Abstract
Abstract: :
Purpose: To provide summary statistics that capture features that are visualized in polarimetry images, comparing normal subjects to patient groups. Methods:We imaged the maculas of 2 groups of subjects: normal subjects and patients with age–related maculopathy (ARM). Noninvasive polarimetry images were obtained from raw data using a GDx ( LDT) and in–house software (Matlab, Mathworks). Returning light is collected by two detectors: a parallel polarized and a crossed detector. There were 40 images: parallel polarized and cross polarized image pairs at each of 20 input polarizations. Filtering in the Fourier domain across the 20 input polarizations reduced pixel noise. We computed a depolarized image (minimum of the crossed detector) and a confocal image (mean of both detectors). Image metrics were computed in a 213x213 pixel region of interest, omitting the central 31x31 pixels. The mean, S.D., and C.V. were calculated as a metric of the overall amount of depolarized or polarization–retaining light for each computed image. We also computed a 2–d discrete Fourier transform of selected image types and compared the amplitude as a function of frequency for ARM patients and normals. Long range scatter and illumination artifacts contribute to the lowest frequencies, while pixel noise contributes to the highest frequencies. Fisher’s tests were used to compare metrics across patient groups. Results: Images computed from depolarized light, which have a strong contribution from multiply scattered light, were of higher intensity for the ARM patients compared with normal subjects, p < .0072 for ARM. The overall amplitude of light return did not vary among groups (p = .97). The ages of the groups also varied, with normals younger than ARM (p < .0001). Analysis with FFT ruled out the possibility that the increased brightness of the depolarized light images for ARM patients was not due to a veiling effect (contrast reducing) from anterior segment scattered light. Specifically, the amplitude at frequencies above steady–state were higher than in normals. Conclusions: There is an increase in multiply scattered light in the eyes of ARM patients, and this cannot be solely explained by optical artifacts anterior to the retina.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • age–related macular degeneration • drusen