changes and resolution of IRMAs. 7.12 ISOLATED POSTERIOR VITREOUS DETACHMENT Regression of angiogenesis may accelerate scarring (gliosis) at the vitreo-retinal interface which in turn may induce posterior vitreous detachment. As an early complication of pan-retinal laser, posterior vitreous detachment may convert a sub-hyaloid haemorrhage into an intra-gel haemorrhage making further laser difficult. More commonly, it is a late complication of pan-retinal laser, leading to a selflimiting intra-gel vitreous haemorrhage as the vitreous detaches from inactive new vessel remnants. 7.13 IMAGING Imaging is playing an increasingly important role in the classification of diabetic retinopathy. The classification of diabetic retinopathy will need to be reflect the rapid technological advances. 7.13.1 Digital photography Digital photographyhas become the mainstay of documentation of diabetic retinopathy and is the methodology of choice for retinal screening. Colour photography is best for demonstrating the presence of white lesions such as exudate and cotton wool spots. All other lesions are best visualised using red-free images. Although most features can be ascertained as long as third order vessels at 62 thefovea are also visible, intra-retinal microvascular anomalies can only be confidently documented if the nerve fibre layer is also visible. 7.13.2 Fluorescein angiography Historically, fluorescein angiography has had an important role in demonstrating the presence of subtle new-vessel formation and guiding laser, particularly macular laser for oedema and fill-in laser for proliferative retinopathy. Only fluorescein angiography can readily demonstrate the extent and location of capillary drop out. However, the use of fluorescein angiography is waning with the advent of OCT and antiVEGF medications. 7.14 PATTERNS OF LEAKAGE 7.14.1 Neovascular New vessels of proliferative diabetic retinopathy unlike those formed in utero, are fenestrated. As a result fluorescein leakage throughout the angiogram run occurs. Occasionally early new vessels leak minimally, despite their obvious clinical appearance, most often noted with early NVD. Unlike collaterals, the lumens of these non-leaking new vessels at the disc are very narrow (fine) compared to other vessels at the disc. Clinical acumen should take precedence, particularly if such non-leaking new vessels are noted at the disc where extent of peripheral significant capillary drop out should be assessed to decide if pan-retinal laser should be considered. 7.14.2 Macular Unlike age-related macular degeneration the classification of fluorescein leakage at the macula is not established. There are, however, some similarities. 7.14.3 “Focal” leakage In diabetic macular oedema, some patients may show early leakage in transit phase of angiogram which may be “discrete” (focal) with progressive leakage from “culprit” microaneurysms. These patients often have accompanying circumferential exudates (circulate exudates); such discrete leaky spots respond well to macular laser, especially those in extrafoveal areas. 7.14.4 “Indeterminate” In many patients with diffuse diabetic macular oedema, a similar “indeterminate” appearance in the late phase of the angiogram occurs and which shows little or no correlation to the presence of microaneurysms. These patients often have diffuse retinal thickening, sometimes with intra-retinal cysts (cystoid macular oedema) and often without exudate formation. These patients respond poorly to macula laser, particularly if leakage is subfoveal. 63 7.14.5 “Mixed” Many patients, with diabetic macular oedema have a mixed pattern of leakage. Additionally, there may be additional component of ischaemic maculopathy. 7.15 PATTERNS OF MACULAR ISCHAEMIA Both – focal and diffuse – patterns of macular leakage may be associated with areas of capillary occlusion seen as discrete zones of capillary drop out in macula. Indeed all patients with macular oedema, by the very nature of the pathogenesis of diabetic retinopathy, would have some degree of ischaemia. Macular ischaemia may be central (involving the foveal avascular zone -FAZ) seen as enlarged foveal avascular zone or peripheral (i.e. involving the temporal vascular arcade watershed zone or extra foveal areas of macula). If the perifoveal capillaries of the foveal avascular zone are affected then visual prognosis is poor and laser is ineffective in restoring macular function. 7.16 RETINAL ISCHAEMIA Peripheral retinal ischaemia, in the absence of surrogate markers or capillary drop out (blot haemorrhage, venous beading, intra-retinal microvascular anomalies) may not always be readily discernible clinically and hence retinal angiography especially wide field retinal angiography is useful in detecting ischaemic changes. Angiography readily identifies such areas and is particularly useful in identifying potential areas of retreatment for persistent or recalcitrant new vessel formation. It is also useful in classifying those patients with isolated intra-retinal microvascular anomalies into those with significant capillary dropout who required close supervision, and those without capillary dropout, who do not. 7.17 OPTICAL COHERENCE TOMOGRAPHY (OCT) OCT has complemented our understanding of maculopathy and highlighted shortcomings of the slit lamp examination alone in identification of retinal thickening and intra-retinal oedema. OCT has revolutionised the identification of macular oedema, however, it is limited by its inability to identify the source of leakage, nor the degree of capillary drop out present. It is particularly suited to determining whether retinal fluid is centre involving or not, thus helping to select those patients which are best suited for intravitreal injection therapy (centre involving) or best suited for laser (extrafoveal). Fluorescein angiography may still be necessary in some cases to guide treatment, for example in cases of juxta foveal leakage and retinal thickening – cyst formation. In addition to identification of fluid collection, optical coherence tomography will reveal the presence of haemorrhage, exudate and photoreceptor atrophy which can be enhanced by colour photography. OCT is