Changes In Retinal Blood Flow Research Articles

Physiological perturbation of ocular and cerebral blood flow as measured by scanning laser ophthalmoscopy and color doppler imaging

Retinal blood flow regulation in health remains poorly described. We hypothesized that retinal perfusion is controlled to provide constant O 2 delivery to that tissue, and that changes in retinal blood flow in response to chemical stimuli parallel changes in carotid and retrobulbar perfusion. Accordingly, in 11 young adults with normal eye examinations, we measured retinal blood flow indices (via scanning laser ophthalmoscopy [SLO] during fluorescein angiography) and carotid, ophthalmic, and central retinal arterial blood flow indices (via Doppler imaging [CDI]) under control, hypoxic (alveolar PO 2 = 55 ± 3 mmHg) and hyperoxic (alveolar PO 2 = 655 ± 18 mmHg) conditions. The three conditions were counterbalanced in order and isocapnia was maintained in each. Retinal arterial mean dye velocity and arteriovenous passage time, as measured by SLO, were slowed by hyperoxia and accelerated by hypoxia, in rough proportion to the changes in arterial O 2 content (± 10%; p < 0.05). In the seven subjects in which relative measurements of retinal arterial diameters were obtained, neither hypoxia nor hyperoxia significantly altered vessel diameter. At the same time, mean retinal capillary transit velocity was independent of PO 2, suggesting that, in health, retinal capillaries may be recruited as PO 2 falls. O 2-induced changes in carotid, ophthalmic, or central retinal arterial blood flow velocities (via CDI) were not found, though a wide coefficient of variation (30% for CDI vs. 14% for SLO) may have contributed to this failure. We conclude that, under isocapnic conditions, retinal perfusion may be regulated to provide constant O 2 delivery. The lack of precision of CDI in this study leaves open the possiblity that chemical regulation of the retinal flow may parallel that of other brain regions.

Regional retinal blood flow reduction following half fundus photocoagulation treatment.

Regional changes in retinal blood flow following inferior and subsequent superior argon laser half fundus photocoagulation treatment were measured in six diabetic patients with advanced retinopathy. Centreline blood velocity, vessel diameter, and blood flow in major inferior and superior temporal retinal arteries were measured at baseline and following each treatment using the bidirectional laser Doppler technique and monochromatic fundus photography. Inferior fundus laser treatment produced a significant blood flow decrease in inferior temporal arteries ranging from 60% to 78%. Blood flow changes in superior temporal arteries were not significant, ranging from -7% to +14%. Subsequent superior fundus laser treatment produced a significant blood flow decrease in superior temporal arteries ranging from 50% to 66%. Subsequent blood flow changes in inferior temporal arteries were not significant, ranging from -19% to +21%. The results indicate that regional laser treatment produces a regional reduction in retinal blood flow, consistent with measurements of preretinal and intraretinal oxygen tension which have indicated increases in oxygen over photocoagulated regions.

Part II: Hemodynamic and structural changes in early glaucoma

The central theme of the papers in this portion of the volume is a description of early morphological alterations in glaucoma and the manner in which these pathological changes may be altered by medical treatment. The detection and evaluation of pathological change in the retina is completely dependent upon the development of new tools for observing the retina and optic disc. Dr. Airaksinen’s paper described new photographic methods for evaluation of both the optic disc, in particular the neuroretinal rim, and the nerve fiber layer. He demonstrated that changes in the nerve fiber layer precede abnormalities in the optic disc and visual field defects. Dr. Grunwald employed a new method, laser Doppler velocimetry, to analyze the effect of timolol on retinal blood flow. He demonstrated that timolol increased retinal blood flow, and that this effect may result from the increase in perfusion pressure and a change in the manner in which the retina regulates its blood supply. In the normal eye, there is not a significant correlation between perfusion pressure changes and retinal blood flow changes. With timolol treatment, however, a significant correlation between these two variables can be observed. Thus, the retinal blood flow seems to follow more passively the changes in systemic blood pressure after timolol treatment. The data that I presented also demonstrated the utility of computer-aided video analysis for detecting early retinal changes in glaucoma patients. Our experiments with the Optic Nerve Head Analyzer again demonstrated the prognostic value of early changes in the neuroretinal rim in glaucoma patients. Photogrammetry and computer analysis of the optic disc were also emphasized in the study presented by Dr. Schwartz. He demonstrated that treatment with timolol can reduce cupping in the optic disc, and that the bottom portion of the cup was the site of the most pronounced differences between the timolol-treated and untreated eyes. His data also demonstrated the importance of repeated testing of suspect eyes. Such testing permitted the identification of pathological trends that were not apparent in a single examination.

Retinal laser Doppler velocimetry: toward its computer-assisted clinical use

Clinical use of laser Doppler velocimetry of absolute red blood cell velocity V(max) in the center of major retinal vessels becomes possible with recent advances in microcomputer technology- Speed and automation of Doppler photocurrent analysis and identification of proper laser beam positioning are the major requirements in making direct quantitative assessment of retinal hemodynamics a routine diagnostic tool. We discuss our efforts toward achieving this goal and illustrate our current capabilities with examples of changes in retinal blood flow in response to physiologic maneuvers. In veins, V(max) can now be determined on-line. In arteries, current computing speed only supports intermittent on-line data acquisition.