How does the structure of the vertebrate eye show the effects of evolutionary constraints?

In the context of Darwinian medicine, the structure of the vertebrate eye serves as a clear example of how evolutionary constraints can result in suboptimal biological design.

The vertebrate retina is described as "inverse," meaning that the light-sensitive rods and cones are positioned behind layers of neurons and blood vessels. Consequently, light must pass through these non-sensitive layers before reaching the photoreceptors. Furthermore, because the nerve fibers must exit the eye to reach the brain, they burrow through the retina at a specific point, creating a blind spot where no visual information can be captured.123

This arrangement contrasts with the octopus eye, which is "everse"—the nerve fibers leave from the rear of the photoreceptors, resulting in no blind spot. These differences highlight that evolution does not produce perfect engineering; rather, it shapes traits based on historical phylogeny and existing constraints, often resulting in trade-offs that leave the body vulnerable to functional limitations.31