Page 38 - Computational Retinal Image Analysis

28 CHAPTER 3 The physics, instruments and modalities of retinal imaging

2.5 Spectral characteristics of the eye
The characteristics of retinal images vary strongly with wavelength and imag-
ing modality as can be appreciated by the multispectral retinal images shown in
Fig. 5 (recorded with a hyperspectral fundus camera [12]) and the two-wavelength
images in Fig. 6 (recorded with a two-wavelength SLO operating in non-confocal
and hybrid-confocal modes [30]). The differing recording principles of the fundus
camera and the SLO are discussed in Sections 3.3 and 3.5. We discuss here the rea-
sons for the variation of the appearance of these images with wavelength and imag-
ing modality. It should be noted that the intensity of retinal images varies greatly

FIG. 5
Two sets of narrowband images of normal retina recorded with a hyperspectral fundus
camera [12]. Arterioles and venules are highlighted by red and blue arrows respectively.
The arterioles exhibit much lower contrast at the longer wavelengths due to the lower
extinction coefficient of oxygenated blood. The lighter retinal pigmentation for the left
images results in increased visibility of the choriocapillaris at red wavelengths.