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Deepta Abhay Ghate, Vikas Gulati, Shane Havens, Shan Fan, William Thorell, Carl Nelson, Junfei Tong, Linxia Gu, Sachin Kedar; Episcleral Venous Pressure And Intraocular Pressure As Biomarkers For Intracranial Pressure Changes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4305.
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There is need for non-invasive reliable intracranial pressure (ICP) monitoring. We hypothesize that ICP changes will affect ocular venous drainage and consequently affect the episcleral venous pressure (EVP), intraocular pressure (IOP) and retinal vein diameter (RVD) of the eye. EVP measurement is routine in aqueous humor dynamics glaucoma research. EVP has a predicted 1:1 correlation with IOP.
A lumbar drain was used to vary ICP in 5 female domestic pigs in this established non-survival animal model. A parenchymal monitor (Integra Camino, USA) was inserted for accurate ICP monitoring. ICP was varied using normal saline infusion in 5 mmHg increments. The following parameters were measured at baseline and at all ICP increments after 10 minutes of ICP stability. 1) Right eye: IOP (pneumotonometry), EVP (venomanometry) 2) dilated left eye: OCT of optic nerve (Heidelberg Engineering, Germany). Retinal veins were identified on the OCT composite image and 2 independent graders measured RVD of 2 veins/ pig. The univariate correlation of EVP, IOP and RVD with ICP changes was evaluated using linear mixed models with random intercepts.
The baseline ICP was 4.5 mmHg (range 1.5-8 mmHg). Maximum stable ICP achieved ranged from 13-40 mmHg. The EVP increased with increase in ICP (β=0.26, p = 0.01). IOP increased with increase in ICP (β=0.36, p=0.0002). There was a subjective increase in anterior segment congestion and venous congestion on examination and photography. There was an increase in retinal vein diameter thickness with ICP; this was correlated with EVP (β=6.12, p=0.05).
EVP is a novel biomarker for increased ICP. Acute ICP increase causes increased ocular venous congestion resulting in significant increase in EVP and IOP in a pig model. The increased EVP is correlated to RVD. This increased congestion could potentially be due to an increase in cavernous sinus pressure which drains the central retinal vein and episcleral veins.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure 1: Scattergraph of ICP vs EVP and IOP in 5 pigs
Figure 2: Disc photos, anterior segment photos, OCT in the pig. Disc and episcleral vessels show congestion with increasing ICP. Blood vessel diameter (BVD) is measured by 2 graders on the OCT composite image. Baseline image is set as the reference image, so radial lines used to measure distance from center are in exactly the same position in all readings. SVP (spontaneous venous pulsations)
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