA increased an average of 1,039.12 μm2 (P = 0.05). Individually, there were no significant changes in SC-CSA in the nasal or temporal quadrants. Total SC-IOD and nasal SC-IOD increased an average of 2.35 μm (P = 0.01) and 2.96 μm (P = 0.04), respectively. There were no significant changes in temporal quadrant SC-IOD. There were no significant changes in TM thickness in either quadrant.&#x0D; Conclusions: Implantation of the iStent Trabecular Micro-Bypass stent significantly increases SC-IOD in the nasal quadrant at the location of implant, with no evidence of SC diminution in the temporal quadrant. It remains unclear how these observations relate to the surgical efficacy of trabecular bypass procedures.

Schlemm Canal and Trabecular Meshwork Features in Highly Myopic Eyes With Early Intraocular Pressure Elevation After Cataract Surgery

To investigate the morphologic features of the Schlemm canal and trabecular meshwork in highly myopic eyes with early intraocular pressure (IOP) elevation after cataract surgery. Retrospective case-control study. Eighty-eight highly myopic eyes of 88 patients after uneventful cataract surgery were included, 31 of which had early postoperative IOP elevation and 57 of which did not. The morphologic features of the Schlemm canal and trabecular meshwork, collected with swept-source optical coherence tomography before surgery, were reviewed. Backwards stepwise multiple linear regression was used to investigate the anatomic risk factors for early IOP elevation in highly myopic eyes. Highly myopic eyes with early postoperative IOP elevation had smaller Schlemm canal vertical diameter and area, as well as smaller trabecular meshwork thickness and width, in each quadrant than the non-elevation group. There was no significant difference in Schlemm canal horizontal diameter between the IOP elevation and non-elevation groups. In the highly myopic eyes, average Schlemm canal vertical diameter, Schlemm canal area, trabecular meshwork thickness, and width were all correlated negatively with the IOP elevation. A multivariate analysis showed that average Schlemm canal vertical diameter (β=-0.262, P= .004) and trabecular meshwork thickness (β=-0.173, P < .001) were significantly associated with early transient IOP elevation in highly myopic cataract eyes. A smaller vertical diameter of Schlemm canal and a thinner trabecular meshwork are 2 anatomic risk factors for early IOP elevation after cataract surgery in highly myopic eyes.

Disease-related and age-related changes of anterior chamber angle structures in patients with primary congenital glaucoma: An in vivo high-frequency ultrasound biomicroscopy-based study.

To provide in vivo measurements of anterior chamber angle structures and their relationship with age as evaluated by high-frequency ultrasound biomicroscopy (UBM) in patients with primary congenital glaucoma (PCG). High-frequency UBM was done for 51 PCG eyes from 40 patients (aged from 3 to 96 months) and 11 unaffected contralateral eyes. Parameters, including the proportion of observable abnormal tissue membrane and Schlemm's canal, the largest cross-sectional area (CSA) of Schlemm's canal (SC), SC meridional diameter, trabecular-iris angle (TIA), trabecular meshwork (TM) thickness, iris thickness, ciliary process length, and corneal limbus thickness were compared between the two groups and their relationship with age was explored in PCG eyes. Abnormal tissue membrane was detected in 27.5% of PCG eyes and none in unaffected eyes. SC was observed in 73.1% of PGC eyes compared to 100% in unaffected eyes (P<0.001). The largest CSA of SC, SC meridional diameter, iris thickness, and corneal limbus thickness were all significantly smaller in PCG eyes compared to unaffected eyes (all P<0.05). TIA and ciliary process length in unaffected eyes were smaller than PCG eyes (both P<0.05). The largest CSA of SC, TM thickness, iris thickness, and ciliary process length were all significantly correlated to age in PCG eyes (P<0.05). The anatomical information evaluated by high-frequency UBM may provide glaucoma specialists a useful tool to aid in understanding the dysgenesis and changes with age of anterior chamber angle in PCG.

Effect of topical application of adrenaline on Schlemm canal, trabecular meshwork and intraocular pressure.

