GDx Variable Corneal Compensation Research Articles

Follow-up of the retinal nerve fiber layer thickness of diabetic patients type 2, as a predisposing factor for glaucoma compared to normal subjects.

PurposeTo evaluate and follow-up the retinal nerve fiber layer (RNFL) thickness in patients with diabetes mellitus type 2 compared to a group of healthy individuals with similar demographic characteristics.Patients and methodsThis is a prospective, noninvasive, observational case series study. For the purposes of the study, 27 eyes of diabetic patients without diabetic retinopathy, 24 eyes of patients with mild retinopathy, and 25 normal age-matched subjects (control group [CG]) were examined. All participants underwent complete ophthalmological examination and imaging with GDx variable corneal compensation scanning laser polarimetry. Follow-up was 2 years for all three groups.ResultsThe mean inferior average was statistically significantly lower in both diabetic groups compared to CG at baseline examination and during follow-up. The nerve fiber indicator (NFI) was higher in both diabetic groups compared to CG, both at baseline examination and during follow-up. The NFI was 21.7±11.9 and 22.0±11.8 for the diabetic group without retinopathy, 20.8±9.6 and 21.9±9.8 for the group with mild retinopathy, and 15.3±5.4 and 15.9±5.5 for the normal subjects, at baseline and 24 months, respectively. There was no statistically significant reduction of the RNFL thickness in all three groups compared to baseline examination.ConclusionThis is the first long-term study documenting the RNFL thickness in diabetic patients in comparison with normal controls. Although the lower RNFL was found thinner in diabetics, the 2-year follow-up showed no significant reduction of RNFL thickness in all groups, indicating that RNFL damage may occur early in diabetic patients.

Correlation in retinal nerve fibre layer thickness in uveitis and healthy eyes using scanning laser polarimetry and optical coherence tomography.

To evaluate the correlation of retinal nerve fibre layer (RNFL) thickness measured using spectral domain optical coherence tomography (SD-OCT) and scanning laser polarimetry (SLP) in uveitic eyes compared with healthy eyes. A descriptive, observational, prospective, consecutive, cross-sectional, controlled, monocentre case series was conducted from May to October 2015. Clinical characteristics, best-corrected visual acuity, intraocular pressure, RNFL thickness measurement with SD-OCT and SLP using GDx variable corneal compensation (GDx VCC) were performed for each patient. An evaluation of anterior chamber inflammation with laser flare-cell meter was also carried out. Correlations between SD-OCT and GDx VCC RNFL measurement were evaluated by linear regression analysis. Fifty-four patients were included and divided into two groups: 50 healthy eyes in 29 patients and 42 uveitic eyes in 25 patients. The mean RNFL thickness was 98.08(±8.42) and 113.21(±20.53) μm in the healthy group and the uveitic group, respectively, when measured with SD-OCT (p<0.001); and 56.43(±5.24) and 58.77(±6.67) μm, respectively, when measured with GDx VCC (p=0.078). There was a strong correlation between total average RNFL thickness measured using SD-OCT and GDX (r=0.48, p<0.001) in healthy eyes but there was no correlation in the uveitic eyes (r=0.2, p=0.19). RNFL thickness was significantly greater when measured using SD-OCT in active uveitis as compared with GDx. There was no correlation between the RNFL thickness measurements obtained using the two techniques in uveitic eyes. The discrepancies between the results suggest that for these patients both techniques should be used in conjunction to obtain an accurate measurement of RNFL. IRB 00008855 Société Française d'Ophtalmologie IRB#1.

Retinal Blood Vessel Distribution Correlates With the Peripapillary Retinal Nerve Fiber Layer Thickness Profile as Measured With GDx VCC and ECC.

