Assessment of Circumferential Angle Closure with Swept-Source Optical Coherence Tomography: a Community Based Study

Anterior chamber morphological and refractive outcomes following phacoemulsification in pseudoexfoliative eyes: A case-control study

PURPOSE

To compare changes in angle morphology, anterior chamber depth (ACD) and refractive prediction error (PE) after phacoemulsification between pseudoexfoliative (PEX) and non-PEX eyes.

METHODS

Prospective case-control study of eyes submitted to cataract surgery. Biometric data and angle parameters - Anterior Chamber Angle (ACA), Angle Opening Distance (AOD), Scleral Spur Angles (SSA) and Trabecular Iris Space Area (TISA) - were measured preoperatively and 1-month postoperatively through swept-source anterior segment optical coherence tomography. Postoperative refractive prediction error (PE) was calculated using an optimized A-constant and the Kane formula.

RESULTS

Sixty eyes (30 PEX and 30 non-PEX) of 60 patients were included. Preoperative angle analysis revealed a lower ACA, AOD, SSA and TISA in PEX group (p < 0.05), without biometric differences (p > 0.05). A tendency for a higher magnitude of morphometric angle changes in PEX eyes was observed, with a superior increase of SSA at 500 µm (0°) and TISA at 750 µm (0°) (p = 0.030 and p = 0.041, respectively). The anterior chamber deepened in both groups (p = 0.01), with arithmetic and percentile change being higher in PEX group (p = 0.017 and p = 0.047, respectively). A significant PE hyperopic shift was observed (p = 0.035) only in PEX group.

CONCLUSIONS

Pseudoexfoliative eyes with cataract have narrower angles, revealing a tendency for higher angle opening after surgery, along with an increased ACD deepening compared to non-PEX eyes, which may be explained by PEX-associated zonular laxity. Moreover, a significant hyperopic shift was observed in PEX eyes, a relevant fact to take into consideration when selecting intraocular lens power.

Novel hyperparallel optical coherence tomography for angle closure assessment: comparison with swept-source OCT and gonioscopy

AIM

To evaluate reproducibility and agreement of angle closure assessment by a novel hyperparallel optical coherence tomography (OCT) system (HP-OCT, Cylite Optics, Melbourne, Australia), in comparison with swept-source OCT (SS-OCT, CASIA SS-1000, Tomey Corporation, Nagoya, Japan) and gonioscopy.

METHODS

Cross-sectional study. Phakic subjects >40 years, with no relevant ophthalmic history were consecutively recruited from the glaucoma clinic. Subjects underwent same-day evaluation with HP-OCT, SS-OCT and gonioscopy. The primary outcome was the presence of angle closure, defined as iridotrabecular contact in HP-OCT and SS-OCT images at 0°-180° meridional and as non-visibility of the posterior trabecular meshwork (TM) by gonioscopy. Visibility of TM was also assessed (secondary outcome). Intra and interdevice agreement analysis (Gwet AC1) and logistic regression analysis were performed for primary and secondary outcomes, respectively.

RESULTS

154 sectors from horizontal scans of 77 subjects were analysed. The reproducibility of angle closure assessment by HP-OCT was excellent (AC1 of 0.95 for temporal angle and 1.00 for nasal). Agreement for angle closure detection was very good between HP-OCT and SS-OCT (AC1 of 0.88 for temporal and 0.81 for nasal angle) and good between HP-OCT and gonioscopy (AC1 of 0.71 for temporal and 0.78 for nasal angle). TM was identifiable in 64.4% (94/146) of unprocessed HP-OCT images (both open and closed angles), however not visible in any of the SS-OCT unprocessed images.

CONCLUSIONS

HP-OCT showed excellent reproducibility for angle closure assessment and good agreement with SS-OCT and gonioscopy. HP-OCT technology also provides a unique capability to visualise regions around TM and Schlemm's canal, opening new avenues for clinical research of distal outflow pathways.

Diagnostic criteria of anterior segment swept-source optical coherence tomography to detect gonioscopic angle closure

AIMS

To compare the diagnostic performance of 360° anterior segment optical coherence tomography assessment by applying normative percentile cut-offs versus iris trabecular contact (ITC) for detecting gonioscopic angle closure.

METHODS

In this multicentre study, 394 healthy individuals were included in the normative dataset to derive the age-specific and angle location-specific normative percentiles of angle open distance (AOD500) and trabecular iris space area (TISA500) which were measured every 10° for 360°. 119 healthy participants and 170 patients with angle closure by gonioscopy were included in the test dataset to investigate the diagnostic performance of three sets of criteria for detection of gonioscopic angle closure: (1) the 10th and (2) the 5th percentiles of AOD500/TISA500, and (3) ITC (ie, AOD500/TISA500=0 mm/mm2). The number of angle locations with angle closure defined by each set of the criteria for each eye was used to generate the receiver operating characteristic (ROC) curve for the discrimination between gonioscopic angle closure and open angle.

