Transcript:

Approximation of small angles. That is why the eye is only this big. If the eye was any bigger, this approximation would not hold.

So now that the eye is small, this is correct. You can replace sine of theta by theta. And now, this complex integral becomes exactly the one in the Fourier transform.

So, the brain gets a Fourier transform signal, which it can invert uniquely to recreate the actual image. This is how the eye is doing Fourier transforms and inverting them.

It's amazing.