Aim:To measure changes in the sizes of Schlemm canal (SC) and trabecular meshwork (TM) in healthy individuals before and after topical application of 1% adrenaline at 15, 45, and 90 minutes using anterior segment optical coherence tomography (ASOCT).Methods:Anterior chamber angle imaging of the nasal and temporal regions of the right eyes was performed with anterior segment optical coherence tomography (ASOCT) before and after topical application of 1% adrenaline at 15, 45, and 90 minutes. The diameter and area of SC, width and thickness of TM, anterior chamber depth (ACD) and pupil diameter (PD) were measured with ASOCT images. Intraocular pressure (IOP) was also recorded simultaneously.Results:A total of 15 healthy individuals were enrolled and included 7 male subjects and 8 female subjects; Compared with the parameters before intervention, both the SC diameter and area in the 2 quadrants increased after the application of adrenaline at the 3 time points (P < .05). The TM width increased after medication (P < .05). IOP decreased significantly after application (P < .05). There were no statistically significant changes in TM thickness, ACD, and PD at any point of time (P > .05).Conclusion:Topical application of 1% adrenaline in eye led to decrease in IOP with the SC diameter and area as well as the TM width increased after medication. While the TM thickness, ACD, PD seemed to remain constant.

Influence of the Water-Drinking Test on Intraocular Pressure, Schlemm's Canal, and Autonomic Nervous System Activity.

To assess changes in Schlemm's canal (SC), intraocular pressure (IOP), and autonomic nervous system activity in healthy individuals after performing the water-drinking test (WDT). The SC area (SCAR), trabecular meshwork (TM) thickness, IOP, high frequency (HF) of heart rate variability (HRV), heart rate (HR), and systolic (SBP) and diastolic blood pressure (DBP) were measured in 22 young healthy participants before and after the WDT, which involved drinking a 1-liter water load in 5 minutes.The SC and TM profiles were captured using a Spectralis optical coherence tomography device (anterior segment module). HF was recorded using Kubios HRV Premium software to evaluate parasympathetic nervous system activity. Compared with baseline values, IOP increased significantly (14.9 ± 2.7 mm Hg vs. 18.4 ± 3.3 mm Hg; P < 0.001), whereas HF (1587 ± 930 ms2 vs. 2193 ± 863 ms2; P < 0.001), mean SCAR (6521 ± 1360 μm2 vs. 5180 ± 1455 μm2; P < 0.001), and HR (69 ± 9.7 beats/min vs. 63 ± 8.9 beats/min; P < 0.001) values decreased significantly by 15 minutes after water-loading. Least significant difference pairwise comparison revealed significant fluctuations of all parameters (SCAR, IOP, HF, and HR) at 15 minutes and their recovery at 30-minutes post-WDT. TM thickness, SBP, and DBP post-WDT did not differ significantly. The increase in IOP (r = -0.4047; P = 0.010) and HF (r = -0.386; P = 0.014) correlated significantly with the decrease in SCAR. The WDT may cause parasympathetic nervous system stimulation, leading to the collapse of SC, which leads to increased IOP.

Effect of age on the morphologies of the human Schlemm\u2019s canal and trabecular meshwork measured with swept\u2011source optical coherence tomography

PurposeWe aimed to measure the sizes of Schlemm’s canal (SC) and the trabecular meshwork (TM) in healthy individuals and to evaluate variations with age from childhood to old age by using swept-source optical coherence tomography (OCT).MethodsAnterior chamber angle imaging of the superior, inferior, nasal, and temporal regions of the right and left eyes was performed with swept-source OCT. The diameter and area of SC and TM width and thickness were measured manually from OCT images.ResultsA total of 114 healthy individuals were enrolled and included 48 male subjects and 66 female subjects; their ages ranged from 7 to 83 years. Both the SC diameter and area in the four quadrants decreased significantly with aging (P < 0.001) and were wider in the nasal and temporal quadrants compared with the superior and inferior quadrants. Changes in SC size showed significant positive correlations with axial length (AL) and anterior chamber depth (P < 0.001). There was a significant positive association between age and TM thickness in the nasal and temporal quadrants (P < 0.05). The inferior quadrant TM width was the widest among the quadrants. The superior quadrant TM thickness was the thinnest among the quadrants. Changes in TM thickness in the nasal and temporal quadrants showed a significant negative correlation with AL (P < 0.05). There was no statistically significant correlation in SC and TM parameters with central corneal thickness, intraocular pressure, sex, or right or left eye (P > 0.05).ConclusionsWith aging, the SC diameter and area became smaller, TM thickness increased, and TM width seemed to remain constant. Measurements of the sizes of SC and the TM with swept-source OCT could assist in clinical assessments and treatment planning for glaucoma.

