Purpose. To highlight the importance of using the Farnsworth Panel D-15 Hue test in colour vision testing in patients on ethambutol treatment. Case Report. A 70 year-old lady received ethambutol as part of her anti-tuberculous regime. She developed blue-yellow colour defect detectable with the Farnsworth Panel D-15 Hue test, but not with the Isihara Pseudoisochromatic Plates. Ethambutol was imm...