Enhanced Corneal Compensation Research Articles

Detecting glaucomatous progression using GDx with variable and enhanced corneal compensation using Guided Progression Analysis

ObjectiveTo compare detection of glaucoma progression with scanning laser polarimetry using two methods for corneal compensation.MethodsNormal, glaucoma suspects and glaucoma patients with 36 months' follow-up meeting the eligibility criteria were...

Rates of Progressive Retinal Nerve Fiber Layer Loss in Glaucoma Measured by Scanning Laser Polarimetry

To evaluate rates of change measured with scanning laser polarimetry with enhanced corneal compensation (GDx ECC) and compare them to those measured using the variable corneal compensation (GDx VCC) method in a cohort of glaucoma patients and individuals suspected of having the disease followed over time. Observational cohort study. The study included 213 eyes of 213 patients with an average follow-up time of 4.5 years. Images were obtained annually with the GDx ECC and VCC, along with optic disc stereophotographs and standard automated perimetry (SAP) visual fields. Progression was determined by the Guided Progression Analysis software for SAP and by masked assessment of stereophotographs by expert graders. Joint linear mixed-effects models were used to evaluate rates of change in GDx measurements and their relationship with disease progression. Thirty-three patients (15%) showed progression over time on visual fields and/or stereophotographs. Mean rates of average retinal nerve fiber layer (RNFL) thickness change measured by the GDx ECC were significantly different in progressors versus nonprogressors (-1.24 microm/year vs -0.34 microm/year; P < .001). The area under the ROC curve for discriminating progressors from nonprogressors was significantly higher for rates of change measured by ECC compared to VCC (0.89 vs 0.65; P < .001). Rates of RNFL change detected by the GDx ECC were significantly greater in eyes with progressive glaucoma compared to eyes with stable disease. Also, the ECC performed significantly better than the VCC for detection of change, suggesting that it could improve longitudinal evaluation of the RNFL with scanning laser polarimetry.

Diffuse Glaucomatous Structural and Functional Damage in the Hemifield Without Significant Pattern Loss

To compare the retinal nerve fiber layer (RNFL) thickness and retinal sensitivity in the normal visual hemifield of glaucomatous eyes with localized visual field loss with those of normal eyes and eyes with suspected glaucoma, and to evaluate the relationship between RNFL atrophy and glaucoma severity. One randomly selected eye of each subject underwent standard automated perimetry, stereoscopic photography, scanning laser polarimetry with enhanced corneal compensation, and time-domain and spectral-domain optical coherence tomography (OCT). Mean retinal sensitivity values were calculated in the normal standard automated perimetry hemifield of the glaucoma group and randomly selected hemifields in the normal and suspected glaucoma groups. The mean RNFL thickness values corresponding to the normal hemifield were calculated. Glaucoma severity was judged using standard automated perimetry pattern standard deviation and the Heidelberg retina tomograph-derived linear cup-disc ratio. Fifty subjects were enrolled in each group. Mean RNFL thickness in the normal hemifield obtained using spectral-domain OCT, time-domain OCT, and scanning laser polarimetry with enhanced corneal compensation was significantly (P <or= .01) thinner in the glaucoma group compared with the normal and suspected glaucoma groups. Mean retinal sensitivity in the normal hemifield was significantly (P < .001) reduced in the glaucoma group compared with the normal and suspected glaucoma groups. The Heidelberg retina tomograph-derived cup-disc ratio was significantly correlated with mean RNFL thickness in the normal hemifield obtained using spectral-domain OCT, time-domain OCT, and scanning laser polarimetry with enhanced corneal compensation (P <or= .01). Diffuse RNFL atrophy and retinal sensitivity loss exist in glaucomatous eyes with localized standard automated perimetry deficits. Glaucomatous damage affects both structure and function in a linear proportion.