Purpose:Aim of the present study was to evaluate whether there is a correlation between retinal blood vessel density (RVD) and the peripapillary retinal nerve fiber layer (RNFL) thickness profile.Methods:RNFL thickness of 106 healthy subjects was measured using scanning laser polarimetry, GDx variable corneal compensation (VCC), and GDx enhanced corneal compensation (ECC). A proprietary software was developed in MATLAB to measure the peripapillary retinal vessels using scanning laser ophthalmoscopy fundus images, centered on the optic disc measured by Cirrus spectral domain optical coherence tomography. The individual retinal vessel positions and thickness values were integrated in a 64-sector RVD profile and intrasubject and intersubject correlations were calculated.Results:The mean R value±SD for intrasubject correlation between RVD and RNFL thickness measured with GDx VCC and GDx ECC was 0.714±0.157 and 0.629±0.140, with 105 of 106 subjects presenting significant correlations. In the intersubject linear regression analysis for GDx VCC, 33 of 64 (52%) sectors presented a significant Pearson correlation coefficient between RNFL thickness and RVD values, with a mean R value of 0.187±0.135 (P<0.05).Conclusions:Peripapillary RNFL thickness profiles correlate with the RVD over 50% of the sectors and might explain up to 26% of the interindividual variance of the peripapillary RNFL thickness values as measured with GDx VCC. To our opinion, taking into account RVD might reduce interindividual variation in peripapillary RNFL thickness profiles measured with scanning laser polarimetry.

Glaucoma diagnostics

Glaucoma diagnostics

African Descent and Glaucoma Evaluation Study

The purpose of the study is to determine the degree of intereye asymmetry of optic disc topography and retinal nerve fiber layer (RNFL) thickness in healthy individuals of African descent (AD) and European descent (ED). Observational, clinical study. Five hundred nineteen healthy individuals (AD, n=262, mean age=44.9 years; ED, n=257, mean age=47.1 years) from the African Descent and Glaucoma Evaluation Study and Diagnostic Innovations in Glaucoma Study were tested using Heidelberg retina romograph (HRT), GDx variable corneal compensation (GDx-VCC), and standard, automated perimetry within 6 months of one another. HRT-II measurements included cup area, cup volume, rim area, and rim volume. GDx-VCC measurements included average RNFL thickness. Intereye asymmetry was calculated as the absolute value of the differences in measurements between the right and left eye. AD participants showed significantly higher median asymmetry in cup volume and rim volume (P<0.001 and 0.033, respectively) compared with ED participants. The effect of race lost significance after adjustment for mean disc area and disc area asymmetry in multivariable models. Axial length asymmetry was not correlated with increased asymmetry in any of this study's asymmetry parameters. Normal ranges of asymmetry for the HRT-II measurements of cup area (up to 0.39 mm), cup volume (up to 0.15 mm), rim area (up to 0.45 mm), and rim volume (up to 0.22 mm) were derived, as were asymmetry ranges for GDx-VCC-measured average RNFL thickness (up to 6.25 μm). The effect of race was no longer significant after adjustment for mean disc area and disc area asymmetry. Individuals with asymmetries with magnitudes greater than those of the normal ranges could be considered as suspicious for glaucoma.

Advances in technology helps in early detection of vision disorders

Advances in technology helps in early detection of vision disorders

Effect of Optic Disc Size and Disease Severity on the Diagnostic Capability of Glaucoma Imaging Technologies in an Indian Population

