Blind patients have been able to recognise family members for the first time in years after volunteering for a pioneering gene-editing experiment.

Michael Kalberer, 43, and Carlene Knight, 54, both suffer from an incurable eye disease which robbed them of their vision in adulthood.

Earlier this year, they were among seven patients who allowed scientists to modify their DNA by injecting them with the gene-editing tool CRISPR.

While their vision has not been fully restored, they are able to see colors, navigate hallways and make out silhouettes.

Mr Kalberer, from Long Island, revealed he was able to recognise relatives on the dancefloor of his cousin's wedding, something which had been impossible for years. 

He told National Public Radio: 'I could see the DJ's strobe lights change color and identify them to my cousins who were dancing with me. That was a very, very fun joyous moment.'

Ms Knight, from Portland, Oregon, said she could finally see color clearly for the first time since she was a child, which she described as 'just amazing'. To celebrate, she has dyed her hair her favorite color — green. 

The pair signed up to receive the experimental treatment at the Oregon Health & Science University in May.

It was the first time CRISPR – which has shown promise in treating conditions like sickle cell disease — had ever been used to edit a person's genes inside their body.  

Michael Kalberer, 43, from Long Island, revealed he was able to recognise relatives on the dancefloor of his cousin's wedding, something which had been impossible for years

Carlene Knight, 54, from Portland, Oregon, said she could finally see color for the first time since she was a child, which she described as 'just amazing'. To celebrate, she has dyed her hair her favorite color — green

Both Kalberer and Knight were both born with a rare genetic eye disorder called Leber congenital amaurosis (LCA).

Sufferers have rods and cones - cells that detect dim and bright light, respectively - in the retina that do not function properly. 

Some are blind at birth while others experience visual loss over time, which was the case for Kalberer and Knight.  

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HOW DOES CRISPR DNA EDITING WORK?

The CRISPR gene editing technique is being used an increasing amount in health research because it can change the building blocks of the body.

At a basic level, CRISPR works as a DNA cutting-and-pasting operation.

Technically called CRISPR-Cas9, the process involves sending new strands of DNA and enzymes into organisms to edit their genes. 

In humans, genes act as blueprints for many processes and characteristics in the body – they dictate everything from the colour of your eyes and hair to whether or not you have cancer.  

The components of CRISPR-Cas9 – the DNA sequence and the enzymes needed to implant it – are often sent into the body on the back of a harmless virus so scientists can control where they go.

Cas9 enzymes can then cut strands of DNA, effectively turning off a gene, or remove sections of DNA to be replaced with the CRISPRs, which are new sections sent in to change the gene and have an effect they have been pre-programmed to produce.

But the process is controversial because it could be used to change babies in the womb – initially to treat diseases – but could lead to a rise in 'designer babies' as doctors offer ways to change embryos' DNA. 

Source: Broad Institute 

LCA is estimated to affect between one and two babies out of every 100,000 births, according to the National Organization for Rare Disorders.

Both patients have a version of the disease caused by a defect in the gene CEP290, which regulates a protein that keeps the eye healthy.

While CRISPR normally involves taking cells out of the body, editing them in the lab, and then infusing them back into patients — that's not possible for diseases like LCA.

This is because retinal cells are too fragile to be removed, edit and reinserted, NPR reported.

In the trial, three tiny incisions were made in Knight's left eye and Kalberer's right eye to insert billions of benign virus particles carrying the CRISPR technology.

CRISPR then cut out the genetic mutation of the cells that affect the rods and cones, which spurred the body to produce properly working genes.

Scientists only operated on one eye to begin with, but plan to do the other eye if the patients continue to improve.

Not all patients in the trial saw results, for reasons which are still unknown.

And in those such as Knight and Kalberer, who did see benefit, their vision is still far from perfect.

But the results are so promising that the researchers have been given the go-ahead to move onto a larger group of patients. 

Kalberer said the ability to make out shapes and light, and see better through his peripheral, had restored some normality to his life, including being able to eat out. 

He added: 'It has enabled me to navigate a plate of food and stab food a little bit easier. 

'If I look down at a plate of food and there's spoon or utensil in it I can see the edge of the utensil on the outside of the bowl or plate. 

'So those changes are very, very significant to me.' 

Both Kalberer and Knight (pictured before the treatment) were both born with a rare genetic eye disorder called Leber congenital amaurosis (LCA)

Kalberer said the ability to make out shapes and light, and see better through his peripheral, had restored some normality to his life, including being able to eat out 

To his surprise, he can also now see colors for the first time in years. He noticed it about a month after the procedure when a red car drove past.  

Mr Kalberer has been able to enjoy the simple pleasures in life, such as watching the sun set with friends.  

Ms Knight is also loving her regained ability to make out colors, telling NPR: 'I've always loved colors. 

'Since I was a kid it's one of those things I could enjoy with just a small amount of vision. 

'But now I realize how much brighter they were as a kid because I can see them a lot more brilliantly now. It's just amazing.'