When visual acuity, as assessed by interference fringes before and after cataract surgery, is compared without regard to the stage of the disease, the correlation is much higher than for preoperative and postoperative letter acuity but is still rather moderate (about 0.4 to 0.5). If, however, the cases are classified according to the visibility of the red fundus reflex, those with a readily visible reflex result in a correlation as high as r = .85, whereas those with a considerably diminished reflex range much lower, and those with a mature or almost mature cataract become erratic. In these examinations it is preferable to ask the patient to indicate only the direction of the fringes, since this criterion was found to be better defined than fringe visibility.