The Evolution of the Human Eye

To say we’re obsessed with eyes at the Spectacle Shoppe probably isn’t an overstatement. We’re a Kerrisdale eyewear store after all and we spend our days helping our clients see more clearly (in fantastic looking frames and comfy contact lenses, of course). We thought it might be fun to delve into the research and find out the basics behind eye evolution and it turns out the organ has an interesting story to tell. Charles Darwin himself acknowledged how improbable the whole process must seem because the eye is incredibly complex. However, it has evolved through natural selection making slight variations and gradations to go from a small patch of cells that were sensitive to light to the modern human eye with its collection of parts and incredible abilities. Most of the evolution took place rapidly during the Cambrian period (about 540 million years ago) in what is known as the “Cambrian explosion” and the eye went through the entire process of evolution in less than 364,000 years! Here is the Spectacle Shoppe’s guide to the evolution of the human eye:

The Evolution of the Human Eye

  • The first animals with anything that even slightly resembled an eye lived 550 million years ago. They sported eyespots, which were a small patch of cells that allowed them to sense light. The simplest form consisted of two cells: a photoreceptor and a pigment cell.
  • Eyespots developed a pit or a depression and were no longer flat patches of cells. The depressed eyespots allowed species to differentiate between the intensity of light in more directions. The pit continued to deepen over time and the number of photoreceptor cells increased for precision. Eventually they could even sense the movement of nearby objects.
  • The opening gradually narrowed allowing light to enter through a small hole similar to a pinhole camera. Now organisms experienced true imaging and had dramatically improved directional sensing and could even sense some shapes. There was no cornea or lens yet, so resolution was poor but it was still a big improvement over the original flat eyespot.
  • As animals became more complex, the eye had to change to match. The photoreceptors initially connected to ciliated cells but evolved to connect to muscle cells. Neurons evolved to process signals and elicit the appropriate behavior.
  • The transparent cells that covered the pinhole eye’s opening may have split into two layers with liquid in between them to eventually form the lens on the front of the eye, which took on a convex curvature. The eye could now gather and focus the light into photoreceptors. Additionally, the retina formed, as well as the cornea and iris. With a pupil, the eye could now allow in the right amount of light to see clear images. This gave us the lens in-camera type of eye we enjoy today.
  • The muscles in the eye itself changed and strengthened to allow us to focus and point the eye in different directions.

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Morgan Nahanee
Morgan Nahanee

Author

Morgan is The Spectacle Shoppe’s Lead Technician and Customer Relations Specialist as well as a Principle of Spectacle Shoppe. She is a licensed contact lens fitter and dispensing optician and has been working for The Spectacle Shoppe since 2006. She graduated from Douglas College’s two year Dispensing Optician and Contact Lens Fitting Program in 2008. From contact lens fitting to eyeglass repairs and adjustments Morgan is eager to help you with any optical needs. Connect with Morgan Nahanee on Google+