A selection for an acuity test chart is received in distributed Web content that correlates to a distance between an end user and a display of the test chart. A selection also is received of a trio of lines of different widths in a set of lines defining one of twelve radially equidistant radii of equal length extending from a common vertex in an astigmatism clock chart. An astigmatism fan chart also is generated and presented in the Web content utilizing three of the trio of lines in the selection and including twelve repeating sequences of three radially equidistant radii of different widths corresponding to the different widths of the utilized three of the trio of lines. One of the radii is selected and a prescription computed including the visual acuity value, a cylinder value deriving from the selected trio, and an axis value deriving from the selected radii.