How does the eye know when the image is in focus? There is distance measuring device, only light entering the eye. No outer feedback to be sure that focus is in fact focus not something the eye think is focus.

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Thank you all for your respons and upvotes.

I can now see and focus on the answer of my question 🙂

In: 3993

Your eyes are controlled by your brain. When objects become sharp and defined by the pattern recognition part of your brain, then it stops focusing.

There is continuous feedback from the brain, which guides the focusing in the eye. Without that, you’re right, the eye doesn’t “know” what to focus on. To see this, look at an object that’s close to you. Now, without changing your head or the direction you are pointing your eye, you can focus on an object in the distance. It’s your brain that is telling the eye what to focus on.

It’s simple: it guesstimates based on how clear the image is.

I was looking at an image on my second screen and, because I was unable to focus it AND it looked precisely like being unable to focus an image that is originally sharp, I gaslighted myself into thinking I need new glasses. Then I put in another app that did show things sharply enough that I went “Nevermind!”

I’ve wondered this myself and I’m gonna throw out an idea that there is a mechanism within the eye to focus.

My hypothesis is that the light reflected off the back of the retina would cast a halo of light on the inside of the eye. The retina has light cones over the surface that would seem to be outside of the FOV and our visual cortex false colors a large portion of our view.

If this is correct, then maybe as the eye focuses on the source of light, the halo would be tighter in focus. There also might be a difference in where that focus would be based on the distance to the source.

Our brain, cortex, and eyes all seem to be capable of this process.

Just a thought.