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

Abstract

 

Purpose

 

Evaluation of the anterior chamber angle is essential to diagnose and manage eyes with angle closure disease. Monitoring changes in angle configuration after treatment, such as laser peripheral iridotomy (LPI) or lens extraction (LE), depends on the accuracy and precision of angle measurements. Anterior segment optical coherence tomography (ASOCT) has been used to quantitatively measure these parameters. This study uses ASOCT imaging to evaluate the normal range of a new parameter Trabecular-Iris Circumference Volume (TICV). TICV is determined by integrating Trabecular-Iris Space Area (TISA) from 128 scans over 360 degrees in an eye (Figure 1).

 

Methods

 

Participants with Spaeth D or E gonioscopic grading and otherwise normal appearing anterior segments were recruited. One eye from each participant was included. 3D ASOCT images were obtained with the CASIA SS-1000 (Tomey, Nagoya, Japan). TISA500 and TICV500 were calculated. Analysis of covariance was performed to examine the effects of spherical equivalent and its interaction with age groups.

 

Results

 

Ninety eyes were included. Sixty percent of participants were female, and participants had a mean age of 50.0 ±15.1 years (ranged 20-79). Sixty percent were White, 25.6% Black, 10% Hispanic, and 4.4% Asian. The anterior chamber angle parameters show age-related reduction of anterior angle parameters (P<0.0001; Table 1). Excluding extreme myopia (more than -12D), the data suggests that angle volume increases with increased myopia for all age groups, except for those older than 65 years.

 

Conclusions

 

This study demonstrates age-related reduction in TISA500 and TICV500, a marker of anterior chamber depth as measured by ASOCT, in open angle eyes. This is consistent with the known shallowing of the anterior chamber with aging. This study establishes a normal age-adjusted range of TICV500, a parameter which could potentially be useful for defining criteria for intervention in narrow angles or monitoring the effects of treatment.

 

 

Figure 1. A) Anterior chamber angle 2D image exhibiting trabecular-iris space area (TISA) and the scleral spur landmark (SSL). Adapted with permission from Cumba et al., Journal of Ophthalmology 2012;2012:487309. B) 3D anterior chamber angle image exhibiting trabecular-iris circumference volume (TICV).

 

 

Table 1. Angle measurements for TISA500 and TICV500 (mean[SD])

 

Keywords: 420 anterior chamber • 421 anterior segment • 550 imaging/image analysis: clinical