RESULTS

Of the three sets of diagnostic criteria examined, the area under the ROC curve was greatest for the 10th percentile of AOD500 (0.933), whereas the ITC criterion AOD500=0 mm showed the smallest area under the ROC (0.852) and the difference was statistically significant with or without adjusting for age and axial length (p<0.001). The criterion ≥90° of AOD500 below the 10th percentile attained the best sensitivity 87.6% and specificity 84.9% combination for detecting gonioscopic angle closure.

CONCLUSIONS

Applying the normative percentiles of angle measurements yielded a higher diagnostic performance than ITC for detecting angle closure on gonioscopy.

Investigating the determinants of iridolenticular contact area: a novel parameter for angle closure

BACKGROUND/AIMS

To identify ocular determinants of iridolenticular contact area (ILCA), a recently introduced swept-source optical coherence tomography (SSOCT) derived parameter, and assess the association between ILCA and angle closure.

METHODS

In this population-based cross-sectional study, right eyes of 464 subjects underwent SSOCT (SS-1000, CASIA, Tomey Corporation, Nagoya, Japan) imaging in the dark. Eight out of 128 cross-sectional images (evenly spaced 22.5° apart) were selected for analysis. Matlab (Matworks, Massachusetts, USA) was used to measure ILCA, defined as the circumferential extent of contact area between the pigmented iris epithelium and anterior lens surface. Gonioscopic angle closure (GAC) was defined as non-visibility of the posterior trabecular meshwork in two or more angle quadrants.

RESULTS

The mean age of subjects was 62±6.6 years, with the majority being female (65.5%). 143/464 subjects (28.6%) had GAC. In multivariable linear regression analysis, ILCA was significantly associated with anterior chamber width (β=1.03, p=0.003), pupillary diameter (β=-1.9, p<0.001) and iris curvature (β=-17.35, p<0.001). ILCA was smaller in eyes with GAC compared with those with open angles (4.28±1.6 mm2 vs 6.02±2.71 mm2, p<0.001). ILCA was independently associated with GAC (β=-0.03, p<0.001), iridotrabecular contact index (β=-6.82, p<0.001) or angle opening distance (β=0.02, p<0.001) after adjusting for covariates. The diagnostic performance of ILCA for detecting GAC was acceptable (AUC=0.69).

CONCLUSIONS

ILCA is a significant predictor of angle closure independent of other biometric factors and may reflect unique anatomical information associated with pupillary block. ILCA represents a novel biometric risk factor in eyes with angle closure.

Advances in swept-source optical coherence tomography and optical coherence tomography angiography

Background

The fast development of swept-source optical coherence tomography (SS-OCT) and swept-source optical coherence tomography angiography (SS-OCTA) enables both anterior and posterior imaging of the eye. These techniques have evolved from a research tool to an essential clinical imaging modality.

Main text

The longer wavelength and faster speed of SS-OCT and SS-OCTA facilitate better visualization of structure and vasculature below pigmented tissue with a larger field of view of the posterior segment and 360-degree visualization of the anterior segment. In the past 10 years, algorithms dealing with OCT and OCTA data also vastly improved the image quality and enabled the automated quantification of OCT- and OCTA-derived metrics. This technology has enriched our current understanding of healthy and diseased eyes. Even though the high cost of the systems currently limited the widespread use of SS-OCT and SS-OCTA at the first beginning, the gap between research and clinic practice got obviously shortened in the past few years.

Conclusions

SS-OCT and SS-OCTA will continue to evolve rapidly, contributing to a paradigm shift toward more widespread adoption of new imaging technology in clinical practice.

Generalisability and performance of an OCT-based deep learning classifier for community-based and hospital-based detection of gonioscopic angle closure

PURPOSE

To assess the generalisability and performance of a deep learning classifier for automated detection of gonioscopic angle closure in anterior segment optical coherence tomography (AS-OCT) images.

METHODS

A convolutional neural network (CNN) model developed using data from the Chinese American Eye Study (CHES) was used to detect gonioscopic angle closure in AS-OCT images with reference gonioscopy grades provided by trained ophthalmologists. Independent test data were derived from the population-based CHES, a community-based clinic in Singapore, and a hospital-based clinic at the University of Southern California (USC). Classifier performance was evaluated with receiver operating characteristic curve and area under the receiver operating characteristic curve (AUC) metrics. Interexaminer agreement between the classifier and two human examiners at USC was calculated using Cohen's kappa coefficients.

