Sao Vanna sits huddled on a bamboo bench, knees pressed against her chest, as small chickens dart around her in her family home. She gathers up the black cloth of her pant leg to reveal a thick rusty chain fastened to her ankle.

Vanna has been chained up for years, and rarely leaves the room where she is confined. When she needs to relieve herself, her sister brings a basket and places it beneath her in this one-room thatch house, in rural Tuol Pich commune, Ang Snuol district.

Vanna is one of an unknown number of people with a mental disability across Cambodia who are chained, tied or caged by their desperate relatives. Despite the practice clearly violating the rights of people with disabilities, experts say it exists in a legal grey area.

Enduring stigma and a severe lack of services, awareness and money leaves rural families resorting to restraint as their only way to cope.

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For Vanna’s sister, Sin Ry, 59, the care – and the risk – had become too much. “If I release her, she is difficult to control,” Ry says.

“Sometimes she hits me,” she adds, tracing a scar hidden by her hair. She needed stitches after the impact from a bamboo stick that Vanna had grabbed.

Vanna first eyes outsiders with suspicion, but her face breaks into a smile when she speaks.

“I am 30 years old. I feel comfortable because of the handcuff,” she says. “I quit school because I was sick. I had something wrong with my head.”

Vanna’s sister Ry struggles to explain precisely what psychological condition Vanna has. Ry says she was healthy until around the age of 17, but then she started behaving strangely and her eyes began darting around erratically in her head.

She was told her little sister has “broken blood cells”, but can’t name the diagnosis beyond that.

What she does know is the cost of Vanna’s medicine from the Khmer-Soviet Friendship Hospital in Phnom Penh 36,000 riel ($9), every two months. It calms her down.

“I sell my chickens and rice to get the medicine,” Ry says. Sometimes she makes 3,000 riel (about $0.75) a day, sometimes not. Their brother works in construction, and, on occasion, he gives his sisters 100,000 riel ($25).

Vanna has been chained for more than a decade. For half those years, Ry sought out traditional healers before switching to doctors with modern medicine. “We kept believing in healers, another, after another, after another,” Ry says. They would prepare herbal concoctions and splash water, but Vanna remained troubled.

Vanna has certainly made her mark on the thatch palm leaf wall within reach of where she’s chained. Faces have been rendered in black marker they’re actors, she says, that she saw on TV a long time ago.

There are also child-like sketches of flowers: long stalks and big round petals. “The flowers represent a new year,” Vanna says.Shafts of light, meanwhile, stream in though holes she has punched through the thatch.

“I punched it when I got angry with my sister. Then blood came from my knuckles,” she says, adding Ry had taken her hand and treated the cuts with ointment.

Ry says the chain is not just to protect others from Vanna’s anger, but for Vanna’s safety too, a point that was tragically driven home when their sister was raped and murdered three years ago as she went to take a shower near their house.

Their account was confirmed by commune officials and other villagers the perpetrator is now behind bars. But being chained also leaves Vanna vulnerable to abuse. After she lashed out at her brother, he hit her in the face, drawing blood.

“We need to care for her, do everything for her. We have to get to hospital to get medicine for her, and I also have to look for work,” Ry says. “We are poor and we have no money to pay, and they have no organisation to help us. Where is the organisation?”

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The mental health system in Cambodia is under strain. Dr Chak Thida from the Khmer-Soviet Friendship Hospital’s psychiatric department, where Ry collects her sister’s medication, says they see up to 400 follow-up patients a day, with up to 30 new patients daily.

Dr Chhim Sotheara, executive director at the Transcultural Pyschosocial Organisation (TPO), said those who are chained up usually have some kind of psychosis, like schizophrenia, or have behavioural problems stemming from chronic substance abuse.

Mostly, he says, the chains are to prevent them from harming others, or from being attacked by villagers.

“We can understand that the family decided to chain patients because they are not able to control their behaviour, the treatment was unsuccessful, they are too poor or the mental health services are too far from their home,” Sotheara said in an email.

“Since Cambodia has no Mental Health Act, it is not right to say that it is illegal to chain patients.”

TPO’s “Operation Unchain” project began in 2015 with a $5,000 donation from King Norodom Sihamoni and an additional $18,000 raised by the public.

The project currently treats 56 patients in nine provinces, including Kandal. Of those 56, 40 are now unshackled. “The more support from the family, the quicker the patients can be unchained,” Sotheara says.

But Operation Unchain’s funds are dwindling fast, he says, and TPO is focused on treating current patients, rather than recruiting new ones.

“There are more patients who request treatment from us, but we cannot offer it yet due to financial difficulty,” he says. “No one is interested in funding this.” He has approached Cambodian tycoons to no avail, but is hopeful friends in Australia may help.

Ung Sambath, deputy director at the Disability Action Council, says poverty fuels the practice. “If your family is very, very poor, and you have a person with a disability in the family, what do you choose? The food to eat, or the health care for the person? This is the real situation,” Sambath says.

Ngin Saorath, executive director of the Cambodian Disabled People’s Organization, says shackling people violates their freedom and independence – and it affects both the body and mind.

“If society does not value them, they will become worse and worse, they cannot enjoy their rights or participate in society,” he says.

Dr Chhit Sophal, director of the Ministry of Health’s department of mental health and substance abuse, did not respond to multiple requests for comment, but has previously said the government is developing a Strategic Plan for Mental Health and Substance Abuse 2017-2020 despite “limited resources”.

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After collecting green pea-sized eggplants in a basket for their lunch, Ry says she wants to be able to unshackle her sister, but feels she cannot.

Vanna, excitably, tells Ry she wants to help cook, she wants to wash clothes but Ry shakes her head. “She only says this, but she does not know,” Ry says. “It is it difficult, very, very difficult.”