Scanning Laser Polarimetry Images Research Articles

Henle fiber layer phase retardation changes associated with age-related macular degeneration.

To quantify and compare phase retardation amplitude and regularity associated with the Henle fiber layer (HFL) between nonexudative AMD patients and age-matched controls using scanning laser polarimetry (SLP) imaging. A scanning laser polarimeter was used to collect 15 × 15° macular-centered images in 25 patients with nonexudative AMD and 25 age-matched controls. Raw image data were used to compute macular phase retardation maps associated with the HFL. Consecutive, annular regions of interest from 0.5 to 3.0° eccentricity, centered on the fovea, were used to generate intensity profiles from phase retardation data and analyzed with two complementary techniques: a normalized second harmonic frequency (2f) of the fast Fourier Transform (FFT) analysis and a curve fitting analysis using a 2f sine function. Paired t-tests were used to compare the normalized 2f FFT magnitude at each eccentricity between the two groups, the eccentricity that yielded the maximum normalized 2f FFT between paired individuals across the two groups, and curve fitting RMS error at each eccentricity between the two groups. Normalized 2f FFT components were lower in the AMD group at each eccentricity, with no difference between the two groups in the maximum normalized 2f FFT component eccentricity. The root-mean-square (RMS) error from curve fitting was significantly higher in the AMD group. Phase retardation changes in the central macula indicate loss and/or structural alterations to central cone photoreceptors in nonexudative AMD patients. Scanning laser polarimetry imaging is a noninvasive method for quantifying cone photoreceptor changes associated with central macular disease.

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.

Event-based progression detection strategies using scanning laser polarimetry images of the human retina

Monitoring glaucoma patients and ensuring optimal treatment requires accurate and precise detection of progression. Many glaucomatous progression detection strategies may be formulated for Scanning Laser Polarimetry (SLP) data of the local nerve fiber thickness. In this paper, several strategies, all based on repeated GDx VCC SLP measurements, are tested to identify the optimal one for clinical use. The parameters of the methods were adapted to yield a set specificity of 97.5% on real image series. For a fixed sensitivity of 90%, the minimally detectable loss was subsequently determined for both localized and diffuse loss. Due to the large size of the required data set, a previously described simulation method was used for assessing the minimally detectable loss. The optimal strategy was identified and was based on two baseline visits and two follow-up visits, requiring two-out-of-four positive tests. Its associated minimally detectable loss was 5–12μm, depending on the reproducibility of the measurements.

Quantification of Change in Axonal Birefringence Following Surgical Reduction in Intraocular Pressure

the purpose of this study was to examine the hypothesis that retinal nerve fiber layer (RNFL) birefringence increases following surgical reduction of intraocular pressure (IOP). twenty-six glaucomatous eyes requiring trabeculectomy or drainage implant were enrolled. Optical coherence tomography (OCT), scanning laser polarimetry (SLP), and IOP measurements were performed preoperatively and 3 months postoperatively. The OCT and SLP images were aligned using a new algorithm that aligns the vessels in an OCT image to those in the corresponding SLP reflectance image. The SLP retardance values at the location of the OCT scan circle were then extracted using the OCT scan circle position inferred by the algorithm. Sixty-four corresponding RNFL segments were extracted from SLP and OCT to calculate RNFL birefringence. A significant birefringence change was defined as 1.96 times the weighted test-retest standard deviation in four contiguous segments. preoperative IOP (19.3 ± 6.1 mm Hg) was significantly (P < .001) lower than postoperative IOP (10.4 ± 3.7 mm Hg). Average birefringence magnitude did not change (P = .19) postoperatively. Localized birefringence magnitude increased significantly in 6 (23%) eyes and decreased significantly in 7 (27%) eyes. in this cohort, variable changes in localized birefringence were observed following surgical reduction of IOP.

