A national charity that is based in Buckingham is sending a team of 27 runners to this year's London Marathon.
Retina UK, whose national headquarters is based at Wharf House on Stratford Road in the town, was started in 1976 by Lynda Cantor, who lives near Buckingham.
Lynda lives with the progressive sight loss condition Retinitis Pigmentosa.
Retina UK supports people affected by inherited progressive sight loss and aims to ensure they lead fulfilling lives.
The charity has invested almost £16 million in medical research since it was founded and provides support including a telephone helpline staffed by volunteers, numerous information days and an annual conference which will be held in Milton Keynes in September.
This year Retina UK has 27 runners taking part in the London Marathon and the charity is hopeful they will raise around £50,000 between them.
Retina UK's runners are based all over the UK - for some it is their first marathon while others are seasoned marathon runners.
Many of them are visually impaired and some will run with a licensed sighted guide who will have undertaken specific training to fulfil this role.
One of the charity's runners Liz Pimperton said: “I love running, cycling and swimming, and have taken part in the Prudential Ride London 100 mile bike ride, the two mile Swim Serpentine, and once I’ve completed the London Marathon I will receive the London Challenge medal for doing all three.
"I also have a big love of cake which is why I run!”
Training is difficult for visually impaired runners such as Ashley Campbell who uses a running machine in his shed at the bottom of his garden.
Ashley has completed the London Marathon twice before but this will be the first time he will have run with a sighted guide.
Faye Maguire's son has Retinitis Pigmentosa, one of the conditions the charity supports.
He is the reason she will be running in the London Marathon at the weekend.
Retina UK will be sending representatives to support their team of runners - official cheerers will be located half way around the route to encourage and motivate the charity's runners.
Anyone interested in taking part in next year's London Marathon is encouraged to get in touch with Emily by calling 01280 815900 or emailing emily.purchase@RetinaUK.org.uk
To find out more about the charity and how you can get involved visit www.RetinaUK.org.uk