Final answer:
A contrast agent is given intravenously to visualize the choroidal vascular network, particularly useful in conditions affecting the retinal blood vessels like idiopathic juxtafoveal retinal telangiectasia.
Step-by-step explanation:
To visualize the choroidal vascular network outside the surgical setting, a substance known as a contrast agent is given intravenously. The choroid is a highly vascular tissue in the wall of the eye that supplies the outer retina with blood. Often, for conditions like idiopathic juxtafoveal retinal telangiectasia, which involves dilated, twisted retinal blood vessels, such imaging is crucial for accurate diagnosis and management. When a patient is dehydrated and needs to receive fluids intravenously, typically an isotonic saline solution is administered. In oncology, for example, chemotherapy drugs may also be delivered directly into the bloodstream via a vein to treat various types of cancer.