As used in Sections 21963 and 21964, “blind,” “totally blind,” and “partially blind,” mean having central visual acuity not to exceed 20/200 in the better eye, with corrected lenses, as measured by the Snellen test, or visual acuity greater than 20/200, but with a limitation in the field of vision such that the widest diameter of the visual field subtends an angle not greater than 20 degrees.