Verify the resolution limit of change in spherical power
diopter
Starting from the diopter of red-green balance point of equal clarity obtained by adjusting the spherical power at an interval of 0.25D, the diopter of spherical power was increased and decreased by one time of resolution limit, respectively. The volunteers were asked for any changes in the clarity of the red and green optotypes either from equal clarity to green clarity or red clarity. If there was no change, the point of equal clarity was used as the starting point again, and the diopter of spherical power was changed by 2 times the resolution limit. The volunteers were then asked for any changes in the clarity of optotypes. If still no change, the point of equal clarity was taken as the starting point to further increase the range of changes in the diopter of spherical power (an integer multiple of the resolution limit) until the clarity of optotypes changed.In case of failure to identify the red-green balance point of equal clarity by adjusting the spherical power at an interval of 0.25D, the maximum diopter of red clarity (an increase of  − 0.25D to be green clarity) should be taken as the starting point, and the resolution limit as the interval to find the point of equal clarity. After identifying the point of equal clarity, the limit of differences in the visually resolved diopter of spherical power could be validated following the above steps. If the point of equal clarity was still not found at the interval of the resolution limit, the diopter of spherical power was increased by one time the resolution limit from the maximum diopter of red clarity to get green clarity, and the volunteer's resolution limit was denoted as 1/2 of the resolution limit.The prescription and the best-corrected visual acuity were obtained by adjusting the spherical power at an interval of 0.25D and the resolution limit, respectively. The prescription of spherical power was determined according to the following principles: In case of a red-green balance point, the diopter of equal clarity is taken as the prescription diopter of spherical power. In absence of the red-green balance point, the maximum diopter of red clarity is taken as the prescription diopter of spherical power. The two sets of trial case lenses were of the same substrate material, manufacturing process and manufacturer (Minghao Technology (Beijing) Co., Ltd.). The visual acuity chart was an international standard one, and the recorded values were converted to the logarithm of the minimum angle of resolution (LogMAR).