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March 28, 2008
Not Frosties
How does a collection of cells, comprised many of water it has to be said, with a selection of fancy chemicals and a dash of electricity, have such sensitivity to light that it can determine the dimensional landscape about us?
This is indeed the central argument in the evolution/intelligent design debate, but we won’t open that particular can of Oligochaeta.
Suffice it to say they do, and they do it, naturally, in the eye.
This is the back of my eye. It’s weird looking at my own eye, it’s the equivalent of being able to chew your own teeth. Thanks to Rebecca at Vision Express for the photograph.
The squiggly bits are the blood vessels, the pale round bit to the left is the start of my Optic Canal, where the optic nerves disappear en route to the visual cortex in my brain, leaving a Blind Spot. The darker bit to the right of the Optic Canal is the Macula, which is where all the cones are concentrated, remember?
So that little dark bit deals with 99% of what I see, all the colour and daylight and reaching for a packet of biscuits on the top shelf. The rest of it is all rods, which are for the dusky moments, groping around in the gloaming for the handle of the cistern in the wee hours. They work in black and white only – which is why coloured bathroom fixtures are so pointless.
You naturally focus the light entering your eye on the Macula, for clarity, and so you don’t get run over by the No73 bus. But at night, when you look at something you see nothing, because there aren’t any night time receptive rods in the target area. If you want to see something at night, look away from the object and keep your eye moving, the rods will pick out it’s shape. You won’t be able to navigate because rods don’t have any spatial awareness.
What they do have however is great motion sensitivity. The rods are there so that when we go out of the cave, in the cold dark primordial night, for a pee, we can spot the tiger jumping at us, 4 nanosecond before it’s claws sink into our hairy pelt.
Giving us ample time to shake the last drips from the perpendicular appendage, and or indeed whatever it is the female of the species did to keep the ladygarden dry after voiding the bladder, before retreating into the relative safety of the cave, with a casual "Ah, that reminds me, I must get some Frosties for breakfast".
Posted by john at March 28, 2008 02:11 PM
Comments
....I seem to remember thinking at the point of the bright light,when I had the same eye test of my eye balls,to see if I had actually got any sight problems, that I probably wouldn't be able to see anything ever again anyway regardless of any previous sight problems I may have had, after the light from the machine entered my iris at such close quarters to take that kind of photograph.
;-0
Posted by: paula at March 28, 2008 03:11 PM
...........By the way did you know that by eating Spinach daily it can regenerate areas of the eyes. So you better swap the frosties for more of the green stuff,beware this may lead to the desire of wanting an anchor tattooed on your forearm : )
Posted by: paula at March 28, 2008 04:56 PM
What you don't explain in this is why I can look, but you can see.
Posted by: Daphne at March 30, 2008 12:27 AM