Fig. 3.26 Anterior segment ßuorescein angiogram: capillary phase. Note the total lack of perfusion of the inferior one-fourth of the vascular plexuses in the scleral/episcleral Þeld (below the bright area of normal capillary Þlling)

leak ßuorescein, probably because they have thicker endothelium and fewer fenestrations [92]. They may Þll late.

Radial arterioles of the iris begin to Þll, either coinciding with Þlling of the anterior ciliary arteries or 1Ð2 s later, implying that the iris receives arterial supply from the anterior ciliary circulation.

Capillary Phase

Episcleral and conjunctival capillaries are difÞcult to differentiate at this stage, but both emerge from the anterior episcleral arterial circle and branches of the anterior ciliary arteries. Usually, all the capillaries are Þlled between 6 and 30 s after ßuorescein injection; episcleral capillaries and limbal arcades are the latest to Þll (Fig. 3.24).

Venous Phase

Anterior conjunctival venules and limbal arcades drain into the limbal venous circle, which is a circle of Þne venules behind the limbal arcades and medial to the anterior episcleral arterial circle (Fig. 3.25). The limbal venous circle drains into episcleral collecting venules that run toward the recti muscles. These collecting venules meet anterior episcleral venules and perforating scleral venules before they leave the globe over the recti muscles as anterior ciliary veins [94, 116].

Although leakage from conjunctiva and episcleral capillaries in low-dose ßuorescein angiography can Þrst be seen at 4Ð10 s, there is not much masking of anatomical structures before 30 s after ßuorescein injection [94]. Limbal arcades are the latest to leak (always after 30 s); it is thought that this leakage may be the result of diffusion from the surrounding subconjunctival space.

In the interpretation of an anterior ßuorescein angiogram, particular attention must be paid to areas of vascular hypoperfusion or occlusion (Fig. 3.26). Other important considerations are transit time or time between arteriole and venule Þrst Þlling (early, normal, or delayed), type of arteriolar or venular Þlling (early, normal, delayed, or absent), and type of capillary leakage (early, normal, or delayed).

3.2.7Anterior Segment Indocyanine Green Angiography

Indocyanine green (ICG) is a water-soluble tricarbocyanine dye that offers several advantages over ßuorescein because of its molecular weight of 775 kD. ICG is rapidly and almost completely bound (96%) to plasma protein, mainly albumin and a1-lipoproteins; hence, it does not leak through fenestrated choriocapillaries. Both ßuorescence angiography and ICG can be performed in the same session. A bolus of 1 ml of 20% ßuorescein is injected intravenously and photographs are taken until the ßuorescein disappears. Then, a bolus of 25 mg ICG dissolved in 10 ml of 5% dextrose solution is injected intravenously and photographs are taken for 20 min or until the dye has disappeared. ICG offers several advantages over ßuorescein: it distinguishes totally occluded vessels from the temporary obstruction caused by vascular spasm seen with ßuorescein and localizes better the site of maximum inßammation; therefore, it is more valuable in assessing the effects of treatment and when to withdraw it.

In diffuse scleritis, both anterior segment ßuorescein and ICG angiographies show rapid Þlling and short transit times with a structurally normal ßow pattern. After prolonged inßammation or recurrences, an abnormal vascular pattern with