Fundus camera
From Wikipedia, the free encyclopedia
A fundus camera is a specialized low power microscope with an attached camera designed to photograph the interior surface of the eye, including the retina, optic disc, macula, and posterior pole (i.e. the fundus).[1][2]
Fundus cameras are used by optometrists, ophthalmologists, and trained medical professionals for monitoring progression of a disease, diagnosis of a disease (combined with retinal angiography), or in screening programs, where the photos can be analysed later.
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[edit] Optical principles
The optical design of fundus cameras is based on the principle of monocular indirect ophthalmoscopy.[1][2] A fundus camera provides an upright, magnified view of the fundus. A typical camera has a field of view of 30 degrees, and a magnification of 2.5x, and some allow modification of this relationship through zoom or auxiliary lenses from 15 degrees which provides 5x magnification to 140 degrees with a wide angle lens which minifies the image by half.[2] The optics of a fundus camera is similar to that of an indirect in that the observation and illumination systems follow dissimilar paths. The observation light is focused via a series of lenses through a doughnut shaped aperture, which then passes through a central aperture to form an annulus, before passing through the camera objective lens and through the cornea onto the retina.[3] The light reflected from the retina passes through the un-illuminated hole in the doughnut formed by the illumination system. As the light paths of the two systems are independent, there are minimal reflections of the light source captured in the formed image. The image forming rays continue towards the low powered telescopic eyepiece. When the button is pressed to take a picture, a mirror interrupts the path of the illumination system allow the light from the flash bulb to pass into the eye. Simultaneously, a mirror falls in front of the observation telescope, which redirects the light onto the capturing medium, whether it is film or a digital CCD. Because of the eye’s tendency to accommodate while looking though a telescope, it is imperative that the exiting vergence is parallel in order for an in focus image to be formed on the capturing medium.
[edit] References
- ^ a b Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainsville, Florida: Triad Publishing Company, 1990.
- ^ a b c Saine PJ. "Fundus Photography: What is a Fundus Camera?" Ophthalmic Photographers' Society. Accessed September 30, 2006.
- ^ Saine PJ. "Fundus Photography: Fundus Camera Optics." Ophthalmic Photographers' Society. Accessed September 30, 2006.
