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Diagnostic Performance of Anterior Chamber Angle Measurements for Detecting Eyes with Narrow Angles an Anterior Segment OCT Study

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Diagnostic Performance of Anterior Chamber Angle Measurements for Detecting Eyes with Narrow Angles an Anterior Segment OCT Study EPIDEMIOLOGY SECTION EDITOR: LESLIE HYMAN, PhD Diagnostic Performance of Anterior Chamber Angle Measurements for Detecting Eyes With Narrow Angles An Anterior Segment OCT Study Arun Narayanaswamy, DNB; Lisandro M. Sakata, MD, PhD; Ming-Guang He, MD, PhD; David S. Friedman, MD, PhD; Yiong-Huak Chan, PhD; Raghavan Lavanya, MD; Mani Baskaran, DNB; Paul J. Foster, PhD, FRCS(Ed); Tin Aung, PhD, FRCS(Ed) Objective: To assess the diagnostic performance of angle and ARA to assess the performance of these measure- measurements from anterior segment optical coherence ments in detecting eyes with narrow angles. tomography (AS-OCT) images for identifying eyes with narrow angles. Results: Of 2047 individuals examined, 582 were excluded mostly because of poor image quality or inability to locate Methods: We conducted a community-based cross- the scleral spur. Of the remaining 1465 participants, 315 sectional study of individuals 50 years or older who had (21.5%) had narrow angles on gonioscopy. Mean (SD) age phakic eyes and who underwent AS-OCT imaging in the was 62.7 (7.7) years, 54.1% were women, and 90.0% were dark by a single operator and gonioscopy by an ophthal- Chinese. The AUCs were highest for AOD750 in the nasal mologist masked to AS-OCT findings. An eye was con- (0.90 [95% confidence interval, 0.89-0.92]) and temporal sidered to have narrow angles if the posterior pig- (0.91 [0.90-0.93]) quadrants. mented trabecular meshwork was not visible for at least 180° on gonioscopy. Horizontal AS-OCT images were ana- Conclusions: The AOD750 is the most useful angle mea- lyzed for the following measurements using customized surement for identifying individuals with gonioscopic nar- software: angle opening distance (AOD) at 250, 500, and row angles in gradable AS-OCT images. Poor definition 750 µm from the scleral spur; trabecular-iris space area of the scleral spur precludes quantitative analysis in ap- (TISA) at 500 and 750 µm; and angle recess area (ARA) proximately 25% of AS-OCT images. at 750 µm. Areas under the receiver operating charac- teristic curves (AUCs) were generated for AOD, TISA, Arch Ophthalmol. 2010;128(10):1321-1327 HE NUMBER OF PEOPLE WHO Anterior segment optical coherence to- are blind because of glau- mography (AS-OCT) is capable of provid- coma is likely to reach 60.5 ing objective high-resolution images of the million worldwide by angle, and these images can be analyzed 2010.1 More than half of qualitatively and quantitatively.3-8 Imaging Tglaucoma blindness will be due to pri- of the angle with AS-OCT can be per- mary angle-closure glaucoma, and more formed in less than a minute by a techni- than 80% of people with angle-closure dis- cian and does not require contact with the ease are likely to be living in Asia.1 A key eye. Customized software can be used for initiative would be to enhance the abili- semiautomated analysis of AS-OCT im- ties of health care professionals to diag- ages9 to obtain several measurements of the nose and detect angle closure at an early anterior chamber angle, and the results of stage. Gonioscopy is the current refer- this analysis could be useful for detecting ence standard for detecting eyes with or eyes at risk of angle closure.10 A previous at risk of angle closure. Although techni- community-based study by our group11 in- cally a simple procedure, many subjec- volving a qualitative analysis of AS-OCT tive influences govern its interpretation,2 images showed a suboptimal diagnostic and a level of ability and expertise is re- performance for detection of narrow Author Affiliations are listed at quired to ensure that gonioscopy find- angles, mostly because of poor specificity the end of this article. ings are accurate. values. (REPRINTED) ARCH OPHTHALMOL / VOL 128 (NO. 10), OCT 2010 WWW.ARCHOPHTHALMOL.COM 1321 ©2010 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/02/2021 The aim of this study was to evaluate the diagnostic AS-OCT imaging technology have been described previously.3 performance of quantitative AS-OCT angle measure- Briefly, this technology permits image acquisition at a rate of 8 ments for detecting eyes with gonioscopic narrow angles. frames/s (2000 A-scans/s), with a transverse resolution of 60 µm and an axial resolution of 10 to 20 µm. Furthermore, the use of wide-field scanning optics (16 mm) and a deep axial scan range METHODS (8 mm) allows AS-OCT to image a cross section of the anterior chamber in a single image frame. After acquisition, the scanned Subjects for this study were participants in a study evaluating the images are processed by a customized (“dewarping”) software that usefulness of new imaging devices for detecting narrow