Imagine if you had to live without your glasses or contact lenses, assuming you are one of the three-quarters of UK adults who need eyesight correction.
Basic everyday tasks like commuting to work, watching TV and cooking would become hard, even impossible.
It's hard to imagine but that is precisely the situation faced by a third of the world's population, 2.5 billion of whom have uncorrected poor vision.
It's a global issue we don't hear much about. However, the technology sector – and one man in particular – hopes to change all of that: the Clearly campaign, a one-year initiative launched in April 2016 by Hong Kong-based entrepreneur and investor James Chen.
A lack of global access to eye care is an issue he's been working on for well over a decade, but he says in 2016 "technology is truly converging with need".
Clearly's mission is to ensure everyone in the world can see clearly by 2035. Why 2035?
"That's when Elon Musk and NASA expect humans to first land on Mars," Chen tells Techworld. "If we can do that, everyone on earth should surely be able to see by then."
One of the first things Chen aims to do is raise awareness. "People aren't aware of this problem. 99 percent in the developed world take being able to see for granted. And it's an easily solvable issue. Technologies to help exist everywhere," he says.
Poor eyesight is a huge problem across the developing world but it's almost at the bottom of the priority list for funding, which tends to go to life and death issues like Malaria and AIDS. Perhaps that is because eyesight is a harder to communicate, less direct – yet still just as deadly – health issue.
"In Africa road traffic accidents are projected to be the largest killer in the next five years and 60 percent are a result of drivers who don't have good vision," Chen claims.
So why is there such a disparity over access to eye care within the developing and developed world?
Chen partly blames the current, expensive model of shops, expensive machines and highly trained professionals, which make the barriers to entry for eye care unnecessarily high.
"It doesn't seem to me it should be that difficult," Chen says. "The optical community are used to this model, so I guess it does take someone to ask why not. And I don't think a good enough answer is 'just because that is the way it is'."
Chen decided to use Rwanda as a testbed for his ideas. He launched 'Vision for a Nation' in 2009 and the country has seen amazing results since.
When it started there was one ophthalmologist for every million people, but now all 10.5 million Rwandans have access to affordable eye care. "The eye community said it was impossible but we have done it," Chen says.
Any Rwandan citizen can now buy a pair of glasses for $1.50, equivalent to five days' discretionary income, although the poorest 20 percent get them for free from the government, according to Chen.
How? A combination of technology and training.
"Ophthalmologists train for three years. They said we can do three months. We made that three days' training for nurses in local centres across the country," he explains. It's a model he hopes to emulate around the world.
Thanks to smartphones, virtually anyone has the ability to make a diagnosis in their pocket, Chen adds.
Clearly is now investigating whether they can make the diagnosis process faster using machine learning. Chen has had meetings with Google DeepMind to discuss how their technology, in particular their work with Moorfields Eye Hospital, could help.
The campaign is also keen to make use of drone delivery for eye care supplies. Rwanda already has a project called 'Zipline' which delivers urgent medical supplies and blood using drones, which drop cardboard boxes using paper parachutes. Chen believes this could be used for eye care too.
"Previously it would take four hours or even the next day but now you put the order in on a smartphone and using global GPS the drone can drop supplies in 15 minutes. I can easily see them delivering glasses too," he says.
"Thanks to technology, for the first time now in 700 years we are on the cusp of being able to solve the biggest unaddressed disability in the world today. That really excites me."