A technique for noninvasive determination of the pressure in the cerebrospinal fluid (CSF) has been proposed. This technique would involve two main steps: First, an optical coherence tomographic scanner would be aimed into an eye and used to image the optical disk (see figure). Next, the resulting tomographic imagery would be digitized and processed to determine the thickness of the neural fiber layer, which thickness is known to increase with the CSF pressure.
Heretofore, the spinal tap has been the standard technique for measuring the CSF pressure (also known as the intracranial pressure or "ICP"). Spinal taps are painful, dangerous, and expensive. The proposed technique could make it unnecessary to perform spinal taps.
Papilledema — swelling of the optic-nerve axons in the optic disk — is known from previous studies to be associated with an increase in the intracranial pressure beyond the normal limit of approximately 14 mm of Hg (about 1.9 kPa). The neural fiber layer can swell to as much as 20 times its normal thickness within hours after the onset of elevated intracranial pressure.
Papilledema can be seen through an ophthalmoscope. Stereoscopic fundus photography and optic-nerve-head analysis also reveal aspects of papilledema. The common limitation of these previously developed optical techniques is that they depend on changes in surface topography. The proposed version of optical coherence tomography would measure the thickness of the neural fiber layer regardless of changes in surface topography, and should be capable of revealing swelling of axons earlier than do the previously developed optical techniques.
By use of a previously constructed optical coherence tomographic scanner, it has been found that the thickness of the neural fiber layer in normal individuals varies by no more than 3 µm. This instrument has also been found capable of revealing early thinning of the neural fiber layer associated with glaucoma. Thus, it has been reasoned, it should be possible to use optical coherence tomography to measure early neural-fiber-layer swelling associated with intracranial hypertension. If the instrument could be modified to achieve a tenfold refinement of its resolution, then the instrument would be correspondingly more sensitive as an indicator of intracranial pressure. The modified instrument could be used in research on the sequence of events in papilledema because it could also provide information on deep and surface changes in the optic disk, flows of blood in veins and arteries, and shifts in the spectral reflectance of the optic disk.
This work was done by Mark S. Borchert and James L. Lambert of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Bio-Medical category. NPO-20079
This Brief includes a Technical Support Package (TSP).
Noninavisive determination of pressure in cerebrospinal fluid
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Overview
The document presents a concept proposal for a noninvasive method to measure cerebrospinal fluid (CSF) pressure using Optical Coherence Tomography (OCT). Developed by Mark S. Borchert, M.D., and James L. Lambert, Ph.D., this innovative approach aims to address the limitations of traditional CSF pressure measurement techniques, such as lumbar punctures, which are invasive, painful, and carry certain risks.
The primary focus of the proposal is on the condition known as papilledema, which is characterized by swelling of the optic nerve head due to elevated intracranial pressure (ICP). This condition can be observed through an ophthalmoscope and, while it does not immediately result in vision loss, prolonged presence can lead to significant visual impairment. The document explains that the swelling occurs when there is increased pressure in the subarachnoid space surrounding the optic nerve, leading to stasis in axoplasmic transport and subsequent axonal swelling.
The proposed solution leverages the fact that the thickness of the neural fiber layer (NFL) in the eye increases significantly—over twenty times its normal thickness—as CSF pressure rises. By using an OCT scanner, clinicians can measure the NFL thickness noninvasively, providing a reliable indication of CSF pressure without the discomfort and risks associated with traditional methods.
The document outlines the technical aspects of the invention, emphasizing its novelty and potential impact on patient care. It highlights the advantages of a noninvasive approach, which could facilitate easier monitoring of patients with conditions related to elevated ICP, such as those with brain tumors, hydrocephalus, or other neurological disorders.
Additionally, the proposal notes that the work was conducted at the Jet Propulsion Laboratory (JPL) under a contract with NASA, indicating a collaboration between aerospace technology and medical innovation. The document also includes disclaimers regarding the accuracy and liability associated with the information presented.
In summary, this concept proposal outlines a promising advancement in the field of neurology, offering a safer, more efficient method for measuring CSF pressure that could significantly improve patient outcomes and streamline clinical practices.
