New Perspectives in the Imaging of Age-Related Macular Degeneration by Polarization Sensitive Optical Coherence Tomography

Abstract

Purpose: : Spectral domain (SD) optical coherence tomography (OCT) has brought new insights into the pathophysiologic understanding of age-related macular degeneration (AMD). However, SD-OCT lacks to provide information on the origin of hyperreflective tissue especially at the level of the retinal pigment epithelium (RPE). Polarization sensitive OCT (PS-OCT) was used to identify and characterize typical findings in AMD.

Methods: : 32 eyes of 32 patients with AMD were included representing the entire spectrum from early disease with drusen (n=10) to geographic atrophy (GA,n=11) and neovascular AMD before treatment (nAMD, n=11). Cirrus (Carl Zeiss Meditec) and a Spectralis (Heidelberg) SD-OCT systems were used for comparative imaging of the macular region. For PS-OCT imaging, an SD PS-OCT instrument (center wavelength 840 nm, bandwidth 50 nm, depth resolution in tissue: 4-5 µm, speed: 20000 A-lines/s) was developed that records three parameters simultaneously: reflectivity, retardation, and optic axis orientation. Recording time for a full 3D PS-OCT data set is 3 seconds.

Results: : In early disease PS-OCT was capable to identify a continous RPE band, often associated with mild focal alterations whereas a central atrophic gap and surrounding transition zones (TZ) could be visualized in GA. Three-dimensional (3D) RPE segmentation enabled PS-OCT to measure lesion areas accurately in GA. Autofluorescence patterns correlated to the PS-OCT findings but did not show the TZ. In nAMD PS-OCT showed multiple foci of RPE disease and breakthrough within the depolarization pattern before treatment. It enabled to differentiate depolarizing from other hyperreflective but none-depolarizing tissues at the level of the RPE. 3D segmentation of the RPE allowed for 3D-visualization of the RPE and its depolarizing properties within the entire central retina. Conventional SD-OCT systems were able to image the Photoreceptor/RPE complex in comparable detail but did not allow to differentiate between hyperreflective tissues at the level of the RPE.

Conclusions: : PS-OCT provided specific information on the status of underlying RPE disease in AMD patients, which can not be gathered from current SD-OCT. Recognition of disease specific polarization patterns of the RPE in dry as well as wet forms of AMD are of particular relevance to identify the disease status and progression in order to highlight therapeutic effects as well as the pathogenesis and prognosis.

Keywords: age-related macular degeneration • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal pigment epithelium