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Optic Nerve Head and Peripapillary Morphometrics in Myopic Glaucoma

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Optic Nerve Head and Peripapillary Morphometrics in Myopic Glaucoma Glaucoma Optic Nerve Head and Peripapillary Morphometrics in Myopic Glaucoma Sieun Lee,1 Sherry X. Han,2 Mei Young,2 Mirza Faisal Beg,1 Marinko V. Sarunic,1 and Paul J. Mackenzie2 1School of Engineering Science, Simon Fraser University, Burnaby, British Columbia, Canada 2Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, British Columbia, Canada Correspondence: Sieun Lee, School PURPOSE. To investigate morphological characteristics of optic nerve head and peripapillary of Engineering Science, Simon Fraser region with myopia and glaucoma. University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6; METHODS. Ten normal and 17 glaucomatous myopic participants were imaged with a custom [email protected]. 1060-nm swept-source optical coherence tomography system. The three-dimensional images Mirza Faisal Beg, School of Engi- were processed and segmented for inner limiting membrane (ILM), posterior border of retinal neering Science, Simon Fraser Uni- nerve fiber layer (RNFL), Bruch’s membrane (BM), and posterior border of choroid. Seven versity, 8888 University Drive, shape parameters were measured: nerve fiber layer (NFL) thickness; Bruch’s membrane Burnaby, BC, Canada V5A 1S6; opening (BMO) area, eccentricity, and planarity; BMO and BM depths; and choroidal [email protected]. thickness. The results were analyzed by group and regional sector, and multiple regression Marinko V. Sarunic, School of Engi- was performed on each shape parameter with age, axial length, and glaucoma severity, neering Science, Simon Fraser Uni- measured by mean deviation (MD). versity, 8888 University Drive, Burnaby, BC, Canada V5A 1S6; RESULTS. Bruch’s membrane opening area (P < 0.001), eccentricity (P ¼ 0.025), and planarity [email protected]. (P ¼ 0.019) were correlated with axial length but not with MD, such that larger, more PaulJ.Mackenzie,Departmentof elliptical, and less planar BMO was associated with longer axial length. Several BMOs Ophthalmology, University of British displayed a saddle-like shape configuration whose orientation appeared to be aligned with Columbia, 2550 Willow Street, Van- that of the BMO ellipse. All BM showed posterior deformation toward BMO such that BM couver, BC, Canada V5Z 0A6; closer to BMO was more posterior than that farther from BMO. Bruch’s membrane depth was [email protected]. correlated with axial length (P ¼ 0.014) and MD (P ¼ 0.040) in intersubject regression, and Submitted: March 4, 2014 BMO depth (P ¼ 0.003) and BM depth (P ¼ 0.006) were correlated with MD in intereye Accepted: May 5, 2014 regression. Bruch’s membrane depth was also associated with age. Choroidal thickness was negatively correlated with age (P ¼ 0.001) and with axial length to a smaller degree (P ¼ Citation: Lee S, Han SX, Young M, Beg 0.034), but not with glaucoma severity. MF, Sarunic MV, Mackenzie PJ. Optic nerve head and peripapillary mor- CONCLUSIONS. Axial length was a significant factor in BMO and BM shape in normal and phometrics in myopic glaucoma. In- glaucomatous myopic subjects. Posterior deformation of BM was observed in all eyes and vest Ophthalmol Vis Sci. significantly associated with functional glaucomatous damage and age. 2014;55:4378–4393. DOI:10.1167/ iovs.14-14227 Keywords: ONH, glaucoma, myopia, shape analysis, image analysis he pathophysiology of glaucoma, although not fully and pale neuroretinal rim of high myopia make optic nerve T understood, involves damage to the retinal ganglion cell head assessment difficult. Myopic individuals can show axons at the level of the lamina cribrosa.1–3 Uncontrolled abnormal results on structural and functional testing because intraocular pressure (IOP) likely triggers several parallel, but normal databases are composed of individuals with low interacting, mechanisms including direct axonal damage, refractive error.21,22 Coexisting pathologies, particularly myo- disturbances in neurometabolism and microvascular supply, pic degeneration, cloud interpretation of visual field changes in glial activation, and extensive remodeling of the connective advanced glaucoma. Cup-to-disc ratio and retinal nerve fiber tissues of the lamina cribrosa and surrounding tissues layer (RNFL) thickness measured by commercial optical throughout the development and progression of glaucoma.4–15 coherence tomography (OCT) and confocal scanning laser The peripapillary tissues that surround the optic nerve itself ophthalmoscopy (CSLO) were shown to be less effective in have also been implicated as possible contributors to glau- discriminating glaucomatous and nonglaucomatous subjects comatous changes, in both experimental and modeling with high myopia,23 with several studies reporting RNFL studies.16 Atrophic features of the peripapillary tissues that thinning associated with myopia.24–26 There are theoretical appear to be associated with glaucoma can include thinning of grounds to suggest