Scanning laser polarimetry with variable corneal compensation in migraine patients

This study aimed to compare scanning laser polarimetry measurements of retinal nerve fibre layer (RNFL) thickness in eyes of migraine patients with those in eyes of age-matched, healthy subjects. The study was designed as an observational, prospective, cross-sectional study. It included 57 eyes of 57 patients with migraine with or without aura according to the criteria of the International Headache Society and 44 eyes of 44 age-matched healthy controls. Scanning laser polarimetry images were obtained using a commercial GDx VCC system (Version 5.3.1; Laser Diagnostic Technologies, Inc.). At each sitting, three sets of GDx VCC measurements were acquired for each patient and used in the analysis. Image acquisition was performed in undilated eyes in all subjects. The mean ± standard deviation RNFL average thickness parameter in the migraine subjects was significantly lower than in the control group, at 50.4 ± 4.8 μm versus 54.7 ± 3.4 μm, respectively (p < 0.0001). However, there were no differences between migraine subjects and controls in mean RNFL thickness in superior and inferior areas. In the migraine group the mean migraine disability assessment (MIDAS) score was 34.3 ± 15.3 and the mean number of attacks per year was 17.1 ± 6.9 (range 6-28). The mean RNFL average thickness parameter was significantly correlated with MIDAS score (r = - 0.86, p < 0.0001) and frequency of attacks (r = - 0.86, p < 0.0001). The mean RNFL average thickness parameter was found to be thinner in migraine patients. In addition, we found a strong correlation between migraine severity and RNFL average thickness parameters.

Determination of foveal location using scanning laser polarimetry

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.

Analysis of the Origin of Atypical Scanning Laser Polarimetry Patterns by Polarization-Sensitive Optical Coherence Tomography

To analyze the physical origin of atypical scanning laser polarimetry (SLP) patterns. To compare polarization-sensitive optical coherence tomography (PS-OCT) scans to SLP images. To present a method to obtain pseudo-SLP images by PS-OCT that are free of atypical artifacts. Forty-one eyes of healthy subjects, subjects with suspected glaucoma, and patients with glaucoma were imaged by SLP (GDx VCC) and a prototype spectral domain PS-OCT system. The PS-OCT system acquires three-dimensional (3D) datasets of intensity, retardation, and optic axis orientation simultaneously within 3 seconds. B-scans of intensity and retardation and en face maps of retinal nerve fiber layer (RNFL) retardation were derived from the 3D PS-OCT datasets. Results were compared with those obtained by SLP. Twenty-two eyes showed atypical retardation patterns, and 19 eyes showed normal patterns. From the 22 atypical eyes, 15 showed atypical patterns in both imaging modalities, five were atypical only in SLP images, and two were atypical only in PS-OCT images. In most (15 of 22) atypical cases, an increased penetration of the probing beam into the birefringent sclera was identified as the source of atypical patterns. In such cases, the artifacts could be eliminated in PS-OCT images by depth segmentation and exclusion of scleral signals. PS-OCT provides deeper insight into the contribution of different fundus layers to SLP images. Increased light penetration into the sclera can distort SLP retardation patterns of the RNFL.

Longitudinal Measurement Variability of Corneal Birefringence and Retinal Nerve Fiber Layer Thickness in Scanning Laser Polarimetry With Variable Corneal Compensation

To investigate the longitudinal corneal birefringence (corneal polarization axis [CPA] and corneal polarization magnitude [CPM]) variability in scanning laser polarimetry with variable corneal compensation and its effect on retinal nerve fiber layer measurements. Method We analyzed scanning laser polarimetry images obtained every 6 months for 3.2 years in 16 healthy eyes, 38 eyes with ocular hypertension, and 53 eyes with glaucoma in 107 white participants. Differences in values between each intraeye CPA and CPM measurement and the first measurement were used to investigate the variability and any trend with time, and any association with age or diagnosis. We also calculated the percentage of these values within the range of +/-5 degrees or +/-5 nm, respectively. Any effect of corneal birefringence variability on the retinal nerve fiber layer measurements was also evaluated. The CPA and CPM measurement variability showed no trend with time and did not differ between diagnostic groups. It did not appear to be affected by age. With more than 90% of the CPA and CPM measurement variability within the range of +/-5 degrees or +/-5 nm, no significant effect on the retinal nerve fiber layer measurements was observed. The CPA and CPM measurement variability did not differ between groups, showed no trend over time, was independent of subject age, and did not seem to systematically affect retinal nerve fiber layer reproducibility.