Rho- Kinase Inhibitor Y-27632 Decreases the Thickness of Trabecular Meshwork in Juvenile Rats Mod-el Injected with Sodium Hyaluronate

Most glaucoma drugs lower the intraocular pressure (IOP) by decreasing the aqueous humor production and increasing the outflow through uveoscleral pathway. None of these drugs work mainly on increasing outflow through the trabecular pathway. Consequently, the experiment to develop glaucoma drugs directly target at the trabecular outflow pathway is highly required. The purpose of this study is to reveal the effect of rho-kinase inhibitor Y-27632 on the thickness of trabecular meshwork in juvenile rats model injected with sodium hyalu-ronate. This study was an experimental study with posttest only control group design. Twenty-four rats were included in this study. Each eye of the rat would be considered as one sample. Samples were divided into 6 groups, negative control group, positive control I group with intracameral sodium hyaluronate injection, posi-tive control II group with topical Y-27632 10 mM, and three experimental groups with intracameral injection of sodium hyaluronate and Y-27632 10-1 mM, 1 mM, and 10 mM respectively. After the procedures all rats were sacrificed and enucleated. Trabecular meshwork tissue was stained with Hematoxilene-Eosin and evalu-ated under 400× microscopic magnification. Quantitative measurements were taken using computerized image analysis with dot slide program. There were significant statistic differences among the positive control I group and the experimental groups (p-value < 0.05) as well as the positive control II group and the experi-mental groups (p-value < 0.05). The highest mean of decreasing trabecular meshwork thickness was noted in the group given by sodium hyaluronate and Y-27632 10 mM with value of 118.42 µm. There was decreasing thickness of trabecular meshwork due to the effect of rho- kinase inhibitor Y-27632 in juvenile rats injected with sodium hyaluronate.

Schlemm's canal and trabecular meshwork morphology in high myopia.

Myopes have a higher risk for open-angle glaucoma; however, the reason is not clear. This study aims to explore the morphologic alterations of Schlemm's canal and trabecular meshwork size in highly myopic eyes. Forty myopic eyes from 40 patients with high myopia and 40 control eyes from 40 subjects with low myopia, emmetropia or low hyperopia were enrolled. Optical coherence tomography (OCT) was used to image Schlemm's canal and trabecular meshwork size. The correlations between the morphological alterations of Schlemm's canal and trabecular meshwork, spherical equivalent refractive error, axial length, and intraocular pressure were analysed. Subjects with high myopia had a significantly larger Schlemm's canal diameter in the nasal (188.1±85.6μm vs 127.4±46.7μm, P<0.001), temporal (200.1±7.2μm vs 147.6±68.1μm, P=0.001) quadrants and average value (173.1±48.1μm vs 137.3±39.6μm, P=0.001), and larger Schlemm's canal area in the nasal (7333.2±3877.7μm2 vs 3833.2±2094.7μm2 , P<0.001), temporal (7274.8±3247.4μm2 vs 4631.1±2431.9μm2 , P<0.001) inferior (5512±2504.9μm2 vs 3922.6±1935.6μm2 , P=0.003) quadrants and average value(6165.4±2080.5μm2 vs 4044.4±1581.1μm2 , P<0.001). In the high myopia group, trabecular meshwork thickness of the nasal and temporal quadrants was significantly smaller (108.8±31.6μm vs 126±42.2μm, P=0.045; 100.5±15.4μm vs 118.4±26.8μm, P=0.001, respectively) compared with the control group, as well as the average value (106.4±16.5μm vs 120.9±23.5μm, P=0.002). In the high myopia group, Schlemm's canal and trabecular meshwork size were not correlated with spherical equivalent refractive error and axial length (P>0.05), while Schlemm's canal area showed a significant negative correlation with intraocular pressure (r=-0.33, P=0.039). This study reports for the first time that eyes with high myopia have a larger Schlemm's canal diameter and area, as well as decreased trabecular meshwork thickness, which may help to understand the close association between high myopia and open-angle glaucoma. Schlemm's canal and trabecular meshwork analysis by OCT images may help to characterise the underlying pathophysiological mechanisms involved in high myopia.