RESULTS

The classifier was tested using 640 images (311 open and 329 closed) from 127 Chinese Americans, 10 165 images (9595 open and 570 closed) from 1318 predominantly Chinese Singaporeans and 300 images (234 open and 66 closed) from 40 multiethnic USC patients. The classifier achieved similar performance in the CHES (AUC=0.917), Singapore (AUC=0.894) and USC (AUC=0.922) cohorts. Standardising the distribution of gonioscopy grades across cohorts produced similar AUC metrics (range 0.890-0.932). The agreement between the CNN classifier and two human examiners (Ҡ=0.700 and 0.704) approximated interexaminer agreement (Ҡ=0.693) in the USC cohort.

CONCLUSION

An OCT-based deep learning classifier demonstrated consistent performance detecting gonioscopic angle closure across three independent patient populations. This automated method could aid ophthalmologists in the assessment of angle status in diverse patient populations.

Assessment of Iris Trabecular Contact in Eyes with Gonioscopic Angle-Closure

PURPOSE

To investigate the extent of iris trabecular contact (ITC) measured by anterior segment OCT (AS-OCT) and its association with primary angle-closure (PAC) and PAC glaucoma (PACG) in eyes with gonioscopic angle-closure and to determine the diagnostic performance of ITC for detection of gonioscopic angle-closure.

DESIGN

Multicenter, prospective study.

PARTICIPANTS

A total of 119 healthy participants with gonioscopic open-angle and 170 patients with gonioscopic angle-closure (94 with PAC suspect and 76 with PAC/PACG) were included.

METHODS

One eye of each subject was randomly selected for AS-OCT imaging. Angle-opening distance (AOD500) and trabecular iris space area (TISA500) were measured every 10° for 360°. Two criteria of ITC500 were examined: (1) AOD500 = 0 mm and (2) TISA500 = 0 mm². The association between the extent of ITC500 and PAC/PACG in eyes with gonioscopic angle-closure was analyzed with logistic regression analysis.

MAIN OUTCOME MEASURES

Sensitivity and specificity of ITC500 for detection of gonioscopic angle-closure; odds ratio (OR) of PAC/PACG.

RESULTS

The sensitivity of ITC500 ≥ 10° for detection of gonioscopic angle-closure ranged from 82.4% (AOD500 = 0 mm) to 84.7% (TISA500 = 0 mm²), and the specificity was 85.7% (for both AOD500 = 0 mm and TISA500 = 0 mm²). The extent of ITC500 determined by AS-OCT, not cumulative gonioscopy score (i.e., the sum of the modified Shaffer grades over 4 quadrants), was associated with the odds of PAC/PACG in eyes with gonioscopic angle-closure; the odds of PAC/PACG increased by 5% for every 10° increase in ITC500 (OR, 1.051, 95% confidence interval [CI], 1.022-1.080 for AOD500 = 0 mm; OR, 1.049, 95% CI, 1.022-1.078 for TISA500 = 0 mm²). Axial length and anterior chamber depth were not associated with PAC/PACG in eyes with gonioscopic angle-closure (P ≥ 0.574).

CONCLUSIONS

A greater extent of ITC measured by AS-OCT, not angle-closure determined by gonioscopy, was associated with a greater odds of PAC/PACG in eyes with gonioscopic angle-closure.

Assessment of Iridotrabecular Contact and Its Association With Intraocular Pressure After Phacoemulsification in Primary Angle Closure

PURPOSE

To investigate the association between the quantitative assessment of iridotrabecular contact (ITC), measured by swept-source anterior segment optical coherence tomography (SS AS-OCT), and intraocular pressure (IOP) control after phacoemulsification in patients with primary angle closure disease (PACD).

DESIGN

Retrospective, clinical cohort study.

METHODS

Preoperative and postoperative anterior chamber angle parameters were measured using SS AS-OCT. IOP was measured preoperatively and until 6 months postoperatively. Percent IOP reduction and fluctuation after surgery were calculated, and their relationships with SS AS-OCT parameters were assessed by correlation analyses and locally weighted scatterplot smoothing (LOWESS) regression with change-point analysis.

RESULTS

A total of 51 eyes of 51 PACD patients were included. Preoperative ITC index and area (r = 0.626, r = 0.551), as well as changes in ITC index and area (r = 0.632, r = 0.543) after surgery, were significantly correlated with postoperative IOP reduction, after adjusting for age and gender (all P <.001). Higher postoperative ITC index (r = 0.405, P = .005) and ITC area (r = 0.460, P = 0.001) were associated with greater postoperative IOP fluctuations. Change points on LOWESS curves were observed for preoperative ITC index (33.0%) and change in ITC index (27.0%) and percent IOP reductions were significantly correlated with them above (β = 0.386, β = 0.664, all P < .001) but not below the change points.

CONCLUSIONS

Quantitative assessment of circumferential ITC can predict postoperative IOP control after phacoemulsification, and thus it may be used as a reference for determining lens extraction in PACD eyes.

Angle closure extent, anterior segment dimensions and intraocular pressure

AIM

To investigate the association between the extent of iridotrabecular contact and other quantitative anterior segment dimensions measured by swept-source optical coherence tomography (SS-OCT; CASIA SS-1000, Tomey, Nagoya, Japan) with intraocular pressure (IOP).

