Purpose of Review A pressure difference between the intraocular and intracranial compartments at the site of the lamina cribrosa has been hypothesized to have a pathophysiological role in several o ...

/pdf/intracranial-and-intraocular-pressure-at-the-lamina-cribrosa-5aksfxj4g9.pdf

Intracranial and Intraocular Pressure at the Lamina Cribrosa: Gradient Effects.

Previous studies correlating ultrasound (US)-based optic nerve sheath diameter (ONSD) and intracranial pressure (ICP) in children were performed under general anesthesia. To apply ONSD in daily clinical routine, it is necessary to investigate patients awake. It is furthermore essential for ICP-assessment with ONSD to know if ONSD-ICP correlation varies within individuals. In this study, we report on the influence of wakefulness, method of ICP measurement, intraindividual correlations, and dynamic changes of ONSD and ICP after ICP decreasing therapy. The overall study included 72 children with a median age of 5.2 years. US ONSD determination was performed immediately prior to invasive ICP measurement, and the mean binocular ONSD was compared to ICP. In 10 children, a minimum of 3 ONSD/ICP measurements were performed to investigate a correlation within subjects. In 30 children, measurements were performed before and after therapy. Twenty-eight children were investigated awake with an excellent correlation of ONSD and ICP (r = 0.802, p < 0.01). In 10 children, at least three simultaneous ONSD and ICP measurements were performed. The intraindividual correlations were excellent (r = 0.795–1.0) however with strongly differing individual regression curves. The overall correlation within subjects was strong (r = 0.78, p < 0.01). After ICP decreasing therapy, all ONSD values decreased significantly (p < 0.01); however, there was no correlation between ∆ICP and ∆ONSD. Awake investigation does not impair the correlation between ONSD and ICP. Even if there is a good overall ONSD-ICP correlation, every individual has its own distinctive and precise correlation line. The relationship between ONSD and ICP is furthermore not uniform between individuals. Strong ICP decreases can lead to smaller ONSD changes and vice versa. This should be kept in mind when using this technique in the clinical daily routine.

The relation of optic nerve sheath diameter (ONSD) and intracranial pressure (ICP) in pediatric neurosurgery practice - Part II: Influence of wakefulness, method of ICP measurement, intra-individual ONSD-ICP correlation and changes after therapy

Despite glaucoma being the second leading cause of blindness globally, its pathogenesis remains incompletely understood. Although intraocular pressure (IOP) contributes to glaucoma, and reducing IOP slows progress of the disease, some patients progress despite normal IOP (NTG). Glaucomatous damage causes characteristic cupping of the optic nerve where it passes through the lamina cribrosa. There is evidence that cerebrospinal fluid (CSF) within the optic nerve sheath has a different composition from CSF surrounding the brain. Furthermore, fluctuations in CSF flow into the optic nerve sheath may be reduced by trabeculae within the sheath, and on standing intracranial pressure (ICP) within the sheath is stabilised at around 3 mmHg due to orbital pressure. Blood pressure has been linked both to glaucoma and ICP. These facts have led some to conclude that ICP does not play a role in glaucoma. However, according to stress formulae and Laplace’s Law, stress within the lamina cribrosa is dependent on the forces on either side of it, (IOP and ICP), and its thickness. On lying flat at night, ICP between the brain and optic nerve sheath should equalise. Most evidence suggests ICP is lower in glaucoma than in control groups, and that the lamina cribrosa is thinner and more posteriorly displaced in glaucoma. Subjects who have had ICP reduced have developed signs of glaucoma. This review finds most evidence supports a role for low ICP in the pathogenesis of glaucoma. Caffeine, theophylline and vitamin A may increase ICP, and could be new candidates for an oral treatment.

/pdf/the-role-of-intracranial-pressure-in-glaucoma-and-1a6p0jzn11.pdf

The role of intracranial pressure in glaucoma and therapeutic implications.