Variations in active outflow along the trabecular outflow pathway

Previous tracer studies have shown segmental outflow in the trabecular meshwork (TM) and along the inner wall (IW) of Schlemm's canal (SC). Whether segmental outflow is conserved distal to SC has not yet been investigated. This study aims to investigate whether the segmented pattern of outflow is conserved in distal outflow pathways by using a newly developed global imaging method and to evaluate variations of active outflow in three distinct regions along trabecular outflow pathway.Six normal whole globe human eyes were first perfused at 15 mmHg to establish a stable baseline outflow facility. The anterior chamber was then exchanged (5 mL) and perfused with fluorescent microspheres (0.002% v/v, 200 μL) to label areas of active outflow. All eyes were perfusion fixed and dissected into anterior segments. The TM and scleral surface were en face imaged globally. Effective filtration area (EFA) and fluorescent tracer distribution and intensity were analyzed in global images for both the TM and episcleral veins (EPVs). Anterior segments were further dissected into a minimum of 16 radial wedges, from which frontal sections were cut, stained, and imaged, using confocal microscopy. EFA from all three locations along the trabecular outflow pathway were measured and compared. Additionally, TM thickness, SC height, and total number of collector channels (CC) were analyzed and compared between active and inactive areas of outflow. Statistical analysis was performed using Student's t-tests and Wilcoxon signed-rank test with a required significance of p ≤ 0.05.All three locations showed a segmental outflow pattern. The TM had a significantly higher mean EFA (86.3 ± 3.5%) compared to both the IW (34.7 ± 2.9%; p ≤ 0.01) and EPVs (41.1 ± 3.8%; p ≤ 0.01). No significant difference in mean EFA was found between IW and EPVs. Preferential active outflow was observed in the nasal and inferior quadrants. TM thickness was significantly larger in areas of active outflow (103.3 ± 4.0 μm; p ≤ 0.01) compared to areas of inactive outflow (78.5 ± 6.5 μm), but there was no significant difference in SC height between active and inactive outflow areas. Among all eyes, a total of 80 CCs were counted with 63 associated with active outflow and 17 associated with inactive outflow. A higher number of CCs associated with areas of active outflow were found in the nasal (26 of 63) and inferior (20 of 63) quadrants compared to the temporal (9 of 63) and superior (8 of 63) quadrants.A segmental nature of outflow is conserved along the trabecular outflow pathway with variations in three distinct locations (TM, IW, and EPVs). IW and EPVs showed a similar mean EFA. Preferential active outflow was observed in the nasal and inferior quadrants of the eye, which are associated with more expanded TM and higher number of CCs. Normal outflow patterns and its variations along the outflow pathway reported in this study will provide the basis for future studies of the outflow changes in eyes with glaucoma.

Evaluation of Outflow StructuresIn Vivoafter the Phacocanaloplasty

Purpose. To evaluate the in vivo changes in Schlemm's canal (SC) and the trabecular meshwork (TM) in patients with primary open-angle glaucoma (POAG) after phacocanaloplasty using anterior segment optical coherence tomography (AS-OCT). Methods. Ten eyes of nine patients with POAG (6 men and 3 women) who underwent phacocanaloplasty. Preoperative and postoperative visual acuity (VA), intraocular pressure (IOP), and use of glaucoma medications were evaluated. The main outcome measures were the area of SC and TM thickness assessed using AS-OCT before and 12 months after surgery. Results. We found statistically significant reduction in IOP (from 26.4 (8.6) mmHg to 12.9 (2.5) (p < 0.05) mmHg), increase in VA from 0.7 (0.4) to 0.9 (0.2), and decrease in glaucoma medication from 2.6 (1.2) to 1.1 (1.3) at 12 months postoperatively. There was a significant increase in the SC area (3081.7 (842.8) μm2 versus 5098.8 (1190.5) μm2, p < 0.001) and a decrease in mean TM thickness (91.2 (18.6) μm versus 81.3 (15.1) μm, p = 0.001) after surgery. We found negative correlations between SC area and IOP before surgery (r = −0.67, p = 0.03) and also between SC area before and IOP reduction 12 months after the phacocanaloplasty (r = −0.80, p = 0.005). Conclusions. Our results showed statistically significant dilation of SC area and reduction of TM thickness after phacocanaloplasty in POAG patients. The degree of SC expansion was related to the IOP decrease.