Purpose:
Measurements of the angle width by ultrasound biomicroscopy (UBM) or anterior segment optical coherence tomography (ASOCT) take measurements 500 microns from the scleral spur, as the trabecular meshwork is assumed to lie within this distance. The aim of this study was to measure the trabecular meshwork width in the anterior chamber angle using Swept Source Optical Coherence Tomography (SS-OCT, SS-1000 CASIA, Tomey Corporation, Nogoya, Japan).
Methods:
One hundred and forty-seven phakic eyes of 147 patients were recruited. All participants underwent dark room gonioscopy and SS-OCT angle imaging in one randomly selected eye. Angle closure was defined if the posterior trabecular meshwork (TM) not visible in 2 quadrants by gonioscopy. High definition SS-OCT images were corrected for refractive distortion by built-in CASIA program and customized software (Image J, NIH ImageJ; National Institutes of Health, Bethesda, Maryland) was utilised to measure TM width (distance between Scleral Spur and Schwalbe’s line), Angle Opening Distance (AOD500) and Trabecular Iris Space Area (TISA500). Linear regression analysis comparing average TM for age, gender, eye, angle status and conventional angle parameters was performed.
Results:
The majority of subjects were Chinese (141/147, 95.9%) with a mean age of 59.5 (8.97) years. There were more females (92/147, 62.6%) and subjects with open angles (118/147, 80.3%). The mean TM width was 0.777 (0.15) mm. The TM width of the right eye was significantly higher compared to the left eye {Mean diff 0.043 (0.16), Beta = -0.037 (95% CI -0.071, -0.003)}. The mean of inferior TM width was significantly wider compared to the other quadrants {inferior 0.888 (0.14) > superior 0.79 (0.14) > nasal 0.708 (0.14) and temporal (0.721 (0.1), p<0.001, analysis of variance}. There was no significant association found for angle parameters or demographic factors with TM width.
Conclusions:
Inferior trabecular meshwork was widest compared to other quadrants. TM width was asymmetric in laterality and was not influenced by angle status. Quantitative angle measurements at 0.75mm instead of 0.5mm are more appropriate in the determination of angle closure using UBM or ASOCT.
Keywords: trabecular meshwork • anterior segment • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)