Relationship Between Pattern Electroretinogram, Standard Automated Perimetry, and Optic Nerve Structural Assessments

To examine the relationship between retinal ganglion cell function measured using pattern electroretinogram optimized for glaucoma screening (PERGLA), retinal nerve fiber layer (RNFL) thickness, and optic nerve head topography. Twenty-nine normal, 28 glaucoma, and 37 glaucoma suspect volunteers were enrolled. All participants were age similar. One randomly selected eye underwent complete eye examination, standard automated perimetry (SAP), scanning laser polarimetry with enhanced corneal compensation (GDxECC), optical coherence tomography, Heidelberg retina tomograph (HRT), and PERGLA measurements. PERGLA amplitude (microV) was converted to dB for comparison with SAP mean deviation (MD) and pattern SD. The correlation between PERGLA amplitude in dB and the average of sensitivity values for 16 central test locations of SAP were calculated. Analysis of variance, Pearson and Spearman rank correlations, coefficient of variation, and intraclass correlation coefficients were calculated. PERGLA amplitude in glaucomatous eyes was significantly lower than normal eyes (0.47+/-0.20 vs. 0.70+/-0.28 microV, P<0.001) but not glaucoma suspects (0.54+/-0.21 microV, P=0.84). PERGLA amplitude was inversely correlated with age (r=-0.31, P=0.002). PERGLA amplitude (in dB) was associated with the sensitivity values of the SAP central 16 test locations (r=0.40, P<0001) across the entire cohort, GDxECC superior RNFL thickness (r=0.38, P<0.001), and HRT Moorfields regression analysis classification (rho=-0.34, P=0.001). The coefficient of variation and intraclass correlation coefficients were 14.5% and 0.89 for PERGLA amplitude, 2.4% and 0.98 for optical coherence tomography average RNFL, 2.2% and 0.97 for GDxECC temporal superior nasal inferior temporal average, and 6.3% and 0.94 for HRT rim area. Retinal ganglion cell function measured using PERGLA is reduced in glaucoma and demonstrates modest correlations with central SAP sensitivity values and structural measures of optic nerve topography and RNFL thickness.

Glaukomdiagnostik mittels Scanning-Laser-Polarimetrie

Scanning laser polarimetry (SLP) is another technology for early glaucoma diagnosis. This technique (represented in the GDx from Carl Zeiss Meditec, Jena, Germany) is based on polarimetry and measures the retinal nerve fiber layer (RNFL) thickness. Compared with previous instruments without customized corneal compensation, the variable corneal compensation technology enables improved differentiation between glaucoma and healthy eyes. Limitations are the atypical birefringence patterns that exist in some eyes, showing false high RNFL values. The newest software uses enhanced corneal compensation (ECC) technology to avoid these atypical patterns and to improve glaucoma diagnosis. Advantages of SLP include independence from drawing a contour line and a reference plane. Follow-up using SLP is limited, but with the use of the new ECC technology, trend and event analyses are possible. Long-term studies will determine the effectiveness of this method.

Predictors of atypical birefringence pattern in scanning laser polarimetry

Aim:To evaluate predictors of atypical birefringence patterns (ABP) observed in scanning laser polarimetry.Methods:A total of 179 eyes from 82 normal subjects and 97 glaucoma patients were included. The retinal nerve...

The Relationship between Intraocular Pressure and Progressive Retinal Nerve Fiber Layer Loss in Glaucoma

