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Editors Selection IGR 17-3

Clinical Examination Methods: Reaching for the Brain: Can IOP help estimate Intracranial Pressure?

Comment by John Liu on:

66262 System for Rapid, Precise Modulation of Intraocular Pressure, toward Minimally-Invasive In Vivo Measurement of Intracranial Pressure, Stockslager MA; Samuels BC; Allingham RR et al., PLoS ONE, 2016; 11: e0147020

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Clinical and laboratory evidences have supported the idea that a high translaminar pressure difference, intraocular pressure (IOP) minus intracranial pressure (ICP), is associated with glaucoma pathogenesis. Accurate but one-time determination of ICP needs a lumbar puncture performed commonly in the lateral decubitus body position, which does not provide dynamic ICP information behind the optic nerve head. Pulsation of central retinal vein has been proposed as a non-invasive tool to estimate ICP. While the mechanism is not fully understood, the larger magnitude of IOP oscillation compared to the magnitude of ICP oscillation during the cardiovascular cycle is believed to lead to the pulsation. A decrease in IOP or an increase in ICP can change the related magnitude of oscillation and reduce or cease the central retinal venous pulsation. A previous human study using anti-glaucoma medication confirmed that IOP lowering can estimate ICP level. Problems were, however, that this is inaccurate and time-consuming.

This is an important step for their proof of the concept that monitoring retinal vein parameters during a fast IOP lowering can accurately determine ICP level

In the current study, the authors designed a minimally invasive mechanical system for a rapid and precise IOP lowering. Using this innovative setup in vivo, a sharp increase in the retinal vein caliber was observed in one tree shrew (Tupaja glis) corresponding to a normal ICP level in this species. This is an important step for their proof of the concept that monitoring retinal vein parameters during a fast IOP lowering can accurately determine ICP level. Such a system is particularly useful for a lower than normal ICP that is associated with glaucoma pathogenesis. There will be much more work to do for the authors. The observation shown in this report needs to be replicated in other tree shrews probably with a range of ICP-controlled experiments. Similar observation has to be verified in other animal species toward eventually a consideration of applications in human patients. In addition, one may question whether the study concept is testable in certain surgical conditions when a rapid IOP fall occurs. Today monitoring changes in retinal vein parameters are not difficult considering advances in non-invasive imaging technology. As a consensus for clinicians and scientists involved in the research of translaminar pressure difference and glaucoma pathogenesis, a leap forward is to develop a reliable and accurate method for determining ICP behind the optic nerve head. The authors' effort is appreciated. Our task is daunting, but the potential reward is high.

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