This was a cross-sectional observational study. Subjects were consecutively enrolled from among patients with PAC or PACG who underwent LPI at the glaucoma clinic of Peking University Third Hospital between January 2009 and December 2009.
PAC was defined according to the following criteria
11: an eye with an occludable drainage angle (an angle in which ≥270° of the posterior trabecular meshwork could not be seen) and features that indicated trabecular obstruction by the peripheral iris had occurred, such as PAS, elevated IOP, or excessive pigment deposition on the trabecular surface. The optic disc did not have glaucomatous damage. PACG was defined as the presence of glaucomatous optic neuropathy (loss of neuroretinal rim with a vertical cup-to-disc ratio of >0.7 and/or notching with nerve fiber layer defect that was attributable to glaucoma) with compatible visual field loss, associated with an occludable angle (an angle in which ≥270 of the posterior trabecular meshwork could not be seen) and raised IOP and/or PAS.
11 Approval of this study was obtained from the Ethics Committee Review Board of Peking University Eye Center, Peking University Third Hospital. This study was conducted in strict adherence to the tenets of the World Medical Association's Declaration of Helsinki. Written informed consent was obtained from each patient enrolled in this study.
Exclusion criteria included (1) cases of secondary angle closure, such as neovascularization of the iris, uveitis, trauma, tumor, lens intumescence or subluxation; (2) eyes that had previously undergone intraocular surgery; (3) subjects unable to tolerate or not suitable for gonioscopy or UBM, for example, those with cornea disease; (4) subjects who did not return for follow-up examinations due to difficult economic conditions and/or who lived distantly; (5) eyes which needed filtering surgery, including those with more than two quadrants of synechia angle closure according to Chinese Guidelines of Glaucoma Diagnosis and Treatment12; (6) eyes with pupil distortion or iris whirling (distortion of the radially orientated iris fibers) which could affect the evaluation of the angle using UBM; and (7) any other ocular diseases, except for mild cataracts. In the event that both eyes of a patient satisfied the criteria, one eye was randomly selected for our analysis. All enrolled eyes underwent LPI. Approximately 1 to 2 weeks (average: 1.3 weeks) after LPI was performed in their studied eyes, all subjects stopped taking miotic drops for 1 week. Then, all subjects underwent a comprehensive ophthalmic examination that included visual acuity, IOP measurement using a Goldmann applanation tonometer, slit-lamp biomicroscopy, gonioscopy, and ophthalmoscopy.
Static and dynamic gonioscopy were performed in the primary position of gaze under the lowest level of ambient illumination that permitted a view of the angle. Using a static Goldmann single-mirror gonioscopy lens (Ocular Instruments, Bellevue, WA, USA), one of the authors (L-lW), an experienced gonioscopist, observed the anterior chamber angle of the four quadrants: superior, inferior, nasal, and temporal. Compression of the angle was avoided. The angle widths of the four quadrants were graded according to Scheie's classification system and defined as wide or narrow (grades I–IV); that is, a wide-angle width defined as visualization of the full extent of the trabecular meshwork, scleral spur, and ciliary processes in the primary position; grade I: difficult to see over the iris root into the recess; grade II: ciliary body band was obscured; grade III: posterior trabeculum was obscured; and grade IV: only Schwalbe's line was visible. Dynamic compression with a Goldmann gonioscopy was used to determine the presence, extension, and height of PAS.
DRPT was performed on all eyes, except for those with IOPs of more than 21 mm Hg (for the safety of patients) and those taking antiglaucoma medication (no matter in the chosen eye or the fellow eye). Senile patients, and those with poorly controlled systemic conditions impairing the tolerance for DRPT also did not receive DRPT. DRPT was performed on subjects that sat in a dark room for one hour and were asked to remain conscious. IOP was measured using a Goldmann tonometer before and after the DRPT. An IOP elevation of 8 mm Hg or more was considered positive.
13 The observer measuring the IOP was masked to gonioscopic and UBM findings.
All subjects were examined using UBM (Paradigm Medical Industries, Salt Lake City, UT, USA) in darkness (<1 lux, measured with an ST-92 luminance meter; Beijing Teachers University Photoelectricity Instrument Factory, Beijing, China). The UBM system was equipped with a 50-MHz transducer, 5.0- × 5.0-mm field of view, and a spatial resolution of approximately 50 μm (Paradigm Medical). Patients were examined in the supine position. After topical anesthesia was applied, an eyecup containing hydroxyethyl cellulose and physiologic saline was placed on the globe. Then, UBM assessments in the central axis and a 360° radiation scan were performed. Images of the limbal area in the superior (12 o'clock), inferior (6 o'clock), nasal (3 or 9 o'clock), and temporal (9 or 3 o'clock) quadrants were captured for our analysis.
UBM images of each quadrant were carefully read by three of our authors independently (Y-jY, L-lW, and G-gX). If two of the authors' opinions were consistent with one another, the final diagnosis was decided. If the opinions were different among all three authors, the three first discussed and then arrived at a mutually agreed diagnosis. Grading was made for each quadrant except for quadrant with PAS in gonioscopy according to the following criteria: PAS-positive quadrant was defined when there was PAS in any position of this quadrant; PAS-negative quadrant was defined when there was no PAS in any position of this quadrant. UBM parameters in PAS-negative quadrant included AAC, plateau iris, thick iris, and anteriorly inserted iris. AAC was diagnosed when the trabecular meshwork and iris were located appositionally on the UBM image (
Fig. 1). Plateau iris was defined according to the most recent standard for diagnosing plateau iris, using UBM.
14 The criteria for defining a plateau iris in any quadrant included the presence of (1) an anteriorly directed ciliary body and an absent ciliary sulcus; (2) a steep iris root from its point of insertion followed by a downward angulation from the corneoscleral wall and the presence of a central flat iris plane; (3) irido-angle contact above the level of sclera spur (
Fig. 2). Thick iris was defined according to our own experience. In published reports, iris thickness is usually measured at 500 μm from the sclera spur and is usually less than 0.5 mm, whereas the corneal thickness at the sclera spur is approximately 1 mm, according to our general knowledge. Based on our experience, a thick iris in any quadrant is defined by whether the iris thickness at 500 μm from the scleral spur is ≥2/3 of the corneal thickness at the scleral spur (
Fig. 3). The classification of an anteriorly inserted iris was based on whether the position of iris insertion was located in 1/3 of the ciliary body near the sclera spur (
Fig. 4).