The Idiotic Design of the Eye

Hermann von Helmholtz, the great nineteenthcentury German scientist (you could call him a physicist, but his contributions to biology and psychology were greater), said, of the eye: 'If an optician wanted to sell me an instrument which had all these defects, I should think myself quite justified in blaming his carelessness in the strongest terms, and giving him back his instrument.' One reason why the eye seems better than Helmholtz, the physicist, judged it to be is that the brain does an amazing job of cleaning the images up afterwards, like a sort of ultra-sophisticated, automatic Photoshop. As far as optics are concerned, the human eye achieves its Zeiss/Nikon quality only in the fovea, the central part of the retina that we use for reading. When we scan a scene, we move the fovea over different parts, seeing each one in the utmost detail and precision, and the brain's 'Photoshop' fools us into thinking we are seeing the whole scene with the same precision. A top-quality Zeiss or Nikon really does show the whole scene with almost equal clarity.

So, what the eye lacks in optics the brain makes up for with its sophisticated imagesimulating software. But I haven't yet mentioned the most glaring example of imperfection in the optics. The retina is back to front.

Imagine a latter-day Helmholtz presented by an engineer with a digital camera, with its screen of tiny photocells, set up to capture images projected directly on to the surface of the screen. That makes good sense, and obviously each photocell has a wire connecting it to a computing device of some kind where images are collated. Makes sense again. Helmholtz wouldn't send it back.

But now, suppose I tell you that the eye's 'photocells' are pointing backwards, away from the scene being looked at. The 'wires' connecting the photocells to the brain run all over the surface of the retina, so the light rays have to pass through a carpet of massed wires before they hit the photocells. That doesn't make sense - and it gets even worse. One consequence of the photocells pointing backwards is that the wires that carry their data somehow have to pass through the retina and back to the brain. What they do, in the vertebrate eye, is all converge on a particular hole in the retina, where they dive through it. The hole filled with nerves is called the blind spot, because it is blind, but 'spot' is too flattering, for it is quite large, more like a blind patch, which again doesn't actually inconvenience us much because of the 'automatic Photoshop' software in the brain. Once again, send it back, it's not just bad design, it's the design of a complete idiot.

Wired backwards with a blind spot.