Volumetric parameters-based differentiation of narrow angle from open angle and classification of angle configurations: an SS-OCT study

Anterior Segment OCT for Detection of Narrow Angles: A Community-Based Diagnostic Accuracy Study

PURPOSE

To assess the diagnostic accuracy of anterior segment OCT (AS-OCT) screening for detecting gonioscopically narrow angles.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

A stratified random sample of individuals aged ≥ 60 years, selected from a door-to-door census performed in low-lying Nepal.

TESTING

Participants underwent AS-OCT, posterior segment OCT, and intraocular pressure (IOP) testing in the community. Those meeting referral criteria in either eye were invited to have a comprehensive eye examination including gonioscopy. Referral criteria included (i) the lowest 2.5% of AS-OCT measurements, (ii) retinal OCT results suggestive of glaucomatous optic neuropathy, diabetic retinopathy, or age-related macular degeneration, and (iii) elevated IOP.

MAIN OUTCOME MEASURES

Sensitivity and specificity of 5 semiautomated AS-OCT parameters relative to gonioscopically narrow angles, defined as the absence of visible trabecular meshwork for ≥ 180° on nonindentation gonioscopy.

RESULTS

Of 17 656 people aged ≥ 60 years enumerated from 102 communities, 12 633 (71.6%) presented for AS-OCT testing. Referral was recommended for 697 participants based on AS-OCT criteria and 2419 participants based on other criteria, of which 858 had gonioscopy performed by a glaucoma specialist. Each of the 5 AS-OCT parameters offered good diagnostic information for predicting eyes with gonioscopically narrow angles, with areas under the receiver operating characteristic curve ranging from 0.85 to 0.89. The angle opening distance at 750 μm from the scleral spur (AOD750) provided the most diagnostic information, providing an optimal sensitivity of 87% (95% confidence interval [CI], 75%-96%) and specificity of 77% (71%-83%) at a cutpoint of 367 μm, and a sensitivity of 65% (95% CI, 54%-74%) when specificity was constrained to 90% (cutpoint, 283 μm).

CONCLUSIONS

On AS-OCT, the AOD750 parameter detected approximately two-thirds of cases of gonioscopically narrow angles when test specificity was set to 90%. Although such a sensitivity may not be sufficient when screening solely for narrow angles, AS-OCT requires little additional effort if posterior segment OCT is already being performed and thus could provide incremental benefit when performing OCT-based screening.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.

The inflammatory cytokine profiles and ocular biometric characteristics of primary angle-closure glaucoma

OBJECTIVE

To investigate the pathogenesis of primary angle-closure disease (PACG) by measuring the anatomical structures of the anterior and posterior segments of the eye and inflammatory markers in the peripheral blood.

METHODS

This case-control study enrolled patients diagnosed with acute PACG (APACG) and chronic PACG (CPACG). It also enrolled control subjects without PACG. The anterior and posterior anatomical features were measured in all study participants. The levels of interleukin (IL)-6, tumour necrosis factor-α and the neutrophil-to-lymphocyte ratio (NLR) in the peripheral blood were measured.

RESULTS

This study analysed a total of 99 eyes: 34 eyes from 34 patients with APACG, 28 eyes from 28 patients with CPACG and 37 eyes from 37 control patients with senile cataract. The axis length, corneal diameter, anterior chamber depth and anterior chamber volume were significantly smaller in the APACG and CPACG groups compared with the controls. The level of IL-6 in the peripheral blood of patients with PACG was significantly lower than that of the controls. The NLR in the peripheral blood of patients with PACG was significantly greater than that of the controls.

CONCLUSIONS

Changes in the ocular anatomy and some inflammatory markers might be involved in the pathogenesis of PACG.

Relationship Between Optical Coherence Tomography and Anterior Chamber Depth After Pupillary Dilation in Primary Angle Closure Suspects

PRCIS

Anterior chamber depth (ACD) change after pupillary dilation is correlated with lens vault (LV) and anterior chamber width (ACW), as observed by swept-source optical coherence tomography (SS-OCT) at both horizontal and vertical scans in patients with primary angle closure suspect and cataract.

PURPOSE

The purpose of this study is to evaluate the association between ACD and other anterior chamber parameters after pharmacological dilation in patients with primary angle closure suspect and cataract.

PATIENTS AND METHODS

SS-OCT was performed for 78 patients at baseline and 1 hour after pharmacological dilation. Measurements were taken at 8 evenly spaced axes at 250, 500, and 750 μm from the scleral spur. Pearson correlation coefficient (ρ) was used to evaluate the relationship between averaged ACD change and other SS-OCT parameters. Multivariable regression analyses were performed to determine the parameters that predict ACD change.

RESULTS

Across all 14 dimension and angle parameters, 12 parameters at the 270-degree axis and 10 parameters at the 0-degree axis yielded significant correlations with ACD change (ρ=0.24-0.55, P <0.05). Angle parameters were most significantly correlated to ACD change 750 µm from the scleral spur. The prediction model for ACD change after pharmacological dilation at 0 degree included decreased LV, wider ACW, and increased trabecular iris space area (all P ≤0.001). The prediction model for ACD change at 270 degrees included: decreased LV, wider ACW, larger change in anterior chamber volume, larger baseline anterior chamber volume, and smaller baseline angle opening distance (all P ≤0.03).

