For purposes of validation, this study compares intracranial pressure measurements obtained with a novel self-calibrating, non-invasive, intracranial pressure measuring (ICP) device, with the values obtained from (a) patients in an intensive care unit (ICU) whose meet standard clinical indications for ICP measurement and whose ICP is measured using gold-standard implanted intracranial instrumentation and in (b) ambulatory subjects who meet clinical indications for lumbar puncture.

This study is designed to validate intracranial pressure measurements obtained with a novel, self-calibrating, non-invasive, intracranial pressure measuring (ICP) device based on trans-cranial Doppler technology. The ophthalmic artery is utilized as a natural ICP sensor. Up to 80 subjects will be recruited in 4 centers to achieve a power of 90% and a p<0.05 compared to the values obtained from (a) patients in an ICU whose meet standard clinical indications for ICP measurement and whose ICP is measured using gold-standard implanted intracranial instrumentation and in (b) ambulatory subjects who meet clinical indications for lumbar puncture. At least two comparative readings, separated by an hour or more, will be obtained from each subject.

Inclusion Criteria:

• ICU patients suspected of having an abnormality of ICP undergoing monitoring with commercially-available, FDA-approved instrumentation.

Exclusion Criteria:

History of:

• Glaucoma or optic hypertension
• Severe orbital or ophthalmic injury
• Orbital or intraocular surgery that might interfere with orbital compliance
• Congenital malformations of the eye and/or orbit that might interfere with orbital compliance or orbital vascular anatomy

Patients hospitalized in an ICU who meet clinical criteria for invasive ICP measurement,