A glimpse of the invisible

A glimpse of the invisible

These images show what we normally cannot see: the cells that compose the lens of the eye. The lens has to be invisible for us to be able to see. But like the other organs of our body, it is composed of cells – and cells are normally not transparent. Lens cells have to undergo an extreme specialisation to become invisible. For example, they have to degrade all of their organelles, tiny structures inside a cell, such as the nucleus that contains the DNA and the mitochondria that produce energy. This elimination of the organelles occurs in a process similar to programmed cell death (apoptosis). Yet lens cells survive their suicide attempt and can live for up to 100 years.

 

 

Lens cells are also enormously long and thin. Like the longitude lines on a globe, each cell reaches from one pole of the lens to the other. Hundreds of concentric shells of these lens fibre cells make up a lens. In each shell, the fibre cells are aligned in parallel. If this precise order breaks down, the lens becomes opaque – a cataract develops. Moreover, lens cells have a regular, hexagonal shape and are arranged very precisely to make the lens transparent.

These two pictures are included in Kurzes Lehrbuch der Zoologie [Brief textbook of zoology] by V. Storch and U. Welsch, 8th edition, Elsevier/Spektrum Akademischer Verlag, München, 2005. Copyright by Ralf Dahm, Max Planck Institute for Developmental Biology, Tübingen, Germany.