Variable corneal compensation improves discrimination between normal and glaucomatous eyes with the scanning laser polarimeter

doi:10.1016/j.ophtha.2003.05.015

Ophthalmology

Volume 111, Issue 2, February 2004, Pages 259-264

https://doi.org/10.1016/j.ophtha.2003.05.015 Get rights and content

Abstract

Purpose

The presently available scanning laser polarimeter (SLP) has a fixed corneal compensator (FCC) that neutralizes corneal birefringence only in eyes with birefringence that matches the population mode. A prototype variable corneal compensator (VCC) provides neutralization of individual corneal birefringence based on individual macular retardation patterns. The aim of this study was to evaluate the relative ability of the SLP with the FCC and with the VCC to discriminate between normal and glaucomatous eyes.

Design

Prospective, nonrandomized, comparative case series.

Participants

Algorithm-generating set consisting of 56 normal eyes and 55 glaucomatous eyes and an independent data set consisting of 83 normal eyes and 56 glaucomatous eyes.

Testing

Sixteen retardation measurements were obtained with the SLP with the FCC and the VCC from all subjects.

Main outcome measures

Dependency of parameters on age, gender, ethnic origin, and eye side was sought. Logistic regression was used to evaluate how well the various parameters could detect glaucoma. Discriminant functions were generated, and the area under the receiver operating characteristic (ROC) curve was determined.

Results

Discrimination between normal and glaucomatous eyes on the basis of single parameters was significantly better with the VCC than with the FCC for 6 retardation parameters: nasal average (P = 0.0003), superior maximum (P = 0.0003), ellipse average (P = 0.002), average thickness (P = 0.003), superior average (P = 0.010), and inferior average (P = 0.010). Discriminant analysis identified the optimal combination of parameters for the FCC and for the VCC. When the discriminant functions were applied to the independent data set, areas under the ROC curve were 0.84 for the FCC and 0.90 for the VCC (P<0.021). When the discriminant functions were applied to a subset of patients with early visual field loss, areas under the ROC curve were 0.82 for the FCC and 0.90 for the VCC (P<0.016).

Conclusion

Individual correction for corneal birefringence with the VCC significantly improved the ability of the SLP to distinguish between normal and glaucomatous eyes and enabled detection of patients with early glaucoma.

Section snippets

Materials and methods

Algorithms to discriminate between normal and glaucomatous eyes were generated from data derived from patients seen at 3 sites (Glaucoma Division, Jules Stein Eye Institute, Los Angeles; Glaucoma Research Unit, Moorfields Eye Hospital, London; and Bascom Palmer Eye Institute, Palm Beach Gardens, Florida). These algorithms were then tested on an independent data set derived from patients seen at a fourth site (Rotterdam Eye Hospital, Rotterdam, The Netherlands).

Algorithm-generating set

There were no statistically significant differences in gender, eye side, or ethnicity among the study groups, but the normal subjects were significantly younger than the patients with glaucoma. Regression analysis was performed on both FCC and VCC normal data to determine the effect of age on all GDx parameters. Several retardation parameters measured with the VCC had a significant correlation with age. These were ellipse average (P = 0.003), superior average (P = 0.008), inferior average (P =

Discussion

Scanning laser polarimetry provides reproducible, quantitative measurements of the peripapillary RNFL based on its birefringent properties.14, 15 Histologic validation of retardation measurements obtained with SLP has been reported in 2 studies. Weinreb and associates performed RNFL thickness measurements on 2 enucleated monkey eyes with the cornea and lens removed, and a good correlation was found between RNFL thickness and retardation.16 In the second study, with intact primate eyes, Morgan

Acknowledgements

The authors thank Nicholas Reus, PhD, of Rotterdam Eye Hospital; Harmohina Bagga, MD, of Bascom Palmer Eye Institute; and Ed White of Moorfields Eye Hospital for their invaluable assistance with data collection.

