Stereoacuity with Frisby and revised FD2 stereo tests

We compared near stereoacuity, measured with the Frisby test, and distance stereoacuity, measured with the revised Frisby-Davis (FD2) test, enabling a comparison with the original version of the FD2. In the revised version of the FD2 test, a white background is used instead of a backlit background. We also examined the effect of age, gender and visual problems. We used the Frisby test at distances ranging from 30-80 cm and FD2 at 6 m. The best possible score was 20 seconds of arc (arcsec) on the Frisby and 5 arcsec on the FD2; participants who could not perform a test despite demonstrating understanding of it were classed as stereonegative. We examined both the whole population recruited, and a sub-population screened so as to exclude visual problems. We analysed our results in three age-groups: "visually developing" (36 children aged 5-10 years); "visually mature" (300 participants aged 11-49 years) and "older" (29 participants aged 50-82). In the whole population, the median stereoacuity on the Frisby test was 25, 20 and 85 arcsec in the three age-groups. In the sub-population with no visual problems, median Frisby stereoacuity was similar at 20, 20 and 80 arcsec respectively. On the FD2, the medians were 10, 10, 20 arcsec for the whole population and 7.5, 10 and 12.5 for the sub-population. Children were more likely than adults to be stereonegative on the FD2, although none of the children were stereonegative on the Frisby. The two tests showed fair agreement when used to classify people into three categories of stereovision. Poor stereovision was often associated with binocular problems such as tropia, but with many exceptions. In line with previous studies, we found improvements in measured stereoacuity in childhood and declines in late adulthood. The new FD2 test gives comparable values to the original FD2.