An Overview of Human Cells for Light Microscopists
Part III - Human Eyes and Insect Eyes
A 3D modelling article
by Mol Smith 2010
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Page:      1  |  2  |   3   |  4  |  5 |  6                       For Part 1 The Human Cell - go here!    Part 2 Human Skin - go here!

 Insect Eyes     Insect's View: Simulation1   Simulation2   Simulation3   Human Eyes1   Human Eyes2   Resources and external links
Human Eyes & Insect Eyes
The most important thing to a light microscopist is his/her eyes. This comes as no surprise because probably, the most important thing to nearly all living entities of the animal kingdom, including insects, is sight. Nature has developed several solutions to the problem of aiding living entities to navigate their reality by detecting light (or other) waves reflected by objects and subjects in the environment. I thought it might be interesting to explore two of these methods here by looking at the human eye and a compound eye - as exploited by bees and flies. It is important to note that not all insects have compound eyes!

For any eye to be of value, it must detect light and shades of darkness, and would be better advantaged if it can detect colour, perceive 360 degree views, be self-cleaning, auto-focussing, and work as one of a pair to enable stereoscopic viewing and thus depth and distance. Since a lot of data would need to be interpreted in real-time, a lot of brain mass would need to be dedicated towards this single task. Although mammals, with their greater size than insects, have sufficient 'processing' capacity to accommodate a complex eye, the insects do not not. This has led to a uniquely different approach by evolution to design an eye which needs minimum processing capability to be useful: the compound eye.

Compound Eye
The compound eye of both a fly and a bee is constructed of hundreds of tiny simple lenses called
ommatidia wiki (individual "eye units"). Insect Compound eyes can typically consist of between 2 and 30,000 individual units. Each unit can perceive a tiny part of the external world, like a piece in a mosaic. All the image chunks are combined within the insect brain to form a complete image, albeit - an incomplete one due to the divisionary walls around each unit. We can only really speculate about what kind of image is perceived inside the insect brain (mind?), and we have no way of telling if the divisionary lines between image pieces are removed as part of the processing, or whether they are left in.

Compound Eyes of Hover Flies (below)

A diagram of a single unit of the compound apposition eye is seen left.
Good fliers like flies or honey bees, or prey-catching insects like dragonflies, have additional specialized zones of ommatidia organized into a fovea area which gives acute vision. In the acute zone the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution.

The image right is a Scanning Electron Microscope of a Fly's eye. You can clearly see the surface of hundreds of ommatidia with tiny whisker-like hairs between some of them.

I have coloured the surface of a single lens red and marked it {A}, which you can compare to the lens marked {A} in the diagram on the left.
  fly eye sem

Amazingly, each lens is actually a
biconvex doublet wiki.
Below, is a cross-sectional view through the eye of a honey bee. The array of
ommatidi is clearly visible. I have marked a single unit to aid you.

The compound eye is only superior to the complex eye of mammals and humans, by its abilities to be extra sensitive to tiny movements, and the fact that data from it can be rapidly processed (much faster than in our eyes). Both of these properties are obviously desirable for a rapidly moving flying insect. In terms of detail, clarity, and information - it is inferior!

So, what would it be like to see the world through the eyes of a fly? Well, using 3d modelling and anaglyph image creation, we can probably get a fairly good idea.
Let's take a look!

Comments to the author
Mol Smith are welcomed.

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Published in Jun 2010 Micscape Magazine.
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