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Phillip Bedggood, Fumi Tanabe, Andrew Turpin, Andrew J Anderson, Allison M McKendrick, Bang V Bui; Displacement of optic nerve head structures following a small acute elevation in intra-ocular pressure. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2106.
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Changes in shape of optic nerve head structures have been reported in animal models of glaucoma, in response to glaucoma treatment in humans, and in humans following acute change of intraocular pressure. We aimed to determine whether the type and degree of tissue displacement might be predicted by various biometric parameters currently measurable in a clinical setting.
We imaged the optic nerve head of 21 healthy participants (22 - 46 years old) before and after ~10 mmHg IOP elevation with ophthalmodynamometry. The Heidelberg Spectralis was used to acquire en face SLO images and a vertical B-scan through the deepest part of the cup. Blinded images were traced manually by 3 graders to determine the transverse displacement of 2 structures (central disc vessels and temporal edge of cup, referenced to disc margin) and axial displacement of 2 structures (disc surface and anterior lamina cribrosa, referenced to Bruch's membrane 1500 µm from disc center). Measured biometric parameters included corneal hysteresis, central corneal thickness (CCT), axial length and intra-ocular pressure (IOP). Pearson correlation was used to assess the strength of relationship between parameters.
IOP elevation induced displacement (mean ± standard deviation, maximum displacement) of the central disc vessels (37±25 µm, max=100 µm), cup edge (35±21 µm, max=77 µm), anterior lamina (20±15 µm, max=60 µm) and optic nerve surface (11±8 µm, max=34 µm). Disc vessels were displaced nasally more often than temporally (p < 0.005, 76% of participants), and disc surface and lamina displacement tended to be more posterior (p<0.005, 86% of participants). Both baseline IOP (R2=0.33; p<0.005) and elevation in IOP (R2=0.43; p=0.001) were correlated with horizontal displacement of cup edge; lower baseline and higher elevation in IOP gave more nasal displacement. CCT was correlated with vertical displacement of the cup boundary (R2=0.35, p=0.007), where lower CCT corresponded to superior shifts of the cup.
Optic nerve structures can be displaced substantially even with mild, acute elevation of intraocular pressure. Transverse displacements of the cup were moderately predictable from measured parameters, but vessel displacements and axial displacements were not. Reliable prediction of how a person's optic nerve will respond to IOP change may require provocative testing under controlled conditions.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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