Ophthalmic Imaging with Multimodal PARS Microscopy

Article: Touchless technology could enable early detection and treatment of eye diseases that cause blindness
Source: University of Waterloo (Canada), via ScienceDaily
Published: June 14, 2021

In-vivo, non-contact, simultaneous imaging of ocular
tissue in mice using a multimodal PARS-OCT system

Engineers in Canada developed a multimodal laser imaging system to measure oxygen saturation and metabolism in living tissue as a potential biomarker for common posterior segment eye diseases. Known as photoacoustic remote sensing (PARS), the technology uses multiwavelength lasers to "almost instantly" image in vivo human tissue noninvasively, with relevant applications for imaging of retinal vasculature and tissue prior to structural changes and functional loss in diseases such as age-related macular degeneration, diabetic retinopathy, and glaucoma. The technical, optical aspects of the technology implement stimulated Raman scattering (SRS), which occurs when the frequency of the emitted light differs from the frequency of the incident light through a material. Multiple wavelengths of light are necessary for oxygen saturation (relative concentration) calculations; however, previous methods using dye lasers or optical parametric oscillators were limited by low pulse repetition rates (i.e., speed) and thus were not suitable for applications of in vivo ocular imaging. Instead, the SRS approach allowed for both high-speed and multiwavelength light sources. The researchers used two excitation wavelengths (532 nm and 558 nm) in this case to estimate the concentration of HbO₂ and Hb. PARS microscopy can be simultaneously combined with swept-source optical coherence tomography (SS-OCT) for enhanced image viewing, and the authors report this being the first instance of combining OCT with optical resolution photoacoustic microscopy (OR-PAM). In contrast to OCT (without the angiography function), photoacoustic microscopy is good at imaging vasculature in greater detail. The project lead comments, “We’re optimistic that our technology, by providing functional details of the eye such as oxygen saturation and oxygen metabolism, may be able to play a critical role in early diagnosis and management of these blinding diseases.” The project is in an early stage and has only been tested in animal models at this point; they are working with several ophthalmologists and hope to start human trials within two years.

See also: Simultaneous multicontrast OR-PAM from single laser source

My rating of this study: ⭐⭐⭐⭐

Hosseinaee Z, Abbasi N, Pellegrino N, et al. "Functional and structural ophthalmic imaging using noncontact multimodal photoacoustic remote sensing microscopy and optical coherence tomography." Scientific Reports.  11(11466). 1 June 2021. https://doi.org/10.1038/s41598-021-90776-5