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Imaging of the optic nerve and retinal nerve fiber layer: An essential part of glaucoma diagnosis and monitoring
2014, Survey of Ophthalmology
Citation Excerpt :
GDx provides reproducible measurement of RNFL thickness.13,23,63,69 GDx VCC outperforms the earlier iterations of this technology that used fixed corneal compensation in its ability to discriminate between healthy and glaucomatous eyes.12,20,59,62 GDx ECC performs better than VCC in the detection of early glaucoma.36,56
Because glaucomatous damage is irreversible early detection of structural changes in the optic nerve head and retinal nerve fiber layer is imperative for timely diagnosis of glaucoma and monitoring of its progression. Significant improvements in ocular imaging have been made in recent years. Imaging techniques such as optical coherence tomography, scanning laser polarimetry and confocal scanning laser ophthalmoscopy rely on different properties of light to provide objective structural assessment of the optic nerve head, retinal nerve fiber layer and macula. In this review, we discuss the capabilities of these imaging modalities pertinent for diagnosis of glaucoma and detection of progressive glaucomatous damage and provide a review of the current knowledge on the clinical performance of these technologies.
Retinal nerve fiber layer assessment in healthy children using scanning laser polarimetry with variable corneal compensation
2008, Journal of AAPOS
To assess the normative data of the retinal nerve fiber layer (RNFL) thickness in healthy children using the scanning laser polarimeter with variable corneal compensation (GDxVCC).
Of the 186 enrolled white school-aged children, 120 subjects of the mean 12.85 ± 3.0 years (age ± SD) fulfilled inclusion criteria. After complete ophthalmic examination, including GDxVCC, 240 normal eyes were analyzed. Evaluation of RNFL thickness in GDxVCC temporal-superior-nasal-inferior-temporal (TSNIT) parameters was performed, and probability of normality was calculated. The influence of sex and age was investigated.
The mean ± SD values in TSNIT Average, Superior Average, Inferior Average, and TSNIT SD were 58.98 ± 6.92 μm, 72.99 ± 8.97 μm, 71.18 ± 10.92 μm, and 26.30 ± 4.92 μm. The values of 5% probability of normality in the same order were 47.6 μm, 58.2 μm, 53.2 μm, and 18.2 μm. The mean values of Inferior Average and TSNIT SD were greater in left eyes by 1.84 ± 6.6 μm (p = 0.003) and by 3.04 ± 3.8 μm (p < 0.00005), respectively. No correlation to sex and age was found.
RNFL thickness assessed using GDxVCC was greater in children compared with previous published data in healthy adults. The values of Inferior Average and TSNIT SD were significantly greater in left eyes.
Scanning laser polarimetry and confocal scanning laser ophthalmoscopy: technical notes on their use in glaucoma
2008, Progress in Brain Research
Citation Excerpt :
This latest version of the RNFL analyzed is named GDx-VCC (variable corneal compensator), which compensates the individual corneal birefringence hence allowing a good correction of the corneal polarization effect. In this way, a more reliable evaluation of the RNFL thickness can be achieved (Weinreb et al., 2002b; Tannenbaum et al., 2004). Before performing the test, it is necessary to insert patients’ personal and clinical data, such as date of birth, gender, ethnicity, associated systemic disease, and spherical equivalent.
The mere intraocular pressure (IOP) measurement and the visual field (VF) examination do not allow early primary open-angle glaucoma (POAG) diagnosis. At present, the morphological and morphometric analysis of the optic disk is considered very important for an early diagnosis and follow-up of the disease. The recent introduction of laser systems equipped with new polarimetry techniques (GDx) and confocal tomography (HRT) allows an objective, quantitative, and reproducible evaluation of the morphometry and morphology of the optic disk and retinal nerve fiber layer (RNFL). The GDx, scanning laser polarimetry, studies the RNFL. The HRT, confocal scanning laser tomography, examines several optic disk and peripapillar area parameters. These devices allow obtaining objective and quantitative data concerning RNFL and optic nerve head. They represent complementary and important examinations in case of uncertain POAG diagnosis. The correct evaluation of the parameters studied by these techniques and the knowledge of the instruments’ limits are needed for an adequate interpretation of the results obtained.
