Purpose Accurate evaluation of the cup-to-disc ratio is crucial for optometrists and may be influenced by their clinical experience. The study’s objective was to compare the thresholds for discriminating vertical cup-to-disc ratio (VCDR) between years 2, 3, and 4 clinical optometry trainees. Methods One hundred fundus photos with various VCDR sizes were selected from a clinic database. The median VCDR (0.43) photo was assigned as the standard, while the other 99 were assigned as the test photos. The participant’s task was to discriminate using a 2-alternate-forced-choice paradigm whether the test photos’ VCDR were larger or smaller than the standard VCDR. Data were fit with a Weibull function, and three discrimination thresholds were determined: the point of subjective equality (PSE), the range of VCDR uncertainty, and the ability to judge VCDR that was 0.1 unit larger than the standard photo. Results Year 4 trainees had better VCDR discrimination thresholds. However, the difference between the three participant groups was not statistically different for all measurements (PSE: F(2,27) = 0.43, p = 0.657; VCDR uncertainty range: F(2,27) = 0.12, p = 0.887), and thresholds for correctly discriminating VCDR 0.1 larger than the standard photo’s VCDR: F(2,27) = 0.69, p = 0.512). Conclusion Although Year 4 optometry trainees performed slightly better at estimating VCDR than their Year 3 and Year 2 peers, the number of years of clinical experiences did not significantly affect their VCDR discrimination thresholds when 2-dimensional fundus photos were used as stimuli.