1. A computer-implemented method of evaluating test-retest precision of vision tests for monitoring visual functions of a plurality of subjects using fractional rank precision (FRP), comprising: a) collecting, by a computer, a test result and a retest result of each of the plurality of subjects, wherein the test result and the retest result are described in one or more feature spaces and one of the test result and the retest result is collected from a vision test machine; b) selecting, by the computer, a first subject from the plurality of subjects and a first test result of the first subject; c) calculating, by the computer, distances from the first test result to the retest result of each of the plurality of subjects; d) assessing, by the computer, a similarity between the first test result and the retest result of each of the plurality of subjects by ranking the distances in a non-descending order; e) assessing, by the computer, a rank precision for the first subject based on a rank of a distance from the first test result to the retest result of the first subject; f) repeating, by the computer, steps b), c), d), and e) for each of the plurality of subjects; and g) evaluating, by the computer, the test-retest precision of one or more vision tests based on the rank precision for each of the plurality of subjects, wherein assessing the rank precision comprises: calculating a normalized rank, the normalized rank being the rank of the distance divided by a total number of subjects of the plurality of subjects; and calculating the rank precision, the rank precision being equal to one subtracted by the normalized rank.