To evaluate the influence of optic disc size and disease severity on the diagnostic validity of optical coherence tomography (Stratus OCT), scanning laser polarimetry [GDx variable corneal compensator (VCC)], and confocal scanning laser ophthalmoscopy [Heidelberg retina tomograph II (HRT II)] in Indian eyes with glaucoma. Ninety-five normal and 125 glaucoma patients underwent imaging with Stratus OCT, GDx VCC, and HRT II. One eye of each person was randomly selected for analysis. Using disc area determined on HRT II, discs were classified as small (<2 mm), moderate (2 to 3 mm), and large (>3 mm). The parameter with the best sensitivity for each device, at a fixed specificity, was compared for different disc sizes. Logistic marginal regression was used to study the effect of disc size and disease severity (mean deviation on standard automated perimetry) on the diagnostic performance of these imaging devices. At a fixed specificity of 84.2%, the sensitivity of HRT II was significantly different for varying disc sizes (P=0.0004). The sensitivities for dissimilar disc sizes were not significantly different for the GDx VCC (P=0.928) or Stratus OCT (P=0.381). Logistic marginal regression also showed that sensitivity of HRT II increased with increasing disc size, whereas sensitivity of OCT and GDx were independent of the disc size. The sensitivity of all 3 technologies increased with increasing disease severity (decreasing mean deviation). Optic disc size affects the diagnostic capability of HRT II but not that of GDx VCC or Stratus OCT. The sensitivity of all 3 imaging technologies increased with increasing disease severity.

Scanning laser polarimetry in glaucoma suspects: influence of the lens

AbstractPurpose to compare scanning laser polarimetry (GDx) variable corneal compensation (VCC) and enhanced corneal compensation (ECC) in glaucoma suspects divided on the basis of lens conditionsMethods 339 eyes of 182 consecutive patients were selected and submitted to complete ophthalmic evaluation, automated perimetry (HFA 24‐2), scanning laser polarimetry of RNFL with GDx VCC and ECC. Patients were divided into 4 groups if pseudophakic (IOL) or with different lens opacities graded according to LOCS‐III (NO/NC 1, 2 or 3). Morphometric parameters as TSNIT average, superior, inferior, nerve fiber indicator(NFI); quality of the image (Q)and typical scan score(TSS) given by the two GDx algorithms were compared applying Wilkoxon signed‐rank test and Lin’s concordance coefficient. Kruskall‐Wallis test was used to compare the 4 groups on the basis of age, intra‐ocular pressure (IOP), perimetric indices as mean defect (MD) and pattern standard deviation (PSD),TSNIT,NFI,Q and TSSResults IOL group was significantly older, with lower IOP and higher MD as compared to the other groups. ECC gave better quality scans, thinner RNFL and higher NFI as compared to VCC. ECC/VCC outcomes were significantly different and concordance was poor to moderate but slightly better with transparent lens than with cataract (NO/NC3) or IOL. IOL and cataract seemed to affect GDx outcomes especially with VCCConclusion different lens conditions seemed to influence laser polarimetry outcomes particularly with VCC. ECC as compared to VCC gave better quality scans, thinner RNFL, higher NFI and was less influenced by lens condition. ECC could possibly better reproduce RNFL thickness, giving a more reliable model of early glaucomatous neuropathy

Influence of atypical retardation pattern on the peripapillary retinal nerve fibre distribution assessed by scanning laser polarimetry and optical coherence tomography

AimTo investigate the influence of atypical retardation pattern (ARP) on the distribution of peripapillary retinal nerve fibre layer (RNFL) thickness measured with scanning laser polarimetry in healthy individuals and to...

Comparative study of retinal nerve fibre layer measurement by RTVue OCT and GDx VCC

AimTo evaluate the diagnostic performances and correlations of retinal nerve fibre layer (RNFL) thickness measured by RTVue OCT and GDx variable corneal compensation (VCC).MethodsThe total and regional RNFL thickness were...

Evaluation of the retinal nerve fiber layer measurements, after photorefractive keratectomy and laser in situ keratomileusis, using scanning laser polarimetry (GDX VCC)

To evaluate the impact of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK), on retinal nerve fiber layer (RNFL) measurements, by means of scanning laser polarimetry (SLP) GDx VCC (with variable corneal compensation). Two groups of 119 myopic patients each were treated by PRK and LASIK respectively; one eye of each patient was randomly selected for the study. RNFL measurements (around the entire calculation circle) was performed in all eyes 1 day before and 1, 3, 6 and 12 months after treatment by using SLP GDx VCC. Corneal compensation was performed in all eyes preoperatively, and in every examination step postoperatively, in order to neutralize the new corneal birefringence. No statistical differences were found between the PRK and LASIK groups, in all preoperative and postoperative RNFL measurements. Only the p values for CCT and mean K-readings preoperatively were statistically significant. PRK and LASIK do not seem to influence the RNFL measurements at 1st, 3rd, 6th and 12th postoperative months when measured with SLP GDx VCC. The corneal compensation reset is necessary in every step of the examination in order to have reproducible results.