METHODS

Cross-sectional study. All subjects who were ≥50 years with no history of glaucoma, ocular surgery or trauma, underwent SS-OCT imaging (eight equally spaced radial scans), Goldman applanation tonometry and gonioscopy on the same day. We measured iridotrabecular contact (ITC) index and area, total volume of trabeculo-iris space area and angle opening distance at 500 and 750 from the scleral spur (TISA 500 and 750, AOD 500 and 750, respectively), anterior chamber depth (ACD), volume, area and width, pupil diameter, lens vault and iris volume.Their relationship with IOP (dependent variable) was assessed by locally weighted scatterplot smoothing (Lowess) regression with change-point analysis and generalised additive models adjusted for confounders.

RESULTS

2027 right eyes of mostly Chinese Singaporeans (90%) were analysed. ITC index above a threshold of ~60% (95% CI 34% to 92%) was significantly associated with higher IOP. Independent of the extent of ITC, ACD was also significantly associated with higher IOP below a threshold of 2.5 mm (95% CI 2.33 mm to 2.71 mm). Greater ITC index and shallower ACD had a joint association with IOP. A model including ACD and ITC index was more predictive of IOP than a model considering these variables separately, particularly for women with gonioscopically closed angles (R² 52.7%, p<0.05).

CONCLUSIONS

The extent of angle closure and the ACD below a certain threshold had a significant joint association with IOP. These parameters, as biometrical surrogates of mechanical obstruction of the aqueous outflow, may jointly contribute to elevated IOP, particularly in women with gonioscopic angle closure.

Diagnostic Performance of Deep Learning Classifiers in Measuring Peripheral Anterior Synechia Based on Swept Source Optical Coherence Tomography Images

Purpose

To develop deep learning classifiers and evaluate their diagnostic performance in detecting the static gonioscopic angle closure and peripheral anterior synechia (PAS) based on swept source optical coherence tomography (SS-OCT) images.

Materials and Methods

Subjects were recruited from the Glaucoma Service at Zhongshan Ophthalmic Center of Sun Yat-sun University, Guangzhou, China. Each subject underwent a complete ocular examination, such as gonioscopy and SS-OCT imaging. Two deep learning classifiers, using convolutional neural networks (CNNs), were developed to diagnose the static gonioscopic angle closure and to differentiate appositional from synechial angle closure based on SS-OCT images. Area under the receiver operating characteristic (ROC) curve (AUC) was used as outcome measure to evaluate the diagnostic performance of two deep learning systems.

Results

A total of 439 eyes of 278 Chinese patients, which contained 175 eyes of positive PAS, were recruited to develop diagnostic models. For the diagnosis of static gonioscopic angle closure, the first deep learning classifier achieved an AUC of 0.963 (95% CI, 0.954–0.972) with a sensitivity of 0.929 and a specificity of 0.877. The AUC of the second deep learning classifier distinguishing appositional from synechial angle closure was 0.873 (95% CI, 0.864–0.882) with a sensitivity of 0.846 and a specificity of 0.764.

Conclusion

Deep learning systems based on SS-OCT images showed good diagnostic performance for gonioscopic angle closure and moderate performance in the detection of PAS.

Evaluation of the Diagnostic Performance of Swept-Source Anterior Segment Optical Coherence Tomography in Primary Angle Closure Disease

PURPOSE

To evaluate the diagnostic performance of swept-source anterior segment optical coherence tomography (SS-OCT) in differentiating eyes with primary angle closure disease (PACD) from eyes of control subjects, as well as eyes with PAC and PAC glaucoma (PACG) from eyes with PAC suspect (PACS) disease.

DESIGN

Multicenter cross-sectional study.

METHODS

Chinese patients were classified into control, PACS, and PAC/PACG groups. The area under the receiving operating characteristic curve (AUC) from logistic regression models was used to evaluate discriminating ability. Sensitivity and specificity were calculated, and performance of the models was validated using an independent dataset.

RESULTS

A total of 2928 SS-OCT images from 366 eyes of 260 patients were recruited to develop diagnostic models. The validation dataset included 1176 SS-OCT images from 147 eyes of 143 patients. For distinguishing PACD from control eyes, average anterior chamber depth had the highest AUC (0.94). With a cutoff of 2.2 mm for average anterior chamber depth, the sensitivity and specificity were 90.2% and 85.2% in the training set. For distinguishing PAC/PACG from PACS, a multivariate model had an AUC of 0.83, with sensitivity and specificity of 82.0% and 62.8% in the training set. The validation set confirmed the findings.

