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Melinda Chang, Andrew Shin, Joseph Park, Aaron Nagiel, Robert Lalane, Steven D Schwartz, Joseph L Demer; Optical Coherence Tomography (OCT) Demonstrates Deformation of Optic Cup and Peripapillary Tissues By Horizontal Duction. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
There has to date been no mutual interaction between extensive literatures on biomechanics of extraocular muscles (EOMs) in ocular motility, and biomechanics of the lamina cribrosa (LC) and sclera in glaucoma. However, MRI studies recently demonstrated that the otherwise sinuous optic nerve (ON) consistently exhausts redundancy in adduction and sometimes abduction, where its sheath exerts traction on the peripapillary sclera and LC as reaction force to EOM tension (Shin et al, ARVO 2016). We sought OCT evidence of deformation of these tissues during horizontal duction.
We studied 8 normal volunteers of average age 21±0.4 (SD) years using a Nidek 3000 scanning laser ophthalmoscope-stabilized spectral domain OCT that tracked and registered subsequent scans to retinal features initially imaged in central gaze. OCT sets were 128 contiguous rasters 9 mm wide x 2.4 mm deep, centered on ON, and repeated in ad- and ab-duction while maintaining constant vertex distance. Eccentric gazes were analyzed relative to central gaze using the nasal retinal pigment epithelium (RPE) as reference plane.
Temporal peripapillary RPE (tpRPE) was progressively posteriorly displaced with increasing adduction. At 30° adduction, tpRPE shifted posteriorly by 81±65 mm (p=0.0003); linear regression demonstrated posterior displacement of 2.43±0.32 (SE) mm/° adduction but -0.69±0.15 mm/° for abduction (p=0.0034). Optic cup depth progressively increased with adduction; at 30°, mean optic cup depth increased by 36±43 mm (p=0.01). Mean nasal peripapillary choroid thickness was 241±45 mm in central gaze, and slightly but significantly thinned in both ad- and abduction to 232-235 mm. Mean temporal peripapillary choroid thickness was 188±25 mm in central gaze, and was significantly thinned to 171±26 mm in 30° adduction (p=0.029).
OCT confirms MRI and biomechanical predictions of marked distortions of the temporal peripapillary tissues in ad- more than ab-duction, with distortion of the optic cup and choroidal thinning. Repetitive mechanical stress on ON and peripapillary tissues may contribute to myopic peripapillary changes and optic neuropathies such as normal tension glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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