angles compensates for index of refraction transition at the air-tear in- among Singaporeans attending a government-run polyclinic mostly terface and the different indices in air, cornea, and aqueous hu- for general medical problems.11 All participants were 50 years or mor to correct the physical dimensions of the images. Seated par- older and were systematically sampled (every fifth patient regis- ticipants were examined by a single ophthalmologist (R.L.) who tered at the polyclinic). Informed consent was obtained from all was masked to other test results before any procedure that involved participants, the institutional review board of the Singapore Na- contact with the eye. Three AS-OCT images of the anterior cham- tional Eye Center approved the protocol, and the study adhered ber angle of each eye were obtained in dark conditions using the to the tenets of the Declaration of Helsinki. single-scan-mode protocol: one image scanning the angle at the After an interview about medical and ophthalmic history, each 3- and 9-o’clock positions (horizontal meridian; Figure 1) fol- participant underwent the following examinations on the same lowed by one scanning the superior angle at 12 o’clock and one day: visual acuity, anterior segment imaging by AS-OCT, ante- scanning the inferior angle at 6 o’clock. Imaging at the 12- and rior chamber depth and axial length measurements (IOL Mas- 6-o’clock positions was obtained separately to avoid possible in- ter; Carl Zeiss Meditec Inc, Dublin, California), slitlamp biomi- terference of the eyelid. During the image capture, the upper eye- croscopy, Goldmann applanation tonometry, gonioscopy, and lid was gently elevated to image the superior angle and the lower stereoscopic posterior pole (optic disc and macula) examina- eyelid was gently pulled down by the operator to image the in- tion. Individuals were excluded if they had a history of intraocu- ferior angle, taking care to avoid inadvertent pressure on the globe. lar surgery, any evidence of aphakia/pseudophakia, or penetrat- The Zhongshan Angle Assessment Program (ZAAP; Zhong- ing trauma in the eye; previous anterior segment laser treatment; shan Ophthalmic Centre, Guangzhou, China)9 was used to ana- a history of glaucoma; or corneal disorders such as corneal en- lyze the AS-OCT images for quantitative measurements. For dothelial dystrophy, corneal opacity, or pterygium, all of which each image, the only observer input was to determine the lo- could influence the quality of angle imaging by AS-OCT. cation of the 2 scleral spurs. All analysis was performed by a single fellowship-trained glaucoma specialist (L.M.S.). The al- GONIOSCOPY gorithm then automatically calculated the following angle mea- surements (Figure 2): angle opening distance (AOD), angle Gonioscopy was performed in the dark in all cases by a single recess area (ARA), and trabecular-iris space area (TISA). examiner masked to AS-OCT findings. The examiner was a Angle opening distance was defined by Pavlin et al14 as the trained ophthalmologist (R.L.) with extensive experience in per- length of a line drawn from the anterior iris to the corneal en- forming gonioscopy in a research setting. A 1-mm light beam dothelium, perpendicular to a line drawn along the trabecular was reduced to a very narrow slit, and the vertical beam was meshwork at a given distance from the scleral spur. The AOD offset horizontally for evaluating nasal and temporal angles and was calculated at 250, 500, and 750 µm from the scleral spur maintained vertical for assessing superior and inferior angles. (AOD250, AOD500, and AOD750, respectively). The ARA and Static and dynamic gonioscopy was performed using a Gold- TISA were measured according to the guidelines by Ishikawa mann 2-mirror lens (Haag-Streit AG, Koeniz, Switzerland) and et al15 and Radhakrishnan et al,16 respectively. The ARA rep- a Sussman 4-mirror lens (Ocular Instruments Inc, Bellevue, resents measurement of the area bordered by the anterior iris Washington), respectively, at high magnification (ϫ16), with surface, corneal endothelium, and a line perpendicular to the the eye in the primary position of gaze. Care was taken to avoid corneal endothelium that is drawn to the iris surface from a light from falling on the pupil and to avoid inadvertent inden- point 750 µm anterior to the scleral spur. The TISA is a mea- tation during examination. In some cases, the gonioscopy lens surement that is further modified by not including the area be- was tilted minimally to permit a view of the angle over the con- low a line drawn from the scleral spur to the anterior iris per- vexity of the iris, avoiding ocular distortion. The angle in each pendicular to the plane of the inner scleral wall. The ARA was quadrant was graded using the Scheie grading system accord- calculated at 750 µm (ARA750), and the TISA was calculated ing to the anatomical structures observed during gonioscopy at 500 and 750 µm (TISA500 and TISA750, respectively).
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