Biologists and Eye doctors have conducted a study of how much energy is used by our vision

In order to compare the "consumed energy" by our vision, the study couldn't be conducted with humans but with so called Mexican cavevish.

The sighted, surface-dwelling, form of Astyanax mexicanus. Credit: Vladimir Wrangel/Shutterstock

There is a species of cavefish which lives inside the cave which has no eyes and cannot see. Another morph of the same species of fish is identcial to the first kind but posesses the sense of vision as it lives outside the caves in rivers.

By comparing the energy intake of both kinds of fish, the energy consumption of vision was between 15 and 5% of their entire metabolism.

Therefore, it can be concluded that vision requires a fair amount of energy to be processed and analyzed.