Comparison between confocal scanning laser tomography, scanning laser polarimetry and optical coherence tomography on the ability to detect localised retinal nerve fibre layer defects in glaucoma patients

Background/aim:To compare the ability of confocal scanning laser tomography (CSLT), scanning laser polarimetry (SLP) and optical coherence tomography (OCT) in recognising localised retinal nerve fibre layer (RNFL) defects.Methods:51 eyes from...

Detection of Glaucoma Using Scanning Laser Polarimetry with Enhanced Corneal Compensation

To evaluate and compare the diagnostic accuracies for glaucoma detection of scanning laser polarimetry (SLP) with enhanced corneal compensation (GDx ECC) and variable corneal compensation (GDx VCC; both by Carl Zeiss Meditec, Dublin, CA), according to different levels of disease severity and presence of atypical retardation patterns. The study included 102 eyes of 68 patients with glaucoma and 94 eyes of 55 normal subjects. All patients underwent SLP imaging with ECC and VCC methods on the same day. Severity of disease was based on the AGIS (Advanced Glaucoma Intervention Study) visual field score. An ROC regression model was fitted to evaluate the influence of disease severity and atypical retardation patterns (typical scan score [TSS]) on the diagnostic performance of the SLP parameters for both methods. GDx ECC performed significantly better than GDx VCC in glaucoma detection in patients with more severe atypical retardation patterns. For average disease severity and arbitrarily chosen TSS values of 20, 50, 70, and 100, the ROC curve areas for GDx ECC were 0.910, 0.935, 0.948, and 0.964. Corresponding values for GDx VCC were 0.684, 0.850, 0.920, and 0.975. For lower values of TSS and lower AGIS scores, GDx ECC performed significantly better than GDx VCC. GDx ECC performed significantly better than VCC for diagnosing glaucoma in patients with more severe atypical patterns of retardation and at earlier stages of disease.

Modeling of scanning laser polarimetry images of the human retina for progression detection of glaucoma

The development of methods to detect slowly progressing diseases is often hampered by the time-consuming acquisition of a sufficiently large data set. In this paper, a method is presented to model the change in images acquired by scanning laser polarimetry, for the detection of glaucomatous progression. The model is based on image series of 23 healthy eyes and incorporates colored noise, incomplete cornea compensation and masking by the retinal blood vessels. Additionally, two methods for detecting progression, taking either one or two follow-up visits into account, are discussed and tested on these simulated images. Both methods are based on Student's t-tests, morphological operations and anisotropic filtering. The images simulated by the model are visually pleasing, show corresponding statistical properties to the real images and are used to optimize the detection methods. The results show that detecting progression based on two follow-up visits greatly improves the sensitivity without adversely affecting the specificity.

Normative Retardation Data Corrected For the Corneal Polarization Axis With Scanning Laser Polarimetry

To evaluate the distribution of retinal nerve fiber layer thickness measurements in normal eyes corrected for corneal polarization axis (CPA). Complete ocular examination, standard automated perimetry, peripapillary and macular scanning laser polarimetry imaging, and CPA measurements were performed in normal eyes. A noninvasive device mounted on a slit lamp that incorporated two crossed linear polarizers and an optical retarder to measure the slow axis of corneal birefringence was constructed. One eye per patient was enrolled. Exclusion criteria consisted of visual acuity of less than 20/40, a refractive error exceeding +/- 5.0 diopter sphere, 2.0 diopter cylinder, or both, previous intraocular surgery, or ocular disease except cataract. According to scanning laser polarimetry, peripapillary retardation parameters within 90% normal limits were recorded as "normal," parameters outside 95% normal limits were recorded as "abnormal," and parameters between 90% and 95% limits were recorded as "borderline." Fifty-one eyes of 51 subjects (14 men, 37 women) were enrolled (mean age, 51 +/- 17 years). Prediction limits (+/- 2 standard deviation outside of regression line) were calculated for 14 peripapillary retardation parameters. The prediction limits of the average thickness of the retinal nerve fiber layer (microm) were reduced 35% by correction of the CPA; for ellipse average (microm), the limits were reduced 33%. Sixteen of 51 normal eyes (31%) had at least one abnormal retardation parameter, and among these 16 eyes there was a bimodal distribution of CPA values (0 degrees to 20 degrees nasally downward, 60 degrees to 80 degrees nasally downward). Correction for CPA reduces the variance of normal retardation measurements. Normal eyes with a CPA of 0 degrees to 20 degrees nasally downward and 60 degrees to 80 degrees nasally downward were characterized by "abnormal" summary retardation parameters as interby scanning laser polarimetry.

