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Bang V Bui, Da Zhao, Zheng He, Algis J Vingrys, Christine T Nguyen; Effect of translaminar pressure modification on the rat optic nerve hea. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4556.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of intracranial pressure (ICP) modification on the rat optic nerve head response to intraocular pressure (IOP) elevation
Anesthetised (60:5mg/kg ketamine:xylazine) adult Long-Evans rats (n=6-7/group) underwent acute translaminar pressure (TLP) modification. ICP was manometrically set to -5, 5, 15, 25 and 30 mmHg via a dual cannula (30G infusion needle inside a 26G measurement needle) placed into the lateral ventricle (-1.5mm from bregma, ±2mm from midline) on the ipsilateral side to the cannulated eye (30G, vitreal chamber). ICP and IOP were continually monitored. At each ICP level, IOP was manometrically set between 10 to 70 mmHg in 10mmHg steps each lasting 3 minutes. At each IOP step the retina centred at the optic nerve head (ONH) was imaged along the horizontal midline using spectral domain-OCT and analysed to return retinal thickness and displacement of the retinal surface (relative to a horizontal reference 1.2mm either side of ONH centre). Data were compared using one- (IOP effect within an ICP level) and two-way ANOVA (IOP effect between ICP levels).
At an ICP of 5 mmHg posterior deformation occurred for IOPs of 40 mmHg (-60±13μm, 0.2mm from ONH centre, P<0.01) or greater (50:-76±14, 60:-99±18, 70:-113±16μm). Significant retinal thinning was observed with IOPs of 40mmHg (-9±4%, P<0.05) or greater (50:-12±5, 60:-17±4, 70:-21±4%). Significant posterior deformation and retinal thinning were found at 0.2-0.6mm from the ONH, whereas at 0.6-1mm there was significant forward deformation of the retinal surface and less thinning. At a lower ICP (-5mmHg) there was more posterior deformation (IOP70mmHg:-145±39μm) and retinal thinning (70mmHg:-30±2%), whereas with higher ICPs there was less deformation (ICP/IOP25/70mmHg:-93±11μm) and thinning (ICP/IOP25/70mmHg:-19±5%). A linear relationship was found between deformation and ICP for a fixed IOP. When expressed as translaminar pressure (IOP-ICP) deformation data can be described by a linear relationship (0.2mm from ONH centre, y=-1.91(TLP)-128, r2=0.89, p<0.01), whose slope was shallower with increasing distance from the optic nerve (0.4mm:-1.17, 0.6mm:-0.52, 0.8mm:-0.18, 1mm:-0.4).
ICP modification modifies the effect of IOP elevation on the rat optic nerve head and retina. A linear relationship exists between the magnitude of deformation and translaminar pressure.
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