Page 275 - Computational Retinal Image Analysis

CHAPTER

OCT fluid detection and

quantification 14

Hrvoje Bogunović, Wolf-Dieter Vogl, Sebastian M. Waldstein,
Ursula Schmidt-Erfurth
Christian Doppler Laboratory for Ophthalmic Image Analysis, Department of Ophthalmology,
Medical University of Vienna, Vienna, Austria

1 Introduction
The presence of fluid in the retina is the main hallmark of several important reti-
nal diseases, including neovascular age-related macular degeneration (nAMD), dia-
betic macular edema (DME), and macular edema secondary to retinal vein occlusion
(RVO). The term macular edema refers to a fluid-induced swelling of the central
retina. Fluid is generally divided into distinct types depending on its anatomical loca-
tion, that is, within the retina, between the retina and the retinal pigment epithelium
(RPE), and beneath the RPE. Furthermore, based on the origin of fluid, one can dif-
ferentiate between exudative fluid and fluid caused by retinal degeneration. In macu-
lar diseases characterized by exudation, the presence and amount of fluid is both a
diagnostic criterion and an important factor in the indication for treatment. In retinal
degeneration, fluid can be measured over time to assess disease progression. A com-
prehensive description of the role of fluid in macular disease is provided in Ref. [1].
Optical coherence tomography (OCT) offers a fast, noninvasive 3D view of the
retina by acquiring a series of cross-sectional slices (B-scans), allowing an in-depth
examination of retinal tissue with cellular-level resolution [2], and has become a
standard of care impacting the treatment of millions of patients every year [3]. OCT
has had a profound impact on early detection of disease, and monitoring its develop-
ment and the treatment response [4]. Fluid causing macular edema can be readily im-
aged and phenotyped using OCT (Fig. 1). The three distinct fluid types readily seen
on OCT and considered relevant imaging biomarkers are introduced next.

Intraretinal cystoid fluid
Intraretinal cystoid fluid IRF (or IRC) is defined on OCT as round or ovoid spaces
within the retina, with a low reflectivity content. This type of fluid is most often located
in the inner and outer nuclear layers of the retina, and less frequently in the ganglion
cell layer [5]. It forms confluent pools within the retinal layers that are interspaced with

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