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Trabecular Meshwork Height in Primary Open-Angle Glaucoma Versus Primary Angle-Closure Glaucoma

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Trabecular Meshwork Height in Primary Open-Angle Glaucoma Versus Primary Angle-Closure Glaucoma Trabecular Meshwork Height in Primary Open-Angle Glaucoma Versus Primary Angle-Closure Glaucoma MARISSE MASIS, REBECCA CHEN, TRAVIS PORCO, AND SHAN C. LIN PURPOSE: To determine if trabecular meshwork (TM) depth, and narrower angle width that predispose to obstruc- height differs between primary open-angle glaucoma tion of the trabecular meshwork.2 Moreover, additional (POAG) and primary angle-closure glaucoma (PACG) anatomic differences at the trabecular meshwork level eyes. may help investigators and clinicians in understanding DESIGN: Prospective, cross-sectional clinical study. novel mechanisms related to the pathophysiology of METHODS: Adult patients were consecutively recruited primary angle-closure glaucoma (PACG). from glaucoma clinics at the University of California, San Anterior segment imaging techniques such as ultrasound Francisco, from January 2012 to July 2015. Images were biomicroscopy (UBM) and anterior segment optical coher- obtained from spectral-domain optical coherence tomog- ence tomography (AS-OCT) provide objective evalua- raphy (Cirrus OCT; Carl Zeiss Meditec, Inc, Dublin, Cal- tions of the angle.3,4 Optical coherence tomography ifornia, USA). Univariate and multivariate linear mixed (OCT) technology has evolved from time-domain to models comparing TM height and glaucoma type were Fourier-domain imaging systems, which have enhanced performed to assess the relationship between TM height signal-to-noise ratio, image resolution, and speed.5 and glaucoma subtype. Mixed-effects regression was Gold and associates6 evaluated the normal aging effects used to adjust for the use of both eyes in some subjects. on the TM using Fourier-domain AS-OCT, and concluded RESULTS: The study included 260 eyes from 161 sub- that TM measurements are not related to age. They found jects, composed of 61 men and 100 women. Mean age that the imaging technique was reproducible and achieved was 70 years (SD 11.77). There were 199 eyes (123 good visualization of the structures. Tun and associates7 patients) in the POAG group and 61 eyes (38 patients) also validated the use of high-definition OCT images to in the PACG group. Mean TM heights in the POAG measure the distance between the scleral spur and and PACG groups were 812 ± 13 mm and Schwalbe line. Furthermore, several studies have shown 732 ± 27 mm, respectively, and the difference was signif- that Fourier-domain OCT allows excellent visualization icant in univariate analysis (P [ .004) and in multivar- and measurement of the TM and its surrounding structures iate analysis (b [ L88.7 [24.05–153.5]; P [ .008). with an acceptable reproducibility.8,9 CONCLUSION: In this clinic-based population, trabec- The aim of the present study is to determine if an addi- ular meshwork height is shorter in PACG patients tional risk factor for PACG could be a shorter TM height, compared to POAG patients. This finding may provide which may also be associated with a greater likelihood for insight into the pathophysiology of angle closure and TM occlusion. provide assistance in future diagnosis, prevention, and management of the angle-closure spectrum of disorders. (Am J Ophthalmol 2017;183:42–47. Ó 2017 Elsevier Inc. All rights reserved.) METHODS DATA COLLECTION: Consecutive patients were HE TRABECULAR MESHWORK (TM), WITHIN THE recruited from the Glaucoma Service at the University of anterior chamber angle, is the primary site for California, San Francisco (UCSF), and written informed T aqueous humor outflow.1 Eyes with angle closure consent was obtained. Institutional review board approval often have anatomic risk factors such as larger iris area/vol- was obtained from the Committee on Human Research at ume, different iris conformation, smaller anterior chamber UCSF (study number 12-09705). This study adhered to the guidelines of the Declaration of Helsinki. Glaucoma was defined based on the International Soci- Supplemental Material available at AJO.com. ety of Geographical and Epidemiological Ophthalmology 10 Accepted for publication Aug 23, 2017. (ISGEO) criteria. We included subjects who met cate- From the Department of Ophthalmology, University of California, San gories I or II of the ISGEO criteria: (1) category 1: visual Francisco, San Francisco, California. Inquiries to Shan C. Lin, Department of Ophthalmology, University of field loss consistent with glaucoma, and cup-to-disc ratio California, San Francisco, San Francisco, CA; e-mail: [email protected] >_ 0.7 or asymmetry >_ 0.2; or (2) category 2: cup-to-disc 42 © 2017 ELSEVIER INC.ALL RIGHTS RESERVED. 