Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


New Hope For Preventing Major Problems Of The Retina


Study findings may offer prevention for avoiding those annoying spots caused by macular degeneration

The primary function of the retina is to capture light and initiate neural signals. The retina contains the photoreceptors, which are the site of sensory transduction in the visual pathway. Major landmarks in the retina are the fovea and macula, where light has a direct pathway to the receptors. An interruption of the blood supply to these landmarks can lead to age-related macular degeneration and diabetes, the cause of severe visual problems.

Dopamine is an intermediate in tyrosine metabolism and precursor of norepinephrine and epinephrine; it accounts for 90 percent of the catecholamines; its presence in the central nervous system and localization in the basal ganglia (caudate and lentiform nuclei) suggest that dopamine may have other functions. Now a new research study reveals that the body’s dopaminergic system plays a role in the regulation of retinal blood flow in the body. In addition, their data presents evidence for an the diminishing effect of dopamine on the pathways coupling sensory input to vascular response.

Dopaminergic functions in the eye are complex and affect several ocular tissues. These include transmitter effects and impacts on intraocular (within the eyeball) pressure (IOP) and ocular blood flow. It is known from several tissues that vascular effects of dopamine are not only mediated via specific dopamine receptors but also by influencing other effector pathways like catecholamine receptors, a major responder to stress.

Vascular dopaminergic effects in the eye in past studies have revealed that dopamine antagonists (domperidone and haloperidol) increase ocular blood flow in rabbits. Other dopamine antagonists had similar effects, whereas dopamine agonists did not affect beating ocular blood flow. Dopamine has been investigated extensively in glaucoma research. One previous effort found that D1 agonists (when combined with receptors initiate drug action) increase pressure within the eye, where D1 antagonists decrease IOP; D2 agents have opposite effects. Dopamine also has an important role in sensory processing. As a neurotransmitter, it is involved in regulating the rod pathway. However, dopamine actions are not restricted to the transmission of nerve impulses. It is also used as a neuromodulator distributed diffusely in the outer retina during light adaptation. The modulatory functions include horizontal cell and photoreceptor coupling to change the receptive field organization. A direct connection exists between sensory input and retinal blood flow. Diffuse luminance flicker stimuli increase retinal vessel diameter in humans. However, the how this pathway works is still elusive.

A New Study

A new study examines the effect of dopamine on retinal vessel diameters and its modulatory effect on flicker-induced vasodilatation, or widening of the vessel’s tubes. Local retinal vascular effects were studied in healthy human subjects after intravenous administration of dopamine. The authors of the study, “Effects of Dopamine on Human Retinal Vessel Diameter and its Modulation During Flicker Stimulation,” are Karl-Heinz Huemer, Gerhard Garhöfer, Claudia Zawinka, Elisabeth Golestani, Brigitte Litschauer, Leopold Schmetterer, and Guido T. Dorner, all from the University of Vienna Medical School, Vienna, Austria. Their findings appear in the January 2003 edition of the American Journal of Physiology—Heart and Circulatory Physiology.


The research entailed a randomized, subject-blinded, placebo and time-controlled, two-way crossover study in 12 healthy male subjects. Placebo or dopamine was administered on two separate study days. After saline infusion, dopamine hydrochloride was infused in three consecutive doses. Plasma levels of dopamine were determined at each perfusion step. Arterial and venous retinal vessel diameters were measured with the use of a Zeiss retinal vessel analyzer. Diffuse luminance flicker stimuli of eight Hz were applied for 60 seconds. Blood pressure and pulse rate were monitored.


Flicker stimulation (8 Hz) increased retinal vessel diameters under basal conditions. The response to 8-Hz flicker light was significantly reduced by dopamine administration. In addition, dopamine slightly but significantly increased retinal vessel diameters. Dopamine hydrochloride significantly increased systolic but not diastolic or mean arterial pressure.

For the first time, evidence exists displaying the for dopaminergic effects on retinal vessels in humans. This indicates that the dopaminergic system plays a role in the regulation of retinal blood flow in vivo. In addition, their data present evidence for an attenuating effect of dopamine on the pathways coupling sensory input to vascular response. The results also reveal that dopamine significantly increases vessel diameters of retinal arteries and veins in a dose-dependent manner. Their finding is that dopamine increases retinal vessel diameters in vivo is an indicator that dopamine probably has a local effect on retinal vessels (also supported by data showing a high density of D1 receptor antibodies in rabbit retinal vessels).


This study finds reveals that flicker response in both retinal arteries and veins is diminished by dopamine. Although this indicates a role of dopamine in the regulation of retinal vascular tone, it does not necessarily prove a crucial role of dopamine in the neuronal pathway regulating this neurovascular response. Their data are, however, compatible with results from many studies showing dopamine release during light-to-dark transitions and during photic stimulation.

On the basis of these previous data, the researchers hypothesize that dopamine increases during flicker-stimulation in the present experiments. Consequently, exogenous administration of dopamine blunts flicker-induced vasodilatation because vessels are already predilated via the dopamine pathway. In conclusion, their data indicate a dopaminergic contribution to retinal vascular tone in the human retina.

Dopamine appears to play a role in flicker-induced vasodilatation. This could implicate possible roles of dopaminergic agents in alleviating the reduction of blood to the retina, thereby saving thousands of Americans from future vision problems.

Source: January 2003 edition of the American Journal of Physiology—Heart and Circulatory Physiology.

The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

Contact: Donna Krupa: 703.527.7357
Cell: 703.967.2751 or

Donna Krupa | The American Physiological Socie

More articles from Health and Medicine:

nachricht Resolving the mystery of preeclampsia
21.10.2016 | Universitätsklinikum Magdeburg

nachricht New potential cancer treatment using microwaves to target deep tumors
12.10.2016 | University of Texas at Arlington

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>