Page 21 - Computational Retinal Image Analysis

10 CHAPTER 2 Clinical motivation

macular edema. In addition to qualitative assessment such as presence of cysts in the
retina or sub/intra-retinal fluids, direct measurements of the macular thickness have
been utilized as a parameter to represent disease severity of diabetic macular edema.
Along with a wide spread use of intra-vitreal injection of anti-vascular endothelial
growth factor to treat macular edema, quantitative retinal thickness assessment is
quite informative to decide initiating or continuing the treatment in addition to the
patients’ visual acuity. It should also be noted that active research has been done in-
vestigating whether RIA provides qualitative classification by adopting deep neural
network to filter images with intra-retinal edema, sub-retinal fluids, epiretinal mem-
branes, or other anatomical signs. Coupled with quantitative and qualitative feature
classification using OCT, there is a huge expectation that the management of macular
edema can be optimized by automated decision support [19].

1.3 Capturing pre-clinical signs of the eye diseases
Even before clinical eye diseases become detectable, there is an expectation that RIA
can provide predictive information by detecting subtle changes in the retina before
developing clinical diseases.
Retinal arteriolar narrowing, for example, is linked to an increased risk of devel-
oping glaucoma. Background hypothesis includes a decreased blood supply or dys-
regulation of blood flow in the retina before glaucoma is clinically detectable. RIA
can measure retinal vessel caliber size as an indicator of blood supply, and narrowing
of the retinal arteriolar vessel caliber seems to precede the clinical development of
glaucoma [20].
Difference in vessel widths between eyes have been also linked to the risk of
developing retinal vein occlusion. Although retinal vein occlusion is considered to
be associated with cardiovascular risks, it develops in one eye at a time, not involv-
ing both eyes at the same time (eventually, there are some patients who develops
retinal vein occlusion in both eyes over time, usually years). Here, un-balanced ratio
of the retina arteriolar and venular vessel widths, known as the arterio-venous ratio,
between right and left eye in the same individual indicates a risk of retinal vein oc-
clusion [21].

1.4 Identifying retinal changes associated with systemic diseases
Retinal signs can be an indicator to some systemic diseases. The retina is a rare
organ in that it allows physicians to observe microvasculature in vivo. Therefore, a
fundus examination provides a window to visualize microvascular changes caused
by systemic disease.
Cardiovascular risks and retinal vascular changes have been studied since retinal
examinations became available. The classic example of retinal vascular change asso-
ciated with systemic disease is its association with hypertension and cardiovascular
diseases. In the late 19th century, Marcus Gunn reported signs in the retina observed
in a series of patients with renal disease with hypertension [22]. Since then, retinal