Effects of Trabecular Meshwork Width and Schlemm's Canal Area on Intraocular Pressure Reduction in Glaucoma Patients

Changes in Schlemm's canal morphology after trabeculectomy in open angle glaucoma assessed using anterior segment optical coherence tomography

CLINICAL RELEVANCE

Determining how Schlemm's canal is affected by trabeculectomy may become a marker for evaluating and monitoring surgical success.

BACKGROUND

This study aims to evaluate the morphological changes in Schlemm's canal after trabeculectomy using anterior segment optical coherence tomography (AS-OCT).

METHODS

Thirty-five eyes of 35 patients who were followed up for open-angle glaucoma and indicated for trabeculectomy were included in the study. AS-OCT was performed preoperatively and at week 1, month 1 and month 3 postoperatively. The coronal and meridional diameters of Schlemm's canal were measured in the temporal and nasal quadrants via AS-OCT.

RESULTS

The meridional diameter length of Schlemm's canal was higher in the nasal quadrant than in the temporal quadrant. Nasally, the mean preoperative meridional diameter length was 326.8 ± 88.5 μm, which increased at postoperative week 1 and month 1. Temporally, it was 271.5 ± 91.5 μm and showed a non-significant change postoperatively. The mean preoperative coronal diameter length was 10.9 ± 6.5 μm and 11.9 ± 6.0 μm in the nasal and temporal quadrants, respectively. A statistically significant increase was found in the measurements of the nasal quadrant at week 1 (p = 0.005) and month 1 (p = 0.049), and in the temporal quadrant at week 1 (p = 0.023).

CONCLUSION

A significant enlargement of the canal occurs at the first postoperative week, followed by a gradual reduction thereafter. The increase in size is mostly observed in the coronal diameters, resulting in the expansion of the canal.

Low Intraocular Pressure Induces Fibrotic Changes in the Trabecular Meshwork and Schlemm's Canal of Sprague Dawley Rats

Purpose

Continuous artificial aqueous humor drainage in the eyes of patients with glaucoma undergoing trabeculectomy likely exerts abnormal shear stress. However, it remains unknown how changes in intraocular pressure (IOP) can affect aqueous humor outflow (AHO).

Methods

Here, we induced and maintained low intraocular pressure (L-IOP) in healthy Sprague Dawley (SD) rats by puncturing their eyes using a tube (200-µm diameter) for 2 weeks. After the rats were euthanized, their eyes were removed, fixed, embedded, stained, and scanned to analyze the physiological and pathological changes in the trabecular meshwork (TM) and Schlemm's canal (SC). We measured SC parameters using ImageJ software and assessed the expression of various markers related to flow shear stress (KLF4), fibrosis (TGF-β1, TGF-β2, α-SMA, pSmad1/5, pSmad2/3, and fibronectin), cytoskeleton (integrin β1 and F-actin), diastolic function (nitric oxide synthase and endothelial nitric oxide synthase [eNOS]), apoptosis (cleaved caspase-3), and proliferation (Ki-67) using immunofluorescence or immunohistochemistry.

Results

L-IOP eyes showed a larger SC area, higher eNOS expression, and lower KLF4 and F-actin expression in the TM and SC (both P < 0.05) than control eyes. The aqueous humor of L-IOP eyes had a higher abundance of fibrotic proteins and apoptotic cells than that of control eyes, with significantly higher TGF-β1, α-SMA, fibronectin, and cleaved caspase-3 expression (all P < 0.05).

Conclusions

In conclusion, a persistence of L-IOP for 2 weeks may contribute to fibrosis in the TM and SC and might be detrimental to conventional AHO in SD rat eyes.

Translational Relevance

Clinicians should consider that aberrant shear force induced by aqueous humor fluctuation may damage AHO outflow channel when treating patients.

Clinical prediction nomogram for steroid-induced ocular hypertension risk in patients with intravitreal dexamethasone implant

Background

Recognizing the risk factors and understanding the mechanisms underlying steroid-induced ocular hypertension (SIOH) are vital to prevent potent vision loss and ensure the safety and effectiveness of dexamethasone (DEX) injections. The study aimed to develop a novel nomogram for predicting the risk of SIOH and determining safety zones for steroid injections.

