Determination of Iridotrabecular Contact Using the Anterior Segment Optical Coherence Tomography in Lights-on and Lights-off Conditions

Objective: To determine the presence of iridotrabecular contact (ITC) and compare the changes in anterior chamber angle (ACA) measurements in room lights-on and lights-off conditions using the anterior segment optical coherence tomography (AS-OCT) in eyes diagnosed as primary angle closure suspects (PACS) by gonioscopy. Methods: This is a retrospective review of 144 eyes of 79 patients (70 females, 9 males) with PACS. All eyes were imaged using the Visante® time-domain AS-OCT (Carl Zeiss Meditec, Dublin, CA). Each eye was imaged twice; the first scan was done with the room lights on followed by a second scan done after turning the room lights off for 2 minutes. The principal outcome measure was the presence of ITC in either lighting condition. Other angle metrics that were assessed included anterior chamber depth (ACD), angle opening distance (AOD), trabecular-iris space area (TISA), and scleral spur angle (SSA). Presence of ITC and differences in the angle metrics between the 2 lighting conditions were then analyzed using the t-tests and logistic regression. Results: ITC was present in 36.8% (53) of the study eyes. Twenty percent (20%) of the study eyes (29) did not initially exhibit ITC in the lights-on phase but developed ITC when imaged with the lights off. Persistent ITC was seen in 16.6% (24 eyes) in both lighting conditions. ITC occurred in 52.2% of the eyes with ACD less than 2.18 mm. Logistic regression showed that there is a 91% decrease in the odds of having ITC in lights-off condition for every millimeter of ACD increase. Age was not associated with the occurrence of ITC in the lights-off condition. All other analyzed parameters decreased significantly in the lights-off condition (p