No abstract

This study examined the sensitivity of broadband spectroscopy algorithms for retinal tissue oximetry to spectral acquisition parameters. Monte Carlo simulations were conducted on a 4-layer retinal model to assess the impact of various parameters. The optimal spectral range for accurate measurements was determined to be 530 nm to 585 nm. Decreased spectral resolution below 4 nm significantly reduced accuracy. Using an acquisition area larger than the blood vessel resulted in an underestimation of oxygen saturation, especially for high values. A threshold was observed where increased light intensity had no significant impact on measurement variability. The study highlights the importance of informed parameter selection for accurately assessing retinal microcapillary oxygenation and studying local hemodynamics.

Significance: The assessment of biomarkers in the eye is rapidly gaining traction for the screening, diagnosis and monitoring of ocular and neurological diseases. Targeted ocular spectroscopy is a new technology that enables the user to concurrently image the eye fundus and acquire high quality spectra from a targeted region - 1.5 degrees - within the imaged area. The combination of imaging and high-sensitivity spectroscopy provides structural, compositional, and functional information of selected regions of the eye fundus. This opens the door to new, non-invasive approaches to the detection of biomarkers in the eye. Aim: The aim of this study was to demonstrate the multi-modal functionality and validation of the targeted ocular spectroscopy developed. This was done in vitro, using a reference target and a model eye, and in vivo. Approach: Images and spectra from different regions of a reference target and a model eye were acquired and analyzed to validate the system. The same eye model was used to obtain fluorescence images and spectra, highlighting the capability of the system to also perform targeted ocular fluorescence spectroscopy. Subsequently, in vivo imaging and diffuse reflectance spectra were acquired to assess blood oxygen saturation in the optic nerve head and the parafovea of healthy subjects. Results: Tests conducted with the reference target showed that spectral analysis could be accurately performed within specific areas of the imaging space. Moving to the model eye, distinct spectral signatures were observed for the targeted spectral analysis done in the optic disc, the retina and the macula, consistent with the variations in tissue composition and functions between these regions mimicked by the model eye. Further, it was shown that the targeted spectral analysis could also be performed in a fluorescence mode to distinguish various fluorophores present within the imaging space. Finally, in vivo ocular oximetry experiments performed in the optic nerve head and parafovea of healthy patients showed significant differences in blood oxygen saturation between these regions (p = 0.004). Conclusions: Enabling non-invasive, sensitive diffuse reflectance and fluorescence spectroscopy in specific regions of the eye fundus opens the door to a whole new range of monitoring and diagnostic capabilities, from assessment of oxygenation in glaucoma and diabetic retinopathy to photo-oxidation and photo-degradation in age-related macular degeneration.

Purpose: Oxygen plays a central role in multiple physiological and pathophysiological processes, and retinal oxygen supply has been found to be an important factor in many ocular diseases. Animal models are often used to study the pathophysiological mechanisms of diseases, especially non‐human primates (NHP) due to their great similarities with humans. Few data are available on the quantification of oxygen in the retina of NHP. The objectives of the study were to establish NHP tissue oxygen saturation (StO2) normative values in different eye fundus regions, compare StO2 in these regions and analyse how StO2 correlates to age, sex and intraocular pressure (IOP). Methods: 44 vervet monkeys (28 males/16 females, 5–28 years old) were included in the study. IOP was measured in both eyes with an ocular tonometer. StO2 was measured in both eyes using the Zilia Ocular oximeter in the temporal (tONH) and nasal (nONH) optic nerve head, the peripapillary region (pPL) and the perifovea (pFV). T‐tests were used to compare between regions (paired), between both eyes (paired) and between sexes (independent). Kendall's tau was used to assess the correlation between StO2 and age, as well as that between StO2 and IOP. Results: Mean StO2 was 55.7% ± 4.3% in the tONH, 55.0% ± 3.9% in the nONH, 63.9% ± 7.3% in the pPL and 74.2% ± 3.4% in the pFV. No significant difference in StO2 was observed between the left and the right eyes, just as no significant difference was observed between tONH and nONH. The StO2 was lower in tONH and nONH than in pPL (p = 0.0226 and 0.0060, respectively). No correlation was found between StO2 and age, StO2 and sex, or StO2 and IOP. Conclusions: StO2 in the retinal tissue of NHP has been assessed for the first time. Regional variations similar to previous human studies were observed. The results of this study show the applicability of the Zilia Ocular on NHP and provide normative values that can serve as a basis for future studies.