Studies of the Retinal Circulation in Man

Abstract

SYSTEMIC DISORDERS often cause pathological changes in the optic fundus. These changes have diagnostic value because of their empirical association with specific illnesses. The value of funduscopic examination would be even further increased by a better understanding of how certain of these fundic lesions are produced. With the ultimate object of investigating this problem, several photographic techniques for study of the retinal circulation and metabolism in man have been adapted or developed and used by the authors and their associates. These techniques are: (1) measurement by fundus photography of changes in the diameter of retinal vessels in response to various stimuli, a procedure previously used by others;1,2 (2) estimation by fundus photography of the arteriovenous blood oxygen difference, (3) a method of photographing fluorescence in circulating blood in the retina, and ( 4) a method for measuring the mean retinal circulation time using fluorescein. It is the purpose of this presentation to summarize some results obtained by these special techniques and to interpret them in relation to the work of others in this rapidly expanding field. MethodsThe methods have been described elsewhere3-8 and will be outlined only briefly here. In most of this work the Zeiss fundus camera has been used. For the measurement of change in vessel diameter, fundus photographs were made with the subject usually in a seated position, first in the control state and then after various test pro¬ cedures. From these photographs, measurements were made of the arteries and veins near the disk using a dissecting microscope with a scale in the ocular. Changes in diameter were ex¬ pressed as a percentage of the control value, and the mean changes for arteries and veins were calculated separately. For examination of patients with retinopathy, the procedure most often used was the inhalation of 100% oxygen, which constricts retinal vessels. The terms, "ret¬ inal arterial reactivity" and "retinal venous re¬ activity," denote the mean percentage decrease in diameter of these vessels after inhalation of oxygen for 5 minutes.The method for measuring oxygen saturation of retinal venous, or arterial, blood was similar in principle to other photometric methods for measuring blood oxygen saturation. However, rel¬ ative light intensities were estimated by the density of the images which they produced on photographic film rather than by a photo¬ electric cell. For fundus photographs a beamsplitting device was used that allows making two simultaneous film exposures, one through a red interference filter with peak transmission at 640 µ, and the other through a green filter with peak transmission at 510 µ. The optical den¬ sity of reduced hemoglobin is much greater than that of oxyhemoglobin at 640 µ, but is the same at 510 µ. The per cent oxygen satura¬ tion of hemoglobin and whole blood bears a linear relationship to the ratio of optical den¬ sities at these red and green wavelengths. In retinal photography the light which strikes the optic disk is la...

Adenosine relaxation in small retinal arterioles requires functional Na-K pumps and KATP channels

“…1 Adenosine is located throughout the body and is widely distributed in the retina within the ganglion cell layer and the inner plexiform layer in proximity to the retinal vessels. 2 Adenosine has vasodilatory properties, and therefore the dilation of retinal vessels seen in the ischaemic retina 3,4 has been attributed to the release of adenosine from the retinal tissue. 4,5,6 The possible mechanisms underlying the vasodilating effect of adenosine in the retinal circulation have been studied in the piglet retina where the effect was mediated by activation of the K ATP channels, 7 but evidence suggests that studies from newborn animals cannot be transferred to grown-up animals in general.…”

Normative Values and Predictors of Retinal Oxygen Saturation

“…Since its initial description, [9][10][11] retinal oximetry has undergone several improvements. Analogous to standard pulse oximetry, retinal oximetry is based on the differential light absorbance of oxygenated and deoxygenated blood at certain wavelengths of light.…”

Retinal Oxygen Metabolism During Normoxia and Hyperoxia in Healthy Subjects

“…Fundus reflectometry was suggested as a tool for measuring oxygen saturation in retinal vessels more than 40 years ago, [14][15][16] and techniques have been improved since then. [17][18][19][20][21][22][23] Given the technical development, particularly in the field of chargecoupled device cameras, several techniques have recently become commercially available that measure oxygen saturation in retinal arteries and veins.…”