vision defects, ophthalmologists and opticians need to determine the corrected visual acuity (lat. visus cum correctione) - i.e. your best corrected visual acuity. The determination of visual acuity is not [...] of arc, then their visual acuity will be 1. If the person being tested has a visual acuity of only 0.5, then the test symbol displayed must be doubled in size in order for it to be recognised.