Effect of age on the morphologies of the human Schlemm's canal and trabecular meshwork measured with swept‑source optical coherence tomography

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

PURPOSE

To evaluate the effect of uneventful cataract surgery on Schlemm's canal (SC) and the trabecular meshwork (TM) in cases with pseudoexfoliation (PX).

METHODS

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.

RESULTS

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).

CONCLUSION

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.

En face optical coherence tomography detection of Schlemm's canal in primary open angle glaucoma

Purpose: To compare the morphological characteristics of Schlemm's canal (SC) in patients with primary open-angle glaucoma (POAG) and healthy controls, using swept-source optical coherence tomography (SS-OCT) with en face reconstruction. Methods: In this Prospective comparative study, we included 100 eyes from 50 patients diagnosed with POAG and 50 healthy controls. Three-dimensional cube and line scans of the temporal and nasal quadrants of the anterior segment of the limbus were acquired using SS-OCT. SC was identified using en face and cross-sectional images. The diameter and area of SC in cross-sectional images and the visible percentage and area of SC in en face images were measured using ImageJ. Results: SC was observed in 84% of en face images and 81% of cross-sectional images in eyes with POAG but in 92% of en face images and 86% of cross-sectional images in control eyes. Significant differences between the POAG and normal control eyes were found in the en face area (0.35 ± 0.14 mm2 vs. 0.56 ± 0.22 mm2 in the temporal quadrant and 0.36 ± 0.14 mm2 vs. 0.58 ± 0.23 mm2 in the nasal quadrant; both p < 0.001) and visible percentage of SC (85.71% vs. 94.91% and 87.10% vs. 95.52% in the temporal and nasal quadrant respectively, both p < 0.001) in en face images as well as the cross-sectional area (2790.9 ± 942.2 μm2 vs. 4138.6 ± 2027.8 μm2 in the temporal quadrant and 2805.7 ± 947.2 μm2 vs. 4224.0 ± 2002.2 μm2 in the nasal quadrant, both p < 0.001) and diameter of SC (123.1 ± 25.4 μm vs. 149.5 ± 34.7 μm in the temporal quadrant and 126.3 ± 28.9 μm vs. 155.3 ± 36.0 μm in the nasal quadrant, both p < 0.001) in cross-section images. In addition, the mean intraocular pressure (IOP) significantly correlated with the en face area, visible percentage of SC, and cross-sectional area in the temporal and nasal quadrants. Conclusion: SS-OCT can obtain high-quality en face images of SC without post-acquisition processing. Eyes with POAG had a decreased en face SC area compared with normal eyes. A correlation between SC area, visible percentage of en face images, and IOP was also observed.

In vivo quantification of human aqueous veins by enhanced depth imaging optical coherence tomography and optical coherence tomography angiography images

AIM

To investigate the aqueous vein in vivo by using enhanced depth imaging optical coherence tomography (EDI-OCT) and optical coherence tomography angiography (OCTA).

METHODS

In this cross-sectional comparative study, 30 healthy participants were enrolled. Images of the aqueous and conjunctival veins were captured by EDI-OCT and OCTA before and after water loading. The area, height, width, location depth and blood flow of the aqueous vein and conjunctival vein were measured by Image J software.

RESULTS

In the static state, the area of the aqueous vein was 8166.7±3272.7 µm2, which was smaller than that of the conjunctival vein (13 690±7457 µm2, P<0.001). The mean blood flow density of the aqueous vein was 35.3%±12.6%, which was significantly less than that of the conjunctival vein (51.5%±10.6%, P<0.001). After water loading, the area of the aqueous vein decreased significantly from 8725.8±779.4 µm2 (baseline) to 7005.2±566.2 µm2 at 45min but rose to 7863.0±703.2 µm2 at 60min (P=0.032). The blood flow density of the aqueous vein decreased significantly from 41.2%±4.5% (baseline) to 35.4%±3.2% at 30min but returned to 45.6%±3.6% at 60min (P=0.021).

CONCLUSION

The structure and blood flow density of the aqueous vein can be effectively evaluated by OCT and OCTA. These may become biological indicators to evaluate aqueous vein changes and aqueous outflow resistance under different interventions in glaucoma patients.

Evaluation of Schlemm Canal Parameters Using Swept-Source Optical Coherence Tomography in Eyes That Underwent Keratoplasty

OBJECTIVES

In this study, we aimed to evaluate Schlemm canal parameters using anterior segment swept-source optical coherence tomography in eyes that underwent keratoplasty and compare them with keratoconus and healthy control groups.

METHODS

The study included 32 patients who underwent penetrating keratoplasty or deep anterior lamellar keratoplasty once due to keratoconus and age-matched and sex-matched 20 keratoconus patients and 30 healthy controls. In all the patients, a single horizontal image centered on the central cornea was obtained from the nasal and temporal quadrants with low-intensity scanning to visualize Schlemm canal.

RESULTS

There was no statistically significant difference between the groups for age and gender ( P ˃0.05). In the keratoplasty group, the area and diameter of Schlemm canal were 2.266±1.141μm 2 and 160.77±65.08 μm, respectively, in the nasal quadrant and 2.623±1.277 μm 2 and 158.81±68.05 μm, respectively in the temporal quadrant, which were statistically significantly lower compared with other groups ( P <0.001 for all). There was no significant difference between the penetrating and deep anterior lamellar keratoplasty subgroups for Schlemm canal parameters.

CONCLUSION

This is the first study to report anterior segment optical coherence tomography after surgery shows SC parameters that are, on average, less than age-matched and keratoconus controls.