CONCLUSIONS

SS-OCT of the anterior segment showed excellent diagnostic performance distinguishing PACD from normal eyes and moderate diagnostic ability distinguishing eyes with PAC/PACG from eyes with PACS. ACD alone may provide a simple and effective way to diagnose PACD from control subjects. As ACD can be obtained using other more available modalities, this has implications for the early diagnosis of PACD.

Diagnostic accuracy of AS-OCT vs gonioscopy for detecting angle closure: a systematic review and meta-analysis

Purpose

This study aims to review the literature that compares the accuracy of Anterior Segment-Optical Coherence Tomography (AS-OCT) against gonioscopy in detecting eyes with angle closure. It is currently unclear how AS-OCT fits into clinical practice for detecting angle closure. This is a systematic review and meta-analysis.

Methods

A literature search was performed on Medline, Embase, Scopus and the Cochrane Central Register of Controlled Trials to identify studies that investigated the diagnostic accuracy of AS-OCT in detecting eyes with angle closure as diagnosed by gonioscopy. Eligible studies included in the analysis met stringent inclusion criteria determining the sensitivity and specificity of AS-OCT.

Results

The initial search identified 727 studies, of which 23 were included in the final analysis. We found substantial variation in the parameters being studied and methodologies. The sensitivity of AS-OCT ranged from 46 to 100% (median 87%). Twenty-one studies identified parameters that showed sensitivity above 80%. The specificity ranged from 55.3 to 100% (median 84%).

Conclusion

AS-OCT demonstrates good sensitivity for detecting angle closure. It may provide an avenue to address high rates of undiagnosed angle closure, such as found in developing Asian countries. However, AS-OCT is not yet able to replace gonioscopy. Clinicians should consider whether the diagnostic accuracy of AS-OCT is acceptable for their specific clinical use before adopting it. More studies are needed to determine the utility of AS-OCT, including longitudinal studies to determine the significance of eyes classified to have closed angles by AS-OCT but open on gonioscopy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00417-021-05271-4.

Diagnostic accuracy of swept source optical coherence tomography classification algorithms for detection of gonioscopic angle closure

PURPOSE

To evaluate the performance of swept source optical coherence tomography (SS-OCT) to detect gonioscopic angle closure using different classification algorithms.

METHODS

This was a cross-sectional study of 2028 subjects without ophthalmic symptoms recruited from a community-based clinic. All subjects underwent gonioscopy and SS-OCT (Casia, Tomey Corporation, Nagoya, Japan) under dark room conditions. For each eye, 8 out of 128 frames (22.5° interval) were selected to measure anterior chamber parameters namely anterior chamber width, depth, area and volume (ACW, ACD, ACA, and ACV), lens vault (LV), iris curvature (IC), iris thickness (IT) from 750 µm and 2000 µm from the scleral spur, iris area and iris volume. Five diagnostic algorithms-stepwise logistic regression, random forest, multivariate adaptive regression splines, recursive partitioning and Naïve Bayes were evaluated for detection of gonioscopic angle closure (defined as ≥2 closed quadrants). The performance of the horizontal frame was compared with that of other meridians.

RESULTS

Data from 1988 subjects, including 143 (7.2%) with gonioscopic angle closure, were available for analysis. They were divided into two groups: training (1391, 70%) and validation (597, 30%). The best algorithm for detecting gonioscopic angle closure was stepwise logistic regression with an area under the curve of 0.91 (95% CI 0.88 to 0.93) using all parameters, and 0.88 (95% CI 0.82 to 0.93) using only ACA, LV and IC of the horizontal meridian scan.

CONCLUSIONS

A stepwise logistic regression model incorporating SS-OCT measurements has a high diagnostic ability to detect gonioscopic angle closure.

Towards 'automated gonioscopy': a deep learning algorithm for 360° angle assessment by swept-source optical coherence tomography

AIMS

To validate a deep learning (DL) algorithm (DLA) for 360° angle assessment on swept-source optical coherence tomography (SS-OCT) (CASIA SS-1000, Tomey Corporation, Nagoya, Japan).

METHODS

This was a reliability analysis from a cross-sectional study. An independent test set of 39 936 SS-OCT scans from 312 phakic subjects (128 SS-OCT meridional scans per eye) was analysed. Participants above 50 years with no previous history of intraocular surgery were consecutively recruited from glaucoma clinics. Indentation gonioscopy and dark room SS-OCT were performed. Gonioscopic angle closure was defined as non-visibility of the posterior trabecular meshwork in ≥180° of the angle. For each subject, all images were analysed by a DL-based network based on the VGG-16 architecture, for gonioscopic angle-closure detection. Area under receiver operating characteristic curves (AUCs) and other diagnostic performance indicators were calculated for the DLA (index test) against gonioscopy (reference standard).

RESULTS

Approximately 80% of the participants were Chinese, and more than half were women (57.4%). The prevalence of gonioscopic angle closure in this hospital-based sample was 20.2%. After analysing a total of 39 936 SS-OCT scans, the AUC of the DLA was 0.85 (95% CI:0.80 to 0.90, with sensitivity of 83% and a specificity of 87%) to classify gonioscopic angle closure with the optimal cut-off value of >35% of circumferential angle closure.