Methods

This single-center, retrospective, case-control study included a total of 154 eyes with available measured axial length that had undergone AS-OCT and DEX implantation at the Yonsei University Health System. The eyes were categorized into the SIOH (n = 39) and post-steroid normal IOP (n = 115) groups. We measured intraocular pressure (IOP) for all eyes prior to DEX implantation, at 1 week post-implantation, and at 1, 2, 3, 6, and 12 months thereafter. We used AS-OCT to analyze the trabecular meshwork (TM) height and ocular parameters.

Results

The predictive nomogram, including TM height, yielded an AUC of 0.807 (95 % confidence interval [CI], 0.737-0.877) and demonstrated significantly higher predictive accuracy than that of previous nomograms, which did not consider TM height and had an AUC of 0.644 (95 % CI, 0.543-0.745) (p = 0.031). The calibration plot demonstrated a strong predictive accuracy for a predicted value of approximately 0.4. We established cutoff values to ensure different levels of sensitivity and specificity within the safety zone following DEX implantation.

Conclusion

Our improved nomogram incorporating TM height as a newly identified risk factor, established a safety threshold for intravitreal DEX implantation, helping identify safe individuals from those who require caution.

Assessment of Schlemm's canal with swept-source optical coherence tomography in Graves' ophthalmopathy

PURPOSE

To evaluate the Schlemm's canal (SC) parameters obtained by swept-source optical coherence tomography (OCT) different in Graves' ophthalmopathy (GO) eyes compared to healthy eyes.

METHODS

This cross-sectional observational study evaluated 64 eyes of 32 GO cases and 56 eyes of 28 healthy controls. The study was conducted between October 2020 and June 2021. SC images were obtained from the temporal limbus of individuals using swept-source OCT. SC length (SCL) and SC area (SCA) were measured. The relationship between SC parameters in the patient group and intraocular pressure (IOP), retinal nerve fiber layer (RNFL) thickness, Graves' disease (GD) duration, and clinical activity score (CAS) was evaluated.

RESULTS

In the GO group, 64 eyes of 32 patients were evaluated, and in the age and gender-matched healthy control group, 56 eyes of 28 individuals were assessed. SC images from 4 eyes of 4 patients in the patient group and 1 eye of 1 patient in the control group were not clear, preventing SCL and SCA measurements for these eyes. SCL and SCA measurements were found to be lower, and IOP and Hertel values were higher in the GO group compared to the healthy controls. However, no significant correlation was observed between SCL and SCA with IOP, RNFL thickness, GD duration, GO duration, or CAS in the GO group. In the GO group, the mean value of SCA was found to be higher in eyes with glaucoma or OHT compared to those without.

CONCLUSION

These findings indicate that SC in GO-affected eyes is shorter and has a smaller area than in healthy individuals. Additionally, higher IOP and Hertel values were observed in the GO group compared to healthy controls. This study suggests that assessing SC using anterior segment OCT could provide valuable insights into the regulation of IOP and the development of glaucoma in GO-affected 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.

Glaucoma Surgery and Ocular Blood Flow in Colour Doppler Imaging: Is There a Link?

Glaucoma is a common cause of blindness worldwide. This disease is characterised by increased intraocular pressure (IOP) and the concomitant disruption of ocular haemodynamic. Several studies have demonstrated that trabeculectomy is associated with changes in extraocular blood flow. In this study, we reviewed the available evidence on the use of colour Doppler imaging to evaluate and manage patients with open-angle glaucoma. We present the detailed anatomy of ocular blood flow to provide a background for the research findings. We also discuss the physiological foundations of ocular blood flow and detailed flow characteristics of specific extraocular vessels. Finally, we reviewed published studies that analysed the effects of glaucoma surgery on the blood flow parameters of the eye.