Iridocorneal angle imaging of a human donor eye by spectral-domain optical coherence tomography

Iridocorneal angle (ICA) details particularly the trabecular meshwork (TM), Schlemm's canal (SC), and collector channels (CCs) play crucial roles in the regulation of the aqueous outflow in the eyes and are closely associated with glaucoma. Current clinical gonioscopy imaging provides no depth information, and studies of 3D high-resolution optical coherence tomography (OCT) imaging of these structures are limited. We developed a custom-built spectral-domain (SD-) OCT imaging system to fully characterize the angle details. Imaging of a human cadaver eye reveals the visibility of details in the TM/SC/CC region via a 'crossline' scanning and a series of image processing. This shows that ICA imaging can be used for preoperative glaucoma inspections in the clinical setting with the proposed prototype.

Evaluation of Schlemm's canal with swept-source optical coherence tomography in primary angle-closure disease

PURPOSE

To perform an in vivo evaluation of the changes in Schlemm's canal (SC) among patients with primary angle-closure disease (PACD) using swept-source optical coherence tomography (SS-OCT).

METHODS

Patients diagnosed with PACD who had not undergone surgery were recruited. The SS-OCT quadrants scanned herein included the nasal and temporal sections at 3 and 9 o'clock, respectively. The diameter and cross-sectional area of the SC were measured. A linear mixed-effects model was performed to analyze the effects of parameters on the SC changes. The hypothesis of interest was related to the angle status (iridotrabecular contact, ITC/open angle, OPN), which was further explored with pairwise comparisons of the estimated marginal means (EMMs) of the SC diameter and SC area. In the ITC regions, the relationship between the trabecular-iris contact length (TICL) percentage and SC parameters was also studied by a mixed model.

RESULTS

A total of 49 eyes of 35 patients were included for measurements and analysis. The percentage of observable SCs in the ITC regions was only 58.5% (24/41), whereas it was 86.0% (49/57) in the OPN regions (χ² = 9.44, p = 0.002). ITC was significantly associated with a decreasing SC size. The EMMs for the diameter and cross-sectional area of SC at the ITC and OPN regions were 203.34 μm versus 261.41 μm (p = 0.006) and 3174.43 μm² versus 5347.63 μm² (p = 0.022), respectively. Sex, age, spherical equivalent refraction, intraocular pressure, axial length, extent of angle closure, history of acute attack and treatment with LPI were not significantly associated with SC parameters. In the ITC regions, a larger TICL percentage was significantly associated with a decrease in SC diameter and area (p = 0.003 and 0.019, respectively).

CONCLUSIONS

The morphologies of SC could be affected by the angle status (ITC/OPN) in patients with PACD, and ITC was significantly associated with a decreasing SC size. These changes in SC as described by OCT scans might help to elucidate the progression mechanisms of PACD.

Dexamethasone Modulates the Dynamics of Wnt Signaling in Human Trabecular Meshwork Cells

Trabecular meshwork (TM) tissue is highly specialized, and its structural integrity is crucial for maintaining homeostatic intraocular pressure (IOP). The administration of glucocorticoids, such as dexamethasone (DEX), can perturb the TM structure and significantly increase IOP in susceptible individuals, resulting in ocular diseases such as steroid-induced glaucoma, a form of open-angle glaucoma. Although the exact mechanism involved in steroid-induced glaucoma remains elusive, increasing evidence suggests that DEX may act through various signaling cascades in TM cells. Despite uncertainty surrounding the specific process by which steroid-induced glaucoma occurs, there is growing evidence to indicate that DEX can impact multiple signaling pathways within TM cells. In this study, we examined the impact of DEX treatment on the Wnt signaling pathway in TM cells, given that Wnt signaling has been reported to play a crucial role in regulating extracellular matrix (ECM) levels in the TM. To further elucidate the role of Wnt signaling in the glaucomatous phenotype, we examined mRNA expression patterns between Wnt signaling markers AXIN2 and sFRP1 and DEX-mediated induction of myocilin (MYOC) mRNA and protein levels over 10 days in DEX-treated primary TM cells. We observed a sequential pattern of peak expression between AXIN2, sFRP1, and MYOC. Based on the study, we propose that sFRP1 upregulation could be a result of a negative feedback mechanism generated by stressed TM cells to suppress abnormal Wnt signaling activities.

Acoustic radiation force optical coherence elastography: A preliminary study on biomechanical properties of trabecular meshwork

Evaluating biomechanical properties of trabecular meshwork (TM) is of great significance for understanding the mechanism of aqueous humor circulation and its relationship to some eye diseases such as glaucoma; however, there is almost no relevant study due to the lack of clinical measurement tool. In this paper, an acoustic radiation force optical coherence elastography (ARF-OCE) system is developed with the advantages of noninvasive detection, high resolution, high sensitivity, and high-speed imaging, by which elastic modulus of the porcine and human TMs is accurately quantified. As the first OCE imaging of TM, our study demonstrates that ARF-OCE may be an effective approach to advance the research of diseases related to aqueous humor circulation.

Efficacy of Toric Intraocular Lens Implantation in Patients Older Than 80 Years with Cataracts and Corneal Astigmatism

INTRODUCTION

This study analyzed the visual outcome following cataract surgery with toric intraocular lenses (IOLs) in patients older than 80 years with corneal astigmatism.

METHODS

A total of 159 patients (159 eyes) older than 80 years with corneal astigmatism (≥ 0.75 D) were included. Fifty-three eyes received Acrysof IQ® toric IOLs (SN6AT2-5), while the others received non-toric IOLs: 51 eyes received Acrysof IQ® IOLs (SN60WF) and 55 eyes received A1-UV IOLs. The uncorrected distance visual acuity, corrected distance visual acuity, and refraction (spherical equivalent, refractive cylinder) were assessed at 3 months postoperatively. The prediction error of refractive outcome and percentages of eyes within ± 0.50 D and ± 1.00 D in the toric IOL group obtained using five toric IOL formulas (Barrett predicted posterior corneal astigmatism (PCA), Barrett measured PCA, Kane, EVO 2.0 and Næser-Savini) were compared.

