Purpose. To investigate age- and position-related changes of anterior chamber angle anatomy in normal, healthy eyes. Patients and Methods. Thirty subjects were separated into a younger and older cohort. The superior and inferior anterior chamber angles of the eyes were measured in supine and sitting positions by ultrasound biomicroscopy (UBM) with bag/balloon technology. Statistical analysis was used to evaluate positional and age-related changes in angle morphology. Results. In the younger cohort, no location or positional differences in angle anatomy were observed. In the older cohort, the inferior quadrant was significantly narrower than the superior quadrant ( ) in the supine position. This cohort also demonstrated an interaction effect between position and location. In the older cohort, the angle was deeper inferiorly while the subject was sitting but was deeper superiorly while the subject was supine. Conclusion. Comparison of positional variations in anterior chamber angle anatomy as measured by UBM has recently become possible. This study found that age-related positional changes in the anterior chamber angle anatomy exist in normal healthy eyes. 1. Introduction Ultrasound biomicroscopy (UBM) provides noninvasive high-resolution in vivo imaging of the anterior segment. While anterior tissues are readily visualized by conventional methods (e.g., slit-lamp biomicroscopy and gonioscopy), structures posterior to the iris are hidden due to absorption of light by the iris pigment epithelium. Such structures may also be undetected by anterior segment optical coherence tomography (ASOCT), given the inability of light to penetrate the iris pigment epithelium. B-scan ultrasonography, though extremely useful in imaging posterior ocular structures, is also not ideal for ciliary body imaging due to the near-field artifact and poorer resolution obtained with lower frequencies. However, the higher frequency ultrasound waves, utilized by UBM, are not obstructed by pigmented tissue and give the required resolution. Thus, UBM can be used to image not only the anterior chamber angle but also the ciliary body, peripheral lens, zonules, and the posterior chamber of the eye [1]. UBM has been demonstrated to be useful in evaluating the anterior segment of eyes with the primary angle closure spectrum of disorders [2]. It also may be used to elucidate the mechanism of malignant glaucoma, pigmentary glaucoma, and anterior scleral disease [3–5]. Therefore, UBM has become the current standard for imaging abnormalities of ciliary body position, as are found in plateau iris
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