To evaluate the relationship between intraocular pressure (IOP) and progressive retinal nerve fiber layer (RNFL) loss, as measured by scanning laser polarimetry with enhanced corneal compensation (GDx ECC), in a cohort of glaucoma patients and individuals suspected of having the disease followed over time. Observational cohort study. The study included 344 eyes of 204 patients recruited from the Diagnostic Innovations in Glaucoma Study (DIGS). There were 98 eyes (28%) with a diagnosis of glaucoma and 246 (72%) were considered glaucoma suspects at baseline. Images were obtained annually with the GDx ECC scanning laser polarimeter, along with stereophotographs and SAP. The study included a total of 1211 GDx ECC visits with an average of 3.5 visits per eye. Progression was determined by the Guided Progression Analysis software for SAP and by masked assessment of stereophotographs performed by expert graders. Random coefficient models were used to evaluate the relationship between IOP and RNFL thickness measurements over time in progressors and nonprogressors. Models were adjusted for baseline diagnosis and central corneal thickness. For all 344 eyes, the overall rate of change for the GDx ECC average thickness at an average IOP of 17 mmHg was -0.25 microm per year (P = 0.002). Each 1-mmHg higher IOP was associated with an additional loss of 0.05 microm per year of RNFL (P = 0.001). Twenty-nine eyes (8%) showed progression on SAP and/or optic disc stereophotographs. These eyes had a significantly higher rate of RNFL change (-0.95 microm/year) than nonprogressors (-0.17 microm/year; P = 0.001). For progressors, each 1-mmHg higher IOP was associated with an additional loss of 0.13 microm per year of RNFL. Higher levels of IOP during follow-up were significantly related to higher rates of progressive RNFL loss detected by the GDx ECC. These findings suggest that the GDx ECC may be helpful in monitoring progression and estimating rates of change in patients with glaucoma or suspected of having the disease. Also, they may contribute to a better understanding of the relationship between IOP and structural deterioration in glaucoma. Proprietary or commercial disclosure may be found after the references.

Comparison of Quantitative Imaging Devices and Subjective Optic Nerve Head Assessment by General Ophthalmologists to Differentiate Normal From Glaucomatous Eyes

To compare the ability of subjective assessment of optic nerve head (ONH) and retinal nerve fiber layer (RNFL) by general ophthalmologists and by a glaucoma expert with objective measurements by optical coherence tomography (Stratus OCT, Carl Zeiss Meditec Inc), confocal scanning laser ophthalmoscope (HRT III; Heidelberg Engineering, Heidelberg, Germany), and scanning laser polarimetry (GDx enhanced corneal compensation; Carl Zeiss Meditec Inc, Dublin, CA) in discriminating glaucomatous and normal eyes. Sixty-one glaucomatous and 57 normal eyes of 118 subjects were included in the study. Three independent general ophthalmologists and 1 glaucoma expert evaluated ONH stereophotographs. Receiver operating characteristic curves were constructed for each imaging technique and sensitivity at fixed specificity was estimated. Comparisons of areas under these curves (aROCs) and agreement (k) were determined between stereophoto grading and best parameter from each technique. Best parameter from each technique showed larger aROC (Stratus OCT RNFL=0.92; Stratus OCT ONH vertical integrated area=0.86; Stratus OCT macular thickness=0.82; GDx enhanced corneal compensation=0.91; HRT3 global cup-to-disc area ratio=0.83; HRT3 glaucoma probability score numeric score=0.83) compared with stereophotograph grading by general ophthalmologists (0.80) in separating glaucomatous and normal eyes. Glaucoma expert stereophoto grading provided equal or larger aROC (0.92) than best parameter of each computerized imaging device. Stereophoto evaluated by a glaucoma expert showed better agreement with best parameter of each quantitative imaging technique in classifying eyes either as glaucomatous or normal compared with stereophoto grading by general ophthalmologists. The combination of subjective assessment of the optic disc by general ophthalmologists with RNFL objective parameters improved identification of glaucoma patients in a larger proportion than the combination of these objective parameters with subjective assessment of the optic disc by a glaucoma expert (29.5% vs. 19.7%, respectively). Diagnostic ability of all imaging techniques showed better performance than subjective assessment of the ONH by general ophthalmologists, but not by a glaucoma expert. Objective RNFL measurements may provide improvement in glaucoma detection when combined with subjective assessment of the optic disc by general ophthalmologists or by a glaucoma expert.

