Abstract
Purpose :
Age-related macular degeneration (AMD) is a leading cause of blindness, with accompanying degeneration/dysregulation of the retinal pigment epithelium (RPE). With recent progress in AMD treatments, better biomarkers are needed. Compared to current fundus imaging techniques and near infrared Optical Coherence Tomography (OCT), visible light OCT provides higher resolution, and better visualization of the outer retina. Here we propose to image RPE melanosomes via spectroscopic analysis of visible light OCT images.
Methods :
5 healthy human subjects (ages 25-40, 1 female), one C57BL/6J (pigmented) mouse (4.5 months, male), and one BALB/cJ (albino) mouse (2 months, male) were imaged with micron-resolution, visible light OCT. Multiple (>100) images offset along the slow axis were acquired. Motion-correction and dispersion compensation were applied. After averaging sub-bands to reduce speckle, background subtraction, and spectral normalization to the inner retina, a weighted spectral centroid was determined.
Results :
An example image of the pigmented human outer retina (Figure 1) shows that each outer retinal layer exhibits distinctive spectral characteristics as light propagates through the photoreceptors and RPE. Importantly, we observe a red shift from the apical to basal RPE and Bruch’s membrane (BM). This red shift is present in pigmented mice but not in unpigmented mice (Figure 2).
Conclusions :
Visible light OCT shows a spectral red shift in the RPE that may arise from the presence of melanosomes. Evidence supporting this interpretation includes: 1) The axial location of the red shift agrees with melanosomes/melanolipofuscin in the apical RPE. 2) The red shift is most prominent in the fovea where RPE melanosomes are most numerous (not shown). 3) The red shift is present in pigmented but not albino mice, suggesting melanin is required. 4) Melanosome absorption and scattering decrease with wavelength, providing a plausible explanation for the observed red shift. This novel signature may enable imaging of RPE melanin in health and disease with high specificity.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.