The resolution limit of the human eye is 5*10^(-4) radians for most people. The Raleigh criterion is generally used to dictate the resolution limit of an imaging system, however, biology is also a factor, so the eye's actual resolution sometimes differs from the Raleigh criterion.
The resolution limit of any imaging system is limited by diffraction: how light behaves when shone through a circular aperture. The Raleigh criterion for a circular aperture is sin(theta) = 1.22*(wavelength/distance), in which theta is the resolution limit. However, the resolution limit dictated by the Raleigh criterion for an iris equal to 5 millimeters and a wavelength equal to 500 nanometers is 1.22*10^(-4) radians, meaning that the resolution limit of an eye is not solely dictated by diffraction and that there are biological factors involved.