RESULTS

At 3 months postoperatively, the average uncorrected distance visual acuity was better in the toric IOL group than the non-toric IOL group (p < 0.001). The mean residual refractive cylinder was lower in the toric IOL group than the non-toric IOL group (p < 0.001). The Næser-Savini formula achieved the lowest mean absolute error (0.39 D) and had the highest percentages of eyes within an absolute error of 0.50 D and 1.00 D (72% and 98%) compared to the other formulas.

CONCLUSION

The results demonstrate the efficacy of toric IOL implantation in patients older than 80 years with corneal astigmatism and provide strong evidence for cataract surgeons to encourage such patients to choose toric IOLs.

Clinical applications of anterior segment swept-source optical coherence tomography: A systematic review

Optical coherence tomography (OCT) is a non-invasive method that provides the opportunity to examine tissues by taking cross-sectional images. OCT is increasingly being used to evaluate anterior segment (AS) pathologies. Swept-source (SS) OCT allows greater penetration and achieves better visualization of the internal configuration of AS tissues due to the longer wavelength employed and high scan speeds. We reviewed the utilization of AS SS-OCT in various conditions including glaucoma, ocular surface pathologies, iris tumors, refractive surgery, cataract surgery, and scleral diseases. A systematic literature search was carried out on PubMed, Scopus, and Web of Science databases between January 1, 2008, and September 1, 2022 using the following keywords: AS SS-OCT; dry eye and SS-OCT; ocular surface and SS-OCT; cornea and SS-OCT; dystrophy and SS-OCT; glaucoma and SS-OCT; ocular surface tumors and SS-OCT; conjunctival tumors and SS-OCT; refractive surgery and SS-OCT; cataract and SS-OCT; biometry and SS-OCT; sclera and SS-OCT; iris and SS-OCT; ciliary body and SS-OCT; artificial intelligence and SS-OCT. A total of 221 studies were included in this review. Review of the existing literature shows that SS-OCT offers several advantages in the diagnosis of AS diseases. Exclusive features of SS-OCT including rapid scanning, deeper tissue penetration, and better image quality help improve our understanding of various AS pathologies.

Topographic distribution and phenotypic heterogeneity of Schlemm's canal endothelium in human donor eyes

Endothelium phenotype is known to be closely associated with flow shear stress. This study is to determine the topographic distribution of endothelial cells and the phenotype of different quadrants and regions of Schlemm's canal using human donor eyes. This study infers differences in flow dynamics based on cell shape and intracellular structure. The Schlemm's canal from 15 human donor eyes were either perfusion labelled using silver stain or dissected for float labeling with Phalloidin to enable visualization of endothelial cell border and intracellular structure. Data were acquired for endothelial cells from the outer and inner wall of Schlemm's canal and grouped according to quadrant of origin. Measurements included endothelial cell length, width, area, and aspect ratio and compared between quadrants. Endothelial cells are mostly spindle-shape and the cell size on the outer wall are larger and longer than those from the inner wall. Significant differences in endothelial cell size and shape were seen in different quadrants. The endothelial cells have varied shapes and orientations close to large ostia in the outer wall and remarkably long endothelial cells were found in the walls of collector channels. F-actin aggregation was found at all endothelial cell borders, and inside some of the endothelial cytoplasm. The presence of various spindle shapes, significant phenotype heterogeneity and F-actin aggregation of endothelial cells indicates aqueous humor flow likely creates variations in shear stress within Schlemm's canal. Further investigation of the relationship between the phenotype heterogeneity and hydrodynamics of aqueous flow may help us understand the mechanisms of outflow resistance changes in glaucoma.

Evaluation of different OCT systems in quantitative imaging of human Schlemm's canal

We examined the performance of human Schlemm's canal (SC) imaging using different OCT devices: CIRRUS 5000 (840 nm, spectral-domain (SD)-OCT), PLEX Elite 9000 (1060 nm, swept-source (SS)-OCT) and CASIA SS-1000 (1310 nm, SS-OCT), and analyzed potential impact factors on visualization and the quantitative assessment of SC morphology in a pilot study. Ten healthy subjects were imaged using three OCT devices by a single experienced operator on the same day. Each eye underwent two cubic scans by each device, one on nasal and the other on temporal quadrant. The B-scan showing the largest SC was manually selected for processing. Four quantitative metrics, including one morphological metric as cross-sectional area (CSA), and three performance metrics as contrast, continuity, and coverage, were derived from the datasets. Repeated-measures ANOVA was used to investigate the difference between these parameters from the three devices (P < 0.05). We found the CSA measured from CIRRUS was significantly larger than PLEX, followed by CASIA. The contrast was highest in CIRRUS, followed by PLEX and CASIA. The coverage was also higher in CIRRUS as compared to PLEX and CASIA. No significant difference was seen in the continuity from the three devices. In summary, we showed the measurements from the three devices were not interchangeable.

The Relationship Between Age and the Morphology of the Crystalline Lens, Ciliary Muscle, Trabecular Meshwork, and Schlemm's Canal: An in vivo Swept-Source Optical Coherence Tomography Study

Purpose: To evaluate the effects of age on the morphologies of the crystalline lens, ciliary muscle (CM), Schlemm’s canal (SC), and trabecular meshwork (TM) using swept-source optical coherence tomography (SS-OCT).

Methods: Images of the crystalline lens and iridocorneal angle were obtained in healthy participants’ eyes using SS-OCT. Morphological parameters of the crystalline lens, CM, and TM/SC were measured, and the relationship between these parameters and age was evaluated.

Results: A total of 62 healthy participants were enrolled, with an age range of 7–79 years. With adjustments for the effects of axial length and sex, both the nasal and temporal SC cross-sectional areas (CSA) and the cross-sectional area of the CM (CMA), distance from the scleral spur to the inner apex of the ciliary muscle (IA-SS), and nasal SC volume were negatively correlated with age (P ≤ 0.041). Meanwhile, the lens thickness (LT) (P < 0.001) and lens vault (LV) (P < 0.001) were positively correlated with age, and the radius of the curvature of the anterior lens (ALR) was negatively correlated with age (P < 0.001).

