The Eye

In the Victorian era, the complexity of the eye was often cited as proof of “intelligent design”, that God had created the world (and living things). Bill Bryson, in his romp through the human body, aptly titled The Body: A Guide for Occupants, points out that:

“It was an odd choice because the eye is really rather the reverse.”

 

First, it is “built back to front”:

“The rods and cones that detect light are at the rear, but the blood vessels that keep it oxygenated are in front of them.”

Even worse:

“There are vessels and nerve fibres and other incidental detritus all over, and your eye has to see through all this.”

And:

“All the nerve fibres leave the eye via a single channel at the back, resulting in a blind spot… in our field of vision.”

 

If you’re wondering why we don’t see a “gap” in our field of view (corresponding to the blind spot), it’s because “your brain continually fills the void for you”. And since the blind spot is not exactly tiny, it leads to a weird situation:

“A significant part of everything you ‘see’ is actually imagined.”

 

Don’t get me wrong: it’s very impressive how the eye works despite all these “design flaws”. Bryson’s point is the irony of the eye being cited as an example of the Creator’s designing skills.

 

When it comes to the eye, everyone’s heard of rods and cones. Rods help us see in dim light, while cones help see colors. But there’s more. And it was only discovered as recently as 1999 when Russell Foster found a third kind of photoreceptor. Its purpose? To detect brightness.

“Almost no one could believe that such a fundamental thing as an ocular cell type could have been missed for so long.”

 

Undeterred by the reaction, Foster dug in. He found that the new cell type “function independently of sight”! They found this by testing a blind lady who had lost her rods and cones to a genetic disease. Yet, she could tell when the lights were switched on or off. Every time. Foster remarks:

“They’re much more gracious about it now.”

 

Bryson’s book is endlessly informative and entertaining. A truly great guide for all occupants of the body indeed.

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