Diagnostic Accuracy of Scanning Laser Polarimetry with Enhanced versus Variable Corneal Compensation
2007, Ophthalmology
Citation Excerpt :
Scanning laser polarimetry has evolved in recent years. Its successive generations have all been capable of differentiating between healthy and glaucomatous eyes.17–19,31–33 However, ABPs may occur in SLP images.
To compare the diagnostic accuracy of scanning laser polarimetry (SLP) parameters between images taken with enhanced corneal compensation (ECC) and those with variable corneal compensation (VCC) and to explore the effect of atypical birefringence patterns on this accuracy.
Cross-sectional observational study.
Forty-one healthy subjects and 92 patients with primary open-angle glaucoma.
Variable corneal compensation and ECC images were obtained of 1 eye per subject, selected randomly if both eyes were eligible. For both ECC and VCC, the areas under the receiver operating characteristic curves (AUROCs) and the sensitivity at a specificity of ≥95% were calculated per parameter in all eyes. The analyses were reperformed separately in eyes with and without atypical birefringence patterns (ABP) images.
The AUROCs and sensitivities at a specificity of ≥95% for various SLP parameters in all eyes and in eyes without ABP images.
The diagnostic accuracy for most standard parameters (temporal-superior-nasal-inferior-temporal [TSNIT] average, superior average, inferior average, and TSNIT standard deviation) in all eyes was statistically significantly higher with ECC than with VCC, except for the nerve fiber indicator (NFI). When only eyes without ABP were used for the analysis, the diagnostic accuracy of SLP parameters with VCC improved, and the differences in diagnostic accuracy between ECC and VCC for these parameters lost their statistical significance.
Standard SLP parameters (except for the NFI) generally had a higher diagnostic accuracy when eyes were imaged with ECC than with VCC because there were fewer ABP images with ECC than with VCC. Enhanced corneal compensation therefore may be more reliable than VCC for the detection of glaucoma. A future automated classifier, similar to the current NFI, may perform better if it is trained on data obtained with ECC. Clinically, retinal nerve fiber layer images with marked ABP, acquired with either ECC or VCC, should be viewed with caution.
Retinal Nerve Fiber Layer Thickness and Visual Sensitivity Using Scanning Laser Polarimetry with Variable and Enhanced Corneal Compensation
2007, Ophthalmology
To compare the strength of the structure–function association between scanning laser polarimetry-measured retinal nerve fiber layer (RNFL) thickness and visual sensitivity. Two methods of corneal compensation were evaluated, variable corneal compensation (VCC) and enhanced corneal compensation (ECC).
Observational case series.
One hundred twenty-seven glaucoma (repeatable abnormal visual fields [VF] by pattern standard deviation and/or glaucoma hemifield test) or glaucoma suspect (glaucomatous-appearing discs by photograph assessment without field defects) participants in the University of California, San Diego Diagnostic Innovations in Glaucoma Study.
One eye of each participant was imaged using GDx VCC and GDx ECC on the same day. Visual fields tested using the Humphrey Field Analyzer (with Swedish interactive threshold algorithm) were obtained within 6 months of imaging.
The associations (R²) using linear and logarithmic regression between RNFL thicknesses measured in 6 sectors (inferior, inferotemporal, temporal, superotemporal, superior, nasal) with VCC and ECC and VF sensitivities (decibel threshold measurements) measured in 6 corresponding sectors were compared. Comparisons were made using paired t tests on the log-transformed absolute values of regression residuals.
