Angle Closure Imaging: A Review

Assessment by Optical Coherence Tomography of Short-Term Changes in IOP-Related Structures Caused by Wearing Scleral Lenses

BACKGROUND

The mechanism that could increase intraocular pressure (IOP) during scleral lens (SL) wear is not fully understood, although it may be related to compression of the landing zone on structures involved in aqueous humor drainage.

METHODS

Thirty healthy subjects were fitted with two SLs of different sizes (L1 = 15.8 mm, L2 = 16.8 mm) for 2 h in the right eye and left eye as a control. Central corneal thickness (CCT), parameters of iridocorneal angle (ICA), Schlemm's canal (SC), and optic nerve head were measured before and after wearing both SLs. IOP was measured with a Perkins applanation tonometer before and after lens removal and with a transpalpebral tonometer before, during (0 h, 1 h, and 2 h), and after lens wear.

RESULTS

CCT increased after wearing L1 (8.10 ± 4.21 µm; p < 0.01) and L2 (9.17 ± 4.41 µm; p < 0.01). After L1 removal, the ICA parameters decreased significantly (p < 0.05). With L2 removal, nasal and temporal SC area and length were reduced (p < 0.05). An increased IOP with transpalpebral tonometry was observed at 2 h of wearing L1 (2.55 ± 2.04 mmHg; p < 0.01) and L2 (2.53 ± 2.22 mmHg; p < 0.01), as well as an increased IOP with Perkins applanation tonometry after wearing L1 (0.43 ± 1.07 mmHg; p = 0.02).

CONCLUSIONS

In the short term, SL resulted in a slight increase in IOP in addition to small changes in ICA and SC parameters, although it did not seem to be clinically relevant in healthy subjects.

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.

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.

Optical sectioning and high resolution visualization of trabecular meshwork using Bessel beam assisted light sheet fluorescence microscopy

Glaucoma, one of the leading causes of blindness, is an eye disease caused by irregularities in the ocular aqueous outflow system causing an elevated intraocular pressure. High resolution imaging of the aqueous outflow system comprising trabecular meshwork is immensely valuable to vision analysts and clinicians in comprehending the disease state for the efficacious analysis and treatment of glaucoma. Currently available ocular imaging devices are unable to deliver high resolution images for the visualization of the trabecular meshwork. A method to obtain high resolution (sub-micrometer) images of the trabecular meshwork using Bessel-Gauss beam scanned light sheet fluorescence microscopy is presented and the optical sectioning capability of this technique to obtain three-dimensional volumetric images of the trabecular meshwork of an intact eye without any physical dissection is demonstrated. Figure: Three-dimensional visualization of trabecular meshwork of porcine eye.

Evaluation of anterior chamber parameters with spectral-domain optical coherence tomography

PURPOSE

To evaluate several anterior chamber parameters in healthy young adults using spectral-domain optical coherence tomography and to describe the repeatability and reproducibility of this method.

STUDY DESIGN

Prospective clinical study.

METHODS

Fifty-two eyes of 52 healthy volunteers were enrolled. Manual measurements of the anterior chamber angle (ACA₅₀₀ and ACA₇₅₀), angle opening distance (AOD₅₀₀ and AOD₇₅₀), angle-to-angle distance (ATA), anterior chamber width (ACW), and lens vault (LV) were obtained.

RESULTS

The mean nasal ACA₅₀₀ was 44.87 ± 12.92°; ACA₇₅₀, 43.94 ± 10.41°; AOD₅₀₀, 672.54 ± 270.19 µm; AOD_750, 881.87 ± 290.55 µm. The mean temporal ACA₅₀₀ was 41.46 ± 11.20°; ACA₇₅₀, 41.27 ± 11.31°; AOD₅₀₀, 603.15 ± 232.28 µm; AOD_750, 823.46 ± 308.76 µm. The differences between the corresponding nasal and temporal parameters were statistically significant. The ACW was 11.97 ± 0.42 mm, the ATA was 12.10 ± 0.43 mm, and the LV was 3.71 ± 232.93 µm. The ACA was highly associated with the LV. The intraclass correlation coefficients ranged from 0.984 to 0.999 for the intraobserver repeatability and from 0.966 to 0.998 for the interobserver reproducibility.

CONCLUSIONS

This study assessed anterior chamber parameters in healthy young adults using spectral-domain optical coherence tomography. This technique reveals the spatial relationships of the ocular structures, provides high-resolution images, and results in high degrees of intraobserver and interobserver repeatabilities.