Imagine being in excruciating pain every time you blink. Imagine this pain lasting several years until eventually you lose your eyesight. This is the reality for millions of people in the Commonwealth who are affected by trachoma – a completely preventable and treatable condition.

No one should suffer from blindness or poor eyesight when it can be prevented or corrected, yet too often they still do.

Earlier this month I had the honour of visiting Uganda in my capacity as one of the founding Trustees of The Queen Elizabeth Diamond Jubilee Trust. The Trust is working with many partners, under the shared mission of the International Coalition for Trachoma Control, to eliminate the world's leading infectious cause of blindness across the country. Uganda is one of 12 Commonwealth countries where the Trust is tackling the disease.

We travelled for many hours on unpaved roads to the village of Kiringa in the Iganga district in south-eastern Uganda. The village is one of thousands that in 2014, before the work of the Trust's Trachoma Initiative began, was burdened with endemic levels of trachoma.

Around the world, 200 million people are at risk of trachoma. It is a painful, debilitating disease of the rural poor, who have limited access to clean water, basic sanitation and healthcare.

Trachoma is an ancient scourge. It is mentioned as early as 1550BC in the ancient Egyptian Ebers Papyrus. In the 5th century BC the blinding stage of trachoma is included in The Hippocratic Corpus, the collection of work from the Hippocrates school of medicine. Appropriately, the word trachoma comes from the Greek word for rough.

And rough it is.

Repeated infection causes scarring under the eyelids, which turns them inwards. With every excruciating blink, the eyelashes scrape the surface of the eye. Without treatment, it can lead to irreversible blindness. In fact, there are 1.9 million people in the world who have lost their sight to the condition.

Yet when caught early enough, trachoma can easily be treated with antibiotics. Even in more severe cases, surgery can stop the eyelashes rubbing against the eyeball, and halt the cycle of repeated infection, saving that person's sight. The spread of infection can also be stopped by good hygienic practices and improving people's access to water and sanitation, so they can wash their hands and clothes regularly

As we entered the village in Uganda we were given the warmest welcome by local school children who sang and danced. I noticed an elderly woman among them, dancing with the same energy and delight as the children. Her joy was infectious and undeniable.

I was later introduced to her. Zabina is an 80-year-old woman from Kiringa. She lived with her daughter and six grandchildren and had recently recovered from successful eye surgery.

Zabina was first affected by trachoma during her teenage years. She ceased going to school because of the pain and effect on her eyesight. In later years she could not cook, or farm, her only source of income.

Under the committed leadership of the Ministry of Health, the Trust's Trachoma Initiative has been able to provide sight-saving and pain-relieving surgery to over 27,000 people across Uganda. Zabina was one very grateful recipient. As she shook my hand heartily, her face lit up with joy. She said 'I'm so happy I can see again. My life was in darkness before and now after the surgery I can dance and live.'

The progress in the Trust's Trachoma Initiative in just four years to rid the country of the blight of trachoma is quite remarkable.

In 2014, before the Trust's Trachoma Initiative began work in Uganda, 10 million people were at risk of the disease. Now just 300,000 people require attention before the country can declare itself free from trachoma as a public health problem.

I was struck by the dedication and determination of the individuals and communities I met. They show what can be achieved when people come together to fight this disease.

Witnessing Zabina's joy made it all too clear how deeply precious sight is. The delight in her face will stay with me. Good vision releases the potential of individuals to learn, to work and to lead fulfilled and productive lives.

We can end trachoma and prevent or treat other forms of blindness and poor eyesight. Yet more than 85 million people in the Commonwealth are affected by poor eye health, and without urgent action these numbers are set to triple by 2050.

This week, as leaders come together for the Commonwealth Heads of Government Meeting in the United Kingdom, the Trust, Sightsavers, The Fred Hollows Foundation, Peek, Clearly and the International Coalition for Trachoma Control (ICTC), are uniting under the Vision for the Commonwealth banner to call on each country to take one significant action towards bringing vision to everyone in the Commonwealth by 2020.

Now, the Commonwealth has the opportunity to show the world, as we have done in Uganda, that by stepping up efforts to bring eye health to all, the potential of millions of people is unlocked, for the benefit of themselves, their communities and their countries – now, and into the future.

Lord Chartres is a former bishop of London and a trustee of The Queen Elizabeth Diamond Jubilee Trust.