Coloured-light in Retinitis Pigmentosa.

This study will assess the effect of 2 different colours of light on colour vision in adults with retinitis pigments (RP). Participants will be 18 years or above with a genetically confirmed molecular diagnosis of RP. After informed consent, participants will have their letter chart vision and colour vision measured in their study eye. They will then be they will be randomly allocated to one of 2 groups. The study team will not know which group they have been assigned to. Group 1 will be given a coloured-light hand-held torch and be asked to apply it to their study eye for 3 minutes at home each morning between 8 - 10 am for 28 days. Group 2 will be given a different colour hand-held torch and be asked to do the same. All participants will have their letter chart vision and colour vision measured at the end of study on day 28 (+ 7 days).