The lamina cribrosa of the optic nerve head serves two contrasting roles; it must be porous to allow retinal ganglion cell axons to pass through, and yet at the same time, it must also provide adequate structural support to withstand the stresses and strains across it. Improvements in imaging such as optical coherence tomography image capture and image processing have allowed detailed in vivo studies of lamina cribrosa macro- and micro-architectural characteristics. This has aided our understanding of the optic nerve head as a complex biomechanical structure. In this review, we first aim to frame the biomechanical considerations of lamina cribrosa in a clinical context; in doing so, we also explore the concept of the translaminar pressure difference. Second, we aim to highlight the technological advances in imaging the lamina cribrosa and its accompanying clinical implications, and future directions in this quickly progressing field.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/ceo.13126

Imaging of the lamina cribrosa and its role in glaucoma: a review

Purpose: We aimed to image the optic nerve, subarachnoid space and optic nerve sheath in emmetropes and myopes ultra-high field (7-Tesla) magnetic resonance imaging (MRI). We targeted the retrobulbar distance of approximately 3 mm behind the eyeball, an area of clinical interest because of optic nerve sheath distensibility and pressure-related enlargement. 

Methods: Eleven emmetropes (+0.75 to −0.50D, aged 20–41 years) and 10 myopes (−4.5 to −12D, aged 21–37 years) participated. Cross-sectional area of the optic nerve, subarachnoid space and optic nerve sheath at approximately 3 mm behind the eye were measured from two-dimensional T2-weighted coronal oblique MRI images obtained through the left optic nerve. Axial length of the left eye was measured from T2-weighted axial MRI images. In nine emmetropes and seven myopes, the optic nerve head was imaged with optical coherence tomography to compare retrobulbar and intraocular measures. 

Results: Retrobulbar optic nerve, subarachnoid space and optic nerve sheath dimensions differed between myopes and emmetropes. Myopes tended to have smaller optic nerve and subarachnoid space. Longer MRI-derived axial length was associated with smaller optic nerve area (P = 0.03). Bruch's membrane opening area did not predict retrobulbar optic nerve area (P = 0.48). 

Conclusions: This study demonstrates the feasibility of using 7-Tesla MRI to measure optic nerve, subarachnoid space, and optic nerve sheath dimensions behind the eye. In healthy adults, the retrobulbar optic nerve and subarachnoid space size are influenced by the degree of myopia. 

Translational Relevance: ultra-high field MRI is a practical tool for assessing the morphometry of the optic nerve and surrounding anatomy behind the eye.

https://minerva-access.unimelb.edu.au/bitstream/handle/11343/262686/Nguyen et al_Ultra-high field magnetic resonance_i2164-2591-10-2-8_1612850763.29295.pdf

Ultra-High Field Magnetic Resonance Imaging of the Retrobulbar Optic Nerve, Subarachnoid Space, and Optic Nerve Sheath in Emmetropic and Myopic Eyes

To investigate on the relationship between the optic nerve sheath diameter (ONSD) and the lumbar cerebrospinal fluid pressure (CSF-p) in Caucasian patients with normal tension glaucoma (NTG). Retrospective analysis of medical records of patients with open-angle glaucoma in the period from 2005 to 2015 from the Ophthalmology Department, Cantonal Hospital Aarau, Switzerland was performed. A total of 38 patients (mean age 68.6±11.3 years, 21 females and 17 males) fulfilled the diagnostic criteria of NTG and underwent computed tomography (CT) of the orbit and lumbar puncture (LP). In total, 38 age- and gender-matched Caucasian subjects (mean age: 68.9±10.9 years) without known ON diseases served as controls for ONSD measurements. ONSDs were measured at a distance of 3 mm from the posterior globe and lumbar CSF-p was related to the measurements. Statistical analysis was performed by using the independent two-tailed t-test and the non-parametric Spearman's correlation test. The mean ONSD in NTGs measured 6.4±0.9 mm and in controls 5.4±0.6 mm. The difference between NTGs and controls showed statistical significance (t-test: P<0.000). The mean CSF-p in NTG was 11.6±3.7 mm Hg. There was no statistical significant correlation between ONSD and CSF-p (Spearman's correlation coefficient ρ=0.06, P=0.72). This study demonstrates enlarged ONSDs and normal lumbar CSF-p in 38 Caucasian NTG patients. As enlarged ONSDs generally are associated with increased intracranial CSF-p, these results can be explained by a disturbed communication of CSF-p between the intracranial and intraorbital subarachnoid spaces.

/pdf/relationship-between-the-optic-nerve-sheath-diameter-and-2sep2qp2xk.pdf

Relationship between the optic nerve sheath diameter and lumbar cerebrospinal fluid pressure in patients with normal tension glaucoma.

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Relationship between the optic nerve sheath diameter and lumbar cerebrospinal fluid pressure in patients with normal tension glaucoma.