March 2012
Volume 53, Issue 14
Free
ARVO Annual Meeting Abstract  |   March 2012
Non-mydriatic, 68° Wide Fundus Imaging with Low Cost Components
Author Affiliations & Notes
  • Bernhard Hoeher
    Chair for Microwave Engineering and High Frequency Technology, University of Erlangen-Nuremberg, Germany
    Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, Germany
  • Thomas Koehler
    Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, Germany
    Pattern Recognition Lab, University of Erlangen-Nuremberg, Germany
  • Bernhard Schmauss
    Chair for Microwave Engineering and High Frequency Technology, University of Erlangen-Nuremberg, Germany
    Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, Germany
  • Georg Michelson
    Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, Germany
    Department of Ophthalmology, University of Erlangen-Nuremberg, Germany
  • Footnotes
    Commercial Relationships  Bernhard Hoeher, None; Thomas Koehler, None; Bernhard Schmauss, None; Georg Michelson, None
  • Footnotes
    Support  Erlangen Graduate School in Advanced Optical Technologies (SAOT), Medical Valley EMN Leading-Edge Cluster
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 3106. doi:
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    • Get Citation

      Bernhard Hoeher, Thomas Koehler, Bernhard Schmauss, Georg Michelson; Non-mydriatic, 68° Wide Fundus Imaging with Low Cost Components. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3106.

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Abstract
 
Purpose:
 

We propose an imaging method for a non-mydriatic wide field fundus camera using low cost components for telemedical diagnostics in developing countries.

 
Methods:
 

To get wide field images of the retina we take advantage of an eyepiece for amateur astronomy being available on the mass market for about 150 US$. The eyepiece offers a viewing angle of 68° into the eye at a focal length of 22mm.Non-mydriatic fundus imaging with large viewing angles is challenging due to the large corneal reflections compared to the pupil of the eye. Therefore we developed a concept that allows to illuminate one half of the visible circle on the retina. Thus the size of the resulting corneal reflection in the vertical axis is reduced by a factor of two. Thereby the height of the resulting reflection is small enough to be successfully shielded by a vertical bisected aperture. One section contains the illuminating rays and the other the imaging rays. Applying this bisection not only to the aperture plane but also to the image plane makes it possible to guide remaining reflexes to the unused half of the image.For illumination we use a triple LED with dominant emission wavelengths of 625nm (red), 527nm (green) and 470nm (blue). The images are acquired by a monochrome CCD camera with a resolution of one megapixel. Color images are created by additive color mixing of three sequential acquired images each illuminated with one of the three primary colors emitted by the LED. For reflection reduction within the optics we use polarizers and subtract reference images made without a subject.

 
Results:
 

We are able to continuously acquire image sequences with 40 color images per minute. The images cover a semicircle on the retina with a diameter corresponding to a 68° viewing angle. Figure a) shows the raw fundus image of the right eye of a 27 year old subject and figure b) the same image after subtracting the reference frames and increasing contrast and sharpness.

 
Conclusions:
 

We introduced a method that is capable of taking wide field fundus images of non-mydriatic eyes.We can take advantage of image restoration techniques based on image sequences which can be acquired with 40 frames per minute. The costs of the components of the fundus camera do not exceed 1300 US$ which paves the way for an application in developing countries.  

 
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina 
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