Using GDx VCC, 32 scans had a typical scan score (TSS) ≤ 78 (lowest quartile) and no ECC scans had TSS<86. Most RNFL thickness measurements obtained using GDx VCC were significantly greater than those measured using GDx ECC. Regional structure–function associations (R²) ranged from 0.03 (temporal RNFL) to 0.22 (superotemporal RNFL) for VCC and from 0.01 (temporal RNFL) to 0.26 (superotemporal RNFL) for ECC. Associations generally were slightly stronger for ECC than for VCC, although these differences were only significant for inferotemporal RNFL (R² = 0.19 and 0.11, for ECC and VCC, respectively).
The RNFL thickness associations with VF sensitivity are stronger using ECC compared with VCC, suggesting that ECC provides a better cross-sectional representation of visual function than VCC.
Scanning Laser Polarimetry With Variable and Enhanced Corneal Compensation in Normal and Glaucomatous Eyes
2007, American Journal of Ophthalmology
To investigate whether correction for atypical birefringence pattern (ABP) using scanning laser polarimetry with enhanced corneal compensation (SLP-ECC) reduces the severity of ABP compared with variable corneal compensation (SLP-VCC) and improves the correlation with visual function.
Prospective observational study.
Normal and glaucomatous eyes enrolled from four clinical sites underwent complete examination, automated perimetry, SLP-ECC, and SLP-VCC. Eyes were characterized in three groups based upon the typical scan score (TSS): normal birefringence pattern (NBP) was defined as TSS ≥ 80, mild ABP as TSS 61 to 79, and moderate-severe ABP as TSS ≤ 60. For each of four SLP parameters, the area under the ROC curve (AUROC) was calculated to compare the ability of SLP-ECC and SLP-VCC to discriminate between normal and glaucomatous eyes.
Eighty-four normal volunteers and 45 glaucoma patients were enrolled. Mean TSS was significantly (P < .001) greater using SLP-ECC (98.0 ± 6.6) compared with SLP-VCC (83.4 ± 22.5). The frequency of moderate-severe ABP images was significantly (P < .001, McNemar test) higher using SLP-VCC (18 of 129, 14%) compared with SLP-ECC (one of 129, 0.8%). Two SLP-ECC parameters (temporal superior nasal inferior temporal [TSNIT] average and inferior average) had significantly (P = .01, P < .001) higher correlation (r = .45, r = .50, respectively) with MD compared with SLP-VCC (r = .34, r = .37). Among eyes with moderate-severe ABP (n = 18), inferior average obtained using SLP-ECC had significantly (P = .03) greater AUROC (0.91 ± 0.07) compared with SLP-VCC (0.78 ± 0.11).
SLP-ECC significantly reduces the frequency and severity of ABP compared with SLP-VCC and improves the correlation between RNFL measures and visual function.

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Manuscript no. 220879.

Supported in part by National Institutes of Health grants R01EY12738 (JC) and R01-EY08684 (DSG).

The authors have no financial interest in any device or technique described in this article. Drs Caprioli, Greenfield, and Lemij are members of the Clinical Advisory Board, Laser Diagnostic Technology, San Diego, California.

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Original articleVariable corneal compensation improves discrimination between normal and glaucomatous eyes with the scanning laser polarimeter☆

Abstract

Purpose

Design

Participants

Testing

Main outcome measures

Results

Conclusion

Section snippets

Materials and methods

Algorithm-generating set

Discussion

Acknowledgements

Am J Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

Ophthalmology

Spatially resolved birefringence of the retinal nerve-fiber layer assessed with a retinal laser ellipsometer

Appl Optics

Microtubule contribution to the reflectance of the retinal nerve fiber layer

Invest Ophthalmol Vis Sci

Corneal polarization in the living human eye explained with a biaxial model

J Opt Soc Am A Opt Image Sci

A numerical test of the normal incidence uniaxial model of corneal birefringence

Cornea

Original article
Variable corneal compensation improves discrimination between normal and glaucomatous eyes with the scanning laser polarimeter☆