CONCLUSIONS

The DLA exhibited good diagnostic performance for detection of gonioscopic angle closure on 360° SS-OCT scans in a glaucoma clinic setting. Such an algorithm, independent of the identification of the scleral spur, may be the foundation for a non-contact, fast and reproducible 'automated gonioscopy' in future.

Clinical role of swept source optical coherence tomography in anterior segment diseases: a review

PURPOSE

To note the comprehensive role of swept source anterior segment optical coherence tomography (SS-ASOCT) in anterior segment diseases.

METHODS

A systematic literature search was carried out on various medical databases using the keywords, swept source anterior segment optical coherence tomography; SS-ASOCT; Cornea and SS-ASOCT; SS-ASOCT and glaucoma; SS-ASOCT and cataract; SS-ASOCT and biometer; SS-ASOCT and tear film and ocular surface.Original works and novel reports describing the potential role of SS-ASOCT in various anterior segment conditions were included.

RESULTS

After a thorough assessment of literature, it was clear that the SS-ASOCT did provide newer insights into many anterior eye conditions. The rapid scan acquisition, deeper tissue penetration, and higher magnification did enhance many of our understandings, which were previously not possible. In addition, lenticular assessment under complex clinical scenarios with automated values on objective scale has made it a worthy tool with immense future possibilities.

CONCLUSIONS

SS-ASOCT unveiled various anterior segment findings which were of clinical importance.

Objective quantification of lens nuclear opacities using swept-source anterior segment optical coherence tomography

Background/aims

The primary objective is to quantify the lens nuclear opacity using swept-source anterior segment optical coherence tomography (SS-ASOCT) and to evaluate its correlations with Lens Opacities Classification System III (LOCS-III) system and surgical parameters. The secondary objective is to assess the diagnostic performance for hard nuclear cataract.

Methods

This cross-sectional study included 1222 patients eligible for cataract surgery (1222 eyes). The latest SS-ASOCT (CASIA-2) was used to obtain high-resolution lens images, and the average nuclear density (AND) and maximum nuclear density (MND) were measured by a custom ImageJ software. Spearman’s correlations analysis was used to assess associations of AND/MND with LOCS-III nuclear scores, visual acuity and surgical parameters. The subjects were then split randomly (9:1) into the training dataset and validating dataset. Receiver operating characteristic curves and calibration curves were constructed for the classification on hard nuclear cataract.

Results

The AND and MND from SS-ASOCT images were significantly correlated with nuclear colour scores (AND: r=0.716; MND: r=0.660; p<0.001) and nuclear opalescence scores (AND: r=0.712; MND: r=0.655; p<0.001). The AND by SS-ASOCT images had the highest values of Spearman’s r for preoperative corrected distance visual acuity (r=0.3131), total ultrasonic time (r=0.3481) and cumulative dissipated energy (r=0.4265). The nuclear density had good performance in classifying hard nuclear cataract, with area under the curves of 0.859 (0.831–0.886) for AND and 0.796 (0.768–0.823) for MND.

Conclusion

Objective and quantitative evaluation of the lens nuclear density using SS-ASOCT images enable accurate diagnosis of hard nuclear cataract.

Anterior Chamber Angle Assessment Techniques: A Review

Assessment of the anterior chamber angle (ACA) is an essential part of the ophthalmological examination. It is intrinsically related to the diagnosis and treatment of glaucoma and has a role in its prevention. Although slit-lamp gonioscopy is considered the gold-standard technique for ACA evaluation, its poor reproducibility and the long learning curve are well-known shortcomings. Several new imaging techniques for angle evaluation have been developed in the recent years. However, whether these instruments may replace or not gonioscopy in everyday clinical practice remains unclear. This review summarizes the last findings in ACA evaluation, focusing on new instruments and their application to the clinical practice. Special attention will be given to the comparison between these new techniques and traditional slit-lamp gonioscopy. Whereas ultrasound biomicroscopy and anterior segment optical coherence tomography provide quantitative measurements of the anterior segment’s structures, new gonio-photographic systems allow for a qualitative assessment of angle findings, similarly to gonioscopy. Recently developed deep learning algorithms provide an automated classification of angle images, aiding physicians in taking faster and more efficient decisions. Despite new imaging techniques made analysis of the ACA more objective and practical, the ideal method for ACA evaluation has still to be determined.

Non-contact tests for identifying people at risk of primary angle closure glaucoma

BACKGROUND

Primary angle closure glaucoma (PACG) accounts for 50% of glaucoma blindness worldwide. More than three-quarters of individuals with PACG reside in Asia. In these populations, PACG often develops insidiously leading to chronically raised intraocular pressure and optic nerve damage, which is often asymptomatic. Non-contact tests to identify people at risk of angle closure are relatively quick and can be carried out by appropriately trained healthcare professionals or technicians as a triage test. If the test is positive, the person will be referred for further specialist assessment.

