Dual wavelength retinal vessel oximetry – influence of fundus pigmentation

Abstract

Background Clinical methods examining oxygenation parameters in humans have been used in many different care settings, but concerns have been raised regarding their clinical utility when assessing people with darker skin pigmentation. While saturation values can be crucial in emergency medicine, they are equally valuable in assessing disease mechanisms and monitoring change in disease progression. Retinal pigmentation varies across individuals and hence, can impact on retinal oxygen parameters. The objective of this study was to quantify and eliminate the impact of retinal pigmentation on retinal vessel oxygen saturation parameters measured in the superficial retinal arterioles and venules. Methods 105 healthy individuals of varying skin colour, iris colour and heritage were included. Following a full eye exam to exclude any ocular abnormality, all participants underwent intraocular pressure, systemic blood pressure measurements and dilated dual wavelength retinal photography. Rotation matrices were employed to minimise the dependency of retinal pigmentation on arterial and venous oxygen saturation measurements determined in a concentric measurement annulus. Results Retinal oxygen saturation in venules showed a linear correlation with retinal pigmentation (y = 0.34 × x + 38.598), whereas arterial saturation followed a polynomial pattern (y = 0.0089 × x2 + 0.7499 × x + 85.073). Both arterial and venous saturation values were corrected using local fundus pigmentation. Pre-correction retinal arterial and venous oxygen saturation were 89.0% (±13.1) and 43.7% (±11.5), respectively, and post- correction values were 94.8% (±8.7) for arteries and 56.3% (±7.0) veins. Conclusions When assessing multi-ethnic cohorts, it is important to consider the impact of pigmentation on imaging parameters and to account for it prior to clinical interpretation.

Ethnicity is not biology: retinal pigment score to evaluate biological variability from ophthalmic imaging using machine learning

“…[31] Additionally, saturation values from retinal oximetry vary according to retinal pigmentation. [32] We found associations between the RPS and multiple genetic loci previously associated with skin, hair, and iris colour, suggesting that the RPS reflects the degree of retinal pigmentation. Of the 20 genome-wide significant loci identified by conditional analysis in the discovery GWAS analysis, 17 had previously studied associations with hair, skin or iris pigmentation, including 3 that are known to be associated with oculocutaneous albinism (TYR, OCA2 and TYRP1).…”

Potential measurement error from vessel reflex and multiple light paths in dual‐wavelength retinal oximetry

“…The reduction in oxygen consumption detected by oximetry is a biomarker for retinitis pigmentosa and glaucoma (Stefánsson et al, 2017). Patients with higher levels of pigmentation, including those of African descent, may be at higher risk for oximetry defects and measurement errors, and although a correction for pigment is available (Hammer et al, 2008; Hirsch et al, 2022), its full assimilation and testing across race would significantly improve the reliability of retinal oximetry for clinical applications. Such studies are representative of many latent possibilities for clinical diagnostics; however, this goal remains unattained in part due to uncertainty concerning accuracy and calibration.…”

Variations in Retinal Oxygen Saturation in a Diverse Healthy Population

“… 9 More recently, Kirsch et al noted differences in large vessel oxygen saturation measures of both arterioles and venules are related to retinal and iris pigmentation. 11 Studies have also shown differences in oxygen saturation with diseases such as diabetes. From those studies, observed retinal vessel oxygen saturation increases in subjects with diabetes, although the amount of change depends on the severity of the disease.…”