Agreement for Detecting Glaucoma Progression with the GDx Guided Progression Analysis, Automated Perimetry, and Optic Disc Photography

To evaluate the ability of the GDx Variable Corneal Compensation (VCC) Guided Progression Analysis (GPA) software for detecting glaucomatous progression. Observational cohort study. The study included 453 eyes from 252 individuals followed for an average of 46+/-14 months as part of the Diagnostic Innovations in Glaucoma Study. At baseline, 29% of the eyes were classified as glaucomatous, 67% of the eyes were classified as suspects, and 5% of the eyes were classified as healthy. Images were obtained annually with the GDx VCC and analyzed for progression using the Fast Mode of the GDx GPA software. Progression using conventional methods was determined by the GPA software for standard automated achromatic perimetry (SAP) and by masked assessment of optic disc stereophotographs by expert graders. Sensitivity, specificity, and likelihood ratios (LRs) for detection of glaucoma progression using the GDx GPA were calculated with SAP and optic disc stereophotographs used as reference standards. Agreement among the different methods was reported using the AC(1) coefficient. Thirty-four of the 431 glaucoma and glaucoma suspect eyes (8%) showed progression by SAP or optic disc stereophotographs. The GDx GPA detected 17 of these eyes for a sensitivity of 50%. Fourteen eyes showed progression only by the GDx GPA with a specificity of 96%. Positive and negative LRs were 12.5 and 0.5, respectively. None of the healthy eyes showed progression by the GDx GPA, with a specificity of 100% in this group. Inter-method agreement (AC(1) coefficient and 95% confidence intervals) for non-progressing and progressing eyes was 0.96 (0.94-0.97) and 0.44 (0.28-0.61), respectively. The GDx GPA detected glaucoma progression in a significant number of cases showing progression by conventional methods, with high specificity and high positive LRs. Estimates of the accuracy for detecting progression suggest that the GDx GPA could be used to complement clinical evaluation in the detection of longitudinal change in glaucoma.

Correlation of Disc Morphology Quantified on Stereophotographs to Results by Heidelberg Retina Tomograph II, GDx Variable Corneal Compensation, and Visual Field Tests

Quantification of disc morphology by computer-assisted planimetry on stereophotographs and to compare the results with those by other fundus structure imaging devices and visual field tests. Cross-sectional study. Fifteen normal eyes of 15 normal subjects and 69 glaucomatous eyes of 69 open-angle glaucoma patients. Sequential digital stereophotographs of the optic discs were obtained by a nonmydriatic fundus camera. Intraobserver reproducibility for the 3 repeated traces and interobserver reproducibility for the three individual examiners were determined. The obtained results were correlated to those by Heidelberg Retina Tomograph (HRT) II, GDx with variable corneal compensation (VCC) and visual field tests obtained within 2 months of the photography. Optic disc parameters such as disc area, cup area, rim/disc area ratio, vertical cup diameter/disc diameter (Cd/Dd) ratio and rim width/disc diameter (Rw/Dd) ratio at radial arbitrary angles. Interclass correlation coefficients (ICC) and coefficients of variance (CV) for the optic disc parameters and their correlation with HRT II, GDx VCC, and visual field test results. Intra- and interobserver ICC and CV were 0.88 to 0.99, 1.1% to 9.6%, and 0.72 to 0.98, 2.2% to 11.9% for area parameters, 0.81 to 0.92, 2.4% to 4.0% and 0.71 to 0.78, 4.3% to 5.0% for Cd/Dd ratio, and 0.73 to 0.91, 9.2% to 23.0% and 0.65 to 0.82, 16.9% to 27.2% for Rw/Dd ratios, respectively. Significant correlation was seen between disc and cup area and the corresponding parameters by HRT II (r(s) > 0.81; P<0.001), as well as between vertical Cd/Dd ratio and global TSNIT average by GDx VCC and visual field test indices (|r(s)| > 0.51; P<0.001), and between superior and inferior Rw/Dd ratio and their corresponding sectoral HRT II, GDx VCC and visual field test indices (r(s) > 0.31; P<0.006), respectively. Correlation with visual field test indices was comparable among stereophotographs, HRT II, and GDx VCC parameters. Optic disc morphologic parameters quantified on stereophotographs by our software showed satisfactory reproducibility and good correlation with those measured by other fundus structure imaging devices and visual field test results, indicating its clinical usefulness, especially in the mass screening of glaucoma.

