Foveal localization in non-exudative AMD using scanning laser polarimetry

To determine whether custom scanning laser polarimetry (SLP) images, differing in polarization content, can be used to accurately localize the fovea in the presence of non-exudative age-related macular degeneration (AMD). To determine whether alterations to the foveal structure in non-exudative AMD significantly disrupts the birefringent Henle fiber layer, responsible for the macular cross pattern in some SLP images. To determine whether phase retardation information, specifically color-coded information representing its magnitude and axis, allow better foveal localization than images including retardation amplitude only.

SLP images were acquired in 25 AMD subjects and 25 age-matched controls. Raw data were used to generate five custom image types differing in polarization content. The foveal location was marked by three graders in each image type for each subject. The difference in variability was compared between the AMD subjects and matched controls. We further determined whether the orientation of Henle fiber layer phase retardation improved localization in 10 subjects with the highest variability in images including only phase retardation amplitude.

Images that differed in polarization content led to strikingly different visualizations of AMD pathology. The Henle fiber layer remained sufficiently intact to assist in fovea localization in all subjects but with more variability in the AMD group. For both the AMD and matched control group, images containing birefringence amplitude and orientation information reduced the amount of intragrader, intergrader, and interimage variability for estimating foveal location.

The disruption in Henle fiber birefringence was evident in the eyes with AMD but nevertheless was sufficient to help in foveal localization despite macular pathology. Phase retardation amplitude and axis of orientation can be a useful tool in foveal localization in patients with AMD.