Impact of diabetic retinopathy on quantitative retinal nerve fiber layer measurement and glaucoma screening

PURPOSE: To investigate the impact of diabetic retinopathy on quantitative retinal nerve fiber layer (RNFL) assessment and diagnostic power for glaucoma by scanning laser polarimetry (GDx-VCC) and optical coherence tomography (StratusOCT). METHODS: The individual RNFL parameters of GDx and OCT were obtained for 170 eyes (one eye from each of 170 subjects [45 healthy, 47 glaucoma, 40 diabetes, and 38 glaucoma with diabetes]) and were compared among the four groups. Diabetic eyes had mild to moderate nonproliferative diabetic retinopathy (NPDR) without maculopathy. In glaucomatous eyes with or without diabetes, the ability to discriminate glaucoma was assessed by the areas under the receiver operating characteristic curves (AUROCs) and the sensitivities at more than 80% and 90% of specificities for each technique. RESULTS: Using GDx-VCC, significant differences (P < 0.05) in RNFL measurement parameters were found for all comparisons except those between glaucomatous eyes with diabetes and without diabetes. StratusOCT parameters did not detect significant differences between age-matched healthy and diabetic eyes. Among the parameters included, the nerve fiber indicator (NFI) of GDx-VCC and the inferior quadrant thickness (IQT) of StratusOCT had the largest AUROCs and sensitivities at specificities greater than 80%: NFI (0.912, 86%) and IQT (0.902, 85%) in glaucomatous eyes with diabetes; NFI (0.935, 92%) and IQT (0.921, 91%) in simple glaucomatous eyes. CONCLUSIONS: Mild to moderate NPDR causes a quantitative discrepancy in RNFL measurements between GDx-VCC and StratusOCT in simple diabetic eyes. However, mild to moderate glaucomatous optic neuropathy can be highly discriminated by the two imaging devices in eyes with diabetic retinopathy.     

The relationship between optical coherence tomography and scanning laser polarimetry measurements in glaucoma

PURPOSE: To investigate the relationship between optical coherence tomography (OCT) and scanning laser polarimetry (SLP) in measuring peripapillary retinal nerve fiber layer (RNFL) thickness in glaucomatous eyes. METHODS: Fifty glaucomatous eyes were evaluated in this study. Evaluations were analyzed two ways. First, parameters of the Stratus OCT (average thickness, superior/inferior average) and GDx VCC (TSNIT average, nerve fiber indicator (NFI), superior/inferior average) were correlated using the Pearson's correlation coefficient (r). Secondly, comparison (r) of these parameters was completed using the mean deviation (MD) of visual field defect. RESULTS: The following parameters were found to be significantly correlated (P < 0.005). TSNIT average/average thickness (r = 0.673), NFI/average thickness (r = -0.742), superior average (r = 0.841), and inferior average (r = 0.736). In the correlation analysis using the severity of visual field defect, all these parameters had statistically meaningful correlations (P < 0.005). CONCLUSIONS: GDx VCC and Stratus OCT are highly correlated in glaucomatous eyes. Therefore, peripapillary RNFL thickness measured by Stratus OCT and GDx VCC may be equally helpful in the diagnosis of glaucoma.     

Scanning laser polarimetry with variable corneal compensation and optical coherence tomography in normal and glaucomatous eyes

PURPOSE: To evaluate the relationship between visual function and retinal nerve fiber layer (RNFL) measurements obtained with scanning laser polarimetry with variable corneal compensation (SLP-VCC) and optical coherence tomography (OCT). DESIGN: Cross-sectional analysis of normal and glaucomatous eyes in a tertiary care academic referral practice. METHODS: A commercial GDx nerve fiber analyzer was modified to enable the measurement of corneal polarization axis and magnitude so that compensation for corneal birefringence was eye specific. Complete examination, SLP with fixed corneal compensation (FCC) and variable corneal compensation (VCC), optical coherence tomography (OCT) imaging of the peripapillary RNFL, and automated achromatic perimetry were performed in all subjects. Exclusion criteria were visual acuity less than 20/40, diseases other than glaucoma, and unreliable perimetry. RESULTS: Fifty-nine patients (59 eyes; 29 normal, 30 glaucomatous) were enrolled (mean age, 56.7 +/- 20.3 years, range, 20-91). All eyes with glaucoma had associated visual field loss (average mean defect, -8.4 +/- 5.8 dB). Using SLP-FCC, nine of 12 retardation parameters (75%) were significantly less in glaucomatous eyes. Using SLP-VCC, 11of 12 retardation parameters (92%) were significantly less in glaucomatous eyes. Multiple regression models constructed for each retardation parameter with visual field demonstrated that the following VCC parameters were statistically significant whereas FCC parameters were not: ellipse average (FCC, P =.28, VCC, P =.001), superior average (FCC, P =.38, VCC, P <.001), inferior average (FCC, P =.10, VCC, P =.008), average thickness (FCC, P =.30, VCC, P =.031), and superior integral (FCC, P =.43, VCC, P =.001). Similar results were obtained for multiple regression models constructed with OCT-derived RNFL thickness: ellipse average (FCC, P =.99, VCC, P =.002), superior average (FCC, P =.90, VCC, P <.001), inferior average (FCC, P =.61, VCC, P =.007), and superior integral (FCC, P =.92, VCC, P <.001). CONCLUSIONS: Compared with fixed compensation, mean-based SLP parameters generated with SLP-VCC have greater correlation with visual function and RNFL thickness assessments obtained with OCT.     

