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Billy Pan, Benjamin Xu, Paul Israelsen, Dandan Wang, Rohit Varma; Evaluating the Inter-Quadrant Variations in Anterior Chamber Angle Measurements Using Anterior Segment OCT. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4976.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies of the anterior chamber angle have divided the angle into four quadrants reflecting the conventions set by the classic 4-mirror goniolens. However, the anatomical distinctions of the different angle quadrants are not well studied, especially with objective measures such as anterior segment OCT. Recent advances in OCT technology now permit the near-simultaneous acquisition of angle measurements from multiple quadrants. While this technique has been used to study local variations in the anterior chamber angle, it has not been used to compare inter-quadrant differences. Here we represent each of the angle quadrants using multiple OCT images to evaluate inter-quadrant differences in a variety of angle parameters and to improve our understanding of angle anatomy.
We analyzed 8 anterior segment OCT images from one eye each of 141 patients randomly selected from the Chinese American Eye Study (CHES) - a population based study of Chinese Americans in Los Angeles, CA. These 8 images were divided to represent the four cardinal quadrants (centered on 0, 90, 180 or 270 degrees) or the four diagonal quadrants (centered on 45, 135, 225 or 315 degrees). We compared measurements of 13 angle parameters, including angle opening distance (AOD) and angle recess area (ARA), for both of the quadrant designations.
When the quadrants were divided into the 4 cardinal directions, the majority of angle measurements were 10 to 15% greater temporally and inferiorly when compared to superiorly. When the quadrants were divided diagonally, angle measurements were largest in the inferotemporal quadrant and smallest in the superonasal quadrant; measurements from the superotemporal and inferonasal quadrants were roughly equal and intermediate. A few of the parameters, such as anterior chamber width (ACW), varied only in one quadrant designation but did not in the other.
The anatomical variations between the anterior chamber angle quadrants have not been well studied even though the angle is commonly divided into quadrants both clinically and scientifically. This study represents the first evidence derived using objective measures that there are significant inter-quadrant differences in some but not all angle parameters. These differences need to be carefully studied to better our understanding of the impact of anterior chamber structure on IOP and angle closure.
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