Conclusion: Increasing age was associated with a thicker crystalline lens, a steeper anterior lens curvature, an anteriorly located and smaller CM, and a narrower SC.

Clinical Trial Registration:https://register.clinicaltrials.gov/prs/app/action/Select Protocol?sid=S000A3JZ&selectaction=Edit&uid=U00019K7&ts=4&cx=-c5xxp8, identifier [NCT04576884].

Visualization of Anterior Chamber Angle Structures With Scattering- and Polarization-Sensitive Anterior Segment Optical Coherence Tomography

Purpose

The purpose of this study was to compare three optical coherence tomography (OCT) modalities in the observation of anterior chamber angle structures; trabecular meshwork (TM), Schlemm's canal (SC), and band of extracanalicular limbal lamina (BELL).

Methods

Three OCT modalities were used: (1) 2 × 2 Jones-matrix scattering OCT (S-OCT) representing conventional intensity OCT, (2) polarization-diverse S-OCT that was calculated as summation of all elements of the Jones-matrix to eliminate the influence of artifacts caused by sample birefringence, and (3) polarization-sensitive OCT (PS-OCT) to assess depth-resolved phase retardation.

Results

In a total of 97 eyes of 55 subjects, nasal and temporal angles were scanned. The detection rate of TM and BELL was significantly different among modalities; highest with PS-OCT (95.1% and 99.2%), followed by 2 × 2 Jones-matrix S-OCT (71.1% and 88.7%) and polarization-diverse S-OCT (33.2% and 25.0%), indicating the influence of artifacts on 2 × 2 Jones-matrix S-OCT measurements. SC was visible with 2 × 2 Jones-matrix S-OCT, polarization-diverse S-OCT, and PS-OCT in 14.2%, 14.9%, and 0.3% of images, respectively. The intergrader agreement as evaluated with the prevalence-adjusted bias-adjusted κ value was higher with PS-OCT than with other S-OCTs.

Conclusions

Visibility of anterior chamber angle structures was assessed with three OCT modalities. For TM and BELL that are rich in collagen fibers, PS-OCT provides significantly better visibility than S-OCT without the influence of artifacts arising from polarization or birefringence. Visualization of SC was more difficult with any OCT modalities.

Translational Relevance

PS-OCT is a useful tool to investigate the anterior chamber angle structures which are difficult to observe with conventional OCT.

Intraocular Pressure Reduction by Femtosecond Laser Created Trabecular Channels in Perfused Human Anterior Segments

Purpose

This study investigated the initial feasibility of using femtosecond laser trabeculotomy (FLT) to create open channels through the trabecular meshwork into Schlemm's canal to lower intraocular pressure (IOP) in a perfused anterior segment model.

Methods

Human anterior segments (12 eyes) were assigned to either treatment (n = 6) or sham treatment (n = 6) groups. Both groups were perfused until a baseline IOP was recorded upon which a direct FLT treatment or a sham treatment was administered. IOP was recorded before and after the treatment. Spectral domain optical coherence tomography and second harmonic generation imaging we used to investigate the FLT channels.

Results

In the FLT group, there was a significant mean decrease in the IOP of 22% compared with the pre-FLT IOP (7.13 ± 2.95 mm Hg to 5.34 ± 1.62 mm Hg; P < 0.05). In the control group, the post-sham IOP remained relatively unchanged compared with the pre-sham IOP (6.39 ± 3.69 mm Hg to 6.67 ± 4.12 mm Hg).

Conclusions

The results of this study indicate that FLT treatment can significantly decrease the IOP in a perfusion model and may provide a potential noninvasive treatment option for primary open angle glaucoma.

Translational Relevance

Investigating the use of femtosecond lasers for photodisrupting the trabecular meshwork can lead to a clinically relevant alternative to current glaucoma procedures.

Numerical simulation of the flow of aqueous humor in the Schlemm's canal

Schlemm's canal (SC) is a ring structure responsible for maintaining fluid homeostasis in the anterior chamber of the eye by draining aqueous humor (AH) from the trabecular meshwork (TM) into the collecting channel (CC). Obstruction of the AH flow in this conventional pathway leads to an elevation of intraocular pressure in glaucoma, which is internationally recognized as the most common cause of blindness. Although there are obvious morphological differences between patients and healthy individuals, the AH drainage capacity of SC with specific parameters is difficult to quantitatively evaluate due to the limitations of analyses or experimental technologies. In this paper, the AH flow dynamic features under various SC morphological parameters are studied by numerical simulations of 3D models. The axis length of the SC cross-section and the level of openness are chosen as the main morphological factors according to the clinical data. The flow features, including the velocity, streamline and wall shear stress, are analyzed. This study aimed not only to explore the feasibility of 3D numerical modeling in evaluating the SC drainage capacity, but also to reveal the relationship between SC morphological parameters and the dynamic features of AH drainage.

