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IOP, systemic pressure in head-down position may assess glaucoma risk
Assessment of systemic and intraocular pressure changes in the head-down body posture may provide an important element for risk assessment in the clinical management of glaucoma, according to a study.
The study included 28 glaucoma suspects and 11 similarly aged healthy controls monitored twice a year with pattern electroretinography (PERG) and OCT for retinal fiber layer (RNFL) thickness changes over a period of 5 years. At baseline, all patients had PERG, IOP and brachial blood pressure measured in the seated and head down body tilt (HDT) position.
While RNFL thickness was normal in all the study subjects at baseline, nine of them displayed significant thinning over the follow-up period and were classified as “thinners” or T, as opposed to the 19 “nonthinners” or NT.
Looking retrospectively at the results of baseline PERG and pressure measurements, interesting correlations were found. PERG amplitude and phase were smaller in RNFL T compared with RNFL thickness NT and controls. Upon HDT, the amplitude decreased significantly in both NT and T, but not in controls.
Posture strongly affected IOP in all groups, with significant elevation in the HDT posture. Mean arterial pressure (MAP) and ocular perfusion pressure (OPP) tended to be higher in the T group as compared with NT and controls, and OPP increased significantly upon HDT posture in glaucoma suspects, both NT and T, but not in the control group.
These variables, assessed by HDT provocative tests, might have a predictive value for RNFL thinning in glaucoma suspects and deserve further evaluation, according to the authors. They announced that a randomized clinical trial (NCT02390284), including HDT provocation in glaucoma suspects, has been initiated at the Bascom Palmer Eye Institute. – by Michela Cimberle
Disclosure: The authors report no conflicts of interest.
Perspective
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Wouldn’t it be great to have a crystal ball? Not one of Tolkien’s scary palantír, but a good old-fashioned Brothers Grimm version. Imagine the possibilities: Confidently decline the extended warranty, make a bit of money during March Madness and accurately predict those glaucoma suspects who will progress to manifest disease.
Pattern ERG testing can objectively quantify retinal ganglion cell dysfunction prior to the detection of visual field defects through subjective (AVF) analysis. Building on previous work, Porciatti’s group (which includes OGS member John McSoley, OD) has demonstrated that baseline PERG abnormalities – and their transient change following modest IOP elevation induced by 10° head-down posture – can also identify glaucoma suspects who go on to develop structural (RNFL) change.
Although clinical assessment of the optic nerve complex remains the foundation of glaucoma care, a growing understanding of risk factors and the results of targeted ancillary testing afford invaluable support. Structural testing has evolved to include optic nerve head, RNFL and macular ganglion cell analyses, while functional evaluation seems poised to encompass both subjective (AVF) and objective (PERG) components, providing complementary guidance even earlier in the complex decision-making continuum that characterizes glaucoma diagnosis and management.
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Porciatti V. et al. J Glaucoma. 2017. doi: 10.1097/IJG.0000000000000648