Researchers demonstrated that a vertical cavity surface emitting laser (VCSEL) diode, which is extensively used in telecommunications and lidar applications, might provide a lower-cost light source for swept-source optical coherence tomography (OCT). This advancement might pave the way for ophthalmologic OCT devices that can be used outside of the ophthalmology clinic, even at home.
Although single-mode VSCELs typically operate at a constant current, the researchers changed the current to create the wavelength or color shifts required for swept source OCT. The researchers disclose their unique OCT setup, which includes a VCSEL and powerful post-processing techniques, in the Optica Publishing Group journal Optics Letters. They utilized the apparatus to get full-eye scans from a healthy participant.
“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,” Kendrisic explained. “It could also enable home-based treatment monitoring for patients with age-related macular degeneration or eye health in diabetes patients to monitor treatment or detect abnormal changes early, preventing vision loss and ultimately preserving the quality of life.” This might be accomplished, for example, by renting easy-to-use equipment from your insurance provider.”
Identifying a less costly laser
Swept-source OCT is a relatively recent OCT technique that was first used in clinical eye imaging in 2010. It employs a laser with wavelengths that shift over time to provide high-quality imaging of several areas of the eye. Despite the fact that this new technique provides details that are utilized to better study and diagnose eye diseases, swept-source lasers often cost tens of thousands of dollars.
The goal of the new study was to investigate if a considerably cheaper VCSEL diode might be used instead of the pricey swept-source laser. While VCSEL diodes normally produce a laser output beam at a specific well-defined wavelength, the output wavelength will fluctuate if the diode’s operating temperature varies.
“Our idea was to leverage an unwanted effect of wavelength shifting with temperature to make these diodes usable for OCT,” Kendrisic explained. “We purposefully induce a temperature change by rapidly ramping up the driving current to values far exceeding its original specifications.” This is followed by a cooling phase to prevent diode material degeneration, allowing us to tune the diode over a wider bandwidth than would otherwise be feasible.”
Other organizations have shown that VCSELs can be utilized for OCT, but those devices were not built for ocular imaging. Because the human eye is mainly water, the researchers employed a VCSEL that operates at 850 nm, a wavelength that is not substantially absorbed by water. This permits the laser light to pass through the eye, to the retina, and back to the detector without being absorbed.
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“Even though commercial swept sources have larger spectral bandwidths, we demonstrated that the small range we achieved with a VCSEL is sufficient for OCT,” Kendrisic explained. “If purchased in bulk, these laser diodes could cost as little as a few dollars per unit and also allow for large distance ranging, which is required for covering the entire length of the human eye from the cornea to the retina.”
Obtaining photographs of the eyes
The researchers incorporated it into an optical setup for conducting ophthalmic OCT imaging after determining the optimum approach to add current to the VCSEL without harming the laser while still assuring the finest possible imaging resolution. This system worked admirably, particularly in terms of sensitivity and image depth, despite the addition of certain additional components to preserve system performance and advanced post-processing techniques.
They next put the device through its paces by imaging the eye of a healthy volunteer and extracting biometric data such as axial eye length and anterior chamber depth with axial precision equivalent to commercial OCT systems. The findings also demonstrate the technology’s potential for application in biometric eye scanner systems used for security.
“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,” Kendrisic explained. “Our paper emphasizes the use of this technology for ophthalmic applications, but lowering the price of OCT devices will allow for the easier introduction of OCT technology in other fields as well – both medical and technical.”
Before a VSCEL-based system for eye examinations could be marketed, large-scale clinical trials and source lifespan testing would be required to demonstrate the system’s clinical usefulness and longevity.