https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evolution_eye.svg https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evo... Lefthand is a verteb

https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evolution_eye.svg https://en.wikipedia.org/wiki/Cephalopod_eye#/media/File:Evo... Lefthand is a vertebrate eye, righthand is a squids eye. In Vertebrates (really in all Chordata), the light sensitive "tips" of the sensory cells point inwards, aka. the exact wrong direction. At the base of the cells are the axons (nerve connections) which transmit the information into the brain. Due to the aforementioned orientation, these axons run along the outer layer of our light sensitive cells, and at some point have to travel "invards" towards the brain. At that point there can be no cell bodies, and that's the "visual blind spot" of our eyes. A squids eye doesn't have that problem; all the light sensitive cells point outwards, the axons are at the innermost layer, and connectivity can be achieved without a blind spot (also, they don't need a reflective layer).