Who owns your (valuable) health data?

Last week, at a conference in London, Dr Pearse Keane beamed an image on to the wall of an orange globe with a dark centre, encircled by red storms and a bright moon. It looked like a dying planet in a distant galaxy. In fact, it was a beautifully detailed scan of the back of a human eye, as awesome in its way as the night sky.

These days, Dr Keane said, that single image betrays a lot of information. "We can now look at a retinal photograph and say: 'This is a woman. She's 58, she's a non-smoker. She's not a diabetic, her BMI [body mass index] is around 25. And her blood pressure is 150 over 85. That's pretty amazing."

Dr Keane and his colleagues at Moorfields Eye Hospital in London can tell so much because of "deep learning" analysis by computers trained on many thousands of such images. From all that data, computers have learnt to spot patterns and draw eerily accurate conclusions.

Dr Keane and his team are going further. In a project called AzEye, they have linked more than three million scans from Moorfields with a central NHS database called Hospital Episode Statistics.

If a retinal scan can reveal so much, how about headphones that detect contagious disease or bathroom sensors for cardiovascular health.

"We now know every patient at Moorfields who's gone on to develop a heart attack, or dementia or a stroke or a range of other conditions," he said. "Huge amounts of data."

One day a single retinal scan might be able to reveal much, much more than the health of a patient's eye. "The potential," he says "is huge."

The secrets we're revealing

No wonder data about your health is valuable. And there's a mass of it out there: not just records on you held by the NHS, but also those compiled by trackers and apps developed by private firms that we wear and download on to our phones.