The purpose of this study is to explore the inter-device reliability between the NPi-200 and NPi-300.

Paired assessments will be made on patients who are consented; and on healthy controls who have verbally assented to participate. We plan to enroll 20 patients and 50 healthy controls. Assessments will be made at the convenience of the patient and healthy controls. Each assessment will include bilateral PLR reading within a 5 minute interval. The first assessment will be completed with the NPi-200 and the second assessment will use the NPi-300. The data will be entered into a CRF.

If there is a significant difference between readings from the NPi-200 and the NPi-300, we will repeat the bilateral assessment in the following hour and the regularly scheduled time.

Inclusion Criteria (Patient Cohort):

• Subjects will be included if they are adults (>18 years of age) and have a neurological or neurosurgical diagnosis that place them at risk for cerebral edema. Subjects also have to be admitted to the enrolling site. Persons consenting for the study (whether patient or LAR) will need to be able to consent for the study in English.

Exclusion Criteria (Patient Cohort):

• Patients that will be excluded from the study are those that are prisoners, under 18 years of age, or pregnant women.

Inclusion Criteria (Healthy Control Cohort):

• Staff in the enrolling site

Exclusion Criteria (Healthy Control Cohort):

• None

Patient Cohort: Patients admitted with a neurological or neurosurgical diagnosis that place them at risk for cerebral edema.

Healthy Cohort: Faculty/Staff who interact with patients at the enrolling site