Retinal Imaging:
“The eyes are the window to the soul” 16th century proverb
The retina gives an unobstructed view of the human vascular.
Also, retinal imaging is important for diagnosing retina diseases.
Fundus camera:
Is a device for photographing the retina.
It is based on the indirect ophthalmoscopy principle, where the Observer’s eye is replaced with a camera.
So, A fundus camera or (retinal 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 (eye).
Optical principles:
The optical design of fundus cameras is based on the principle of monocular indirect ophthalmoscopy.
A fundus camera provides an upright, magnified view of the fundus. A typical camera views 30 to 50 degrees of retinal area, with a magnification of 2.5x, and allows some 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. The optics of a fundus camera are similar to those of an indirect ophthalmoscope 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.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 Charge-coupled device.
