PURPOSE: Gray crescents characterized by darkly pigmented regions on the optic nerve head could make assessment of cupping difficult by obscuring the true anatomic disc border. On slit-lamp examination, 2 morphologically distinct types of gray crescents at the curved disc boundary exist. The in vivo histologic characteristics differentiating these 2 types are described using spectral-domain (SD) OCT. METHODS: A prospective interventional case series in a single tertiary referral center. Sixteen eyes of 10 patients with gray crescents determined through clinical examination and fundus photography underwent cross-sectional optic nerve head and parapapillary imaging using high-resolution SD OCT. In vivo histology of gray crescents was characterized. RESULTS: In SD OCT images across the areas of gray crescent, type A gray crescents represent regions where the retinal pigment epithelium (RPE)-Bruch's membrane complex is absent and the dark underlying choroid is directly visible. In contrast, type B gray crescents represent regions of the retina where the RPE is clumped or thickened, typically appearing to be folded upon itself, revealing the embryonic continuity of the RPE and neuroretina. CONCLUSIONS: Shields type A and B gray crescents appear different clinically because histologically they represent differences in RPE. Type A grey crescents lack RPE, whereas type B crescents have thickened, folded RPE. Gray crescents can obscure the true disc border and result in pseudo-cupping of the optic nerve head. Identification of gray crescents is clinically important because failure to recognize pseudo-cupping can contribute to overdiagnosis of glaucoma.
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