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Chapter-02 Basic Principles

BOOK TITLE: Fundus Fluorescein and Indocyanine Green Angiography

Author
1. Chopdar Amresh
ISBN
9788180619649
DOI
10.5005/jp/books/10320_2
Edition
1/e
Publishing Year
2007
Pages
12
Author Affiliations
1. East Surrey Hospital, Redhill, Surrey, UK, Surrey and Sussex NHS Trust, East Surrey Hospital, Redhill, Surrey, UK
Chapter keywords

Abstract

The ophthalmic artery arises from the internal carotid artery and enters the orbit through the optic foramen. It sends two, sometimes three, posterior ciliary arteries to supply the choroid, and a separate retinal artery to supply the inner retina. The central artery of the retina arises as an independent branch from the ophthalmic artery. The central artery divides into the superior and inferior division that in turn divide to form the nasal and temporal branches. The retinal circulation is drained by venules from all corners. The upper and lower halves of the retina drain their respective nasal and temporal quadrants. They follow a similar pattern to their counterpart, the central retinal artery. The macula is divided into four zones, perifovea, parafovea, fovea, and foveola. The central 1.5 mm diameter area is the fovea and the depression within it is the foveola. The foveola is only 0.35 mm in diameter. Retinal pigment epithelium is a monolayer of hexagonal cells in intimate contact with the Bruch’s membrane outside and the outer segment of photoreceptors inside. Optic nerve head derives its blood supply both from the retinal and posterior ciliary circulation. The retinal vessels are impermeable to almost all solutions and dye. The choriocapillaries are permeable to a variety of substances, but their passage to the retina is halted by the tight junction of the retinal pigment epithelial cells. The amount of melanin pigment present within the pigment epithelium is critical to the degree of background choroidal fluorescence reflected during fluorescein angiography. However, indocyanine green angiography penetrates through the retinal pigment epithelium thus allows the choroidal vessels to be visible with reasonable clarity.

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