Viewing the choroid: where we stand, challenges and contradictions in diabetic retinopathy and diabetic macular oedema

Abstract

Diabetic macular oedema (DMO) is the leading cause of vision loss in the working-age population. Blood-retinal barrier (BRB) dysfunction in diabetic retinopathy (DR), mainly at the level of the retinal vessels, has long been related with leakage and fluid accumulation, leading to macular oedema. However, the nourishment of the macula is provided by the choroid and a diabetic choroidopathy has been described. Therefore, there has been a growing interest in studying the role of the choroid in the pathophysiology of DR and DMO, mainly by optical coherence tomography (OCT). Nevertheless, there are conflicting results in the different studies. We summarize the results from the available studies, describe the limitations and confounding factors and discuss future procedures to avoid bias.

Diabetic choroidopathy

“…Thinner diabetic choroids were found with increased microalbuminuria (Campos et al, 2016). A significantly thinner subfoveal choroid was found in all groups of type 2 Diabetic eyes compared to healthy eyes using 1060 nm OCT (Esmaeelpour et al, 2011).…”

“…Both anti-VEGF and panretinal photocoagulation caused a decrease in choroidal thinning perhaps due to reduction in permeability of the choroidal vasculature (Melancia et al, 2016). An in depth discussion of these differences is reviewed by Melancia et al and Campos et al (Campos et al, 2016; Melancia et al, 2016). The consensus from these reviews is that choroid thins in diabetic eyes without DME and treatment of DME with anti-VEGF causes thinning of choroid.…”

“…Blood flow is reduced in subfoveal choroidal vasculature (Nagaoka et al, 2004; Schocket et al, 2004) and areas of hypofluorescence and late filling undoubtedly represent areas of vascular loss and/or compromise (Shiragami et al, 2002; Weinberger et al, 1998). Perhaps, as a result of vascular insufficiency, the choroid appears to thin in DC unless macular edema is present (Campos et al, 2016; Melancia et al, 2016). EDI-SD OCT and SS OCT have documented the tortuosity and loss in intermediate and large blood vessels in Sattler’s and Haller’s layer (Ferrara et al, 2016; Hua et al, 2013; Murakami et al, 2016) seen previously with histological techniques.…”

Emerging Issues for Optical Coherence Tomography

“…Conversely, choroidal thinning has been extensively reported in patients with DR, although correlation with disease severity remains uncertain [50] . Most of the evidence points toward a reduction of CT in eyes with DME, even if contradictory results have been reported [46][47][48]51] .…”

“…Although contradicted by some studies, it is widely accepted that anti-VEGF agents cause a decrease in CT [55][56][57] . The role of CT to predict treatment response is still under debate: thicker choroid at baseline seems to correlate with good treatment response; on the contrary, variation of CT is not linked to therapeutic outcomes [50] . Variation in CT can be due to modification of vasculature, stroma or both.…”