Figure 1.1 Farnsworth D-15 hue test set with 15 coloured caps with a natural hue progression

Figure 1.2 Patients are asked to select a coloured cap that most closely resembled the hue of the reference cap.

Figure 1.3 All 15 caps are arranged in sequence based on the patient's perception of colour

Figure 1.4 After completing the task, the wooden box is flipped over and the corresponding numbers are shown.

Figure 2.1 Normal result – no cross-lines

Figure 2.2 Protanope – cross-lines parallel to protan axis

Figure 2.3 Deutanope – cross-lines parallel to duetan axis

Figure 2.4 Tritanope – cross-lines parallel to tritan axis

Figure 2.5 Non-specific color vision defect – cross-lines do not obey any axis