Researchers have demonstrated that an inexpensive light source for swept-source optical coherence tomography (OCT) might be provided by a vertical cavity surface emitting laser (VCSEL) diode, which is often used in telecommunications and lidar applications. This development could result in ophthalmologic OCT devices that are useful outside of ophthalmology offices, even at home.
The researchers changed the current to create the shifts in the wavelength, or color, required for swept source OCT even though single-mode VSCELs typically operate with a constant current. Researchers from the Optica Publishing Group explain their unique OCT setup, which includes a VCSEL and cutting-edge post-processing techniques, in the journal Optics Letters. They utilized the set-up to get full-eye scans on a volunteer who was in good health.
To enable eye exams without visiting an ophthalmologist, Kendrisic stated, “We intend to design low-cost OCT equipment that might be used in a general practitioner’s office, a pharmacy, or even a supermarket. It may also make it possible for people with diabetes or age-related macular degeneration to monitor their eye health or detect aberrant changes early on, preventing vision loss and ultimately maintaining the quality of life. You may accomplish this, for instance, by renting a simple gadget from your insurance company.
locating a more affordable laser
In 2010, swept-source OCT, a relatively novel OCT technique, was made clinically available for use in imaging the eyes. It makes use of a laser whose wavelengths fluctuate over time to provide precise viewing of various eye structures. Although swept-source lasers typically cost tens of thousands of dollars, this new method provides features that are being utilized to better study and diagnose eye problems.
The goal of the new research was to determine whether the pricey swept-source laser might be replaced by a significantly less costly VCSEL diode. While VCSEL diodes normally produce a laser output beam at a specific, predetermined wavelength, the output wavelength will fluctuate if the diode’s operating temperature varies.
According to Kendrick, “Our concept was to take advantage of an undesirable wavelength shifting with temperature effect to make these diodes usable for OCT.” “By quickly ramping up the driving current to high values above its initial specs, we purposefully produce a temperature shift. After then, the diode is cooled to prevent the material from degrading, allowing us to tune it over a wider bandwidth than would otherwise be feasible.
Although other research teams have shown that VCSELs can be utilized for OCT, those devices weren’t made for imaging the eyes. The researchers employed a VCSEL that works at 850 nm, a wavelength that is not heavily absorbed by water since the eye is mostly composed of water. As a result, there is no signal loss due to absorption when the laser light passes through the eye, strikes the retina, and returns to the detector.
“We proved that even the modest range we attained with a VCSEL is adequate to accomplish OCT,” said Kendrisic. “Commercial swept sources have greater spectral bandwidths. These laser diodes enable great distance ranging, which is required to span the whole length of the human eye from the cornea to the retina, and might cost as little as a few dollars apiece if purchased in quantity.
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taking pictures of the eye
The researchers integrated 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 and also guaranteeing the finest possible resolution for imaging. This system functioned quite well, notably in terms of sensitivity and image depth. It also featured several additional components to preserve system performance.
The device was then put to the test by imaging the eye of a healthy volunteer. They were able to extract biometric data with axial precision equivalent to commercial OCT systems, such as the axial eye length and anterior chamber depth. The outcomes also demonstrate the technology’s potential for usage in biometric eye scanner security systems.
Even though VSCEL-based systems have certain picture quality drawbacks, Kendrisic asserts that they nevertheless have the potential to increase access to diagnostic imaging and enhance patient care in places where conventional OCT systems would not be readily available or reasonably priced. Although the use of this technology for ophthalmic applications is highlighted in our article, decreasing the cost of OCT devices will make it simpler to apply it to other disciplines, both technological and medical.
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Large-scale clinical investigations and source lifetime testing would need to be carried out to demonstrate the system’s clinical relevance and durability before a VSCEL-based system for eye examinations could be marketed.