OBJECTIVES

To determine the diagnostic accuracy of non-contact tests (limbal anterior chamber depth (LACD) (van Herick test); oblique flashlight test; scanning peripheral anterior chamber depth analyser (SPAC), Scheimpflug photography; anterior segment optical coherence tomography (AS-OCT), for identifying people with an occludable angle.

SEARCH METHODS

We searched the following bibliographic databases 3 October 2019: CENTRAL; MEDLINE; Embase; BIOSIS; OpenGrey; ARIF and clinical trials registries. The searches were limited to remove case reports. There were no date or language restrictions in the searches.

SELECTION CRITERIA

We included prospective and retrospective cross-sectional, cohort and case-control studies conducted in any setting that evaluated the accuracy of one or more index tests for identifying people with an occludable angle compared to a gonioscopic reference standard.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed data extraction and quality assessment using QUADAS2 for each study. For each test, 2 x 2 tables were constructed and sensitivity and specificity were calculated. When four or more studies provided data at fixed thresholds for each test, we fitted a bivariate model using the METADAS macro in SAS to calculate pooled point estimates for sensitivity and specificity. For comparisons between index tests and subgroups, we performed a likelihood ratio test comparing the model with and without the covariate.

MAIN RESULTS

We included 47 studies involving 26,151 participants and analysing data from 23,440. Most studies were conducted in Asia (36, 76.6%). Twenty-seven studies assessed AS-OCT (analysing 15,580 participants), 17 studies LACD (7385 participants), nine studies Scheimpflug photography (1616 participants), six studies SPAC (5239 participants) and five studies evaluated the oblique flashlight test (998 participants). Regarding study quality, 36 of the included studies (76.6%) were judged to have a high risk of bias in at least one domain.The use of a case-control design (13 studies) or inappropriate exclusions (6 studies) raised patient selection concerns in 40.4% of studies and concerns in the index test domain in 59.6% of studies were due to lack of masking or post-hoc determination of optimal thresholds. Among studies that did not use a case-control design, 16 studies (20,599 participants) were conducted in a primary care/community setting and 18 studies (2590 participants) in secondary care settings, of which 15 investigated LACD. Summary estimates were calculated for commonly reported parameters and thresholds for each test; LACD ≤ 25% (16 studies, 7540 eyes): sensitivity 0.83 (95% confidence interval (CI) 0.74, 0.90), specificity 0.88 (95% CI 0.84, 0.92) (moderate-certainty); flashlight (grade1) (5 studies, 1188 eyes): sensitivity 0.51 (95% CI 0.25, 0.76), specificity 0.92 (95% CI 0.70, 0.98) (low-certainty); SPAC (≤ 5 and/or S or P) (4 studies, 4677 eyes): sensitivity 0.83 (95% CI 0.70, 0.91), specificity 0.78 (95% CI 0.70, 0.83) (moderate-certainty); Scheimpflug photography (central ACD) (9 studies, 1698 eyes): sensitivity 0.92 (95% CI 0.84, 0.96), specificity 0.86 (95% CI 0.76, 0.93) (moderate-certainty); AS-OCT (subjective opinion of occludability) (13 studies, 9242 eyes): sensitivity 0.85 (95% CI 0.76, 0.91); specificity 0.71 (95% CI 0.62, 0.78) (moderate-certainty). For comparisons of sensitivity and specificity between index tests we used LACD (≤ 25%) as the reference category. The flashlight test (grade 1 threshold) showed a statistically significant lower sensitivity than LACD (≤ 25%), whereas AS-OCT (subjective judgement) had a statistically significant lower specificity. There were no statistically significant differences for the other index test comparisons. A subgroup analysis was conducted for LACD (≤ 25%), comparing community (7 studies, 14.4% prevalence) vs secondary care (7 studies, 42% prevalence) settings. We found no evidence of a statistically significant difference in test performance according to setting. Performing LACD on 1000 people at risk of angle closure with a prevalence of occludable angles of 10%, LACD would miss about 17 cases out of the 100 with occludable angles and incorrectly classify 108 out of 900 without angle closure.

AUTHORS' CONCLUSIONS

The finding that LACD performed as well as index tests that use sophisticated imaging technologies, confirms the potential for this test for case-detection of occludable angles in high-risk populations. However, methodological issues across studies may have led to our estimates of test accuracy being higher than would be expected in standard clinical practice. There is still a need for high-quality studies to evaluate the performance of non-invasive tests for angle assessment in both community-based and secondary care settings.

