Imagine a piercing pain every time you blink. Unthinkable, right?

That's the reality of Trachoma, the world's leading cause of infectious blindness, a bacterial infection transported person to person by flies, and any other form of contact. This contagious bacterial infection of the eye is a terrible affliction that causes inflammation and turns the eyelids inwards, and the eyelashes to scratch and scrape the cornea like knives. Slowly, painfully, it causes blindness.

Sufferers often wear home-made tweezers around their necks, not as jewellery but to pluck away the sharp lashes causing them constant pain. It does, of course, only offer momentary relief, as the new lashes grow back sharper, deadlier and more uncomfortable than ever.

Today I am attending President and Mrs Carter's 'Carter Center weekend' in Lake Tahoe, a closed gathering of Carter family, friends and close supporters of the Center's remarkable work, motto 'Waging Peace, Fighting Disease, Bringing Hope'.

President Jimmy Carter and his wife Rosalynn, are nothing short of amazing. Their passion and commitment to good, to making the world a better place, their unstinting energy and their resolve, are humbling for everyone around them, and encourage us all to play our part too in any way we can.

This morning Kelly Callahan, the Carter Center's Director of the Trachoma Programme gave a moving talk about their remarkable efforts to stamp out this debilitating but preventable infection.

The Carter Center's Health Programmes focus on fighting Neglected Tropical Diseases (NTD's), such as Guinea Worm and River Blindness, preventable diseases where their efforts are not being duplicated by other bodies.

The Center has a target to eliminate Trachoma by 2020, a clear disease of poverty, and seen more in children, and women, who are twice as liable to contract the infection. There are currently 200 million people at risk of blinding Trachoma, in 41 countries.

In the late 1990s, the Carter Center took this problem square on and has led the way ever since. President Carter went personally to persuade Pfizer to donate the antibiotic Zithromax, and in the 18 years since the pharma giant and the Carter Center have been responsible for administering 157 million doses.

But the war on Trachoma did not stop with the delivery of medication. The Center has been responsible for 681,000 surgeries to prevent blindness, relatively simple 20-minute surgery costing $35-$40 a go, but transforming the lives of everyone afflicted. Some 250,000 of these surgeries have been on women.

The Center has led education around Trachoma prevention and cleanliness in the worst affected areas in the world, and built nearly 3.5 million latrines - in doing so reducing the number of flies that carry the bacteria to such deadly effect. This weekend, the President said one of the things he would be remembered for, was being 'the biggest toilet builder in the world!'

The Carter Center took on the fight against Trachoma in Amhara, Ethiopia, way back in 2001, where the infection is at its most intense. The team has beaten inaccessible roads, as well as the rain. In 2016 alone they were responsible for 111,000 sight-saving surgeries. Every five minutes someone received surgery, Kelly Callahan told us. In addition to the education about Trachoma prevention, they also administered 17 million doses of Zithromax in Amhara alone last year, and built 589,000 latrines, reducing the flies, fighting the disease. In 2001 Trachoma was prevalent in 61% of the population. Today that figure is 24% and, while there is some way to go to the 5% target with 289,000 surgeries still to perform, huge progress has been made.

Ethiopia is just one country in which the Carter Center is operationally active waging its campaign to eradicate Trachoma. Add in Mali, Niger and South Sudan, among others, all places where safety and security issues make the humane battle so much harder.

Kelly Callahan was moved to tears telling the audience about the commitment of President and Mrs Carter, and the meaningfulness and impact of her work. And the audience were moved too. So much so that John Hussman from the Hussman Family Foundation pledged $500,000 there and then and starting a matching grant: plenty of others followed. The money is needed because in truth the Programme is always underfunded, amazing as it is. "These diseases are called 'neglected' for a reason" Kelly told us, referring to the wider work on Neglected Tropical Diseases undertaken by the Carter Center, just one aspect of its breath-taking work, often undertaken against all odds.

"We are not afraid of failure if we think the end goal is worth it," the President told me. Together with Mrs Carter - who will have been married to Jimmy for 71 years when they celebrate their wedding anniversary in July, and still walk round hand in hand when together - they form the most wonderful and inspiring couple I have had the privilege to meet.