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Assessment of the Scleral Spur in Anterior Segment Optical Coherence Tomography Images

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Assessment of the Scleral Spur in Anterior Segment Optical Coherence Tomography Images CLINICAL SCIENCES Assessment of the Scleral Spur in Anterior Segment Optical Coherence Tomography Images Lisandro M. Sakata, MD, PhD; Raghavan Lavanya, DO; David S. Friedman, MD; Han T. Aung, MBBS; Steve K. Seah, FRCS; Paul J. Foster, PhD, FRCS; Tin Aung, MBBS, PhD, FRCS(Edin) Objective: To assess visibility of the scleral spur in an- Results: Scleral spur location could be determined in 72% terior segment optical coherence tomography (AS-OCT) of the images of the right eye. Its location on AS-OCT im- images. ages was less detectable in quadrants with a closed angle on gonioscopy and also in images obtained in the superior and inferior compared with the nasal and temporal quad- Methods: This cross-sectional observational study in- rants (64%, 67%, 75%, and 80%, respectively; PϽ.001). cluded 502 participants aged 50 years or older who had no previous ophthalmic problems and were recruited from Conclusions: The inability to detect the scleral spur may a community clinic in Singapore. All participants under- hamper quantitative analysis of anterior chamber angle para- went gonioscopy and AS-OCT (Visante; Carl Zeiss Med- meters that are dependent on the location of this anatomi- itec, Dublin, California). Scleral spur location was as- cal structure, particularly in the superior and inferior quad- sessed in AS-OCT images by 2 examiners with glaucoma rants. New parameters independent of the scleral spur may subspecialty training and was defined as the point where be useful for detecting eyes at risk of angle closure. there was an inward protrusion of the sclera with a change in curvature of its inner surface. Arch Ophthalmol. 2008;126(2):181-185 NTERIOR SEGMENT OPTI- METHODS cal coherence tomogra- phy (AS-OCT) is a new Study participants were in a subset of consecu- technology for imaging the tive participants of a larger study conducted to anterior segment of the evaluate the performance of new imaging de- Aeye. It is capable of obtaining real-time im- vices in screening for angle closure. Those in- ages of the anterior chamber angle and rep- cluded in the larger study were aged older than resents a rapid, noncontact method for the 50 years and were attending a community poly- detection of eyes at risk of angle clo- clinic in Singapore, for nonophthalmic rea- 1-5 sons from January to July 2006. Informed con- sure. As with ultrasound biomicros- sent was obtained from all participants. The copy, the evaluation of the anterior cham- study had the approval of the institutional re- ber angle in AS-OCT depends on view board of the Singapore Eye Research In- determining the location of the scleral spur, stitute and adhered to the tenets of the Decla- which anatomically represents the junc- ration of Helsinki. tion between the inner wall of the trabec- After being asked about his or her medical ular meshwork and the sclera. The scleral and ophthalmic history, each participant un- derwent the following examinations on the Author Affiliations: Singapore spur in anterior segment imaging is same day: visual acuity, AS-OCT (Visante; Carl Eye Research Institute and marked by a prominent inner extension Zeiss Meditec, Dublin, California), anterior Singapore National Eye Center, of the sclera (its thickest part)6-8 and rep- chamber depth and axial length measure- Singapore (Drs Sakata, Lavanya, resents an anatomical landmark for the tra- ments (IOL-Master, Carl Zeiss Meditec), slit- H. T. Aung, Seah, and T. Aung); becular meshwork, which is located ap- lamp biomicroscopy, Goldmann applanation Wilmer Eye Institute and Johns proximately 250 to 500 µm anterior to the tonometry, and gonioscopy. Participants were Hopkins Bloomberg School of scleral spur along the angle wall.6 The aim excluded if they had a history of intraocular sur- Public Health, Baltimore, gery or penetrating trauma in either eye, an- Maryland (Dr Friedman); and of this study was to evaluate the visibility terior segment laser treatment, or glaucoma. Institute of Ophthalmology and of the scleral spur in AS-OCT images and Gonioscopy was performed in the dark in Moorfields Eye Hospital, to assess the effect of this on the assess- all participants by a single examiner masked London, England (Dr Foster). ment of angle closure. to AS-OCT findings. A 1-mm light beam was (REPRINTED) ARCH OPHTHALMOL / VOL 126 (NO. 2), FEB 2008 WWW.ARCHOPHTHALMOL.COM 181 ©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/01/2021 results (L.M.S. and T.A. working together). The examiners tried to locate the scleral spur on each AS-OCT image. The scleral spur was defined as the point where there was a change in cur- vature of the inner surface of the angle wall, often appearing as an inward protrusion of the