Imaging Biomarkers of Treatment Response to Dexamethasone Implant in Macular Edema Due to Retinal Vascular Diseases - Diabetic Macular Edema and Retinal Vein Occlusion.

Diabetic retinopathy (DR) and retinal vein occlusion (RVO) are complex multifactorial diseases and the leading causes of visual impairment worldwide. The exact mechanisms leading to Macular Edema (ME) in DR and RVO are not fully understood, actual evidence focuses on the role of inflammation as critical contributing factor in ME pathogenesis and several studies described the association between high levels of systemic and local inflammatory molecules and the development of ME. Even if vascular endothelial growth factor (VEGF) is the most studied factor involved in ME pathogenesis in retinal vascular diseases and the main target of available therapeutic strategies, its role cannot explain alone all the events taking place in the onset and progression of these diseases. VEGF selective inhibition is not sufficient to stop the inflammatory cascade in DR and RVO and anti-VEGF therapies are frequently of transient benefit, especially in DME treatment, needing repeated injections over time and suggesting the involvement of other molecular pathways. Intravitreal corticosteroids block the production of inflammatory mediators (including VEGF) and inhibit leukostasis. In particular, dexamethasone has the highest relative clinical efficacy of any corticosteroid applied to ophthalmology practice. Intravitreal dexamethasone implant (Dex) slowly releases steroids into the vitreous over a period of up to 6 months. Dex 0.7 mg (Ozurdex™; Allergan, Irvine, CA, USA) has been used to reduce ME in patients with DR and RVO and its efficacy in terms of best corrected visual acuity (BCVA) improvement and central macular thickness (CMT) reduction has been demonstrated in many different studies. Thanks to the great advances in retinal imaging technologies of the last years, a new concept of non-invasive "imaging biomarker" of retinal inflammation has emerged and has made its way in the study of patients with DR and RVO. Clinical research has consequently developed great interest in finding specific retinal inflammatory parameters in DR and RVO and there is a growing body of scientific evidence on the importance of this topic. Moreover, the evaluation of these inflammatory biomarkers might be helpful in the prediction of treatment response. Nowadays, main proposed imaging biomarkers of inflammation include subfoveal neuroretinal detachment (SND) and hyperreflective retinal spots (HRS), visible on optical coherence tomography (OCT). SND consists in extracellular fluid accumulation between the outer segments of photoreceptors and the retinal pigment epithelium and is present in approximately 15-30% of eyes with DME and in an even greater number of patients with ME secondary to RVO. The presence of SND has been associated with higher levels of local inflammatory molecules, in particular IL-6. HRS are increased in number in patients with diabetes (with or without DR) and RVO; they have specific characteristics and are thought to represent aggregates of activated microglial cells that progressively migrate from the inner to the outer retina, confirming their role as inflammatory biomarkers. The purpose of this pilot study is to evaluate different imaging parameters in patients with previously treatment-naive DME and ME due to RVO before and after treatment with dexamethasone implant, in order to find specific retinal inflammatory and microvascular biomarkers that may be predictive of treatment outcome. The novelty of this study is a detailed evaluation of multimodal imaging modifications in DME and ME due to RVO after treatment with Dex in order to document its anti-inflammatory effect.