Optic Nerve Head Characteristics in Chronic Angle Closure Glaucoma
Lucy Q. Shen, M.D.
Assistant Professor of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear
Boston, Massachusetts, U.S.A.
Purpose: To compare structural features in prelaminar and laminar tissues of the optic nerve head (ONH) in chronic angle closure glaucoma (CACG), primary open angle glaucoma (POAG) and control subjects.
Methods: ONH imaging was performed using swept-source optical coherence tomography (SS-OCT, Topcon) for measurements of minimum rim width at Bruch’s membrane opening (BMO-MRW), horizontal and vertical lamina cribrosa depth (LCD). Prelaminar defects, categorized as hole and wedge, and lamina cribrosa (LC) defects were identified. Enhanced depth imaging spectral domain OCT (EDI-OCT, Heidelberg) customized to perform high-resolution volume scans was used in conjunction to further characterize prelaminar holes. One eye per subject was analyzed.
Results: Eighty subjects (20 CACG, 40 POAG and 20 controls) were included in the study. CACG and POAG groups had similar mean deviation on Humphrey visual field testing (-6.9±5.1 vs. -6.3±6.0 dB, p>0.05) and IOP on the day of imaging. Thinnest and global BMO-MRW in CACG (120.3±44.8, 225.5±53.9 μm) and POAG (109.7±56.3, 213.8±59.7 μm) groups were lower than controls (200.1±40.8, 308.3±70.8 μm; p<0.001 for both). Prelaminar holes were most frequent in CACG (65.0%) than POAG (25.0%, p=0.008) or control groups (20.0%, p=0.01). After adjusting for demographic and ophthalmic covariates, CACG was associated with increased odds of having prelaminar holes compared to POAG (odd ratio, 9.79; 95% CI, 2.12-45.19; p=0.003). Hole volume was similar between CACG and POAG (p>0.05), but the CACG group had more holes per scan than POAG (maximum 2.5±1.9 vs. 1.2±0.4, p＝0.02). The CACG group did not differ from controls in laminar characteristics, such as LCD and LC defects.
Conclusions: SS-OCT evaluation of the ONH revealed more frequent prelaminar holes in CACG compared to POAG and control patients. This finding may be supported by previous histology studies and suggests distinct pathophysiologic processes in optic nerve damage in POAG and CACG.