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Ningli Wang, Zheng Zhang, Diya Yang, Jinghong Sang, Xiaobin Xie, Zhen Li, Ruowu Hou; Detection of Optic Nerve Head Measurements Change with Heidelberg Retinal Tomography During Valsalva Maneuver. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2819.
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Previous investigations have suggested that low intracranial pressure (ICP), which increased the trans-lamina cribrosa pressure difference (TLCPD), may play an important role in the pathogenesis of open angle glaucoma. Thus, we hypothesize that the structure of the optic nerve head (ONH) may be affected when TLCPD is changed. As it was reported that valsalva maneuver can prominently elevate the intracranial pressure greater than 250 mm water, we proposed to determine whether the retinal nerve fiber layer (RNFL) thickness and other ONH morphology measurement parameters were changed during Valsalva maneuver by using Heidelberg Retinal Tomography (HRT).
20 healthy human subjects (40 eyes) without eye disease were enrolled in this study. Baseline intraocular pressure (IOP) and HRT scanning of ONH were acquired in a prone position. Then, subjects were instructed to exhale into a blowtorch which connected to a mercury manometer in the same prone position and keeping valsalva maneuver for about 20-30 seconds with the mercury column elevated to 30mm Hg. During the valsalva maneuver, IOP measurement and HRT scanning of optic nerve head were done for the subjects respectively. 15 minutes resting were given for the subjects between each valsalva maneuver.
With valsalva maneuver, intraocular pressures were significantly elevated (P<0.001) for about 3.6 mmHg. During valsalva maneuver, HRT measurement of the cup area, cup volume, Cup/Disk area ratio and maximum cup depth were significantly reduced (P<0.05), but parameters of rim area, rim volume and mean RNFL thickness were significantly elevated (P<0.05) compared with baseline. All HRT parameter changes were not correlated with intraocular pressure change (P>0.05).
The principle finding of this study was that with a valsalva maneuver of 30 mmHg, HRT scanning measured parameters of cup area, cup volume, Cup/Disk area ratio and maximum cup depth were significantly reduced, while other parameters like rim area, rim volume and mean RNFL thickness were significantly elevated, IOP was significantly elevated for about 3.6 mmHg. As previous paper reported that valsalva maneuver may elevate ICP greater than 250 mm water (18.4 mmHg), it may be inferred that during valsalva maneuver, there is a more prominent elevation effect on intracranial pressure rather than intraocular pressure. Thus the elevated intracranial pressure or to say a reversely imbalanced trans-lamina cribrosa pressure difference may slow down the axonal flow rate and manifest as a reduction of cup related parameters and elevation of RNFL thickness and rim related parameters.
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