A team of UK scientists and engineers have developed a prototype device for detecting the most common cause of sight loss in the developed world, age-related macular degeneration (AMD), which usually isn’t diagnosed until vision has already begun to degrade.
The technology, produced by Cardiff University and the UK Astronomy Technology Centre (UK ATC), uses very sensitive cameras designed for deep-space telescopes to assess whether the retina is functioning as it should – and could open up study of the eye to find new treatments.
‘This could revolutionise the detection not just of macular disease but of a whole range of conditions,’ research leader Dr Tom Margrain, from Cardiff’s School of Optometry and Vision Sciences, told The Engineer.
He compared the development to that of functional MRI scanning, which measures changing brain activity. ‘We can actually see in images what’s happening at a functional level in the retina, so it’s quite a step forward.’
There is no known treatment for AMD but spotting it earlier could allow patients to make lifestyle changes such as quitting smoking and altering their diets to try to halt its development.
Being able to study the progress of the disease in greater detail could also pave the way for the development of a treatment, said Margrain.
‘It’s a circular argument. One of the reason’s there’s no treatment is there’s no way of picking up or monitoring it… This technology will hopefully act as a catalyst for the development of new treatments of macular disease.’
The device, known as a retinal densitometer, works by illuminating the retina with light of different wavelengths and capturing the resulting images over time. This reveals the colour changes in the retina as it adjusts to decreasing amounts of light (dark adaptation), the speed of which can indicate early-stage AMD.
When the amount of light entering the eye increases, a chemical reaction turns the purple pigment in the retina’s photoreceptors clear, limiting their signals to the brain. When the amount of light decreases, the pigment is regenerated, increasing the eye’s ability to absorb light again.
AMD affects the part of the retina where dark adaptation takes place, known as the macular, and so measuring the rate of pigment regeneration can reveal the disease’s presence.
Existing technologies can also measure dark adaptation but these are either invasive or rely on the patient’s subjective view of the changing light. The new technology, Margrain said, provides an objective measure that can more accurately detect AMD.
The difficulty in measuring dark adaptation in the past has been the need to limit the amount of light that illuminates the eye but capture enough reflected light to create an image, a problem that was solved by using very sensitive cameras used for stargazing.
Engineers at the UK ATC, which is part of the Science and Technology Facilities Council (STFC), adapted the camera by creating a control system to manage the way it captured a series of images illuminated by different wavelengths of light.
‘One thing we realised early on was we needed very good timing control,’ said Dr Dave Melotte, innovation manager at the UK ATC. ‘The signal from the camera links through a series of bespoke control boards to set the measurement sequence off, so you know take each frame with the light of the right wavelength.’
The engineers also had to model the way the light moved through the device into the eye and back again to find the best configuration for capturing the maximum amount of light.
The team is now planning to build a version of the device for clinical trials that is easier for opticians to use but also doesn’t require the patient to keep perfectly still for five minutes while the images are captured.
To do this, they plan to develop an eye tracking system that keeps the camera aligned with the patient’s pupils at all time.
The project was funded by the National Institute for Health Research’s Invention for Innovation (i4i) programme and the STFC’s Commercial Proof of Concept Fund and Futures Programme.
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