Development and Evaluation of the Prognostic Nomogram to Predict Refractive Error in Patients With Primary Angle-Closure Glaucoma Who Underwent Cataract Surgery Combined With Goniosynechialysis

Objective: To evaluate the accuracy of different intraocular lens (IOL) power calculation formulas and develop prognostic nomograms to predict the risk of postoperative refractive error in primary angle-closure glaucoma (PACG) patients. Methods: A total of 111 eyes with PACG underwent goniosynechialysis combined with phacoemulsification and IOL implantation were included. SRK/T, Barrett II, Hoffer Q, and Kane formulas were used to predict postoperative refraction. Prediction error (PE) and absolute predictive error (APE) produced by the four formulas were calculated and compared. An APE >0.50 D was defined as the event. Binary logistic regression analysis and prognostic nomogram models were conducted to investigate reliable predictors associated with postoperative refraction. Results: The Kane (-0.06 D) and Barrett II (-0.07 D) formulas had mean prediction error close to zero (p = 0.44, p = 0.41, respectively). The Hoffer Q and SRK/T produced significantly myopic outcomes (p = 0.003, p = 0.013, respectively). The percentage of eyes within ± 0.5 D was 49.5% (55/111), 44.1% (49/111), 43.2% (48/111), and 49.5% (54/111), for the Kane, Barrett II, Hoffer Q, and SRK/T formula, respectively. Nomogram showed that AL had the greatest impact on the refractive outcomes, indicating a shorter preoperative AL is associated with a greater probability of refractive error event. The area under the receiver operator curve (AUC) of the nomogram for the Kane, Barrett II, Hoffer Q, and SRK/T was 0.690, 0.701, 0.708, and 0.676, respectively. Conclusions: The Kane and Barrett II formulas were comparable, and they outperformed Hoffer Q and SRK/T in the total eyes with PACG receiving cataract surgery combined with goniosynechialysis. The developed nomogram models can effectively predict the occurrence of postoperative refractive error events.

Effect of aging on heat transfer, fluid flow and drug transport in anterior human eye: A computational study

There are a lot of geometrical and morphological changes that happen in the human eye with age. Primary open-angle glaucoma, which is caused by the increase in intraocular pressure inside the anterior chamber of the eye is also associated with the physiological aging of the eye. Therefore, it is crucial to understand the effects of aging on drug delivery in the human eye when applied topically. Consequently, a numerical model of topical drug delivery for an aging human eye has been developed using commercial software COMSOL Multiphysics in the current study. Three different age groups (young, middle and old) have been considered and the changes in geometrical and tissue properties of different domains of the eye with age have been included in the numerical model. The effect of aging on heat transfer, aqueous humor flow, intraocular pressure and drug concentration in different domains and orientations of the eye have been investigated. Additionally, an attempt has been made to predict the best class of anti-glaucomatic treatment in silico that should be preferred to treat primary open-angle glaucoma effectively. Results illustrate that there is a decrease in the average corneal temperature and an increase in the temperature deviation across the cornea with age. Further, there is a decrease in the aqueous humor flow magnitude in the anterior chamber of the eye and an increase in intraocular pressure in the anterior chamber of older age groups, which leads to primary open-angle glaucoma. The reduced aqueous humor flow leads to increased drug concentration in the anterior chamber as well as iris and reduced drug concentration in the trabecular mesh of the older age groups, thereby affecting the treatment efficacy. Additionally, our simulated results demonstrate that anti-glaucomatic treatments should be more focused on treating the trabecular mesh rather than the ciliary body of the eye.

Intraocular lens power calculation in the elderly population using the Kane formula in comparison with existing methods

PURPOSE

To assess the accuracy of the Kane formula for intraocualr lens (IOL) power calculation in comparison with established formulas in the elderly population.

SETTING

Shiley Eye Institute, University of California San Diego, USA.

DESIGN

Retrospective cohort.

METHODS

Retrospective data from 90 patients (90 eyes) aged 75 years or older who underwent uneventful cataract surgery with SN60WF intraocular lens (IOL) implantation were evaluated. The first operated eyes of patients with final corrected distance visual acuity 20/40 or better and axial length 22 to 26 mm were included. Prediction errors were calculated for Barrett Universal (BU) II, Haigis, Hoffer Q, Holladay 1, Kane, and SRK/T formulas. A subgroup analysis based on age (75-84 and ≥85 years old) was performed.

RESULTS

Use of both BUII and Kane formulas resulted in the highest percentage of eyes with prediction errors within ±0.50 diopters (D) (72% each) and significantly higher than Hoffer Q, Holladay 1, and SRK/T (P = .001). Rates of predictability within ±0.25 D and ±1.00 D were 31% to 38% and 87% to 92%, respectively, with no significant differences between formulas. No statistically significant difference was seen between formulas in the median absolute error. These tendencies remained consistent in both age groups when analyzed separately. Subgroup analysis showed better predictability of all formulas in the younger age group.

CONCLUSIONS

To the authors' knowledge, this is the first study evaluating the Kane formula exclusively in the elderly population. The Kane formula was found to be of equal accuracy to the BUII and superior to the Hoffer Q, Holladay 1, and SRK/T formulas. Very elderly patients might have reduced refractive precision using all formulas.

Real-world efficacy of the Hydrus microstent in Black and Afro-Latinx patients with glaucoma: a retrospective study

Purpose:

The purpose was to determine the real-world efficacy of phacoemulsification cataract surgery and Hydrus microstent in Black and Afro-Latinx patients with glaucoma.

Methods:

A retrospective noncomparative single-center study of 76 Black and Afro-Latinx patients with glaucoma who underwent phacoemulsification cataract surgery and Hydrus microstent placement for treatment of glaucoma at single practice. Investigated parameters were intraocular pressure (IOP), number of medications, mean deviation on visual field test, and visual acuity. Patients were also subgrouped into mild, moderate, and advance glaucoma for further analysis.

Results:

We reviewed a total of 76 patients who had 6 months of follow up in the study. The mean number of medications decreased significantly from 2.6 ± 1.5 preoperatively to 0.72 ± 1.4 in 6 months (p < 0.0010), while IOP decreased from 14.7 ± 3.7 to 13.9 ± 4.3 (p = 0.25). At 6 months, 55 patients (74%) of all patients were medication free (n = 27, 84.4% mild glaucoma; n = 17, 70.8% moderate glaucoma; n = 10, 50% advance glaucoma). There was significant improvement in visual acuity (p < 0.00010) and stabilization of mean deviation on visual field test (baseline −9.2; 6 months −9.1; p = 0.22). The most common adverse effect was a transient IOP spike and transient corneal edema (n = 6, 7.9%; n = 6, 7.9%, respectively) with spontaneous resolution in all cases. No sight-threatening complications were reported at 6 months.

