The regulating mechanisms of retinal and choroidal circulation

Purpose
The purpose of this article was to describe the phenomena related to the mechanisms regulating alterations of vascular blood flow in ophthalmic and retrobulbar circulation. In this review, various indirect and direct methods of evaluating retinal blood flow have been discussed. Laser, contrast and ultrasonographic techniques, including color Doppler ultrasonography, electroretinography, electroencephalography, calorimetric investigations, with the radiographic entities and registering changes in tunica vasculosa circulation were described. Additionally, radiographic investigations, isometric measurements and studies with the use of pharmacological agents, evaluation of partial pressure of oxygen or carbon dioxide in both inhaled and exhaled air, and in daylight as well as in darkness were presented. Although there are many control methods of regulating mechanisms of bulbar circulation, none of those techniques used presently and in the past is ideal, hence the only investigations widely applied for this purpose have been both Doppler ultrasonography and laser methods. In the review influence of myogenic and neurogenic mechanisms on blood flow in eyeball was described. Moreover, the part of vessels coarcting and dilating substances in these hemodynamic phenomena has been included.

Conclusions
In the course of various ophthalmic disease entities of vascular origin, different substances take part in general and local regulation of ocular and retrobulbar circulation, whose action mechanism might be the cause of hemodynamic disorders. Color Doppler ultrasonography remains one of the more frequently used methods which could indirectly register alterations of vascular blood flow in retrobulbar arteries.