Optical imager to help diagnose dry eye disease

Researchers have developed a new non-invasive optical imaging system that promises to improve diagnosis and treatments for dry eye disease, which occurs when there is instability in the inner layer of the tear film that protects the outside of the eye. Their work has been described in the journal Applied Optics.

Today, most cases of dry eye are diagnosed using patient questionnaires, which may be subjective and cannot typically be used to identify the cause of the disease. Objective methods for examining the tear film tend to be invasive and cannot track rapid changing dynamics, which are altered with every blink.

“For the diagnosis of dry eye disease, there have been few significant advancements over recent years,” said research team leader Dr Yoel Arieli, from AdOM Advanced Optical Methods in Israel. “We collaborated with academic and practising physicians who diagnose and treat dry eye to develop an instrument that can be integrated into a clinical setting while very accurately imaging the tear film inner layers, which can be used to diagnose dry eye and understand its cause.”

The instrument in question, known as the Tear Film Imager, is claimed to be the first device that can be used in the ophthalmology or optometry setting to image the tear film and distinguish its inner layers with nanometre resolution. It has the ability to perform spectral measurements across a large field of view in a matter of seconds, acquiring fast and consistent measurements from human eyes even when blinking.

The prototype Tear Film Imager, designed for use in an ophthalmology or optometry office. Image credit: AdOM Advanced Optical Methods.

The instrument uses an eye-safe halogen light to illuminate the eye and then analyses the full spectrum of light reflection over time and space. These spectral measurements are used to reconstruct the structures found in the front of the eye, allowing accurate measurement of the tear film inner layers — especially the aqueous sublayer. This sublayer plays an important role in dry eye but has been difficult to analyse with other methods.

“The broadband illumination source and fine details available from spectral analysis provide nanometre-level insight into subtle changes in each tear film layer and sublayer,” said Dr Arieli. “These measurements are completed automatically in just 40 seconds.”

After demonstrating a resolution of 2.2 nm on a mock tear film, the researchers tested the instrument’s ability to take measurements on the human eye with no intervention while the patient was blinking. According to Dr Arieli, “The device worked impressively and presents no risk because it is non-invasive and uses a simple light source. It not only measured the tear film consistently including blinks every few seconds, but the measurements correlated well with other partially invasive, established dry eye diagnostic techniques.”

The Tear Film Imager has been used in two clinical studies in Israel and Canada, examining dry eye diagnosis with the device and dry eye treatments, which can be precisely evaluated with the imager. The researchers say that future studies could help inform better dry eye treatments, improve surgical outcomes and lead to more accurate fitting of contact lenses. They are also planning to use the imager in larger studies with more diverse groups of patients to set base levels for both healthy eyes and people with dry eye.

Top image: The Tear Film Imager captures a raw image (a) and also generates a thickness map (b) derived from the colour information at each pixel. This can be used to distinguish the tear film’s inner layers. Image credit: AdOM Advanced Optical Methods.

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