Question

What is the diffraction-limited optical resolution of the human eye? (feel free to find the geometrical and optical properties of the eye using literature search)

Answer 1

The human eye is close to being fully diffraction-limited, at least for photopic (cone-based) vision at the center of the visual field (i.e. for images wholly within the fovea), though it's not quite there for most people.

The resolution of the human eye is the smallest object our eye can see. This is limited by the diffraction limit, which is approximated by the angular size ratio of the object's size versus the distance to the object.

When two point sources are resolved from each other, they are separated by at least the radius of the airy disk. When Θ = 1.22 (λ/D) rad ,
where Θ is the angular resolution, λ is the wavelength of light and D is the diameter of the eye. Remember that 360 degrees = 2π radians

The maximum visual acuity of the human eye is 0.4 arc minutes. At 4 inches, the maximum the human eye needs is 2190 ppi/dpi. The human eye should have a resolving power of 20 arcsecs in theory.