Fovea - What our retina sees
We are usually under the impression that – provided we have good eyesight – we can see everything around us clearly. But in fact, most of the image our eyes see is quite blurred.
Light enters the eye through the lens, which focuses an image of the outside world onto the retina (the layer of light sensors inside our eyes). This image is normally well focussed and sharp, but most of the retina samples that image quite poorly. Relatively wide spacing of the light sensors (aka photoreceptors), pooling of the signals from a number of sensors and other factors result in poor resolution of the image the retina picks up.
However, there is one central spot in the retina – called the Fovea – where the photoreceptors are packed much more closely and there is no pooling. This gives us a much sharper image of a tiny portion of our surroundings, while the rest is very fuzzy. That's why our eyes are moving all the time, shifting our gaze from place to place, collecting sharp images of various spots around us. Our brain then assembles all those small spots into what we perceive as a sharp image of our surroundings.
This applet is a simulation of what our retina might see when we look at 'Wondering', a sculpture by Singaporean artist Ng Eng Teng (Image courtesy of NUS Museum). It is an approximate illustration and not intended to be scientifically accurate.