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PNAS 104 (20): 8287-8292

Copyright © 2007 by the National Academy of Sciences.

From the Cover


Müller cells are living optical fibers in the vertebrate retina

Kristian Franze*, Jens Grosche*,{dagger}, Serguei N. Skatchkov{ddagger}, Stefan Schinkinger§, Christian Foja, Detlev Schild||, Ortrud Uckermann*, Kort Travis§, Andreas Reichenbach*,**, and Jochen Guck§,{dagger}{dagger}

*Paul Flechsig Institute of Brain Research, Universität Leipzig, Jahnallee 59, 04109 Leipzig, Germany; {dagger}Interdisciplinary Center of Clinical Research, Inselstrasse 22, 04103 Leipzig, Germany; {ddagger}Center for Molecular Biology and Neuroscience, Department of Biochemistry, School of Medicine, Universidad Central de Caribe, Bayamon, Puerto Rico 00960; §Division of Soft Matter Physics, Department of Physics, Universität Leipzig, Linnéstrasse 5, 04103 Leipzig, Germany; Department of Ophthalmology and Eye Clinic, Universität Leipzig, 04103 Leipzig, Germany; ||Deutsche Forschungsgemeinschaft Molecular Physiology of the Brain Research Center and Department of Neurophysiology and Cellular Biophysics, Universität Göttingen, 37073 Göttingen, Germany; and {dagger}{dagger}Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom

Edited by Luke Lee, University of California, Berkeley, CA, and accepted by the Editorial Board March 27, 2007

Received for publication December 15, 2006.

Abstract: Although biological cells are mostly transparent, they are phase objects that differ in shape and refractive index. Any image that is projected through layers of randomly oriented cells will normally be distorted by refraction, reflection, and scattering. Counterintuitively, the retina of the vertebrate eye is inverted with respect to its optical function and light must pass through several tissue layers before reaching the light-detecting photoreceptor cells. Here we report on the specific optical properties of glial cells present in the retina, which might contribute to optimize this apparently unfavorable situation. We investigated intact retinal tissue and individual Müller cells, which are radial glial cells spanning the entire retinal thickness. Müller cells have an extended funnel shape, a higher refractive index than their surrounding tissue, and are oriented along the direction of light propagation. Transmission and reflection confocal microscopy of retinal tissue in vitro and in vivo showed that these cells provide a low-scattering passage for light from the retinal surface to the photoreceptor cells. Using a modified dual-beam laser trap we could also demonstrate that individual Müller cells act as optical fibers. Furthermore, their parallel array in the retina is reminiscent of fiberoptic plates used for low-distortion image transfer. Thus, Müller cells seem to mediate the image transfer through the vertebrate retina with minimal distortion and low loss. This finding elucidates a fundamental feature of the inverted retina as an optical system and ascribes a new function to glial cells.

Key Words: fiberoptic plate • glial cells • refractive index • light guides • optical trap

Author contributions: K.F. and J. Grosche contributed equally to this work; K.F., S.N.S., S.S., D.S., K.T., A.R., and J. Guck designed research; K.F., J. Grosche, S.N.S., S.S., and O.U. performed research; C.F. contributed new reagents/analytic tools; K.F., J. Grosche, S.N.S., and K.T. analyzed data; and K.F., D.S., A.R., and J. Guck wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission. L.L. is a guest editor invited by the Editorial Board.

This article contains supporting information online at

**To whom correspondence should be addressed. E-mail: reia{at}

© 2007 by The National Academy of Sciences of the USA

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