Conclusion/clinical relevance:

This 6-month retrospective study demonstrated the efficacy of phacoemulsification cataract surgery and Hydrus microstent in reducing the medication burden while maintaining lower IOP in Black and Afro-Latinx patients with glaucoma.

Real World Outcomes of Kahook Dual Blade Goniotomy in Black and Afro-Latinx Adult Patients with Glaucoma: A 6-Month Retrospective Study

INTRODUCTION

To determine the efficacy and safety of Kahook Dual Blade (KDB) goniotomy alone or combined with phacoemulsification cataract surgery to lower intraocular pressure and medication burden in Black and Afro-Latinx patients with open angle glaucoma (OAG).

MATERIALS AND METHOD

A retrospective, single center case series of patients with OAG who were managed with medications and underwent phacoemulsification combined with goniotomy (PE + KDB) using Kahook Dual Blade or goniotomy alone (KDB alone) in pseudophakic patients. Indications for glaucoma surgery included reduction of intraocular pressure (IOP) and reduction of medication burden. Our study parameters included pre- and postoperative information on IOP, the use of IOP-lowering medications, visual field, and adverse events through 6 months of follow-up.

RESULTS

Among all 63 eyes of 63 patients undergoing surgery, Kahook goniotomy with or without phacoemulsification, mean IOP was significantly reduced from 17.4 mmHg at baseline to 14.0 mmHg at month 6 (P = 0.0012), a 19.5% reduction (KDB alone -26.4%, PE + KDB -16.6%). The mean number of topical IOP-lowering medications was reduced from 2.6 at baseline to 1.6 ± 0.3 at month 6 (P = 0.0012), a 38.5% reduction (Kahook alone -10.7%, PE + Kahook -48.0%). Mean visual fields were stable in the PE + KDB group and progressed in the KDB alone group. Postoperative adverse events were mild and included transient hyphema, IOP spikes, posterior capsule opacification, tearing, glare and mild pain.

CONCLUSION

Phacoemulsification combined with Kahook dual blade goniotomy significantly lowers both IOP and medication burden in Black and Afro-Latinx patients with open angle glaucoma. In pseudophakic patients with advanced glaucoma medication burden is not significantly reduced and visual field progression occurred. Adverse events were not sight-threatening and self limited.

Morphological features of anterior segment: factors influencing intraocular pressure after cataract surgery in nanophthalmos

Purpose

To investigate the anterior segment in nanophthalmic eyes and their association with intraocular pressure after cataract surgery.

Methods

Thirty-two nanophthalmic eyes (axial length [AL] < 18.5 mm) in 18 patients and 35 normal eyes (21 ≤ AL ≤ 24.5 mm) in 35 controls who had undergone uneventful cataract surgery were included. Swept-source optical coherence tomography was used to compare the anterior segment structures between the two groups. The associations between the anterior segment characteristics of nanophthalmic eyes and postoperative intraocular pressure (IOP) were also investigated.

Results

The IOP-lowering effect of cataract surgery was remarkably insufficient in nanophthalmic eyes. Peripheral anterior synechiae (PAS) were observed in 56% (18/32) of nanophthalmic eyes, and a characteristic boomerang-shaped iris was observed in 28% (9/32). The anterior surface of the iris seemed “smoother” in nanophthalmic eyes than in normal eyes. Schlemm’s canal (SC) diameter, SC area, trabecular meshwork (TM) thickness, TM width, and TM area were generally smaller in the nanophthalmic eyes. Younger age, higher preoperative IOP, broader PAS, and smaller SC area were main contributors to higher postoperative IOP. AL and SC diameter may also be of great importance in IOP prediction in patients without glaucoma surgery and PAS.

Conclusions

The morphological features of the anterior segment in nanophthalmic eyes are significantly different from those of normal eyes. Influencing factors such as age, AL, preoperative IOP, extent of PAS, SC and TM size could all be prognostic for IOP after cataract surgery in nanophthalmic eyes.

Trial registration

ClinicalTrails.gov, Trial registration number: NCT02182921, Registered 8 July 2014.

Aqueous outflow imaging techniques and what they tell us about intraocular pressure regulation

Recent advances in the medical and surgical management of open-angle glaucoma have increased the number of treatment options available. Several new intraocular pressure (IOP)-lowering treatments target the conventional aqueous outflow (AO) system. However, success rates are variable and outcomes in individual patients are often difficult to predict. Variable treatment responses remain unexplained and highlight deficiencies in our current understanding of AO regulation and IOP homeostasis. Imaging is often relied upon to confirm diagnoses and monitor treatment responses in other ocular and systemic pathologies. As yet no suitable AO imaging tool has been developed to fulfil this role in glaucoma. A variety of imaging techniques have been used to study the AO tracts of humans and animals in ex vivo and in vivo eyes. In this review, results from novel imaging techniques that assess aqueous drainage through the episcleral venous system are considered and we argue these provide new insights into AO regulation. We suggest that the ability to objectively measure AO responses to interventions would be a significant clinical advance, and we have demonstrated that this can be achieved with direct visualisation of aqueous drainage. We predict that the evolution of AO imaging technology will continue to reveal critical components of AO and IOP regulation, and that personalised IOP-lowering treatment in glaucoma care may well become a reality in the near future.

Tissue-Engineered Models for Glaucoma Research

Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and health-related impact of glaucoma-related morbidity worldwide, the surgical and pharmacological management of glaucoma is still limited to maintaining IOP within a normal range. This is in large part because the underlying molecular and biophysical mechanisms by which glaucomatous changes occur are still unclear. In the present review article, we describe current tissue-engineered models of the intraocular space that aim to advance the state of glaucoma research. Specifically, we critically evaluate and compare both 2D and 3D-culture models of the trabecular meshwork and nerve fiber layer, both of which are key players in glaucoma pathophysiology. Finally, we point out the need for novel organ-on-a-chip models of glaucoma that functionally integrate currently available 3D models of the retina and the trabecular outflow pathway.

