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

Topic E15

                    Ocular Blood Flow

"How can ocular blood flow be measured?"There is still no gold standard for the evaluation of blood flow in humans available;and sophisticated and expensive equipment is required."   Schmetterer L. (2006)

LITERATURE 1975−2008 

Autoregulation of ocular blood flow to the choroid was at one time contested.

Armaly MF, Araki M. 1975   Effect of ocular pressure on choroidal circulation in the cat and Rhesus monkey   Vascular bed of the choroid in these experimental animals is a passive one without evidence of active regulation.

Bill A., 1975  Autoregulation of the blood flow is intermediate in the ciliary body and very poor or absent in the choroid...

Bill A, Nilsson SF. 1985   Reductions in perfusion pressure, caused by increments in intraocular pressure, or reductions in mean arterial pressure reduce the blood flow in the choroid. In the retina, there are efficient autoregulatory mechanisms that prevent changes in flow within a wide range of perfusion pressures.

Schmetterer  2005.  Effects of moderate changes in intraocular pressure on ocular hemodynamics in patients with primary open-angle glaucoma and healthy controls The present study does not provide evidence for altered autoregulation in patients with POAG during a moderate increase in IOP. However, these results do not necessarily contradict the concept of vascular dysregulation in glaucoma.

Schmetterer L. 2007.  The data indicate that the choroid regulates its blood flow better during exercise-induced changes in MAP than during an experimental increase in IOP.

Galambos P.  2006.  Compromised autoregulatory control of ocular hemodynamics in glaucoma patients after postural change.  Measuring and interpreting ocular blood flow and metabolism in glaucoma.

Harris A.  2008.  The imaging technologies most commonly used to investigate ocular blood flow, include color Doppler imaging, confocal scanning laser ophthalmoscopic angiography with fluorescein and indocyanine green dye, Canon laser blood flowmetry, scanning laser Doppler flowmetry, and retinal photographic oximetry.  Each imaging technique's ability to define vascular function and reveal pathology is discussed as are limitations inherent to each technology.

Using a xenon flash stroboscope, 1962 the following structures are identified subjectively:

At 12 f.p.s. columns of corpuscles in the peri-foveal retinal capillaries
At 25 f.p.s. hexagons of 20 micron in diameter 
At 30 f.p.s. retinal vasculature down to and including the capillary vessels 

1967  Auto-regulation.  With digital compressions of the globe, the imposed amblyopia begins peripherally, and once apparent, sweeps steadily centripetally, the fovea being the last affected.  After six-seconds of judicious steadily sustained pressure, the amaurosis recedes from the center, and the apparent brightness of the visual field is restored overall. This response is fatigueable, but could be repeated after a two-minute respite.  These findings suggest that the posterior polar circulation is less readily impeded than is the anterior retinal circulation, and that vascular auto-regulations are entoptically detectable. (see E13)  

With a Baillert Opthalmodynamometer, compression of the globe sustained at 40 millimeters enables the retinal capillary chains to be seen; at 60 millimeters of pressure, arteriolar pulsations and hexagons may be seen.  Around 40 millimeters of pressure, the slowed corpuscular flow in the retinal capillary network is seen.  Corpuscular columns and their movement are not perceptible outside of the 12-degree isopter, and detected by the retina only with illumination and angular velocity within a certain range.  Kato (1951) found the rate of capillary flow measured entoptically to be 77 millimeters per second. Retinal corpuscular columns are seen entoptically just prior to the retinal arteriolar systolic pulse-wave crest when the flow appears most retarded in the capillaries.

At about 60 millimeters of pressure, the pulse wave in the arteriolar retinal tree is visible as a dark shadow, which clearly arises from the blind spot and flashes across some two-thirds of the visual field. At mid-diastolic levels when the impedance in the retinal circulation exceeds the zero-flow intercept for diastolic pressure, the following picture may be noted: amblyopia of the field with mosaic pattern pin-wheel vortices in the paramacular area, and hexagons.

(Subjectivity has been progressively excluded from the practice of science, leaving an essentially secular analytical paradigm.  Jahn RG, Dunne BJ.  2007)

April, 1962.  On a sudden releasing pressure, a flash of segmented retinal flow was apparent, possibly indicating the partial obstructions at arterio-venous crossings.  See author's subsequent  branch vein occlusion (2003) below, resolved in three months , re-occurred in November   2011, at the identical location:  site of a unique  anterior V to   posterior   A  crossing , all others  are  A  to V crossings.