UK health technology start-up Siloton is developing a portable optical coherence tomography (OCT) system that uses photonic integrated circuits to miniaturize a tabletop’s-worth of expensive and fragile optical components onto a single coin-sized chip. In a first demonstration by a commercial organization, Siloton has now used its photonic chip technology to capture a sub-surface image of a human retina.

OCT is a non-invasive imaging technique employed as the clinical gold standard for diagnosing retinal disease. Current systems, however, are bulky and expensive and only available at hospital clinics or opticians. Siloton aims to apply its photonic chip – the optical equivalent of an electronic chip – to create a rugged, portable OCT system that patients could use to monitor disease progression in their own homes.

The image obtained using Siloton’s first-generation OCT chip, called Akepa, reveals the fine layered structure of the retina in a healthy human eye. It clearly shows layers such as the outer photoreceptor segment and the retinal pigment epithelium, which are key clinical features for diagnosing and monitoring eye diseases.

“The system imaged the part of the retina that’s responsible for all of your central vision, most of your colour vision and the fine detail that you see,” explains Alasdair Price, Siloton’s CEO. “This is the part of the eye that you really care about looking at to detect disease biomarkers for conditions like age-related macular degeneration [AMD] or various diabetic eye conditions.”

Faster and clearer

Since Siloton first demonstrated that Akepa could acquire OCT images of a retinal phantom, the company has deployed some major software enhancements. For example, while the system previously took 5 min to image the phantom – an impractical length of time for human imaging – the imaging speed is now less than a second. The team is also exploring ways to improve image quality using artificial intelligence techniques.

Price explains that the latest image was recorded using the photonic chip in a benchtop set-up, noting that the company is about halfway through the process of miniaturizing all of the optics and electronics into a handheld binocular device.

“The electronics is all off-the-shelf, so we’re not going to focus too heavily on miniaturizing that until right at the end,” he says. “The innovative part is in miniaturizing the optics. We are very close to having it in that binocular headset now, the aim being that by early next year we will have that fully miniaturized.”

As such, the company plans to start deploying some research-only systems commercially next year. These will be handheld binocular-style devices that users hold up to their faces, complete with a base station for charging and communications. Speaking with over 100 patients in focus groups, Siloton confirmed that they prefer this binocular design over the traditional chin rest employed in full-size OCT systems.

“We were worried about that because we thought we may not be able to get the level of stability required,” says Price. “But we did further tests on the stability of the binocular system compared with the chin rest and actually found that the binoculars showed greater stability. Right now we’re still using a chin rest, so we’re hopeful that the binocular system will further improve our ability to record high-quality images.”

Expanding applications

The principal aim of Siloton’s portable OCT system is to make the diagnosis and monitoring of eye diseases – such as diabetic macular oedema, retinal vein occlusion and AMD, the leading cause of sight loss in the developed world – more affordable and accessible.

Neovascular or “wet” AMD, for example, can be treated with regular eye injections, but this requires regular OCT scans at hospital appointments, which may not be available frequently enough for effective monitoring. With an OCT system in their own homes, patients can scan themselves every few days, enabling timely treatments as soon as disease progression is detected – as well as saving hospitals substantial amounts of money.

Ongoing improvements in “quality versus cost” of the Akepa chip has also enabled Siloton to expand its target applications outside of ophthalmology. The ability to image structures such as the optic nerve, for example, enables the use of OCT to screen for optic neuritis, a common early symptom in patients with multiple sclerosis.

The company is also working with the European Space Agency (ESA) on a project investigating spaceflight-associated neuro-ocular syndrome (SANS), a condition suffered by about 70% of astronauts and which requires regular monitoring.

“At the moment, there is an OCT system on the International Space Station. But for longer-distance space missions, things like Gateway, there won’t be room for such a large system,” Price tells Physics World. “So we’re working with ESA to look at getting our chip technology onto future space missions.”

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