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MB Mellem Kairala, AE Elsner, SA Burns, RB Simmons; Polarimetric Analysis of the Peripapillary Hyperpigmentation in Glaucoma Patients . Invest. Ophthalmol. Vis. Sci. 2002;43(13):245.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the deeper layers of the peripapillary region in glaucomatous eyes, using a novel image processing technique applied to data from polarimetry. Method: Ten patients with clinically detectable peripapillary hyperpigmentation in one or both eyes (6 females, 4 males, mean age = 56 yr) were tested. Visual acuity was better than 20/60 (ametropia < 6 diopters) and IOP was <25 mm Hg. Exclusion criteria were diabetic retinopathy, AMD, and eye trauma or surgery - except for cataract extraction. Five patients had glaucomatous visual field loss, and 5 were Glaucoma Suspects. All patients underwent scanning laser polarimetry (GDx, LDT, San Diego, CA) and stereo color fundus photography. Each GDx series has 20 images, from 2 detectors, differing in illumination polarization. Custom software (MatLab, Mathworks, Inc.) computed images by separating light returning from the retina into 3 components: 2 that retain polarization information (random vs. parallel) and 1 that is depolarized and consists of multiply scattered light from the deeper layers. We computed the area and location by quadrant for hyperpigmentation in the color images, considering an average distance from the optic disc border of 570 µm. To determine whether the software could be useful for detecting small regions of peripapillary change, one patient with atrophy ≷ 30,000 µm2 was excluded from the statistics. We calculated the difference in grayscale for on vs. off pigment and Michaelson contrast in the 3 computed images and R, G, and B channels of the color images. Results: The mean area of hyperpigmentation as measured in color photos was 2.15±1.96 % of the peripapillary region sampled. Peripapillary pigment was distributed as follows: Temporal=162 ± 154, Superior 59 ± 149, Inferior 88 ± 101, and Nasal=0 µm2. The grayscale values were significantly different for on vs. off pigment only for the depolarized light images (p=0.014), and not for the other 2 GDx computed images, or the R, G, or B images from the color slides. Michaelson contrasts were significantly different only for depolarized images (-0.16 ± 0.20, p=0.005) and for the Blue channel (-0.07 ± 0.010, p=0.046). Conclusion: The increased scattering measured in association with peripapillary hyperpigmentation suggests that there is increased tissue disorder at these locations, and not merely absorption changes due to melanin. Polarimetric analysis of images provides additional information concerning the peripapillary region, and is potentially useful in the study of pathophysiology of glaucoma.
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