Progress in the basic and clinical research on the Schlemm's canal

Glaucoma is a leading cause of irreversible blindness in the world. Intraocular pressure (IOP) plays a key role in glaucoma development and progression. Schlemm's canal (SC), an important structure of the anterior chamber angle, regulates the flow of aqueous humor and maintains IOP. Because of its special function of aqueous outflow, the SC has been intensive investigated recently. Several characteristics of SC in anatomy, physiology and pathophysiology have been revealed. Compare to normal, glaucomatous SC cells are more sensitive to substrate stiffness, have higher stiffness and and lower porosity leading to higher outflow resistance. And SC collapse caused by acute IOP increase is partially or totally reversal. With advanced inspection techniques, high-quality images of the SC can be obtained in vivo, which facilitates SC quantitative measurements clinically and allows us to investigate a new therapy paradigm for glaucoma. In this review, we summarize the basic and clinical research that focused on mechanisms of aqueous outflow resistance and SC changes in physiological, pathological, and post-treatment states.

Evaluation of the Relationship Between Age and Trabecular Meshwork Height to Predict the Risk of Glaucoma

This study evaluated age-related trabecular meshwork (TM) height variations in the eyes of adults in different age groups. We hypothesised that a reduction in TM occurs with increasing age. This retrospective, cross-sectional, observational study was conducted at Yonsei University Gangnam Severance Hospital between January 2015 and June 2019. We randomly included 250 eyes of 125 patients who underwent anterior segment optical coherence tomography (AS-OCT). The distance from the scleral spur to Schwalbe's line in patients with normal open anterior chamber angle was measured using AS-OCT. Results were stratified based on patients' age group-≤40, 41-50, 51-60, 61-70, 71-80, and 81-92 years. Thereafter, the results were compared among the age groups. The mean TM height of the patients was 770.929 ± 76.776 μm. TM height was 853.188 ± 94.117 μm in patients aged ≤40 years; it was 815.309 ± 75.723, 798.115 ± 66.040, 770.942 ± 52.774, 726.716 ± 63.979, and 715.968 ± 63.403 μm in patients aged 41-50, 51-60, 61-70, 71-80, and 81-92 years, respectively. The TM height tended to decrease with increasing age (P < 0.001). TM height was significantly shorter in older patients than in younger ones. Therefore, TM height may change with age and may contribute to increased glaucoma risk and prevalence.

In Vivo Imaging of Schlemm's Canal and Limbal Vascular Network in Mouse Using Visible-Light OCT

Purpose

To validate the ability of visible-light optical coherence tomography (vis-OCT) in imaging the full Schlemm's canal (SC) and its surrounding limbal vascular network in mice in vivo through a compound circumlimbal scan.

Methods

We developed an anterior segment vis-OCT system and a compound circumlimbal scanning method, which montages eight rotated raster scans. We calibrated the circumlimbal scan geometry using a three-dimensional printed phantom eyeball before imaging wild-type C57BL/6J mice. We measured SC size by segmenting SC cross sections from vis-OCT B-scan images and imaged the limbal microvascular network using vis-OCT angiography (vis-OCTA). To introduce changes in SC size, we used a manometer to adjust the intraocular pressure (IOP) to different levels. To create additional optical scattering contrast to enhance SC imaging, we surgically increased the episcleral venous pressure (EVP) and caused blood reflux into SC.

Results

Using the compound circumlimbal scan, our anterior segment vis-OCT noninvasively imaged the full SC and limbal microvascular network in mouse for the first time. We observed an average 123% increase in SC volume when we decreased the IOP by 10 mm Hg from the baseline IOP of 7 to 10 mm Hg and an average 72% decrease in SC volume when the IOP level was elevated by 10 mm Hg from the baseline IOP. We also observed location-dependent SC size responses to IOP changes. Blood reflux caused by increased EVP enabled vis-OCTA to directly visualize SC, which matched well with the segmented SC.

Conclusions

Vis-OCT and vis-OCTA can accurately image the entire SC and limbal microvascular network in vivo using the compound circumlimbal scan. Vis-OCT is also able to quantitatively measure SC responses to changing IOP levels.

Age as a risk factor for steroid-induced ocular hypertension in the non-paediatric population

BACKGROUND/AIMS

To evaluate the age-related risk of steroid-induced ocular hypertension by analysing intraocular pressure (IOP) changes after intravitreal dexamethasone (DEX, Ozurdex) implant injection.

METHODS

A retrospective observational study was conducted among patients (n=455; 570 eyes) who had received DEX injection. IOP was measured prior to injection and after 1 week and 1, 2, 3, 6 and 12 months. Results were divided into seven categories based on patient age: 16-30, 31-40, 41-50, 51-60, 61-70, 71-80 and 81-90 years. The IOP elevation rate was compared among the groups.

RESULTS

The IOP elevation rate was 42.9% in patients aged ≤30 years (35.3%, 28.3%, 14.9%, 12.2%, 8.4% and 9.1% in the 31-40, 41-50, 51-60, 61-70, 71-80 and 81-90 groups, respectively). Regardless of how IOP was measured, there was an increasing trend in the incidence of IOP elevation with decreasing age. Furthermore, there was a significant stepwise increase in the OR with decreasing age groups. After the 51-60 group was set as the reference point, the ORs (95% CIs) were 5.048 (1.436 to 17.747), 3.671 (1.101 to 12.238), 2.538 (1.043 to 6.178), 0.947 (0.431 to 2.078), 0.713 (0.312 to 1.626) and 0.646 (0.137 to 3.048) in the ≤30, 31-40, 41-50, 61-70, 71-80 and 81-90 groups, respectively.

