In a healthy person, is intraocular pressure (IOP) or intracranial pressure (ICP) higher?

• A. IOP higher
• B. ICP higher
• C. They are equal
• D. Cannot determine

Answer: (A)

Think about the balance of pressures across the lamina cribrosa, the barrier where the optic nerve exits the eye. The eye maintains its own pressure (intraocular pressure) from the aqueous humor, while the brain-side pressure (intracranial pressure) comes from cerebrospinal fluid and surrounding venous pressure. In a healthy person, the pressure inside the eye is typically greater than the pressure inside the skull, creating a positive gradient from the eye toward the brain. This normal relationship keeps the optic nerve functioning within a stable environment. Because of this, intraocular pressure tends to be higher than intracranial pressure on average. If this balance shifts—ICP rising or IOP rising abnormally—the gradient changes and can lead to issues like papilledema or glaucoma, respectively.