Degree of angle closure and extent of peripheral anterior synechiae: an anterior segment OCT study D H W Su, 1 D S Friedman, 2 J L S See, 3 P T K Chew, 3,4 Y-H Chan, 4 W P Nolan, 2,3 S D Smith, 5 D Huang, 6 C Zheng, 3 Y Li, 6 P J Foster, 7 T Aung 1,4 1 Singapore National Eye Centre, Singapore; 2 Wilmer Eye Institute and Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA; 3 National University Hospital, Singapore; 4 Yong Loo Lin School of Medicine, National University of Singapore, Singapore; 5 Cole Eye Institute, Cleveland, OH, USA; 6 Doheny Eye Institute, University of Southern California Keck School of Medicine, Los Angeles, CA, USA; 7 Moorfields Eye Hospital and Institute of Ophthalmology, London, UK Correspondence to: T Aung, Glaucoma Department, Singapore National Eye Centre, 11 Third Hospital Avenue, Singapore 168751; tin11@pacific.net.sg Accepted 11 June 2007 Published Online First 21 June 2007 ABSTRACT Aims: To evaluate the relationship between angle width as determined by anterior segment optical coherence tomography (AS-OCT) and the presence of peripheral anterior synechiae (PAS). Methods: This was a prospective observational case series in which 203 subjects with primary angle closure or open angles were recruited. Images of the nasal, temporal and inferior angles were obtained with AS-OCT in dark conditions. Subjects then underwent gonioscopy by an independent examiner who was masked to the AS-OCT findings. PAS were identified by gonioscopy and defined as abnormal adhesions of the iris to the angle that were at least half a clock hour in width and present to the level of the anterior trabecular meshwork or higher. The total clock hours of PAS were recorded. Results: Sixty-eight subjects (33.5%) were PACS, 76 subjects (37.4%) had PAC/PACG, 14 (6.9%) had primary open angle glaucoma, and 45 (22.2%) subjects were normal with open angles. There was a weak but significant correlation between the angle opening distance (AOD), trabecular iris space area (TISA) and angle recess area (ARA) with clock hours of PAS (Spearman’s correlation coefficients = 20.30, 20.32 and 20.32, respectively, p,0.001). The mean values of the AOD, TISA and ARA in the nasal, temporal and inferior quadrants were significantly less in eyes with PAS compared with those without (p,0.001, Mann–Whitney U test). Analysis by quadrant showed that these parameters were smaller in the nasal and temporal quadrants in eyes with PAS (p,0.01). Conclusions: Angle width determined by AS-OCT and the extent of PAS were weakly correlated, and angle width was significantly smaller in eyes with PAS. Population-based studies from Mongolia and Singapore have identified an association between gonioscopic angle width and the degree of periph- eral anterior synechiae (PAS), with the narrowest angles having the highest likelihood of PAS. 1 Similar findings were reported in a population based study in southern China. 2 In a clinical trial of Asian patients with primary angle closure glau- coma (PACG), there was also a correlation between the number of clock hours of PAS and the gonioscopic angle width (r 2 = 0.20). 3 While it is important to assess angle width in the diagnosis and management of patients with angle closure, gonioscopy is relatively subjective and prone to variability from changes in illumination and manipulation of the gonioscopy lens. 45 Furthermore, previous studies have also shown that even experienced, cross-trained examiners have only moderate agreement in determining angle width. 67 Anterior segment optical coherence tomography (AS-OCT) has been introduced as an imaging modality for the angle. AS-OCT identifies more persons as having angle-closure than dark-room gonioscopy. This may indicate that AS-OCT has greater diagnostic sensitivity. 89 Being a non-con- tact instrument that can rapidly perform scans of the angles, its could potentially be used as a diagnostic tool for angle closure. The aim of this study was to evaluate the relationship between angle width as determined by AS-OCT with the presence and amount of PAS. METHODS Study participants This study was approved by the Institutional Review Board of the National University Hospital, Singapore and was carried out in accordance with The World Medical Association’s Declaration of Helsinki. Written informed consent was obtained from all subjects. Subjects aged 40 years and older were recruited from glaucoma clinics at National University Hospital. We recruited consecutive subjects with angle closure, classified as primary angle closure suspects (PACS), primary angle closure (PAC) or PACG according to the criteria by Foster et al. 10 Subjects with open angles were also recruited but those with previous cataract or glaucoma surgery were excluded from the study. PACS was defined as the presence of at least 180u of angle in which the posterior pigmented trabecular meshwork was not visible on non-indentation gonioscopy in the primary position. PAC was diagnosed when eyes had in addition peripheral anterior synechiae or raised intraocular pressure .21 mm Hg. Eyes with PAC and evidence of glaucomatous optic neuro- pathy were diagnosed as PACG. Gonioscopy Subjects underwent gonioscopy by an independent examiner who was masked to AS-OCT findings. Each subject was examined in low ambient light conditions with a Goldman 2-mirror lens. A narrow 1-mm beam of light was used; a horizon- tally offset vertical beam was used to assess the superior and inferior angles, while a horizontal beam that was offset vertically was used for the nasal and temporal angles. The assessment was carried out at 6 16 magnification with care taken to avoid light crossing the pupil margin during gonioscopy. All four quadrants were assessed with Clinical science Br J Ophthalmol 2008;92:103–107. doi:10.1136/bjo.2007.122572 103