Differential roles of FOXC2 in the trabecular meshwork and Schlemm's canal in glaucomatous pathology

Impaired development and maintenance of Schlemm's canal (SC) are associated with perturbed aqueous humor outflow and intraocular pressure. The angiopoietin (ANGPT)/TIE2 signaling pathway regulates SC development and maintenance, whereas the molecular mechanisms of crosstalk between SC and the neural crest (NC)-derived neighboring tissue, the trabecular meshwork (TM), are poorly understood. Here, we show NC-specific forkhead box (Fox)c2 deletion in mice results in impaired SC morphogenesis, loss of SC identity, and elevated intraocular pressure. Visible-light optical coherence tomography analysis further demonstrated functional impairment of the SC in response to changes in intraocular pressure in NC-Foxc2 -/- mice, suggesting altered TM biomechanics. Single-cell RNA-sequencing analysis identified that this phenotype is predominately characterized by transcriptional changes associated with extracellular matrix organization and stiffness in TM cell clusters, including increased matrix metalloproteinase expression, which can cleave the TIE2 ectodomain to produce soluble TIE2. Moreover, endothelial-specific Foxc2 deletion impaired SC morphogenesis because of reduced TIE2 expression, which was rescued by deleting the TIE2 phosphatase VE-PTP. Thus, Foxc2 is critical in maintaining SC identity and morphogenesis via TM-SC crosstalk.

First-Generation iStent Bypass Implantation versus ab Externo Canaloplasty Combined with Phacoemulsification in Patients with Primary Open Angle Glaucoma-12-Month Follow-Up

This prospective, non-randomized, interventional clinical study evaluated the efficacy and safety profile of first-generation iStent bypass implantation versus ab externo canaloplasty, both combined with phacoemulsification, in patients with primary open-angle glaucoma (POAG) after 12-month follow-up. A total of 138 patients with POAG and their 138 eyes (69 phaco-iStent and 69 phacocanaloplasty) were included. Postoperatively at 12 months, the mean intraocular pressure (IOP) decreased from 18.44 ± 3.88 to 15.51 ± 2.50 mmHg and from 17.20 ± 4.04 to 14.97 ± 2.37 mmHg in the phaco-iStent (PiS) and phacocanaloplasty (PC) groups, respectively (p = 0.480). In both groups, 35.7% achieved >20% IOP reduction from baseline. A total of 86% and 71.4% of the eyes were medication-free at 12 months in the PiS and PC groups, respectively. In both groups, all eyes showed improvement in best-corrected visual acuity compared with baseline and demonstrated similar safety profiles throughout the 12-month follow-up period. This study showed equal hypotensive effects of PiS and PC. Both procedures significantly reduced the IOP and the requirement for IOP-lowering medications for at least 12 months postoperatively, with no significant differences between the groups.

Association of trabecular meshwork height with steroid-induced ocular hypertension

It is important to identify at-risk patients prior to administering steroid injections to prevent avoidable irreversible blindness inducted by steroid-induced ocular hypertension (SIOH). We aimed to investigate the association of SIOH following intravitreal dexamethasone implantation (OZURDEX) using anterior segment optical coherence tomography (AS-OCT). We conducted a retrospective case control study to assess the association between trabecular meshwork and SIOH. A total of 102 eyes that underwent both AS-OCT and intravitreal dexamethasone implant injection were divided into the post-steroid ocular hypertension and normal intraocular pressure groups. Ocular parameters that can contribute to intraocular pressure were measured using AS-OCT. Univariable logistic regression analysis was used to calculate the odds ratio of the SIOH and significant variables were further analyzed using a multivariable model. Trabecular meshwork (TM) height was significantly shorter in the ocular hypertension group (716.13 ± 80.55 μm) than that in the normal intraocular pressure group (784.27 ± 82.33 μm) (p < 0.001). The receiver operating characteristic curve technique analysis showed that the optimal cut-off of ≥ 802.13 μm for TM height specificity was 96.2%, and TM height with < 646.75 μm had a sensitivity of 94.70%. The odds ratio of the association was 0.990 (p = 0.001). TM height was identified as a newly observed association with SIOH. TM height can be assessed using AS-OCT, with acceptable sensitivity and specificity. Caution must be exercised while injecting steroids in patients with short TM height (especially < 646.75 μm) as it may cause SIOH and irreversible blindness.

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

Purpose

To 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.

Methods

Thirty-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.

Results

AST0 (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.

Conclusions

Compared 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.