Atypical retardation pattern in measurements of scanning laser polarimetry and its relating factors

To assess the prevalence of atypical retardation pattern (ARP) in scanning laser polarimetry (SLP) with variable corneal compensation (VCC) and enhanced corneal compensation (ECC), and to evaluate the factors relating to typical scan score (TSS). Measurements of SLP-VCC, SLP-ECC, and the Humphrey field analyzer (HFA) were performed in 105 normal subjects and 82 open-angle glaucoma (OAG) patients. ARP was defined as an SLP image with TSS<80. Prevalence of ARP with SLP-VCC was 13.3 and 14.6% in normal and OAG eyes, respectively, and that with SLP-ECC (2.9% and 1.2%) was lower than SLP-VCC (P<0.009). TSS with SLP-VCC was significantly correlated with age (partial correlation coefficient (PCC)=-0.22, P=0.003) and refractive error (PCC=0.26, P<0.001) after adjusting for each other. TSS with SLP-ECC was significantly correlated with neither age nor refractive error (PCC=-0.02, P=0.788; PCC=0.10, P=0.177, respectively). In OAG eyes, mean deviation (MD) of HFA was significantly correlated with TSS with SLP-VCC and SLP-ECC (PCC=0.35, P=0.001; PCC=0.23, P=0.039, respectively). In SLP-VCC, MD was significantly correlated with retinal nerve fibre layer (RNFL) thickness only after excluding eyes with ARP (P<0.001). ARP in SLP-VCC measurements was found in more than 10% of normal or glaucomatous eyes, and TSS was significantly lower in older subjects, more myopic eyes, or eyes with more advanced glaucomatous damage. The presence of ARP disturbs the accuracy of RNFL thickness measurement by SLP-VCC. In SLP-ECC measurements, prevalence of ARP was considerably lower and TSS was not affected by age or refractive error, suggesting the advantages of ECC in clinical practices.

Retinal nerve fibre layer assessment in myopic glaucomatous eyes: comparison of GDx variable corneal compensation with GDx enhanced corneal compensation

Aim:To compare the results of scanning laser polarimetry (GDx) with variable corneal compensation (VCC) and enhanced corneal compensation (ECC) when applied to myopic glaucomatous eyes.Methods:Forty glaucoma eyes with moderate myopia...

Relationship between retinal nerve fibre layer measurements and retinal sensitivity by scanning laser polarimetry with variable and enhanced corneal compensation

Aim:To evaluate the relationship between retinal sensitivity and the retinal nerve fibre layer (RNFL) measurements by scanning laser polarimetry (SLP) with variable corneal compensation (VCC) and enhanced corneal compensation (ECC)...

Retinal Nerve Fiber Layer Measurement Repeatability in Scanning Laser Polarimetry With Enhanced Corneal Compensation

To investigate the measurement repeatability of the various standard retinal nerve fiber layer (RNFL) parameters in scanning laser polarimetry (SLP) with enhanced corneal compensation (ECC, released for investigational use on the commercially available GDx with variable corneal compensation, Carl Zeiss Meditec Inc, Dublin, CA) in healthy eyes, eyes with ocular hypertension (OHT), and glaucomatous eyes. Cross-sectional observational study. Sixteen healthy subjects, 32 subjects with OHT, and 35 patients with primary open-angle glaucoma. Eighty-three eyes of eighty-three white participants were imaged with SLP ECC 3 times on a same day. We determined the intraeye RNFL measurement repeatability. Intraeye within-subject standard deviation (Sw), repeatability coefficient, and the 2-way mixed intraclass correlation coefficient for various standard RNFL parameters in SLP ECC. The repeatability of the RNFL measurements was generally good. In glaucomatous eyes, the Sw and repeatability coefficient for the nerve fiber indicator and temporal-superior-nasal-inferior-temporal average were statistically significantly higher than in healthy eyes and eyes with OHT. In each group, the intraclass correlation coefficient values were generally similar across the parameters, except for the intereye symmetry. The Sw values for various parameters were generally considerably less than 9% of the measurement spectrum. RNFL measurements by SLP ECC had, in general, a good measurement repeatability, although some parameters seemed to be less stable in glaucomatous eyes than in healthy eyes and eyes with OHT. SLP ECC may therefore probably be employed for the detection of glaucomatous progression.

