This research is being done to determine the accuracy of two noninvasive methods of measuring the pressure of the spinal fluid, also known as intracranial pressure (ICP).

Recently, astronauts in long-duration spaceflight have been found to have a syndrome consisting of swelling of the optic nerve, impaired vision, and elevated cerebrospinal fluid pressure (also known as intracranial pressure [ICP]) via lumbar puncture (LP), which is similar to the syndrome of idiopathic intracranial hypertension (IIH). In astronauts, this syndrome is called Visual Impairment/Intracranial Pressure (VIIP). It is not possible to perform an LP on astronauts in space. Noninvasive methods of estimating ICP exist but have not been tested against continuous ICP methods in a patient cohort that is physiologically similar to that of astronauts.

The primary objective of this study is to determine the validity, reliability, accuracy, and precision of two noninvasive methods of ICP measurement (tympanic membrane displacement (TMD, Marchbanks Measurements Systems, UK) and distortion product otoacoustic emissions (DPOAE) in comparison to a reference standard, invasive ICP measurement, in human subjects undergoing diagnostic cerebrospinal fluid (CSF) infusion testing.

The two noninvasive methods are based on the responses of the inner ear and middle ear to changes in ICP. The first method is TMD, which measures tiny movements of the ear drum, and the second is DPOAE, which is routinely used for newborn hearing screening.

Adults with hydrocephalus, shunt malfunction, or other disorders of CSF circulation who have been recommended on the basis of standard clinical criteria to have CSF infusion testing are eligible.

Inclusion Criteria:

• Clinical diagnosis of suspected hydrocephalus or shunt malfunction
• CSF infusion testing has been recommended on the basis of standard clinical criteria
• Capable of providing valid signed informed consent
• Normal middle-ear function as determined by tympanometry
• DPOAE meet criteria that are required for the research
• Acoustic stapedial reflex meets criteria that are required for the research
• Subject is willing and able to participate in the study

Exclusion Criteria:

• Subject is pregnant
• Subject lacks decision-making capacity
• Subject is unwilling to participate in the study
• Prior middle-ear disease or surgery, with the exception of tympanostomy tubes that have been removed and are healed
• Participating in the study would significantly delay or interfere with the subject's healthcare
• Subject has excess ear wax that cannot be removed safely and could potentially be pushed onto the ear drum by insertion of the ear plugs needed for the testing
• The TMD or DPOAE do not respond to a change in posture from lying flat to standing up, which means that the anatomic connection between the inner ear and the CSF is absent