Comparison of Shape-based Analysis of Retinal Nerve Fiber Layer Data Obtained From OCT and GDx-VCC

To directly compare in 1 population: (1) the performance of Optical Coherence Tomograph (OCT) and GDx-Variable Corneal Compensator (VCC) when using Wavelet-Fourier Analysis (WFA) and Fast-Fourier Analysis (FFA), (2) the performance of these shape-based and standard metrics, and (3) the shape of the retinal nerve fiber layer (RNFL) temporal, superior, nasal, inferior, temporal (TSNIT) curves obtained by the 2 different devices. RNFL estimates were obtained from 136 eyes of 136 individuals (73 healthy and 63 mild glaucoma). WFA and FFA with and without asymmetry measures were performed on the TSNIT RNFL estimates to identify glaucoma from healthy eyes. Performance of WFA, FFA, and the standard metrics of OCT (Inferior Average) and GDX-VCC (Nerve Fiber Indicator) was evaluated by calculating receiver operating characteristic area. Measurements were obtained at a custom radius (33 to 41 pixels) for GDx-VCC to match the OCT radius (1.73 mm). WFA and FFA shape analysis significantly improved performance of both OCT (0.937) and GDx-VCC (0.913) compared with Inferior Average and Nerve Fiber Indicator (0.852 and 0.833, respectively). With either shape-based or standard metrics, OCT performance was slightly, but not significantly, better than GDx-VCC performance. Comparison of RNFL curves revealed that the GDx-VCC curves were more jagged and the peaks shifted more nasally when compared with the OCT RNFL curves. Performance of both OCT and GDx-VCC devices are improved by shape-based analysis methods. Classification performance was greater when using WFA for the OCT, and greater with FFA for the GDx-VCC. Significant differences between the machines exist in the measured TSNIT thicknesses, possibly because of GDx-VCC's measurements being affected by polarization magnitude varying with angle.

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...

Impact of Atypical Retardation Patterns on Detection of Glaucoma Progression using the GDx with Variable Corneal Compensation

To evaluate the impact of atypical retardation patterns (ARP) on detection of progressive retinal nerve fiber layer (RNFL) loss using scanning laser polarimetry with variable corneal compensation (VCC). Observational cohort study. The study included 377 eyes of 221 patients with a median follow-up of 4.0 years. Images were obtained annually with the GDx VCC (Carl Zeiss Meditec Inc, Dublin, California, USA), 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. The typical scan score (TSS) was used to quantify the presence of ARPs on GDx VCC images. Random coefficients models were used to evaluate the relationship between ARP and RNFL thickness measurements over time. Thirty-eight eyes (10%) showed progression over time on visual fields, stereophotographs, or both. Changes in TSS scores from baseline were significantly associated with changes in RNFL thickness measurements in both progressing and nonprogressing eyes. Each 1-unit increase in TSS score was associated with a 0.19-microm decrease in RNFL thickness measurement (P < .001) over time. ARPs had a significant effect on detection of progressive RNFL loss with the GDx VCC. Eyes with large amounts of atypical patterns, great fluctuations on these patterns over time, or both may show changes in measurements that can appear falsely as glaucomatous progression or can mask true changes in the RNFL.

