STYCAR ball acuity in relation to contrast and blur

The graded balls test of Sheridan is used to screen for vision problems in infants and poorly communicative patients. To simulate what the infant with a refractive error may see, we photographed black and white spheres of identical size through various plus lenses. The results show that the white ball becomes progressively easier to identify with increasing blur. The size of the blur circle is shown to be directly related to background contrast. Because the white balls are viewed against a black cloth at 10 ft to enhance contrast, this may significantly bias the test results. Consequently, a neutral background may be a more appropriate surface upon which to assess the visual acuity by this technique.