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Clark RA, Suh SY, Caprioli J, Giaconi JA, Nouri-Mahdavi K, Law SK, Bonelli L, Coleman AL, Demer JL. Adduction-Induced Strain on the Optic Nerve in Primary Open Angle Glaucoma at Normal Intraocular Pressure. Curr Eye Res 2020; 46:568-578. [PMID: 32911989 DOI: 10.1080/02713683.2020.1817491] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE/AIM The optic nerve (ON) becomes taut during adduction beyond ~26° in healthy people and patients with primary open angle glaucoma (POAG), but only retracts the globe in POAG. We used magnetic resonance imaging (MRI) to investigate this difference. MATERIALS AND METHODS MRI was obtained in 2-mm quasi-coronal planes in central gaze, and smaller (~23-25°) and larger (~30-31°) adduction and abduction in 21 controls and 12 POAG subjects whose intraocular pressure never exceeded 21 mmHg. ON cross-sections were analyzed from the globe to 10 mm posteriorly. Area centroids were used to calculate ON path lengths and changes in cross-sections to calculate elongation assuming volume conservation. RESULTS For both groups, ON path was nearly straight (<102.5% of minimum path) in smaller adduction, with minimal further straightening in larger adduction. ON length was redundant in abduction, exceeding 103% of minimum path for both groups. For normals, the ON elongated 0.4 ± 0.5 mm from central gaze to smaller adduction, and 0.4 ± 0.5 mm further from smaller to larger adduction. For POAG subjects, the ON did not elongate on average from central gaze to smaller adduction and only 0.2 ± 0.4 mm from smaller to larger adduction (P = .045 vs normals). Both groups demonstrated minimal ON elongation not exceeding 0.25 mm from central gaze to smaller and larger abduction. The globe retracted significantly more during large adduction in POAG subjects than normals (0.6 ± 0.7 mm vs 0.2 ± 0.5 mm, P = .027), without appreciable retraction in abduction. For each mm increase in globe axial length, ON elongation in large adduction similarly increased by 0.2 mm in each group. CONCLUSIONS The normal ON stretches to absorb force and avert globe retraction in adduction. In POAG with mild to severe visual field loss, the relatively inelastic ON tethers and retracts the globe during adduction beyond ~26°, transfering stress to the optic disc that could contribute to progressive neuropathy during repeated eye movements.
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Affiliation(s)
- Robert A Clark
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - Soh Youn Suh
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - Joseph Caprioli
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - JoAnn A Giaconi
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - Kouros Nouri-Mahdavi
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - Simon K Law
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - Laura Bonelli
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA
| | - Anne L Coleman
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA.,Department of Epidemiology Fielding School of Public Health, University of California, Los Angeles, USA
| | - Joseph L Demer
- Department of Ophthalmology, University of California, Los Angeles, USA.,Stein Eye Institute, University of California, Los Angeles, USA.,Department of Neurology, University of California, Los Angeles, USA.,Neuroscience Interdepartmental Program, University of California, Los Angeles, USA.,Bioengineering Interdepartmental Program, University of California, Los Angeles, USA
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