Targeted Spectroscopy Can Improve Treatment of Eye Disease

A targeted spectroscopy system developed at Zilia Inc., by a team led by professor Dominic Sauvageau from the University of Alberta, enables concurrent imaging of the eye fundus — a region at the back of the eye — and analysis of high-quality spectra. The system, which holds advantages over typical fundus color imaging and optical coherence, can be used to assess a range of ocular conditions, from oxygenation in glaucoma and diabetic retinopathy to photo-oxidation and photodegradation in age-related macular degeneration.

The spectroscopy system takes detailed images of the eye fundus in real time while measuring the spectral profile of a small target region. The position of the device can be readjusted easily without requiring patient fixation. The device provides three different light paths, to and from the eye fundus, that enable illumination LEDs, a color camera, and a spectrometer to be used at the same time to provide continuous color imaging and spectral measurements.

The targeted spectroscopy system can take detailed images of the eye fundus in real time, while simultaneously measuring the spectral profile of a small target region, whose position can be readjusted easily without requiring patient fixation. These capabilities make it easier to observe the spectral properties of specific structures or lesions in the retina, which can help in the diagnosis of various conditions. Courtesy of Lapointe et al., (www.doi.org/10.1117/1.JBO.28.12.126004).

The device’s spectrometer is precise enough to focus an LED onto a small region of the fundus. Its flexibility allows it to be easily adjusted to change the area of focus by using mechanical actuators to rotate the beamsplitter, which feeds the camera and the spectrometer. The combination of precision and flexibility enables users to take spectral measurements from specific anatomical structures such as the optic nerve, the retina, as well as blood leakage, fat deposits, or any type of lesion.

“The user can select a target and move it to any location within the eye fundus region being imaged without any realignment or change of the fixation target, while continuously receiving spectral information of the targeted sampled area,” Sauvageau said.

While it is enabling the concurrent, continuous acquisition of images, the system obtains full, visible, diffuse reflectance or fluorescence spectra from a targeted location of the eye fundus. The user can obtain reflectance and fluorescence measurements through spectral analysis and can potentially use the measurements to identify ocular oximetry and other biomarkers. The detection of biomarkers in the retina from absorbance or fluorescence spectra depends on many factors that require high sensitivity, high spectral resolution, and short acquisition speed — all characteristics of targeted spectroscopy.

The researchers demonstrated the multimodal functionality of the targeted spectroscopy system through in vitro experiments using a reference target and a model eye, and in vivo experiments with healthy subjects.

To validate the system, the researchers analyzed images and spectra from different regions of a reference target and a model eye. They demonstrated targeted ocular fluorescence spectroscopy using the model. They observed distinct spectral signatures in the model eye for the optic disc, blood vessels, the retina, and the macula, consistent with the variations in tissue composition and functions between these regions.

They acquired in vivo images and diffuse reflectance spectra to assess blood oxygen saturation in the optic nerve head and the parafovea of healthy subjects. The team also used an ocular oximetry algorithm with in vivo spectra from the optic nerve head and parafovea of healthy subjects and showed significant differences in blood oxygen saturation.

Most spectroscopy-based methods can only take measurements over a large region of the eye fundus, which hinders their ability to detect fine spectral changes in small retinal structures. Techniques that can acquire localized spectral measurements can be uncomfortable for the patient, who must be fixated during the process.

The flexible, targeted spectroscopy system could lead to better diagnostic protocols for eye diseases. “Targeted ocular spectroscopy has the potential to assess the presence of different chromophores and fluorophores, such as hemoglobin, oxyhemoglobin, melanin, and lipofuscin, associated with disease progression,” Sauvageau said. “This could open the door to changes in the way we diagnose and treat eye diseases, and targeted ocular spectroscopy could become an increasingly important tool in eye care in the coming years.”

The research was published in the Journal of Biomedical Optics (www.doi.org/10.1117/1.JBO.28.12.126004).