CONCLUSIONS

LV and ACW, as measured in both vertical and horizontal scans, were found to be determinants of the ACD change after pharmacological pupillary dilation. Examination of these parameters may help identify patients at higher risk of developing angle-closure disease.

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.

Segmentation Errors in the Measurement of Volumetric Parameters by Swept-Source Anterior Segment Optical Coherence Tomography

Purpose: To investigate the error rate of segmentation in the automatic measurement of anterior chamber volume (ACV) and iris volume (IV) by swept-source anterior segment optical coherence tomography (SS-ASOCT) in narrow-angle and wide-angle eyes.

Methods: In this study, fifty eyes from 25 narrow-angle subjects and fifty eyes from 25 wide-angle subjects were enrolled. SS-ASOCT examinations were performed and each SS-ASOCT scan was reviewed, and segmentation errors in the automatic measurement of ACV and IV were classified and manually corrected. Error rates were compared between the narrow-angle and the wide-angle groups, and ACV and IV before and after manual correction were compared.

Results: A total of 12,800 SS-ASOCT scans were reviewed. Segmentation error rates of angle recess, iris root, posterior surface of the iris, pupil margin, and anterior surface of the lens were 84.06, 93.30, 13.15, 59.21, and 25.27%, respectively. Segmentation errors of angle recess, iris root, posterior surface of the iris, and pupil margin occurred more frequently in narrow-angle eyes, while more segmentation errors of the anterior surface of the lens were found in wide-angle eyes (all P &lt; 0.001). ACV decreased and IV increased significantly after manual correction of segmentation errors in both groups (all P &lt; 0.01).

Conclusion: Segmentation errors were prevalent in the volumetric measurement by SS-ASOCT, particularly in narrow-angle eyes, leading to mismeasurement of ACV and IV.

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.

Swept Source Optical Coherence Tomography Analysis of the Selected Eye's Anterior Segment Parameters

BACKGROUND

The present study determined the mean reference values of the anterior segment parameters of the selected eye using swept source optical coherence tomography (SS-OCT) in healthy Caucasian participants.

METHODS

A total of 166 volunteers (age 54-79 years), women (n = 92) and men (n = 74), were analyzed. One eye of each subject was randomly selected for anterior segment imaging. The anterior segment of the eye was scanned with CASIA2. The analyzed anterior segment parameters were divided into three groups, namely parameters of the cornea, lens, and angle.

RESULTS

The OCT (e.g., Ks, Kf, pKf, pKs, and central corneal thickness) and Fourier parameters of the cornea were significantly different between females and males. The iridocorneal angle was the smallest in the upper quadrant for all distance from the apex of the angle (250, 500, and 750 µm).

CONCLUSIONS

Therefore, SS-OCT enables the analysis of parameters of the cornea, anterior chamber, lens, and iridocorneal angle, highlighting its clinical utility. Sex-specific differences in the analyzed parameters should be taken into account during the diagnosis of corneal diseases. The configuration of the filtration angle is an important marker during glaucoma diagnosis and drainage implant surgery. Measurements with CASIA 2is characterized by very good repeatability.

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.

Smaller Anterior Chamber Volume Is Associated With Higher Risk of Intraocular Pressure Elevation After Laser Peripheral Iridotomy: A 1-Year Follow-Up Study

PURPOSE

The aim of this study was to analyze the predictive value of swept-source optical coherence tomography (SS-OCT) derived anterior-segment volumetric parameters such as anterior chamber volume (ACV) in the long-term follow-up of primary angle closure disease (PACD).

DESIGN

Longitudinal observational study.

METHODS

In this single-center longitudinal observational study, PACD patients undergoing laser peripheral iridotomy (LPI) were recruited. Anterior segment images of the patients were captured using SS-OCT before LPI, and at 1 week, 1 month, 3 months, 6 months, and 1 year after LPI. Ninety eyes of 81 subjects were enrolled, and 72 eyes of 72 subjects finished the 1 year follow-up. Data of all the 81 subjects were included for analysis. Intraocular pressure (IOP) elevation was defined as IOP >21 mm Hg at any time point after LPI. The association between baseline trabecular-iris space area 750 μm from scleral spur (TISA750), ACV and iris volume (IV), and IOP elevation were analyzed using logistic regression.

RESULTS

Eighty-one subjects were included, 59 were female, and 22 were male, with a mean age of 60.98± 9.44 years. IOP elevation appeared in 14 eyes. Mean TISA750 was negatively associated with IOP elevation (OR = 0.94, P = 0.02). The correlation of TISA750 with IOP elevation varies across quadrants and there was only significant association in temporal TISA750 (OR = 0.98, P = 0.046), whereas in the other 3 quadrants, there was no significant association. Greater ACV was associated with lower risk of IOP elevation (OR = 0.80, P = 0.031), whereas IV was not associated with IOP elevation.

CONCLUSIONS

ACV is a reliable and accurate predictor for the outcome of PACD. Due to its 3-dimensional nature, the robustness of ACV is greater than traditional angle width parameters such as TISA750.

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.