that myopic eyes may be more sensitive to a the peripapillary scleral tissue17 and loss of almost all retinal given IOP as a result of the larger globe size and thinner, more and deeper layers separating the subarachnoid space from the compliant tissues.27–29 vitreous cavity.18 In studies comparing highly myopic glaucomatous eyes to Myopia presents unique challenges for the management of nonhighly myopic glaucomatous eyes, the former showed glaucoma. Population-based studies have indicated a greater significant histological difference in the peripapillary region, prevalence of glaucoma in myopes.19,20 The shallow cupping including elongation and thinning of the scleral flange.30 Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc. www.iovs.org j ISSN: 1552-5783 4378 Downloaded from iovs.arvojournals.org on 09/27/2021 Morphometrics in Myopic Glaucoma IOVS j July 2014 j Vol. 55 j No. 7 j 4379 TABLE 1. Demographics and Clinical Characteristics of the Study Subjects by Group Group No. of Subjects (No. of Eyes Used) Age Axial Length, mm MD, dB Young normal 5 (10) 29.8 6 3.6 25.9 6 1.4 À0.8 6 0.6 Older normal 5 (10) 57.0 6 4.4 25.5 6 1.0 À0.5 6 1.1 Glaucomatous, unilateral 7 (14) 57.2 6 12.4 26.2 6 0.9 À0.5 6 0.5 Glaucomatous, bilateral 10 (19) 55.7 6 12.6 27.1 6 1.8 À14.6 6 8.4 Comparison of color stereo optic disc photography showed house acquisition software that provided real-time en face and more pronounced optic nerve damage, larger and more cross-sectional images to guide acquisition. The 1060-nm light elongated optic discs, and shallower optic cups in myopic source, relative to 830-nm light sources in most commercial glaucomatous eyes.31–33 OCT systems, more clearly visualized deeper structures such as To further understand the features of the myopic optic the choroid. The swept-source configuration allowed an A-scan nerve in glaucoma, we have used a custom 1060-nm swept- line rate of 100 KHz. source OCT system34 to image the optic nerve and surrounding The acquired three-dimensional (3D) image consisted of peripapillary tissues in myopes, both with and without 400 B-scans, each with 400 A-scans, and 1024 pixels per A- glaucoma, and performed quantitative shape measurement scan. The imaged region in physical space spanned an axial and analysis. depth of 2.8 mm and a square area of 5 3 5to83 8mm2. This area, the image dimension in the lateral direction, was calculated for each eye based on the optics of the acquisition MATERIALS AND METHODS system, scan angle, and axial length of the eye. Resulting voxel dimension was 2.7 lm in the axial direction and 12.5 to 20 lm Participants in the lateral direction. A full volumetric image was acquired in A total of 27 subjects were recruited for this study: five young 1.6 seconds. healthy controls (10 eyes, mean age ¼ 29.8 6 3.6 years), five Axial motion artifact was corrected using cross-correlation 35 older healthy controls (10 eyes, mean age ¼ 57.0 6 4.4), seven between adjacent frames. Three-dimensional bounded vari- 36 patients with unilateral glaucoma (14 eyes, mean age ¼ 57.2 6 ation smoothing was applied to reduce the effect of speckles 12.4), and 10 patients with bilateral open-angle glaucoma (19 while preserving and enhancing edges (Figs. 1a, 1b). eyes, mean age ¼ 55.7 6 12.6). Ethics review for this study was approved from Simon Fraser University (SFU) and from the Segmentation University of British Columbia (UBC). The study was conduct- ed in accordance with the guidelines of the Declaration of Inner limiting membrane (ILM), the posterior boundary of Helsinki, and informed consent form was obtained from each nerve fiber layer (NFL), Bruch’s membrane (BM), Bruch’s participant. membrane opening (BMO), and the choroid–sclera boundary All participants had axial lengths greater than 24 mm. A (CS boundary) were segmented for this study (Fig. 1c). The diagnosis of open-angle glaucoma was made clinically by a four surfaces (ILM, NFL, BM, and CS boundary) were fellowship-trained glaucoma specialist (PJM) based on full segmented automatically in 3D using a graph-cut algo- examination including dilated stereoscopic examination of the rithm.37–40 Briefly, a graph was constructed for each volume optic nerve, analysis of stereo disc photography, and typical by assigning a node to each voxel and creating arcs between reproducible Humphrey SITA-Standard white on white visual the nodes based on smoothness of target surfaces and distance field abnormality. No reference to OCT images was made for between the surfaces. We used intensity gradient in the axial the purposes of categorizing subjects for the study. Severity of direction as the cost function such that the minimum s-t cut of glaucomatous visual field loss was quantified by visual field the graph corresponded to smooth edges with strong intensity mean deviation (MD) values. Participant demographics are contrast. Inner limiting membrane and BM, which are imaged tabulated in Table 1 with individual subject information in with higher contrast, were segmented first, and then posterior Supplementary Table S1.
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