Diabetic retinopathy (DR) is a major microvascular complication of diabetes mellitus (DM). The most common causes of vision loss in diabetic retinopathy are the proliferating form of this severe retinal disease and diabetic macular oedema (EMD).
With respect to these ocular complications of DM, imaging techniques play a significant role in early diagnosis, treatment protocol decision-making and prognosis, as well as being crucial in screening patients with di
abete mellitus and in the management of these complications.
Recent developments in ocular imaging
Scientific research in recent decades on EMD has focused on the possibility of using various clinical, laboratory and especially imaging biomarkers to improve the diagnostic process. The latter, in fact, provide an assessment in vivo of the health status of the retina and choroid in a non-invasive manner and are tools that can offer a histological-like assessment of various changes, including retinal capillary density, non-perfusion, vascular remodelling and foveal vascular zone (FAZ) area.
Retinal imaging and biomarkers of diabetic retinopathy and EMD
OCT
Recently, the scientific community has focused its attention on determining the prognostic value of changes observed through optical coherent radiation tomography (OCT), such as:
- foveal intraretinal cysts;
- the presence of oedema;
- the size and location of the oedema;
- the presence of subretinal fluid;
- the integrity of the retinal layers in case of EMD.
L'OCT is an imaging technique that provides high-resolution cross-sectional images of the neurosensory retina and choroid by processing backscattered light. With the advancement of technology, state-of-the-art OCT tools, such as spectral-domain (SD) and swept-source (SS) OCT, are now available: the most advanced technologies for imaging the ocular fundus. Moreover, as OCT is a non-invasive technique, it has been rapidly adopted by physicians for the evaluation of patients with EMD.
FFA
The ocular fundus fluorangiography (FFA) remains, however, the gold standard in the study of the retinal vasculature. FFA can help determine various alterations, such as:
- retinal capillary non-perfusion;
- vascular telangiectasia;
- the dropout of capillaries;
- the enlargement or irregularity of the FAZ;
- the presence of neovascularisation.
In addition, FFA allows rapid assessment of retinal vascular changes, some of which may not be detected during routine fundus examination in mydriasis (pupil dilation). FFA is an important tool to distinguish between intraretinal microvascular abnormalities (IRMA) and neovascularisation (NVE). Furthermore, in cases of EMD, FFA helps to differentiate focal loss from diffuse bed loss.
OCTA
L'OCTA (optical coherence tomography angiography) is a new tool that provides detailed information on the microvascularisation of the retina and choroid. The information provided by the OCTA complements data obtained using FFA, including precise areas of capillary non-perfusion, the presence of collaterals or neovascularisation of the optic nerve head and FAZ abnormalities. The OCTA is an examination that allows each of the three retinal capillary plexuses to be analysed separately, which is important information for understanding pathophysiological changes in diabetic retinopathy.
OCTA is able to identify:
- microaneurysms;
- IRMA,
- areas of capillary non-perfusion and neovascularisation, even before they are appreciated clinically or on ocular fundus photography.
The wide-field version of OCTA has emerged as a promising tool to replicate or replace FFA in diagnosing or monitoring the progression of diabetic retinopathy.
 FAF
Finally, thebackground autofluorescence (FAF) is a rapid and non-invasive imaging technique that can provide new information on the assessment of EMD. In DR, local ocular inflammation and oxidative stress lead to an increase in the amount of lipofuscin and a decrease in the amount of lutein and zeaxanthin in the macula: these changes cause the FAF signal to increase. Numerous studies using short-wavelength FAF have also reported an increase in the signal in patients with EMD.
All these imaging techniques, therefore, can undoubtedly help in the detection of subclinical disease and retinal vascular changes, before they are clinically detectable and/or before the development of visual symptoms.
Bibliography:
Dr. Carmelo Chines
Direttore responsabile
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