New developments in scanning laser polarimetry for glaucoma

Scanning laser polarimetry is a technique that is used to evaluate the thickness of the retinal nerve fiber layer. It has been shown to have a high accuracy for diagnosing glaucoma. In a subset of eyes, atypical retardation patterns may be present that do not match the expected retinal nerve fiber layer appearance. This review summarizes recent advances made to reduce the frequency and severity of these patterns. In addition, recent progress in the development of algorithms for detecting progression is discussed. A new measurement algorithm--enhanced corneal compensation--has been developed to improve the instrument's signal-to-noise ratio. Enhanced corneal compensation has been shown to improve the accuracy of scanning laser polarimetry for diagnosing glaucoma. In addition, enhanced corneal compensation improves the relationship between standard automated perimetry and scanning laser polarimetry measurements. Furthermore, research is being done on detecting progression in glaucoma. Recently, a method for simulating progression has been proposed, thereby diminishing the need for long-term studies to validate numerous measurement algorithms. With enhanced corneal compensation, the diagnostic accuracy of scanning laser polarimetry has been further improved for glaucoma. Newly developed algorithms for detecting any progressive retinal nerve fiber layer thinning await clinical validation.

Scanning Laser Polarimetry with Enhanced Corneal Compensation for Detection of Axonal Loss in Band Atrophy of the Optic Nerve

To compare the abilities of scanning laser polarimetry (SLP) with enhanced corneal compensation (ECC) and variable corneal compensation (VCC) modes for detection of retinal nerve fiber layer (RNFL) loss in eyes with band atrophy (BA) of the optic nerve. Cross-sectional study. Thirty-seven eyes from 37 patients with BA and temporal visual field defect from chiasmal compression and 40 eyes from 40 healthy subjects were studied. Subjects underwent standard automated perimetry and RNFL measurements using an SLP device equipped with VCC and ECC. Receiver operating characteristic (ROC) curves were calculated for each parameter. Pearson correlation coefficients were obtained to evaluate the relationship between RNFL thickness parameters and severity of visual field loss, as assessed by the temporal mean defect. All RNFL thickness parameters were significantly lower in eyes with BA compared with normal eyes with both compensation modes. However, no statistically significant differences were observed in the areas under the ROC curves for the different parameters between GDx VCC and ECC (Carl Zeiss Meditec, Inc, Dublin, California, USA). Structure-function relationships also were similar for both compensation modes. No significant differences were found between the diagnostic accuracy of GDx ECC and that of VCC for detection of BA of the optic nerve. The use of GDx ECC does not seem to provide a better evaluation of RNFL loss on the temporal and nasal sectors of the peripapillary retina in subjects with BA of the optic nerve.

Scanning Laser Polarimetry With Enhanced Corneal Compensation in Patients With Open-angle Glaucoma

To compare the retinal nerve fiber layer thickness (RNFLT) parameters obtained with newly introduced GDx with enhanced corneal compensation (ECC) and those with GDx with variable corneal compensation (VCC) and to evaluate their reproducibility and the correspondence with visual field damage (VFD) in total or sectorized fields in association with refractive errors in open-angle glaucoma (OAG) patients. Measurement reproducibility was assessed in 30 normal and 30 OAG eyes. Correlation between the RNFLT parameters and the corresponding VFD was evaluated in 58 OAG eyes. All parameters of both GDx VCC and ECC showed high intraclass correlation coefficients among the repeated measurements (0.89 to 0.99), suggesting good reproducibility. All RNFLT parameters were significantly correlated between VCC and ECC (intraclass correlation coefficient=0.58-0.92, P<0.001) though they were significantly different. In OAG eyes, correlation between temporal, superior, nasal, inferior, temporal average and mean deviation of VFD was similar in both algorithms (Rs=0.58 and 0.53, P<0.001). When the OAG eyes were subgrouped by refractive error at -5 D, the correlation was significant for both ECC and VCC in the lower myopic group (>-5 D) (Rs=0.71 and 0.74, P<0.0001) but was significant only for ECC in the higher myopic group (<or=-5 D) (ECC: Rs=0.44, P=0.016, VCC: Rs=0.19, P=0.309). In all 58 OAG eyes, significant correlation between the sectorized VFD and the corresponding RNFLT was found in the superior arcuate, inferior arcuate, and inferior para-arcuate areas for both VCC and ECC in the sector analysis (P<0.01), whereas the correlation was significant only for ECC (Rs=0.46, P<0.001) but not for VCC (Rs=0.30, P=0.024) in the superior para-arcuate. The results of GDx ECC were well correlated with those of VCC and had good reproducibility equivalent to that of VCC. Introduction of the ECC algorithm should improve the correspondence with VFD at least in moderate to high myopic OAG patients.