sclera (Figure 1). The anterior chamber angle in a particular quadrant was clas- sified as closed on gonioscopy if the posterior trabecular mesh- work could not be seen (Scheie grade III or IV) during nonin- dentation gonioscopy. A closed anterior chamber angle on AS-OCT was defined by the presence of any contact anterior Figure 1. The location of the scleral spur in an anterior segment optical to the scleral spur between the iris and angle wall. coherence tomography image (arrows). The intraobserver reproducibility in detecting the scleral spur in AS-OCT images was assessed in a random subset of 33 eyes reduced to a very narrow slit, which was offset horizontally for (132 quadrants). Images of the 4 quadrants of the eye were as- assessing superior and inferior angles and vertically for nasal sessed in 2 sessions separated by a 1-week interval. A single and temporal angles. Nonindentation gonioscopy was per- examiner (L.M.S.), masked to the other test results, graded each formed using a Goldmann 2-mirror lens at high magnification quadrant in a dichotomous classification: detectable or unde- (ϫ16) with the eye in the primary position of gaze. Care was tectable scleral spur. In addition, a second analysis aimed to taken to keep the light from falling on the pupil and to avoid evaluate the reproducibility of determining the exact scleral spur accidental indentation during examination. The anterior cham- location in the same 132 AS-OCT images. Its location was plot- ber angle width in each quadrant was determined using the ted in the AS-OCT images using ImageJ software (NIH Im- Scheie grading system,9 which is based on the angle structures ageJ; National Institutes of Health, Bethesda, Maryland). A single visible during the examination. Slight tilting of the gonio- examiner (L.M.S.) obtained the x and y coordinates of the scleral scope lens was permitted in an attempt to gain a view over the spur location in 2 sessions separated by a 1-week interval. The convexity of the iris; the results obtained with this technique distance between the scleral spur (in each particular quad- were used in the analysis. Dynamic gonioscopy with a Suss- rant) was assessed in 78 quadrants, as the examiner could not man 4-mirror lens was also performed. The results of this dy- define its exact location in 54 quadrants. namic examination were not used in the analysis of our study. STATISTICAL ANALYSIS ANTERIOR SEGMENT OPTICAL COHERENCE TOMOGRAPHY Parametric and nonparametric tests were used to compare con- tinuous variables according to data distribution. The ␹2 test was used to compare categorical data. Logistic regression analysis Details of AS-OCT technology have been described previ- was used to assess the factors related to the detectability of the ously.2,3 Briefly, this technology permits image acquisition at a scleral spur on AS-OCT images. For the logistic analysis, only rate of 8 frames/s (2000 A-scans/s) with a transverse resolution 1 quadrant of 1 eye per participant was randomly selected for of 60 µm and an axial resolution of 10 to 20 µm. Furthermore, analysis. The intraobserver reproducibility in determining the the use of wide-field scanning optics (16 mm) and deep axial presence of a detectable scleral spur was assessed using ␬ sta- scan range (8 mm) permit the AS-OCT to image the entire an- tistics.11 PϽ.05 was considered statistically significant. Statis- terior chamber in a single frame. After acquisition, the scanned tical analyses were performed using JMP5 (SAS Institute Inc, images are processed by a customized “dewarping” software, Cary, North Carolina) and MedCalc (MedCalc, Mariakerke, Bel- which compensates for the index of refraction transition at the gium) software. air-tear interface and the different group indices in air, cornea, and aqueous to correct the images’ physical dimensions.10 Participants were examined in the sitting position by a single RESULTS masked examiner (H.T.A.) before any procedure that in- volved contact with the eye. Anterior segment optical coher- A total of 504 consecutive participants were included in ence tomography images of the anterior chamber angle were this study, of whom 274 (54.6%) were women. Most par- obtained in dark conditions using the standard anterior seg- ment single-scan protocol. To obtain the best quality image, ticipants were Chinese (463 [92%]), the rest being Ma- the examiner adjusted the saturation and noise and optimized lay (9 [2%]), Indian (20 [4%]), and other races (12 [2%]). the polarization for each scan during the examination. Three The mean (SD) age was 61.3 (7.6 [range, 51-93]) years. AS-OCT images of the anterior chamber angle of each eye were The mean (SD) anterior chamber depth of the partici- obtained: 1 scanning the angle at the 3- and 9-o’clock posi- pants’ right eyes was 3.12 (0.36) mm. Mean (SD) axial tions, 1 scanning the angle at the 12-o’clock position, and 1 length was 23.71 (3.25) mm.
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