We’re in the forest in Tuscany when a Fallow Deer approaches us from a herd we can see in a woodland glade.
It’s a real character and rushes over, obviously used to human company. I look closely into its face and our eyes meet. It’s then that I notice something odd.
I know that many mammals have different shaped pupils and this deer is no exception. It has wide postbox pupils to go with its wide field of monocular vision. The wide pupils help deer gather light from the corners of their vision. It’s a commonly evolved adaptation of many animals which are predated and need to be observant. That’s because all the ones without it were eaten. The pupils themselves are so small they are just slits in this light. They are difficult to see as the iris that surrounds them is a dark colour too.
Then I notice something fascinating. As the deer bends to graze the pasture in the woodland glade I can see that its pupils are still horizontal even though its head has rotated. How cool is that?
That means its eyes must have rotated in their sockets. In fact the left eye must have rotated clockwise and the right eye anti-clockwise.
If I told you it was called cyclovergence, would you roll your eyes at me?