Page 18 - 21st Century Perspective - Glaucoma Supplement

Ocular Perfusion Pressure

Ocular Perfusion Pressure

Stated simply, a good blood supply to the optic nerve is essential for its health. A sort of tug-of-war
occurs here, in which the intraocular pressure presses against the optic nerve head, and systemic

blood pressure tries to perfuse these same tissues. Again, simply stated, the ocular perfusion
pressure is the arithmetic difference between the diastolic blood pressure and IOP. When this
number is 50 or lower, there is an increasing risk for glaucomatous progression. For example, if the
patient has a blood pressure of 110/65, and IOP is 20 mm Hg, then the ocular perfusion pressure is
45 mm Hg, thus placing this patient at increased risk for glaucoma development and/or progression.

The concern here is twofold: First, a subset of patients has quite suppressed nocturnal hypotension
and are known colloquially as — “dippers” — that is, their diastolic blood pressure dips low enough

to suboptimally perfuse the blood supply to the optic nerve. Of note, these same individuals are also
at risk for anterior ischemic neuropathic events. Second, because of an epidemic of systemic
hypertension in the United States, numerous patients take medication to reduce their hypertension
with the general intent of reducing their risk for stroke; however, these medicines, especially calcium
channel blockers, can greatly decrease blood pressure. Thus, this subset of patients — “dippers” —
who have glaucoma and who take one or more of these oral hypotensive medications, could be

experiencing suboptimally low nocturnal blood pressure.

What does all this mean? Patients with normal-tension glaucoma who also take an oral hypotensive
medication could be unintentionally hindering the health of the optic nerve. In these situations, which
are common, we revisit the medical history. If a patient is taking one of these oral hypotensive drugs
in the evening, then we write the prescribing doctor and ask him or her to consider directing the
patient to take the blood pressure medication(s) in the morning, rather than in the evening. This is a
well recognized and scientifically sound consideration, and one that requires a team approach with

general medical providers. Furthermore, this is yet another reason it is important to measure the
patient’s blood pressure in the office, especially if he or she is a glaucoma patient who has normal
IOP.

Finally, unless we are checking the IOP at different times of the day or are embracing Icare HOME
tonometry, what we assume to be normal-tension glaucoma could well be missed (or undetected)
increased IOP. Of course, pachymetry also must be considered in assessing IOP.

18