Fruit flies move their retinas much like humans move their eyes
Fruit flies can move the retinas of their otherwise rigid compound eyes to visually follow objects and successfully cross obstacles. This is what researchers at the Max Planck Institute for Biological Intelligence (in formation) and colleagues in the USA have discovered. The retinal movements are made by two small muscles in the fly's eye and closely resemble those of the human eye. They help the insects to see crisp images of moving objects and could also provide them with information on the distance of nearby objects.
Pick an object in front of you – a teacup, for example – and fix your gaze on it. You may think that you’re keeping your eyes still, but you’re not: Your eyes are frequently moving unbeknownst to you, making tiny involuntary jitters called microsaccades.
In fact, these jitters are the reason you continue to see the teacup at all – they introduce just enough variety in the light patterns on your eyes to prevent your visual neurons from completely adapting to what they’re looking at. Without microsaccades, the image of the teacup would soon start to fade, in the same way your nose may go blind to a constant odor.