The fundus camera uses the optical principles of indirect ophthalmoscopy. It is essentially an indirect ophthalmoscope with a perforated mirror taking the place of the faceplate of the indirect ophthalmoscope that separates the observation and illumination pathways, and the aerial image is simply reimaged onto the camera’s film or sensor array.
With the addition of different filters, fluorescein angiography can be performed with the fundus camera. Fluorescein has its absorption maximum at about 490 nm, in the blue part of the spectrum, whereas the emission maximum is at about 530 nm, in the green part of the spectrum. In fluorescein angiography, an “excitation filter” permits blue light to pass and excite the fluorescein; on the return path, a “barrier filter” allows the green light to pass, but blocks the background blue light, allowing the fluorescent image to be recorded with high-resolution monochrome film or sensor array.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.