Visual Memory Research
The Genesis of Mnemonic Visual Systems 
Recurrent Dynamics in Excitable Media

E Series

A Visual Marker reflects Ocular Blood Flow Maximal at 40 Hz.

"The linkage at ~40 Hz between maximal neuro-retinal activity and ocular perfusion levels now appears incontrovertible."   Riva C., 2005
"Purple Entoptic Phenomenon" is visually evident at 40 Hz, offers a simple means to assess acute fluctuations in ocular neuro-metabolism, and indicates the prompt auto-regulation of ocular perfusion levels.

The source of this phenomenon, its topography and the mechanisms which enable its subjective perception are of interest, and have possible clinical application.  Limited testing in a clinical setting distinguished low-tension glaucoma from ocular-hypertension.

Pathology delays the onset of this phenomenal annulus.  By  reversing  the  initial  testing order of the two eyes  one can then  differentiate the  performances between the two eyes , and  thus  distinguish  any  unequal  performances as being attributable either  to monocular pathology  or simply  to the asymmetrical prior light  adaptation    

Aging, with diminishing ocular circulation, contributes significantly to prolonged delayed onset of the marker, often to 40 seconds. "40% decrease seen in choroidal thickness by age 75."   (Cristini, Forlani, Scardovi, Choroidal Circulation in Glaucoma, 1962)  

Anomalies.  Interestingly the dimensions, morphology, topology, bandwidth and the kinetics of this "purple" phenomenon have been attested to by an albino patient, 1964, and  also  by  two severely red-green color-blind individuals, 1966, 2002.