0002-9394/$36.00 http://dx.doi.org/10.1016/j.ajo.2017.08.018 ratio >_ 0.9 or asymmetry >_ 0.3, if the patient was unable to perform adequate visual field examination. In addition, all subjects were on glaucoma medication therapy. Eyes were further classified into primary open-angle glau- coma (POAG) or PACG based on gonioscopy results. POAG was diagnosed if the anterior chamber angles did not have more than 180 degrees graded as 1 or less by Shaffer criteria and did not possess peripheral anterior synechiae (PAS). PACG was diagnosed if there was the presence of PAS in any of the quadrants, or there was 180 degrees or greater of grade 1 or less on gonioscopy (prior to iridotomy). Inclusion criteria for this study included the following: FIGURE. Image of the anterior chamber angle taken by optical coherence tomography (Cirrus OCT; Carl Zeiss Meditec, Inc, (1) age >_18 years, and (2) diagnosis of POAG or PACG Dublin, California, USA). The anterior portion of the trabec- (according to the above criteria). Exclusion criteria ular meshwork is delimited by the Schwalbe line and the poste- included (1) history of uveitis, significant retinal or neuro- rior part by the scleral spur. Landmarks are identified as follows: logic diseases, or congenital ocular anomalies; (2) history of *Schwalbe line, **Schlemm’s canal, ***scleral spur. ocular trauma; or (3) any intraocular surgery. Eyes in the PACG group with history of laser peripheral iridotomy (LPI) and eyes in the POAG group with history of selective laser trabeculoplasty (SLT) were not excluded, and statisti- Light Meter [Model EA30; Extech Instruments, Inc, cal adjustment was performed to account for their Waltham, Massachusetts, USA]). Images were oriented inclusion. Both eyes of patients were included in the study in the horizontal (0–180 degrees) meridian and imaged in if they met the inclusion and exclusion criteria. Mixed- the single anterior segment imaging mode. AS-OCT effects regression was performed to account for the use of images were quantitatively assessed using the Zhongshan both eyes of some subjects. Angle Assessment Program (ZAAP; Zhongshan In PACG eyes with no previous LPI there is usually poor Ophthalmic Centre, Guangzhou, China). visualization of angle landmarks (scleral spur and Schwalbe Anterior segment parameters obtained by AS-OCT line), and therefore it becomes difficult and likely inaccu- (Visante OCT) were defined as follows: lens vault (LV) rate in eyes prior to LPI to determine the main outcome is the perpendicular distance from the anterior pole of (TM height). Consequently, closed-angle eyes with LPI the lens to the horizontal line joining the scleral spurs; were included for the analysis. theangleopeningdistanceat500mm(AOD500)isthe Every participant underwent clinical ophthalmic evalu- distance between the posterior corneal surface and the ation including best-corrected visual acuity (BCVA), anterior iris surface on a line perpendicular to the trabec- slit-lamp assessment, intraocular pressure measurement by ular meshwork, 500 mm from the scleral spur; the Goldmann applanation, gonioscopy, and visual field trabecular-iris space area at 500 mm (TISA500) is the testing (24-2 Swedish Interactive Threshold Algorithm, surface area of a trapezoid with the following boundaries: HFA2; Carl Zeiss Meditec, Inc, Dublin, California, anteriorly, the angle opening distance at 500 mmfromthe USA). Gonioscopy was performed using a Zeiss-style scleral spur; posteriorly, a line drawn from the scleral spur 4-mirror gonioscopy lens (model OPDSG; Ocular Instru- perpendicular to the plane of the inner scleral wall to the ments, Inc, Bellevue, Washington, USA) by the same iris; superiorly, the inner corneoscleral wall; and inferi- glaucoma specialist (S.L.) in a darkroom setting. Angles orly, the iris surface. Measures were obtained by trained were graded in all 4 quadrants (superior, nasal, temporal, operators and ZAAP analysis was performed by the same and inferior) based on the Shaffer classification. Dynamic investigator. gonioscopy was performed to detect PAS, which was For the trabecular meshwork imaging, measures were recorded as number of clock hours in each quadrant and obtained using Fourier-domain OCT (Cirrus OCT; Carl in terms of position. Zeiss Meditec, Inc, Dublin, California, USA). A Additional measures, such as axial length (AL) and cen- high-magnification anterior segment image of the tempo- tral corneal thickness (CCT), were obtained for all patients ral TM oriented horizontally was taken in dark conditions using optical low-coherence reflectometry (Lenstar LS 900; (0 lux using the Extech EasyView Digital Light Meter Haag-Streit Holding AG, Koniz, Switzerland). [Model EA30; Extech Instruments, Inc, Waltham, For anterior segment parameters, AS-OCT images were Massachusetts, USA]). To obtain an optimal-quality captured using the Visante OCT (Carl Zeiss Meditec, Inc, image, the patient was asked to look in the opposite direc- Dublin, California, USA) by trained researchers who
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