Glial Fiber Optics

Science's STKE  22 May 2007:
Vol. 2007, Issue 387, pp. tw175
DOI: 10.1126/stke.3872007tw175

Specialized glial cells called Müller cells support the function and survival of retina neurons. Franze et al. show that these cells also have special optical properties that allow them to pass light to the retina. Because of these properties, the light scattering, refraction, and reflection that would be expected based on the inverted structure of the eye and the need for the light to pass through multiple layers of tissue to reach the retina, are minimized. Light transmission and reflection microscopy of the inner retina (without the photoreceptor cells) revealed that light was transmitted to discrete points, and z-axis reconstruction revealed the presence of "tubes" that transmitted the light most effectively with minimal light scattering. These tubes corresponded to the Müller cells, and dissociated Müller cells exhibited higher refractive index than retinal neurons, which would be consistent with minimizing light loss through the length of the cell. Optical engineers use waveguide characteristic frequency (the V parameter) as a measure of the light guidance through a propagating model, and this is the most applicable model for the Müller cells because of their complex morphology. Calculations of the V parameter for Müller cells indicate that these cells could function as waveguides for visible light. Indeed, Müller cells efficiently transmitted light when placed in a modified dual-beam laser trap (the cells were aligned along their length between two optical fibers, thus allowing light to transmit from one fiber, through the cell to the other fiber).

K. Franze, J. Grosche, S. N. Skatchkov, S. Schinkinger, C. Foja, D. Schild, O. Uckermann, K. Travis, A. Reichenbach, J. Guck, Müller cells are living optical fibers in the vertebrate retina. Proc. Natl. Acad. Sci. U.S.A. 104, 8287-8292 (2007). [Abstract] [Full Text]