The eye (any eye) is a miracle of evolution, which has filled its structure at every scale with an apparent intentionality that is the hallmark of complicated systems under intensive selective pressure. It is very much possible to look at almost every design feature and state a compelling reason why it’s there, which makes it a rich place for the engineering-minded to find fun little design features.

This post is meant to discuss topics that are less frequently discussed elsewhere, and not often discussed in introductory courses, rather than anything that can be quickly gleaned off of common summaries. Another way to describe it is that I intend to dive a bit into the kind of fridge-logic questions you might come up with randomly after opening the evolutionary eye-fridge, particularly the ones that turn out to have interesting answers.

As such, this post is going to be a bit of a grab bag of topics, rather than a focused point-by-point breakdown of the eye. I’m still going to group topics broadly into general categories, just for organizational reasons.

One thing I will not go into is visual processing in the retina or visual cortex–even though this is a fascinating topic and one of the best understood parts of neuroscience (relative to the rest of the brain). That’s simply for space considerations; including that topic would balloon this post to enormous sizes. Maybe next time.

Part I: Optics and the Lens

Biology Basics (Brief)

To talk about any of this, it is necessary to have some basic grasp of the eye’s anatomy and functioning. That is, you need to know the following key facts and have some sense of the diagrams below:

Key parts of the eye, in order from outside to inside:
1. Cornea - outermost part you can touch (don’t touch)^[1]
2. Aqueous humor - thin watery goop
3. Lens - it’s a lens, it focuses light
4. Vitreous humor - thick watery goop, most of the eye by volume
5. Retina - thin layer of tissue at back of eye, has the famous rods and cones that actually detect light
6. Optic nerve - transmits signal from retina to brain
Basic functioning: Light hits your face, is focused by the cornea^[2] and natural lens, resulting in an image projected onto the retina, which then does a ton of image processing before passing its in-progress data to the optic nerve. (which connects to the visual cortex in the brain which does the rest of the processing)

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Ricardo Romero

Ricardo Romero