2 Fundal Photography
Photography of the fundus enables a permanent record to be obtained. The addition of fluorescein angiography enables photographic information to be obtained about the retinal vasculature and the state of the blood-retinal barrier.
THE FUNDUS CAMERA
A fundus camera is a specialised low power biomicroscope with an attached 35mm, Polaroid or digital camera back, to photograph the retina.
Mydriatic Camera
Fundus cameras are described by the angle of view – the optical angle of acceptance of the lens. An angle of 30°, considered the normal angle of view, creates a film image 2.5 times larger than life. Wide-angle fundus cameras capture images between 45° and 140° and provide proportionately less retinal magnification. A narrow angle fundus camera has an angle of view of 20° or less.
A viewing light, generated from a tungsten halogen lamp, is projected through a set of filters onto a mirror.
This mirror reflects the light up into a series of lenses, which focus the light. Light is reflected onto a mirror with a central aperture, which exits the camera through the lens, and proceeds into the eye. The resulting retinal image leaves the eye through the central aperture of the previously described mirror back to the single lens reflex camera system. An electronic flash source is utilised to take the photographs.
With a mydriatic camera, the patient’s pupils need to be widely dilated (at least 6mm in diameter) before retinal photography can be performed; this is done by the instillation of drops.
Mydriatic cameras are used in a variety of conditions:
- glaucoma
- diabetes
- inflammatory disorders
- age-related macular degeneration
- vascular occlusions
Mydriatic fundus cameras can also be used to perform dynamic tests such as fluorescein angiography and indocyanine green angiography.
FLUORESCEIN ANGIOGRAPHY
Fluorescein angiography is a diagnostic test that documents the dynamic flow of fluorescein dye in the blood vessels of the eye. After sodium fluorescein has been injected into the patient’s vascular system (usually a vein in the arm), a rapid sequence of photographs records the dye as it flows through both the choroidal and retinal blood vessels. Fluorescein acts as a marker, detailing precise areas of vascular leakage, or conversely, the absence of dye in the blood vessels. These photographs are used for both diagnosis and as a guide to patient treatment.
