EYES under the microscope

Text and images by Jan Parmentier


Pin hole eye of Haliotus, the abalone

Eyes are fascinating organs. That is true as much for the optical part as it is for the information processing part. In the retina of a human eye you will find one million cones of three different types and 100 million rods. With the cones we see colours, each type is sensitized for a different colour. In the cones and rods, photochemical processes lead to electric pulses in the optic nerve. The optic nerve has one million nerve fibres and is able to transmit 10 million bits of information per second. That is something different from my fast modem with 56000 bits per second.  
The number of bits per second is determined by the intensity of the light. In the end, in the neuron circuits of the cerebrum part of our brain an image is formed, a sort of virtual reality, a process of an unbelieveable complexity that we do not understand at all. As a microscopist, eyes have always stimulated my curiosity, mostly from a practical point of view. But really studying eyes seemed impossible for an amateur microscopist until one of my friends, John Wells, sent me a beautifully prepared slide with a cross section of the eye of the snail Helix aspersa.

Cross section through the eye of the garden snail, Helix aspersa

A Helix species (Helix pomatia), three tentacles are visible

Intrigued by this slide, I succeeded in collecting some more slides with preparations of molluscs eyes. Easy to buy nowadays, also in our own microscopy shop on the Net.

Page 2 will show you the more advanced eyes of Cephalopods


Comments to the author Jan Parmentier are welcomed.

or visit Jan's HOME PAGE

Preparation of the eye of a garden snail: John Wells
Other preparations by Johannes Lieder, Germany

All photographs Jan Parmentier 1999

html by Wim van Egmond


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