Quantitative evaluation of anterior chamber parameters using anterior segment optical coherence tomography in primary angle closure mechanisms in Caucasian eyes

BACKGROUND: The purpose of this study was to evaluate different mechanisms of primary angle closure disease (PACD) and quantify anterior chamber parameters in these mechanisms using anterior segment optical coherence tomography (ASOCT) in a Caucasian population. DESIGN: Hospital-based cross-sectional observational study/Clinic based study. PARTICIPANTS: 144 eyes (73 patients) with newly diagnosed primary angle closure disease (PACD), classified into three subtypes: primary angle closure suspect (PACS), primary angle closure (PAC), and primary angle closure glaucoma (PACG), were enrolled to the study. MATERIAL AND METHODS: Participants underwent ASOCT (SS-1000 CASIA, Tomey Corporation, Nagoya, Japan) under the same standardized dark room conditions. ASOCT images were categorized into one of 4 groups based on the angle-closure mechanisms: pupillary block (PB), plateau iris configuration (PIC), thick peripheral iris (TPI), and large lens vault (LLV). Anterior chamber depth (ACD), anterior chamber area (ACA), anterior chamber volume (ACV), anterior chamber width (ACW), iris area (IA), iris curvature (IC), iris curvature area (ICA), iris thickness (IT750, IT2000), lens vault (LV), pupil diameter (PD), angle opening distance (AOD500, AOD750), angle recess area (ARA 500, ARA750), trabecular iris angle (TIA500, TIA750) and trabecular iris space area (TISA500, TISA750) were determined using 360o SS-OCT viewer software (version 5.0, Tomey, Nagoya, Japan). RESULTS: Among 144 examined eyes, 83 eyes (57.6%) were classified as PB, 42 eyes (29.2%) as PIC, 14 eyes (9.7%) as TPI, and 5 eyes (3.5%) as LLV. 73.6% had a single underlying PAC mechanism, and the rest had more than one (combined mechanism) of PAC. Anterior chamber parameters (ACD, ACA, ACV) were the highest in the PIC group and the lowest in the LLV group. Angle parameters (AOD 500, AOD 750, TIA 750; SSAngle 500; SSAngle 750) showed the strongest relevance and were the highest in the PIC group and the lowest in the TPI group. LV was the greatest in the LLV and the lowest in the TPI and PIC groups. Axial length (AL) was the largest in PIC, followed by PB, and the smallest in the LLV group. CONCLUSION: Anterior chamber and anterior chamber angle parameters showed significant differences between the four angle closure mechanisms. Identifying the angle closure mechanisms could lead to better disease management by individualizing the treatment.