Trabecular-Iris Circumference Volume in Open Angle Eyes Using Swept-Source Fourier Domain Anterior Segment Optical Coherence Tomography

Abstract

Purpose. To introduce a new anterior segment optical coherence tomography parameter, trabecular-iris circumference volume (TICV), which measures the integrated volume of the peripheral angle, and establish a reference range in normal, open angle eyes. Methods. One eye of each participant with open angles and a normal anterior segment was imaged using 3D mode by the CASIA SS-1000 (Tomey, Nagoya, Japan). Trabecular-iris space area (TISA) and TICV at 500 and 750 µm were calculated. Analysis of covariance was performed to examine the effect of age and its interaction with spherical equivalent. Results. The study included 100 participants with a mean age of 50 (±15) years (range 20–79). TICV showed a normal distribution with a mean (±SD) value of 4.75 µL (±2.30) for TICV500 and a mean (±SD) value of 8.90 µL (±3.88) for TICV750. Overall, TICV showed an age-related reduction (P = 0.035). In addition, angle volume increased with increased myopia for all age groups, except for those older than 65 years. Conclusions. This study introduces a new parameter to measure peripheral angle volume, TICV, with age-adjusted normal ranges for open angle eyes. Further investigation is warranted to determine the clinical utility of this new parameter.

Agreement between Gonioscopic Examination and Swept Source Fourier Domain Anterior Segment Optical Coherence Tomography Imaging

“…Gonioscopy does not grade at a single axis, but as an area, which may be a clock hour or a quadrant, while with the FD ASOCT, measurement is taken in a single meridian. It might be appropriate in a future study to compare a quadrantric measurement, such as a quadrant of trabecular-iris circumference volume (TICV [5]), to gonioscopy rather than a single plane measurement. Unfortunately, that was beyond the scope of the current study as FD ASOCT measurements were taken with 2D images, which cannot be used for TICV.…”

“…All raw study images were exported from the FD ASOCT after data collection was complete and imported to customized software, Anterior Chamber Angle and Interpretation (ACAI, Houston, TX), as described in previous publications [3–5]. Two experienced FD ASOCT readers (AZC, LAB) identified scleral spur landmarks (SSLs) on superior angles (12 o'clock) and graded iris insertion using Spaeth definitions (A, B, C, D, or E).…”

“…Anterior segment optical coherence tomography (ASOCT) is widely used because it is quick and noncontact and provides reproducible images of the angle, and image acquisition can be performed by a technician with minimal training [1–5]. However, most ASOCT instruments measure only horizontal and vertical meridians, with up to 80% of superior angles not adequately visible [6].…”

“…The CASIA SS-1000 ASOCT (Tomey Corporation, Nagoya, Japan) uses Fourier domain (FD) swept source technology to provide high-resolution images (10  μ m axially and 30  μ m transversally for 2D images) for both horizontal and vertical meridians in 1.2 seconds. From our prior studies, we have found that this device provides high-quality images of the superior angle that can be reliably analyzed using customized software [3–5, 13]. …”

Comparing Laser Peripheral Iridotomy to Cataract Extraction in Narrow Angle Eyes Using Anterior Segment Optical Coherence Tomography

“…Anterior segment optical coherence tomography (ASOCT) can be used to image the peripheral ACA consistently and reproducibly and quantify ACA parameters such as angle opening distance (AOD), trabecular-iris space area (TISA), and trabecular-iris circumference volume (TICV) [17, 18]. …”