Around 8% of UK males have red/green colour deficiency (deuteranomoly)

Acquired colour problems suggest optic nerve or retinal problems. Test colour vision when suspecting

• Optic neuritis
• Graves Orbitopathy (GO)

The simplest (and best screening) test for aquired colour defect is subjective red desaturation:

Show the patient a red top specimen bottle to each eye in turn. Ask whether the brightness and redness of the colour was the same.

For a more repeatable test, use the Ishihara colour testing book, plates 1-17.