Detailed study procedures have been reported elsewhere.
6 In brief, 1405 subjects aged 50 years and over were enrolled from Liwan District, Guangzhou, using cluster random sampling. Ethical approval was obtained from the Zhongshan University Ethics Review Board, and approval was granted by the Research Governance Committee of Moorfields Eye Hospital, London. The study was conducted in accordance with the tenets of the World Medical Association’s Declaration of Helsinki. Written, informed consent was obtained from all subjects. Examination of the subjects was performed between September 2003 and February 2004 in Guangzhou, the capital city of Guangdong Province.
Slit lamp (SL-8Z; Topcon, Tokyo, Japan; with a D1x digital image system; Nikon, Tokyo, Japan) gonioscopy was performed by using a Goldmann-type, one-mirror lens (Haag Streit, Bern, Switzerland) at ×25 magnification with low ambient illumination by the same observer (MH), whose observations were standardized against those of an experienced gonioscopist (PJF). A narrow vertical beam 1 mm in length was offset vertically for superior and inferior quadrants, horizontally for nasal and temporal quadrants. Care was taken to prevent light from falling on the pupil. Small movements of the lens were made, if necessary, to visualize the drainage angle over the convexity of the iris, taking care not to cause inadvertent indentation. Dynamic examination with increased illumination using the Goldmann lens was performed after static gonioscopy of all four quadrants was completed. In cases in which iridotrabecular contact could not be satisfactorily reversed, a four-mirror lens was used (Carl Zeiss Meditec, Oberkochen, Germany). Angle width was estimated in the superior and inferior quadrants as the angle in degrees between a tangent to the surface of the trabecular meshwork (TM) and a tangent to the peripheral third of the iris and then was recorded in five-point categories (0°, 10°, 20°, 30°, and ≥40°). This grading of geometric angle width was adapted from the Shaffer system
7 with an attempt to standardize the reporting and make it comparable to data in other studies, although we did employ Spaeth’s principle of estimating angle width between the TM and the peripheral third of the iris. Furthermore, iris insertion was recorded as: A (anterior to Schwalbe’s line), B (behind Schwalbe’s line), C (at the scleral spur), D (with a narrow, visible ciliary body band), and E (with a very wide ciliary body band). The point of presenting contact between the iris and the posterior surface of the corneoscleral coat before indentation was recorded as the “apparent” iris insertion, whereas the point of contact identified during dynamic examination was recorded as the “true” iris insertion.
8 Dynamic gonioscopy was also used to identify the existence and extent of PAS and pathologic changes of angles (including iris stomal pigment deposition on TM). The iris profile was classified as steep, plateau, regular, and concave, with the grade chosen to best reflect the entire 360° architecture. The plateau iris profile was added to the traditional Spaeth grading scheme and was deemed to be present if the iris rose steeply from its point of insertion but then made an abrupt angulation away from the corneoscleral wall, resulting in a relatively deep axial anterior chamber and a centrally flat iris plane.
The overall angle status was further classified as narrow or not. A narrow angle (synonymous with suspect PAC and an occludable angle) was defined as one in which the posterior, usually pigmented, TM was hidden from view during static gonioscopy (i.e., apparent iris insertion).
All data are presented for right phakic eyes only. Given that the gonioscopic angle width and iris insertion are ordinal variables but do not comply with normal distribution, the Wilcoxon rank test was used for comparison between two groups, the Wilcoxon Kruskal-Wallis test for multiple-group comparison, and the Wilcoxon signed rank test for matched-pair comparison.
9 The χ
2 test was used to test the similarity of the proportions. A regression model was fitted with a mean of angle width on superior and inferior quadrants as an outcome, with age and sex as explanatory variables. Logistic regression was used when assessing for factors associated with the posterior pigmented TM’s being visible in more than one quadrant.