Our laboratories are active in working with image analisys and applied research. Currently, togehter with the Group of Medical Retina leaded by Dr. Francisco Gomez-Ulla at the Department of Ophthalmology and the groups of Prof. Diego Cabello at the Department of Electronics and Computation and Prf. Jose Maria Barja at the University of Coruņa, we are developing a technique for measuring retinal blood flow based on scanning laser images.

The image above shows a retinal angiography of the left eye. The image was taken with a Laser Scanning Ophthalmoscope after intravenous fluorescein injection. Fluorescein is a dye that produces green light when excited with blue light. In this image the arteries appear white because they are filled with fluorescein and the veins appear dark because they do not have the dye. The changes in luminance are related with the blood flow and therefore they can be used to calculate the blood flow velocity (Image from Dr. Gomez-Ulla, Medical Retina Unit, Santiago University Hospital, Spain).

In this picture a drawing of the orbital anatomy (left) and the image of the same region obtained by Color Doppler Imaging (CDI) (right) are shown. CDI is a technique that allows measurements of serveral hemodynamic paramentes such as velocity and resistence index. It also produces a bidimensional image of the orbital structures as it can be seen if left anr right images are compared. Yellow-red colors are arteries and blue colors are veins. The picture in the right clearly shows the ophthalmic artery. This technique is useful to detect blood flow anomalies in the eye and periocular structures.

Color Doppler Imaging (see pervious figure) is able to produce 'flow waves' of orbital vessels. In the lower part of this figure the blood flow velocity waves of the central retinal artery of the right eye are shown. As indicated in the picture, the Peak Systolic Velocity and the End Diastolic Velocity can be directly measured from the waves.

The graphs in the figure above represent the relatioship between blood flow velocity and the radius of the vesel (left) and between the blood flow (volume/time) and the blood flow velocity (right) based on the 'Poiseuille's law'. It can be observed that, if the blood pressure is kept constant, increment of radius (vasodilatation) produces increment of flow velocity (left), which in turn produces increment of blood flow. Thus, it can be said that changes in blood flow velocity measured with Color Doppler Imaging indicate changes in blood flow in terms of volume per time. Such technique showed that the drug 'dorzolamide' is able to increase the blood flow of some ocular and periocular vessels (Martinez A, Gonzalez F, Perez R, Capeans C, Sanchez-Salorio M. (1999) Dorzolamide effect on ocular blood flow. Invest. Ophthalmol. Vis. Sci. 40:1270-1275.