The Blind Spot of the Vertebrate Retina

Because of its formation, the vertebrate retina has a "blind spot" at the point where the collected bundles of the nerve fiber layer pass through it and become the optic nerve proper. This is an inevitable consequence of the design, and all vertebrates have it.

Interestingly, the eye of the cephalopod molluscs (octopi and squids), which closely resembles the vertebrate eye in almost all respects, doesn't arise from an invaginated cup-like structure: consequently these eyes, which are a classic example of convergent evolution, do not have a blind spot, though in almost every other way they can hardly be told apart from those of vertebrates.

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