Scanning laser polarimetry and detection of progression after optic disc hemorrhage in patients with glaucoma.

To examine retinal nerve fiber layer changes with scanning laser polarimetry (SLP) in the eyes of patients with glaucoma and optic disc hemorrhage. Automated perimetry and SLP were performed in 17 eyes of 17 patients identified prospectively with optic disc hemorrhage. Criteria for visual field progression were based on decreased sensitivity seen at 3 adjacent points on the total deviation plot. Progression on SLP images was defined as a 15% or more decrease in the average thickness of the affected quadrant (superior or inferior), a 25% or more reduction in the affected quadrant ratio, an increase in the nerve fiber analyzer number of 10 or more (GDx Nerve Fiber Analyzer; Laser Diagnostic Technologies), or any change on Serial Analysis of the SLP images. Visual field progression and SLP image progression. The mean follow-up was 31 months (minimum, 12 months). Of the 17 eyes, 10 (59%) had visual field progression. No significant change was seen on SLP images for either the total group or the group with visual field progression. Five eyes (29%) showed progression on SLP images, 3 of which also showed visual field progression. Ten eyes showed progression on SLP images that was not confirmed on subsequent imaging. In eyes with visual field progression after optic disc hemorrhage, a significant change in the SLP image was not seen. Fluctuation of SLP results in patients with glaucoma necessitates confirmation of progression seen on SLP images.

Correction for corneal polarization axis improves the discriminating power of scanning laser polarimetry

PURPOSE: Corneal polarization axis (CPA) has been reported to affect retardation measurements obtained with scanning laser polarimetry (SLP). The purpose of this investigation was to prospectively determine whether correction for CPA improves the discriminating power of SLP for detection of mild-to-moderate glaucoma.DESIGN: Cross-sectional analysis of normal and glaucomatous eyes.METHODS: We constructed a noninvasive slit-lamp-mounted device incorporating two crossed linear polarizers and an optical retarder to measure the slow axis of corneal polarization. Complete ocular examination, standard automated perimetry, SLP imaging, and CPA measurements were performed on normal and glaucomatous eyes. One eye/subject was enrolled; if both eyes of a patient were eligible for the study, the right eye was selected. For each of the 13 SLP parameters, logistic regression was used to determine if including CPA in the model influenced the ability to discriminate between normal and glaucomatous eyes.RESULTS: Forty-three normal eyes (average visual field mean defect, −0.53 ± 1.4 dB) and 33 glaucomatous eyes (average visual field mean defect, −5.93 ± 6.5 dB) were enrolled. CPA was significantly correlated with summary retardation parameters (average thickness and integral values) in normal (r = 0.72–0.83, P < .001 for all values) and glaucomatous eyes (r = 0.43–0.62, P = .013 to < .001). Including CPA in the model improved the ability to discriminate between normal and glaucomatous eyes for five retardation parameters quantifying retinal nerve fiber layer (RNFL) thickness (range of P values: 0.045–0.001). For inferior average thickness, area under the receiver operating characteristic (ROC) curve increased significantly (P = .002) from 0.70 to 0.78 after accounting for CPA; with a sensitivity set at 80% specificity improved from 33% to 72%. Correlations between visual field corrected pattern standard deviation and average thickness, ellipse average, superior average, and inferior average significantly increased (range of P values, .018–.001) after adjustment for CPA (r = −0.35 and −0.45, −0.38 and −0.47, −0.46 and −0.57, and −0.42 and −0.49, respectively).CONCLUSIONS: Correction for CPA significantly increases the correlation between retinal nerve fiber layer structural damage and visual function and significantly improves the discriminating power of SLP for detection of mild-to-moderate glaucoma.