Diabetic Retinopathy (DR) remains a significant cause of blindness in working-age
populations across the world. The gold-standard method for assessing its severity is the
modified Airlie House classification developed for the Early Treatment Diabetic
Retinopathy Study (ETDRS), still used by clinical trials for developing of DR therapeutic
and management guidelines.
ETDRS Diabetic Retinopathy Severity Score (DRSS) is based on the identification of DR
lesions on colour fundus photography's (CFP) obtained in different locations of the
retina. The photography acquisition protocol consists in acquiring seven stereoscopic
pairs of overlapping 30° fields images of the ocular fundus to map out the macula and
mid-peripheral retina. Photographers and fundus camera systems usually need training and
certification by external reading centres to guarantee proper images quality and fields
definition in a process that can be challenging with a considerable learning curve.
Patient collaboration to follow a fixation point in different locations and withstand
intense flashes of light, a good dilation of eye pupil and the difficulty to obtain well
focused images in peripherical gaze positions are some of the main difficulties for
obtaining gradable images using this 7-fields acquisition protocol.
On the other side, the grading process of ETDRS 7-fields images can be extremely
labour-intensive and strongly dependent on the quality of the images, presence of
artifacts and the definition of the peripherical fields, requiring well-trained people to
identify and recognise features that can be very subtle or easily get unnoticed.
Moreover, the retinal area documented with the ETDRS 7-fields protocol represents
approximately only 35% of the retina surface. Substantial diabetic retinal pathology can
exist in the retinal periphery located outside this area which is being emphasized by
advanced retinal imaging technology. Predominantly Peripheral Lesions (PPL) like the
presence of venous beading, new-vessels, haemorrhages and microaneurysms in the extreme
periphery have been correlated with peripheral non-perfusion, neurodegenerative changes
and consequent increase of DR progression.
Recent instrumentation like OptosTM (Optos, Dunfermline, UK) or Clarus 500TM (Carl Zeiss
Meditech Inc., Dublin, USA) allow wide-field acquisitions that document up to 90% of the
retina surface in just one or two images decreasing patients tiredness and discomfort and
overcoming most of the quality and fields definition issues described above.
OptosTM equipment can acquire almost 200º of the retina in just one picture without the
need for pupil dilation and using ultra-widefield scanning laser ophthalmoscopy (SLO)
technology. Its final image is based on the superimposition of two images acquired with 2
different laser wavelengths: a green and a red wavelength, giving a semirealistic colour
image that despite its high contrast and sharpness, gives the retina a greenish and
unreal aspect. Also, its 200º field amplitude is usually disturbed by artifacts caused by
the presence of eyelashes or eyelids, that mainly obscure the peripherical area of the
retina.
On the other hand, Clarus 500 TM equipment uses an imaging technique called Broad Line
Fundus Imaging that is a hybrid of confocal SLO (cSLO) and traditional fundus
photography. This technology provides higher resolution images with more accurate
coloration of the fundus. A single image capture with this system obtains 133-degrees of
view but with the acquisition of just two pictures (a temporal and nasal image of the
retina), a 200-degree of view can be achieved.
Several studies have suggested moderate to substantial agreement between Optos ultra-wide
field (UWF) and ETDRS 7-fields imaging and have shown that DR occurs in areas peripheral
to the ETDRS fields in up to 40% of eyes, which may imply a more severe level of DR in 9%
to 15% of eyes. However, there is only limited data regarding the validity of DR
assessment using Clarus 500TM imagine technique obtained in cross-sectional studies with
few patients.
On this basis, the aim of this work is to identify and compare the ETDRS severity level
of diabetic patients using 3 different images modalities: the 30º ETDRS 7-fields colour
fundus photography's protocol, the 2 wide-field images technique with Clarus 500 TM and
the 1 wide-field image of OptosTM, in a prospective, longitudinal, and randomized study.
The ETDRS 7-fields area will be superimposed on both wide-field equipment's images so
equivalent retinal areas will be analysed. Our goal is to demonstrate that ETDRS severity
level can be accurately evaluated using only two Clarus 500TM high quality images with
wider amplitude, decreasing the effort and collaboration skills that are required in
older techniques, while improving the quality and identification capability of key
disease features with less artifacts than other wide-field systems. Additionally,
peripheral retina outside the ETDRS 7-fields area will also be analysed to assess the
presence of PPL and evaluate its relevance and association with disease severity level
and progression.
Finally, the investigators expect to evaluate patients' opinion about their experience in
each imaging modality, evaluating their discomfort and satisfaction degree while
submitted to each procedure.