| Background. The current gold standard for assessing the anterior chamber angle (ACA) is gonioscopy, a relatively difficult and subjective technique. Due to the difficulties of ACA assessment, many risk factor studies for angle closure glaucoma have focused on biometric factors other than the ACA (anterior chamber depth (ACD), limbal depth, and so on). We investigated novel approaches to evaluating the ACA.; Methods. A case-control study to assess ACA findings associated with acute angle closure (AAC) was conducted in Singapore. Cases were recruited prospectively from March 1999 through July 2001. Controls were selected from a previously completed population-based study of eye disease prevalence among Chinese in Singapore. Ocular biometry was collected including radius of corneal curvature, gonioscopy, ACD, axial length, and lens thickness. In addition, Scheimpflug photography and ultrasound biomicroscopy (UBM) of the ACA were performed on cases and controls as were provocative tests.; Results. 212 cases presented with a potential diagnosis of AAC: 99 were eligible and participated. Contralateral eyes of cases had shorter axial length, shallower ACD, thicker lenses, and steeper radii of corneal curvature after adjusting for age and sex. Contralateral eyes were 19 times more likely to have limbal ACD of 25% or less (Odds Ratio = 19.1, 95% CI = 8.3 to 45.2). UBM parameters indicated substantially narrower ACA (more than 50% narrower), and a more crowded angle recess in contralateral eyes. Contralateral eyes of cases were substantially more likely than controls to have at least one quadrant closed on UBM (Odds Ratio = 29.2, 95% CI = 15.3 to 55.3). Angle width in the contralateral eyes of cases was nearly 30% narrower using the Scheimpflug camera. Contralateral eyes of cases responded with greater angle closure when going from bright illumination to darkness, and with less angle opening in response to pilocarpine.; Conclusion. The ACA of the contralateral eyes of AAC-affected persons have important physiological differences when compared to population-based controls. Contralateral eyes of individuals suffering AAC are measurably shorter, have thicker lenses, steeper radii of corneal curvature, shallower ACD, and more crowded filtering angles. Furthermore, when placed in the dark, they experience greater shallowing, and when given 4% pilocarpine therapy, they deepen less than normal control eyes. These findings suggest the need to investigate new mechanisms in AAC. |
