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Per G Soderberg, Filip Malmberg, Camilla Sandberg Melin; Angular structure of Pigment Epithelium Inner limit of the retina Minimal Distance (PIMD) in the optic nerve head allows detection of local nerve fiber bundle loss without calibration to the retinal structure. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4002.
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© ARVO (1962-2015); The Authors (2016-present)
To elucidate if frontal plane angular PIMD recorded from the optic nerve head (ONH) is sufficiently specific to allow angular adjustment of recordings of PIMD-2Pi, for comparison of angular segments of PIMD between occasions within glaucoma subjects.
3D representations of the ONH was captured with Topcon OCT-2000 from one eye of each of totally 18 subjects with early stage primary open angle glaucoma. Altogether, 3 volumes were captured at two occasions within 3 months and PIMD was semi-automatically segmented in each volume in 500 equally spaced angular segments distributed over 2Pi in the frontal plane, around the manually identified center of the ONH.
Plots of the angular distribution of PIMD for all subject revealed specific low frequency overlaid with higher intermediate frequencies, seemingly specific for each subject and high frequencies that appeared similar for all subjects. A fast Fourier transform of the angular PIMD revealed a high to low frequency content ratio, ([1;40] cycles/2Pi)/([>40;80] cycles/2Pi) = 0.33, consistent for all segmentations of PIMD-2Pi. The rotational displacent of angular PIMD in the frontal plane among segmentations, volumes and occasions was determined with cross-correlation. Then, all PIMD-2Pi were rotationally phase adjusted in the frontal plane over segments, volumes and occasions. Phase adjustments required were found to be [-28;62], [-38,67], and [-39;21] Pi/500 radians for segments, volumes and occasions, respectively. Finally, the rotation of PIMD-2Pi was adjusted to a standard rotation. This allows comparison of angular segments of PIMD-2Pi between visits.
Angular PIMD of the ONH in the frontal plane is enough subject specific to to allow angular adjustment of PIMD-2Pi between occasions. Angular adjustment between occasions opens the possibility to compare PIMD averaged over a specific angular segment corresponding to an ONH notch in a glaucoma patient with high precision without calibrating the rotation of PIMD-2Pi to retinal structures.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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