Episode 31 - Fundus Photography & Angiography

In this episode, we explore the scientific foundations of fundus imaging and ocular angiography, building from core optical principles through to clinical vascular assessment.

We begin with the principles of fundus photography, examining how illumination and observation pathways are separated within the fundus camera, how reflection from the retinal pigment epithelium enables image formation, and how optical media clarity influences image quality. The role of filters, flash illumination, and photographic documentation in retinal disease monitoring is discussed.

We then turn to fluorescein angiography, analysing the physical basis of fluorescence — excitation and emission wavelengths, barrier filters, and the dynamics of sodium fluorescein within the retinal and choroidal circulation. We explain the normal angiographic phases, mechanisms of leakage, pooling, staining, and blockage, and how breakdown of the blood-retinal barrier alters imaging patterns.

Finally, we examine indocyanine green (ICG) angiography, focusing on its near-infrared absorptionproperties, protein binding, and improved penetration through pigment, haemorrhage, and fluid. Its value in imaging the choroidal circulation and conditions such as polypoidal choroidal vasculopathy is explained.

By the end of this episode, you will understand not only how these imaging modalities work, but why they reveal pathology in the patterns that they do — linking physics, vascular physiology, and clinical interpretation into a coherent framework.