Thickness of the Retinal Nerve Fibre Layer Estimated With the Scanning Laser Polarimeter in Healthy Children

The scanning laser polarimeter [GDx variable corneal compensation (VCC)] measures the thickness of the retinal nerve fibre layer (RNFL) and has, therefore, a possible potential for the diagnosis and follow-up of glaucoma in children. The aim of the present study is to establish reference values of the RNFL thickness in children. The RNFL thickness was measured with a GDx VCC in 72 children aged 4 to 15 years without ocular diseases. The difference in the temporal-superior-nasal-inferior-temporal (TSNIT) average (TA), superior average (SA), and inferior average (IA) between the boys and the girls was estimated with a t test. A 95% confidence interval (CI) of the TA, SA, and IA was calculated for the whole group and compared with those of 4 previous studies. The reproducibility of the examination was estimated in 10 consecutive children and was expressed as 95% CI of the differences between the repeated measurements. There were no statistically significant differences in the TA, SA, and IA between the boys and girls. The 95% CI for the TA, SA, and IA was 61.1+/-1.5, 73.5+/-2.3, and 73.5+/-2.0 microm, respectively. These values did not overlap with those reported previously in the adult groups, confirming a statistically significant age-related thinning of the RNFL. The 95% CI of the differences between the repeated measurements was -0.4+/-1.4 microm for TA, -1.5+/-3.6 microm for SA, and 1.6+/-3.9 microm for IA, suggesting that the examination was reproducible. The GDx VCC examination is reproducible in children. The present RNFL results should represent useful reference values in the evaluation of pediatric glaucoma.

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...

Atypical Retardation Pattern: Can Performance of Classification be Improved?

(1) To evaluate and compare the classification performance of Wavelet-Fourier analysis (WFA), Fast-Fourier analysis (FFA), and the standard GDx-variable corneal compensator (VCC) output in identifying glaucomatous eyes from a mixed group of healthy and glaucomatous eyes with atypical retardation pattern (ARP). (2) To investigate if classification performance improves when only the superior and inferior quadrants are used for WFA and FFA. (3) To evaluate the classification performance as a function of severity of ARP. Retinal nerve fiber layer (RNFL) estimates were obtained from 445 eyes of 240 individuals. On the basis of typical scan score (TSS), 348 eyes had typical retardation pattern (TRP) and 97 had ARP (78% TRP and 22% ARP). The classification performance of WFA and FFA classifiers was tested using three different ways: (1) Classifiers were trained on the TRP data, and tested on ARP data. (2) Classifiers were trained on TRP and 90% ARP data using 10-fold cross validation technique and tested on ARP data (10%). (3) Classifiers were trained and tested using the ARP data using 10-fold cross validation technique. Sensitivity, specificity, and Receiver Operating Characteristic Curve (ROC) areas were calculated. The classification performance was also assessed for the standard parameters of GDx-VCC. Of the standard GDx-VCC parameters, the nerve fiber indicator (NFI) had the highest ROC area (0.80). Of the shape-based analyses, WFA and FFA of the complete temporal, superior, nasal, inferior, and temporal curve had the highest ROC area (0.85 and 0.82, respectively). The difference in the ROC areas did not reach the statistically significant level (p = 0.07). On eyes with severe ARP (TSS < 60) all metrics performed similarly, but in case of moderate ARP (TSS 60 to 79), the ROC area of WFA and FFA were both greater than that of NFI (the difference was 9% and 7%, respectively). Although the WFA and FFA classification performance was greater than NFI as assessed by ROC area the difference was not statistically significant.

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.