Fundus Camera Imaging
The fundus camera uses a variation of indirect ophthalmoscopy in which the objective lens is used to deliver a cone of light through the entrance pupil, subsequently forming a flat inverted aerial image within the body of the camera, using light reflected from the eye. This image is transferred and projected on to an image sensor through a system of relay lenses. Fundus cameras use flash illumination to obtain high-quality images of the eye. Color fundus photography provides photographic records of the state of a patient’s fundus for the patient’s medical records; these images may also be used in research and for teaching. Because a large amount of information can be extracted from a simple color fundus photograph (Fig 2-1), this mode of imaging has been the cornerstone of many large epidemiologic and treatment studies. The color rendition is the best of any imaging system in terms of color accuracy, noise, and resolution. With the use of filters, the fundus camera can also be used to obtain fluorescein and indocyanine green angiography, in addition to autofluorescence. Imaging from fundus cameras may suffer from cloudy media in which light scattering obscures fundus details and reduces image contrast. A capacitor must be charged to power the flash unit; therefore, fundus cameras are typically only able to record images at a speed of approximately once per second.
Figure 2-1 Multimodal imaging of refractile drusen and associated atrophy. A, Color fundus photograph of geographic atrophy with refractile drusen. B, Enlarging the section within the white square from A shows a remarkable amount of information, even the diamond-like particles that seem to correspond to hydroxyapatite spherules seen in histologic sections of drusen. C, Fundus autofluorescence (AF) image shows attenuated autofluorescence in areas of geographic atrophy also shown in the color photograph; it also reveals an absence of autofluorescence colocalizing in the locations of the refractile drusen.
(Courtesy of Richard F. Spaide, MD.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.