CONCLUSION

The rate of adverse elevations in IOP after steroid use was significantly lower in older patients than in younger patients. Therefore, caution is required when prescribing steroids to younger patients (<51 years).

The 360° circumferential opening of Schlemm's canal in normal individuals detected by enhanced depth imaging optical coherence tomography

We aimed to observe the opening status and morphological parameters of Schlemm's canal (SC) in normal eyes using enhanced depth imaging optical coherence tomography (EDI-OCT).Consecutive EDI-OCT scans were used to examine the right eye of 20 normal individuals. EDI-OCT was performed clockwise for 8 regions (at the 12:00, 1:30, 3:00, 4:30, 6:00, 7:30, 9:00 and 10:30 o'clock positions). Image processing and analysis in java software was used to measure the area, perimeter, and diameter of SC. Twenty-one serial scans of each region were evaluated and a total of 168 images were included in the analyses of each eye.The SC was detected in 100.0% of the sections. The distribution of individual measurements of SC was highly variable. The mean values of SC size significantly differed among the different clock-face positions. The mean values of the area, perimeter, and diameter of SC in the 9:00 o'clock position were the lowest, and those at the 7:30 o'clock position were the highest (P < .05). There was no obvious association between intraocular pressure and SC size at any clock position.Although SC tends to open circumferentially in normal individuals, the distribution of individual measurements is highly variable. Morphological manifestation of SC measured by EDI-OCT is a useful way to evaluate the circumferential opening status of SC.

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

OBJECTIVES

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).

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Accuracy of IOL power calculations in the very elderly

Background/objectives

To analyze the refractive predictability and outcomes of cataract surgery in the very elderly (≥85 years old).

Subjects/methods

A retrospective case-series performed at the Shiley Eye Institute, University of California San Diego, USA. Electronically pulled data of 2444 surgeries revealed 147 surgeries on 133 very elderly patients. Chart review was conducted for all very elderly and corresponding control patients (75–84 years old). The first operated eyes of patients with final best-corrected visual acuity ≥20/40, axial length (AL) 22–26 mm, and implanted SN60WF IOL were included. Patients with ocular comorbidities and/or intra- or post-operative complications were excluded. Prediction errors of refractive outcome and percentage of eyes within ±0.50D and ±1.00D were compared between the groups for the Holladay 1 and Barrett Universal II (Barrett) formulas. Logistic regression analysis for achievement of ±1.00D was conducted.

Results

Final analysis included 90 eyes (n = 44, very elderly, n = 46, control patients). Median absolute refractive error (MedAE) with Holladay 1, but not Barrett formula, was significantly higher in the older group (p = 0.02 and p = 0.07, respectively). The MedAE in the older group was lower using the Barrett compared to Holladay 1 (p = 0.02). Fewer older patients than younger patients achieved refraction within ±0.50D and ±1.00D from goal, using the Holladay 1 (p = 0.049 and p = 0.002 respectively). Logistic regression analysis supported the relationship between Holladay 1 predictive refractive error of >1.00D and patient’s age (p = 0.046).

Conclusions

Very elderly patients undergoing cataract surgery may be prone to reduced refractive precision, particularly with utilization of the Holladay 1 formula.

Measuring changes in Schlemm's canal and trabecular meshwork in different accommodation states in myopia children: an observational study

PURPOSE

The aim of the study was to evaluate changes in size of Schlemm's canal (SC) and trabecular meshwork(TM) in response to accommodation stimuli and cycloplegia states in myopia children.

METHODS

In total, 34 children were enroled in this study. A -6.0 D accommodation stimulus was achieved by looking at an optotype through a mirror. Cycloplegia state was induced with 1% tropicamide. Two states were confirmed by measuring the central lens thickness (CLT), anterior chamber depth and pupil diameter. The size of SC and TM was measured using swept-source optical coherence tomography. The association between changes in SC size and CLT was analysed.

RESULTS

Compared with that in the relaxation state, SC size increased significantly under -6.0 D accommodation stimuli. SC area (SCA) increased from 6371 ± 2517 μm² to 7824 ± 2727 μm², SC length (SCL) from 249 ± 10 μm to 295 ± 12 μm and SC width (SCW) from 27 ± 9 μm to 31 ± 8 μm. Under the cycloplegia state, SCA decreased to 5009 ± 2028 μm²; SCL to 212 ± 14 μm, and SCW to 22 ± 5 μm. Changes in SCA (r = 0.35, P = 0.0007), SCL (r = 0.251, P = 0.0172) and SCW (r = 0.253, P = 0.016) were significantly correlated with changes in CLT. TM size was not significantly altered compared to that in the relaxation state. TM length (TML) increased from 562 ± 45 μm to 587 ± 47 μm after exposure to -6.0 D accommodation stimulus.

CONCLUSION

SC size enlarged in response to -6.0 D accommodation stimuli and shrunk under cycloplegia. TM length increased under the accommodation stimulus state.

Glaucoma - Next Generation Therapeutics: Impossible to Possible

The future of next generation therapeutics for glaucoma is strong. The recent approval of two novel intraocular pressure (IOP)-lowering drugs with distinct mechanisms of action is the first in over 20 years. However, these are still being administered as topical drops. Efforts are underway to increase patient compliance and greater therapeutic benefits with the development of sustained delivery technologies. Furthermore, innovations from biologics- and gene therapy-based therapeutics are being developed in the context of disease modification, which are expected to lead to more permanent therapies for patients. Neuroprotection, including the preservation of retinal ganglion cells (RGCs) and optic nerve is another area that is actively being explored for therapeutic options. With improvements in imaging technologies and determination of new surrogate clinical endpoints, the therapeutic potential for translation of neuroprotectants is coming close to clinical realization. This review summarizes the aforementioned topics and other related aspects.