Quantification and Repeatability of Drusen and Geographic Atrophy by Polarization-Sensitive Optical Coherence Tomography

Abstract

Purpose: : To demonstrate the ability of polarization-sensitive optical coherence tomography (PS-OCT) to assess retinal pathologies in age-related macular degeneration (AMD) in a quantitative way. To test the reproducibility of measured drusen areas as well as volumes and areas of atrophic zones in dry AMD.

Methods: : A prototype PS-OCT device was used to record three-dimensional (3D) data sets in the eyes of AMD patients. PS-OCT provides additional contrast based on the polarization properties of different retinal structures. In this study, the depolarizing character of the retinal pigment epithelium (RPE) was used to segment this layer. Several evaluation software algorithms were developed and used for quantitative assessment of retinal pathologies: Drusen were identified by computing the deviation of the determined RPE position from its normally expected position. Drusen were mapped, and their volume and area was automatically derived. Further, by measuring the thickness of the segmented layer, atrophic zones were detected as areas devoid of depolarizing tissue in the eyes of dry AMD patients. In order to evaluate the reproducibility of the pathologic features‘ dimensions found by PS-OCT, 5 eyes of patients suffering from drusen and 5 eyes with geographic atrophy (GA) repeatedly were imaged 5 times.

Results: : From the 3D PS-OCT data sets, en-face maps of drusen and GA were generated. Using the novel evaluation algorithms, pathologic retinal features were quantified: Total drusen areas sized 3.23 to 9.80 mm² (mean area: 5.74 mm²) were measured in the investigated retinal regions of the 5 eyes diagnosed with drusen. The standard deviation (SD) of measured areas was 0.42 mm² (8 % of the respective total area). The volume of drusen amounted to 0.21 mm³ in average (range: 0.08 to 0.46 mm³). Computed drusen volumes fluctuated by 7 % corresponding to an average SD of 0.01 mm³. The areas of segmented atrophic patches were in the range from 0.26 to 7.79 mm² (average patch area: 1.96 mm²). Total areas from 0.62 mm² to 7.79 mm² (mean total area: 3.13 mm²) were measured. The SD of determined total GA area of 0.32 mm² corresponds to 9.2 %.

Conclusions: : PS-OCT allows for 3D high-resolution imaging of retinal pathologies with additional contrast. Software algorithms for quantitative assessment of drusen and GA were developed and applied to data sets acquired in AMD patients. Measured areas and volumes showed good reproducibility.

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