The effect of dot size in random-dot stereograms on the results of stereoacuity measurements

BACKGROUND: This study aimed to evaluate the effect of the size of the dots in random-dot stereograms on the results of stereoacuity measurements. METHODS: A stereopsis measurement system was created using a phoropter and two 4 K smartphones. Three dot sizes, including 1 × 1 pixel, 6 × 6 pixels, and 10 × 10 pixels (equivalent to 0.17 min arc, 1 min arc, and 1.68 min arc, respectively), were used to form random-dot arrays, and each test pattern had one Lea symbol hidden within it. The resulting stereograms were tested on 30 subjects with normal acuity and stereoacuity. RESULTS: Stereoacuity measured with the 1-pixel dots was significantly worse than that measured with the 6-pixel dots (Wilcoxon signed-rank test, Z = -4.903, P < 0.001) and the 10-pixel dots (Z = -4.941, P < 0.001). No significant difference was found between 6-pixel dot and 10-pixel dot stereograms (Z = -1.000, P = 0.317). CONCLUSION: The size of the dots in random-dot stereograms affects the test results significantly when the dots are too small for the eye to resolve.