Role of Optical Coherence Tomography in Assessing Anterior Chamber Angles

Abstract

Introduction: Gonioscopy is the gold standard in assessing anterior chamber angles. However, interobserver variations are common and there is a need for reliable objective method of assessment.

Aim: To compare the anterior chamber angle by gonioscopy and Spectral Domain Optical Coherence Tomography (SD-OCT) in individuals with shallow anterior chamber.

Materials and methods: This comparative observational study was conducted in a rural tertiary multi-speciality teaching hospital. A total of 101 eyes of 54 patients with shallow anterior chamber on slit lamp evaluation were included. Anterior chamber angle was graded by gonioscopy using the shaffer grading system. Angles were also assessed by SD-OCT with Trabecular Iris Angle (TIA) and Angle Opening Distance (AOD). Chi-square test, sensitivity, specificity, positive and negative predictive value to find correlation between OCT parameters and gonioscopy grading.

Results: Females represented 72.7%. The mean age was 53.93 ±8.24 years and mean anterior chamber depth was 2.47 ± 0.152 mm. Shaffer grade ≤ 2 were identified in 95(94%) superior, 42(41.5%) inferior, 65(64.3%) nasal and 57(56.4%) temporal quadrants. Cut-off values of TIA ≤ 22° and AOD ≤ 290 μm were taken as narrow angles on SD-OCT. TIA of ≤ 22° were found in 88(92.6%) nasal and 87(87%) temporal angles. AOD of ≤ 290 μm was found in 73(76.8%) nasal and 83(83%) temporal quadrants. Sensitivity in detecting narrow angles was 90.7% and 82.2% for TIA and AOD, while specificity was 11.7% and 23.4%, respectively.

Conclusion: Individuals were found to have narrow angles more with SD-OCT. Sensitivity was high and specificity was low in detecting narrow angles compared to gonioscopy, making it an unreliable tool for screening.

Keywords: Glaucoma; Narrow-angle; OCT tomography.

[Table/Fig-1]:

Measurement of Trabecular Iris Angle (TIA) and Angle Opening Distance (AOD). *TIA 500 is defined as an angle measured with the apex in the iris recess and the arms of the angle passing through a point on the trabecular meshwork 500 μm from the scleral spur and the point on the iris perpendicularly. *AOD 500 is defined as the distance from the corneal endothelium to the anterior iris surface perpendicular to a line drawn along the trabecular meshwork at 500 μm from the scleral spur.

[Table/Fig-3]:

OCT and gonioscopy image showing a closed angle. * OCT image showing TIA of 0° and AOD of 81 μm of the same angle with shaffer grade 0.

[Table/Fig-4]:

OCT and Gonioscopy Image Showing an Open Angle. * OCT image showing TIA of 28.8° and AOD of 389 μm of the same angle with shaffer grade 4.