Relationship between Scanning Laser Polarimetry with Enhanced Corneal Compensation and with Variable Corneal Compensation

PurposeTo evaluate the structure-function relationships between retinal sensitivity measured by Humphrey visual field analyzer (HVFA) and the retinal nerve fiber layer (RNFL) thickness measured by scanning laser polarimetry (SLP) with variable corneal compensation (VCC) and enhanced corneal compensation (ECC) in glaucomatous and healthy eyes.MethodsFifty-three eyes with an atypical birefringence pattern (ABP) based on SLP-VCC (28 glaucomatous eyes and 25 normal healthy eyes) were enrolled in this cross-sectional study. RNFL thickness was measured by both VCC and ECC techniques, and the visual field was examined by HVFA with 24-2 full-threshold program. The relationships between RNFL measurements in superior and inferior sectors and corresponding retinal mean sensitivity were sought globally and regionally with linear regression analysis in each group. Coefficients of the determination were calculated and compared between VCC and ECC techniques.ResultsIn eyes with ABP, R2 values for the association between SLP parameters and retinal sensitivity were 0.06-0.16 with VCC, whereas they were 0.21-0.48 with ECC. The association of RNFL thickness with retinal sensitivity was significantly better with ECC than with VCC in 5 out of 8 regression models between SLP parameters and HVF parameters (P<0.05).ConclusionsThe strength of the structure-function association was higher with ECC than with VCC in eyes with ABP, which suggests that the ECC algorithm is a better approach for evaluating the structure-function relationship in eyes with ABP.

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.

Diagnostic Accuracy of Scanning Laser Polarimetry with Enhanced versus Variable Corneal Compensation

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 > or =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 > or =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.

Structure-Function Relationship Is Stronger with Enhanced Corneal Compensation than with Variable Corneal Compensation in Scanning Laser Polarimetry

To compare the structure-function relationship between peripapillary retinal nerve fiber layer (RNFL) retardation, measured with scanning laser polarimetry (SLP) with both enhanced and variable corneal compensation (ECC [enhanced corneal compensation] and VCC [variable corneal compensation], respectively; features of the GDx Nerve Fiber Analyzer; Carl Zeiss Meditec, Inc., Dublin, CA), and visual field (VF) sensitivity, measured with standard automated perimetry (SAP) in normal and glaucomatous eyes and the effect of marked atypical birefringence patterns (ABPs) on this relationship. Thirty-three healthy subjects, and 68 patients with primary open-angle glaucoma (POAG) took part in the study. ECC and VCC images were taken in one randomly selected eye of each subject. VF tests were also obtained in the same eyes. The structure-function relationship was assessed in six peripapillary sectors and their matching VF areas and was reassessed after eliminating eyes with marked ABPs. Correlations (Spearman's correlation coefficients, r(s)) in the structure-function relationship were generally stronger in images taken with ECC than in those taken with VCC. With ECC, the relationship was significantly more curvilinear when VF sensitivity was expressed in the standard decibel scale and more linear when VF sensitivity was expressed in an antilog scale than with VCC. When eyes with marked ABP images were removed from the analysis, the structure-function relationship with VCC improved, and no statistically significantly differences were found in the relationships between VCC and ECC. The structure-function relationship between RNFL retardation and SAP VF sensitivity was stronger in images obtained with the GDx ECC than with the GDx VCC (Carl Zeiss Meditec, Inc., Dublin, CA). ABPs, which appeared more markedly with VCC than with ECC, weakened the structure-function relationship.

Retinal Nerve Fiber Layer Thickness and Visual Sensitivity Using Scanning Laser Polarimetry with Variable and Enhanced Corneal Compensation

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) < or = 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.