The bead test: a critical appraisal

An evaluation of the visual acuity levels obtained with the candy bead test (Bock) was performed. White beads (1 mm) were placed on a white felt background under controlled illumination. Ten subjects were required to localize randomly placed beads through increased degrees of induced optical blur. The visual acuity was then measured at the blur level yielding 60% accuracy in localization. The results indicate a range of visual acuity from 6/45 to 6/60 (20/150 to 20/200). These findings are significantly worse than the levels of acuity [6/18 to 6/24 (20/60 to 20/80)] found by other authors. Therefore, our findings raise concerns and indicate caution in the clinical interpretation of the bead test.