Determination of foveal location using scanning laser polarimetry
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Abstract:
The fovea is the retinal location responsible for our most acute vision. There are several methods used to localize the fovea, but the fovea is not always easily identifiable. Landmarks used to determine the foveal location are variable in normal subjects and localization becomes even more difficult in instances of retinal disease. In normal subjects, the photoreceptor axons that make up the Henle fiber layer are cylindrical and the radial orientation of these fibers is centered on the fovea. The Henle fiber layer exhibits form birefringence, which predictably changes polarized light in scanning laser polarimetry imaging. In this study 3 graders were able to repeatably identify the fovea in 35 normal subjects using near infrared image types with differing polarization content. There was little intra‐grader, inter‐grader, and inter‐image variability in the graded foveal position for 5 of the 6 image types examined, with accuracy sufficient for clinical purposes. This study demonstrates that scanning laser polarimetry imaging can localize the fovea by using structural properties inherent in the central macula.Keywords:
Scanning laser polarimetry
Fovea centralis
Scanning laser polarimetry
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The chronic nature of idiopathic intracranial hypertension (IIH) represents a risk factor for progressive optic nerve damage and structural abnormalities of the retina.We measured the retinal nerve fiber layer (RNFL) thickness in patients followed with the diagnosis of IIH who had no or mild visual impairment to search for possible structural alterations in the retina for diagnostic and prognostic purposes.Case-control prospective study.The study group consisted of 12 women followed and treated with the diagnosis of IIH in our clinic. The selection criteria were the, normal optic nerve, normal visual fields or mild visual field defects (Grade 1-3) by Humphrey perimeter. Randomly assigned, age-matched 12 healthy women were taken as the control group. Retinal nerve fiber layer thickness was evaluated with scanning laser polarimetry and both eyes were studied for each case in both groups.Mann-Whitney U test.The mean ages of the patient and the control groups were 34.58+/-4.2 and 34.42+/-5.7 years respectively (P=0.87). The mean duration of disease was 5.5+/-3 years. Some parameters related to RNFL thickness were found to differ significantly between patients with IIH and control subjects. Namely superior ratio (P=0.007), inferior ratio (P=0.039), superior-nasal ratio (P=0.025), maximum modulation (P=0.01) and symmetry (P=0.006) were lower in the patient group than controls.Scanning laser polarimetry might be a good adjunct for determining possible structural affects of IIH on the retina in patients with no or mild visual impairment.
Scanning laser polarimetry
Nerve fiber
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Purpose: To determine how myopia and peripapillary atrophy (PPA) affect the measurement of retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (OCT) and scanning laser polarimetry (GDx) with variable and enhanced corneal compensation (VCC and ECC).Methods: We measured RNFL thickness in 20 eyes from 20 subjects without glaucoma and with myopic PPA (PPA group) and 20 eyes from 20 normal subjects without PPA (control group) with various scan circle sizes by OCT, GDx-VCC and GDx-ECC.Results: On OCT analysis, the individual clock-hour RNFL thickness of the PPA group was significantly less than that of the control group in the nasal, superior and inferior areas, whereas the thickness was similar in the temporal area where PPA was most commonly seen.On GDx-VCC and GDx-ECC analyses, the individual clock-hour RNFL thickness of the PPA group was similar or less in the nasal, superior and inferior areas than that of the control group, whereas the thickness was greater in the PPA group than in the control group in the temporal area.This RNFL thickness pattern seen with both OCT and GDx measurement was consistent for all the scan circle sizes even though the scan circle was large enough that it did not encompass the PPA area.Conclusions: When measured by OCT and GDx, the thickening of the RNFL in the temporal area was observed in the PPA group.Our results suggest that PPA per se may not be responsible for the temporal thickening of RNFL in myopic eyes with PPA.
Scanning laser polarimetry
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Scanning laser polarimetry
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Scanning laser polarimetry
Nerve fiber
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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.
Scanning laser polarimetry
Fovea centralis
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Purpose: To determine the effect of temporary intraocular pressure (IOP) elevation during laser in situ keratomileusis (LASIK) on retinal nerve fiber layer measurement by scanning laser polarimetry in a clinical trial. Methods: The duration of IOP elevation was recorded during LASIK and scanning laser polarimetry (GDx Retinal Nerve Fiber Analyzer. Laser Diagnostic Technologies, Inc, San Diego, California) measurements were performed in 60 eyes of 30 consecutive patients before and after the LASIK procedure. Results: The mean duration of IOP elevation during LASIK was 27.24.5 seconds. The mean retinal nerve fiber layer (RNFL) thickness measured by scanning laser polarimetry were 73.212.8 m preoperatively, 65.612.7 at postoperative 1 month and 66.09.8 m at postopertive 3 months. The mean postoperative 1 month and 3 months values showed significantly reduced RNFL thickness. But, there was no relationship between the duration of IOP elevation and the amount of nerve fiber layer thickness reduction. (=0.064, p=0.627) Furthermore, there were no interval change between the retardation values of postoperative 1 month and 3 months (p=0.706). Conclusions: There was no relationship between the duration of IOP elevation during LASIK and the postoperative reduction of RNFL thickness measured by scanning laser polarimetry. When using scanning laser polarimetry as a helpful diagnostic and follow-up tool for glaucoma, care should be taken in the interpretation of the result after LASIK procedure. If a comparison is likely to be needed in the future, this image should be obtained after the LASIK procedure to set the postoperative baseline.
Scanning laser polarimetry
LASIK
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Scanning laser polarimetry
Visual field loss
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Scanning laser polarimetry
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