New VCSEL offers simpler, cheaper OCT

05 Jun 2023

Medical University of Vienna believes inexpensive source could allow OCT imaging at home.

The impact of OCT on medical imaging has been considerable, not least in ophthalmology where it has become a standard clinical procedure.

A 2021 survey by the Medical University of Vienna predicted that the global market for OCT in 2023 will be $1.5 billion, and noted that this would include hand-held OCT units and new end uses, in addition to established integrated systems.

Novel laser sources will play a large part in both the market growth and the use of more portable systems, and a project at the same University has now developed a VCSEL intended to offer a less expensive light source for swept-source OCT.

Reported in Optics Letters, the findings could lead to OCT platforms that are sufficiently low-cost and easy to use that they allow ophthalmology testing outside the clinic, even at patients' homes.

"OCT has become a standard imaging tool in ophthalmology for diagnosing and monitoring diseases like glaucoma, macular degeneration and diabetes-related retinopathy," said project member Milana Kendrisic from the University's Leitgeb and Drexler research lab.

"However, the price of laser sources and the complexity of OCT systems hinder its accessibility outside of clinics and hospitals, in particular for home care or point-of-care use. We want to develop a low-cost OCT device that could be used in a general practitioner’s office, a pharmacy or even a supermarket to allow eye checkups without going to the ophthalmologist."

VCSEL swept-source technology is known to be a route to faster wavelength sweep speeds in OCT and new imaging capabilities, although the nature of traditional VCSEL diodes typically means that the output wavelength is adversely affected by outside factors like the operating temperature.

The Vienna project aimed to make use of this usually unwanted effect, adjusting the operating temperature through modulation of the VCSEL injection current and deliberately causing a change in emitted wavelength.

Rent an OCT platform for treatment monitoring

"We deliberately induce a temperature change by ramping up the driving current in a short time to high values beyond its original specifications," said Kendrisic. "This is followed by a cooling period to avoid deterioration of the diode material, which lets us tune the diode over a broader bandwidth than is otherwise possible."

Although VCSELs have been used as sources in OCT platforms before, those systems were not designed for eye imaging according to the project team. To accommodate the eye's partially aqueous interior, a VCSEL operating at 850 nanometers was used to avoid strong absorption by water as the light travels through the eye to the retina and back to the detector. Numerical methods then assist with image reconstruction.

In trials on the eye of a volunteer, the new platform captured full-eye scans from the cornea to the retina at 25 and 50 kHz, and obtained biometric information such as the axial eye length and anterior chamber depth with axial precision comparable to commercial OCT systems, according to the team.

A lower cost OCT source could allow home-based treatment monitoring for patients with age-related macular degeneration or conditions such as diabetes. The Vienna project envisages patients ultimately being able to rent an easy-to-use device from an insurance provider.

"Although VSCEL-based systems have some limitations in terms of image quality, they still have the potential to expand access to diagnostic imaging and improve patient care in areas where traditional OCT systems may not be available or affordable," said Kendrisic. "Lowering the price of OCT devices will allow an easier introduction of the technology in other fields as well, both medical and technical."