The lower the pulses ox, the worse the perfusion, thus the worse the condition.
Another culprit may be perfusion pressure, or the difference between pressure within the eye and overall blood pressure.
Word Origin and History for perfusion
n.
1570s, from Middle French perfusion and directly from Latin perfusionem (nominative perfusio) "a pouring over," noun of action from past participle stem of perfundere "pour out," from per- "throughout" (see per) + fundere "pour" (see found (v.2)).
perfusion in Medicine
perfusion per·fu·sion (pər-fyōō'zhən) n.
The act of perfusing.
The injection of fluid into a blood vessel in order to reach an organ or tissues, usually to supply nutrients and oxygen.