Evaluation of meridional scans for angle closure assessment with anterior segment swept-source optical coherence tomography

Background/aims

As swept-source optical coherence tomography (SS-OCT) simultaneously obtains 128 meridional scans, it is important to identify which scans are playing the main role in classifying gonioscopic angle closure to simplify the analysis. We aimed to evaluate the diagnostic performance of every meridional scan in its ability to detect gonioscopic angle closure.

Methods

Observational study with 2027 phakic subjects consecutively recruited from a community polyclinic. Gonioscopy and SS-OCT were performed. Gonioscopic angle closure was defined as non-visibility of the posterior trabecular meshwork in ≥180° of the angle, while SS-OCT was defined as iridotrabecular contact anterior to the scleral spur. The area under the receiver operating characteristic curve (AUC) was calculated to assess the diagnostic performance of each single scan, the sequential anticlockwise cumulative effect of those single scans and different combinations of them.

Results

The AUCs of each scan ranged from 0.73 to 0.82. The single scan at 80°–260° had the highest AUC (0.82, 95% CI 0.79 to 0.84) and performed significantly better than most of the temporonasal scans (from 0° to 52° and from 153° to 179°). The superoinferior scans achieved higher AUCs compared with the temporonasal ones. When assessing the cumulative effect of adding individual scans consecutively, the peak AUC (0.80) was obtained when considering the superoinferior scans closer to 80°–85°, but no further positive cumulative effect was seen when adding the rest of the temporonasal scans of the circumference.

Conclusions

In conclusion, the single SS-OCT scan at 80°–260° had the highest diagnostic performance. Our study suggests that the 360° evaluation may not translate to better clinical utility for detection of gonioscopic angle closure.

Recent advances in anterior chamber angle imaging

Differentiating the two main forms of primary glaucoma (open-angle and closed-angle glaucoma) depends on the correct assessment of the anterior chamber angle (ACA). This assessment will determine the management plan and prognosis for the disease. The standard method of examining the angle has been, for many years, slit-lamp gonioscopy. This method, although clinically still useful, is less robust for patient follow up and clinical research, given its low reproducibility. Several imaging technologies have been developed in recent years to improve the evaluation of the ACA and overcome the shortcomings of gonioscopy. These recent advances include three-dimensional and 360° analysis by Swept-Source OCT (SS-OCT, CASIA, Tomey, Nagoya, Japan), the introduction of deep learning algorithms for automatic imaging classification and new goniophotographic systems. SS-OCT allows for the first time the assessment of the circumferential extension of angle closure with moderate to good diagnostic performance compared with gonioscopy. Deep learning algorithms are showing promising results for the automation of imaging analysis, and may potentially save physicians' time in regards of the interpretation of the images. Lastly, goniophotograph systems have the distinct advantage of recordability of gonioscopic findings and are most closely matched to the findings of slit-lamp gonioscopy.

Understanding diagnostic disagreement in angle closure assessment between anterior segment optical coherence tomography and gonioscopy

BACKGROUND/AIMS

Although being a more objective tool for assessment and follow-up of angle closure, reliability studies have reported a moderate diagnostic performance for anterior segment optical coherence tomography (OCT) technologies when comparing with gonioscopy as the reference standard. We aim to determine factors associated with diagnostic disagreement in angle closure when assessed by anterior segment swept source OCT (SS-OCT, CASIA SS-1000; Tomey, Nagoya, Japan) and gonioscopy.

METHODS

Cross-sectional study. A total of 2027 phakic subjects aged ≥50 years, with no relevant previous ophthalmic history, were consecutively recruited from a community polyclinic in Singapore. Gonioscopy and SS-OCT (128 radial scans) for the entire circumference of the angle were performed for each subject. A two-quadrant closed gonioscopic definition was used. On SS-OCT images, angle closure was defined as iridotrabecular contact (ITC) to the extent of ≥35%, ≥50% and ≥75% of the circumferential angle. Diagnostic disagreements between both methods, that is, false positives or overcalls and false negatives or undercalls were defined, respectively, as gonioscopic open/closed angles inversely assessed as closed/open by SS-OCT.

RESULTS

Two hundred and seventy-two (14.7%) resulted in overcall results (false positives) when ≥50% of the angle circumference was closed using SS-OCT. These eyes had significantly wider (anterior chamber width, 11.7 vs 11.6 mm, p<0.001) and deeper (anterior chamber depth (ACD), 2.4 vs 2.2 mm, p<0.001) anterior chambers than eyes assessed by both methods as closed (true positives). Deeper ACD (OR 9.31) and lower lens vault (LV) (OR 0.04) were significantly associated with a false positive diagnosis in the multivariate analysis. Most of these cases had short (52.6%) or irregular (39%) ITC in SS-OCT images.

CONCLUSIONS

We found that anterior chamber dimensions, determined by ACD and LV, were factors significantly associated with diagnostic disagreement between anterior segment SS-OCT and gonioscopy in angle closure assessment.