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Compared to the DRS Research Group scheme, the major change in the AAO classification is the acknowledgment that IRMA and venous beading are strong predictive factors for a rapid progression from NPDR to PDR. In the previous classification, the presence of hard and soft exudates was defined as a significant finding belonging to the mild NPDR level. Later, in the subsequent scheme, physicians removed the presence of hard and soft exudates from the grading list, because they did not reliably predict the evolution to the more severe stage of PDR compared to the prognostic value of IRMA and venous beading.
Currently, the AAO classification of NPDR is a practical and prognostic tool in the hands of retinal specialists, which helps to manage the biomicroscopic signs of DR and to evaluate the data using a standardized method.
Summary 2.2
NPDR is currently classified into different stages of severity, according to the ETDRS and AAO classifications. The ETDRS showed that very severe NPDR has an increased risk of progression to PDR of about 45 and 71 % within 1 and 5 years, respectively. The AAO classification indicated three levels of gravity of NPDR: mild, moderate, and severe.
2.1.3Atypical Forms of NPDR
Diabetic papillopathy (DP) has been first defined by Lubok and Makley in 1971 presenting three cases of bilateral optic disk swelling in type 1 diabetic patients [21]. Later the same definition has been used by other authors describing case reports of transient optic disk edema, associated with minimal visual impairment and spontaneous resolution in most of the cases [22–24]. Currently the term DP defines a unilateral or bilateral form of acute optic disk edema in patients with type 1 and 2 diabetes, often asymptomatic, with little or no appreciable optic disk dysfunction, generally spontaneous resolution, and good visual prognosis. The typical signs of DP include a hyperemic disk swelling, with blurring optic disk margins and superficially radially oriented dilated telangiectatic vessels (Fig. 2.9). Classically, DP is associated with a small cup to disk ratio, with a variable diabetic retinopathy stage, and, in some cases, with macular edema.
The pathogenesis of DP is still unknown and is currently a focus of controversy. Some authors suggested that DP is a form of optic disk ischemia, similar to anterior ischemic optic neuropathy (AION), and it has been hypothesized that DP could represent an impending AION that did not evolve into a manifest disease [25–27]. A second proposed mechanism suggested that DP could be considered as a vasculopathy of peripapillary radial capillaries [22, 23, 28–30]. According to this theory, a local disk microangiopathy of the most superficial layer of the epi-papillary and peripapillary radial capillaries is implicated in the pathogenesis of DP. In fact, there is evidence that radial capillaries are sensible to decreased blood flow, leading to localized non-perfusion, acute endothelial decompensation, and edematous capillaropathy (EC) because of their specific anatomical peculiarities [29]. In fact, radial
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Fig. 2.9 Diabetic papillopathy: vasculopathy of peripapillary radial capillaries. Two different cases before (a, c) and after (b, d) spontaneous regression related to the improvement of systemic control
capillaries are longer than the other retinal capillary network, and they directly connect large caliber arteries to large venous trunk, without anastomosis (Fig. 2.10). This peculiar morphology could explain their high sensibility to different vascular
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Fig. 2.10 Edematous diffuse capillaropathy is an atypical form of DR, frequent in young longlasting ID diabetic female patients. (a) Red-free photograph of the posterior pole showing the presence of a cotton wool spot (arrow). The early phase of FA (b) shows the presence of hypofluorescent areas corresponding to a reduction of vascular perfusion. A typical feature of this form of DR is a diffuse BRB (blood-retinal barrier) breakdown that appears as a suffuse hyperfluorescence of the entire retina in the late phase of FA image (c). This finding is due to the presence of an inflammation of the retinal vessels responsive to a better glycometabolic control. (d) The ischemic condition showed by the cotton wool spot in red-free image is further demonstrated by the presence of ischemic edema in the corresponding OCT section
Fig. 2.11 (a) Schematic diagram of radial peripapillary capillaries (Modified from Henkind [31])
damages, such as glycometabolic dysregulation or hypertensive injury [30]. As a demonstration, the distribution of cotton wool spots and telangiectatic vessels repeats the topography of peripapillary vascular radial network [31] (Fig. 2.11).