Sisters from St Albans and Letchworth Garden City are scaling the 6,000m of Mount Kilimanjaro to raise money for a six-year-old with severe sight loss.
Sienna Parsi developed retinopathy of prematurity (ROP), a condition which happens in premature babies and causes blood vessels in her eye to grow in a disorganised way.
It means she has no sight in her right eye and can see only brightness in her left eye.
Her mum, Catherine Parsi, and aunt, Emma Fletcher, are climbing the African mountain to raise money for Fight for Sight, which funds research into conditions like ROP.
The sisters have nearly raised £2,000 on their fundraising page.
Setting off on October 10, World Sight Day 2019, it will take them seven nights and eight days to complete the challenge.
Catherine said: "With my daughter Sienna living with severe sight loss it's really important to raise vital funds for Fight for Sight and to help raise awareness of their brilliant and necessary work.
"By climbing Mount Kilimanjaro, we hope to raise lots of money for pioneering eye research into new treatments for retinopathy of prematurity and for helping us to build a future that all those with sight loss can see.
"Our challenge will take us eight days, Sienna's is life-long."
Catherine has two other children, one of whom is Sienna's twin Joshua.
She has previously raised money for the charity with a 100km, one day race called Dixons Carphone Race to the Stones and by running the London Marathon blindfolded.
Their fundraising page reads: "Sienna is a remarkable child and through her guts and determination strives to achieve everything her six-year-old twin brother can do... ride a scooter, ride a bike, ride a horse, climb a tree, she attends mainstream school and is learning to read and write braille.
"She is fiercely independent and overcomes adversity every day."
Head of fundraising at Fight for Sight, Ikram Dahman, said: "We know that sight loss doesn't have to be inevitable - it's through our fantastic supporters raising money for research that we will find the next breakthrough."
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