Methods of evaluation of retinal circulation.

The authors emphasize the need for the development of non-invasive objective methods for the study of retinal circulation under physiologic or pathologic conditions. Clinical methods embrace the use of blue field entoptic phenomenon (that estimates leucocy tes circulating in the peri-foveal capillary bed), Laser-Doppler speedometer (that allows the mea surement of erythrocyte.velocity in retinal vessels) and methods based on the use of dyes, either by means of the direct estimation of their velocity (ophthalmoscopy, cineangiography and two-point fluorophotometry) or by measurement of the mean circulation time resorting to dilution curves (using angiography between I and 60 Hz, two-point fluorophotometry and Video-TV re cording). The advantages and drawbacks of each of these methods are examined. Using a perso nal technique of two-point fluorophotometry (direct method) the authors present a study of re producibility based on the evaluation of 5 normal subjects submitted to repeated injections. This study reveals that the minimum time of circulation in an arteriolar segment presents a coefficient of variation comprised between 2.8-4.5% which favours the good reproducibility of this method. This fact may be ascribed to the rise of intraocular pressure associated to the use of suction con tact lenses. Although two-point fluorophotometry permits merely a relative measurement of reti nal circulation speed, the method, in contrast to other available techniques, is readily applicable for pratical purposes.