• Question: Why do we only have two eyes

    Asked by bronaghd to Karen, Shane on 22 Nov 2013.
    • Photo: Shane Mc Guinness

      Shane Mc Guinness answered on 22 Nov 2013:

      Great question Bronagh!
      Well, it’s not just us who have two eyes. Can you think of animal that has three eyes? Or one that has only one?
      So why 2?
      Well, in order to judge depth in our world, to be able to tell how far away something is, we need at least two slightly different views of the world, which our brains then combines to get sense of where things are. This is called “binocular vision”. Two eyes works well for this. But what about 3 eyes? Or four? Surely this would be even better? Well eyes are really complicated and expensive for our bodies to produce. So evolution has made a decision; that it’s better to have two than one, because we can better see where our dinner is! But producing three eyes doesn’t really have enough benefit to make it worth evolving!

      Some insects have more than two “eyes”, but these are not the complex eyes we have. There is one group of animals without backbones who have eyes as complicated as ours…. the squids and octopuses!

    • Photo: Karen McCarthy

      Karen McCarthy answered on 22 Nov 2013:

      Exactly as Shane said!

      Imagine having no perspective Bronagh? (pardon the pun!) Many people, due to defects in their eyes, are unable to see depth or perspective – its like living in a 2D world, like on paper! Stereovision is the ability of the brain to interpret 2 images from 2 eyes, into 1 concise image for the brain to process. Stereo-blindness is a problem where your brain cannot do this, so everything looks at one depth!

      However there has been incidents recently of people going to see 3D movies – and suddenly find there stereo blindness disappears! Its likely that the brain needs to be re-booted or reprogramed to regain 3D vision!