Comparison between GDx VCC scanning laser polarimetry and Stratus OCT optical coherence tomography in the diagnosis of chronic glaucoma

PURPOSE: To compare the abilities of scanning laser polarimetry with the variable corneal compensator (GDx VCC) with those of optical coherence tomography (Stratus OCT) in discriminating between healthy and early-to-moderate perimetric glaucomatous eyes. METHODS: A total of 95 glaucomatous patients (mean deviation - 3.7 +/- 3.0 dB, pattern standard deviation 4.5 +/- 2.7 dB) and 62 control subjects underwent imaging by the GDx VCC and Stratus OCT using both optic nerve head (ONH) and retinal nerve fibre layer (RNFL) scan protocols. One eye per patient was considered. Sensitivity at > or = 90% specificity and area under the receiver operating characteristic curve (AROC) were calculated for each GDx VCC and Stratus OCT index. RESULTS: The largest AROCs with Stratus OCT were associated with cup : disc area ratio (0.88) for ONH scan indices, and with average thickness (0.84) for RNFL scan indices. The nerve fibre indicator provided the greatest AROC for the GDx VCC indices (0.85). CONCLUSIONS: Both the GDx VCC and Stratus OCT instruments were shown to be useful in the detection of glaucomatous damage. The best performing indices for the GDx VCC and Stratus OCT with both ONH and RNFL scans gave similar AROCs, showing a moderate sensitivity in early-to-moderate glaucoma patients.     

Relevance vector machine and support vector machine classifier analysis of scanning laser polarimetry retinal nerve fiber layer measurements

PURPOSE: To classify healthy and glaucomatous eyes using relevance vector machine (RVM) and support vector machine (SVM) learning classifiers trained on retinal nerve fiber layer (RNFL) thickness measurements obtained by scanning laser polarimetry (SLP). METHODS: Seventy-two eyes of 72 healthy control subjects (average age = 64.3 +/- 8.8 years, visual field mean deviation = -0.71 +/- 1.2 dB) and 92 eyes of 92 patients with glaucoma (average age = 66.9 +/- 8.9 years, visual field mean deviation = -5.32 +/- 4.0 dB) were imaged with SLP with variable corneal compensation (GDx VCC; Laser Diagnostic Technologies, San Diego, CA). RVM and SVM learning classifiers were trained and tested on SLP-determined RNFL thickness measurements from 14 standard parameters and 64 sectors (approximately 5.6 degrees each) obtained in the circumpapillary area under the instrument-defined measurement ellipse (total 78 parameters). Ten-fold cross-validation was used to train and test RVM and SVM classifiers on unique subsets of the full 164-eye data set and areas under the receiver operating characteristic (AUROC) curve for the classification of eyes in the test set were generated. AUROC curve results from RVM and SVM were compared to those for 14 SLP software-generated global and regional RNFL thickness parameters. Also reported was the AUROC curve for the GDx VCC software-generated nerve fiber indicator (NFI). RESULTS: The AUROC curves for RVM and SVM were 0.90 and 0.91, respectively, and increased to 0.93 and 0.94 when the training sets were optimized with sequential forward and backward selection (resulting in reduced dimensional data sets). AUROC curves for optimized RVM and SVM were significantly larger than those for all individual SLP parameters. The AUROC curve for the NFI was 0.87. CONCLUSIONS: Results from RVM and SVM trained on SLP RNFL thickness measurements are similar and provide accurate classification of glaucomatous and healthy eyes. RVM may be preferable to SVM, because it provides a Bayesian-derived probability of glaucoma as an output. These results suggest that these machine learning classifiers show good potential for glaucoma diagnosis.     

Scanning laser polarimetry with enhanced corneal compensation for detection of axonal loss in band atrophy of the optic nerve

PURPOSE: 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. DESIGN: Cross-sectional study. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Preperimetric glaucoma assessment with scanning laser polarimetry (GDx VCC): analysis of retinal nerve fiber layer by sectors

PURPOSE: To evaluate the capability of the GDx VCC nerve fiber analyzer to detect preperimetric glaucoma across 12 retinal nerve fiber layer (RNFL) peripapillary sectors. METHODS: Data were obtained in a cross-sectional, hospital clinic-based study; 699 eyes from 699 glaucoma suspects were enrolled in this protocol. All subjects underwent ophthalmologic examination, static automated perimetry [Humphrey 24-2 Swedish interactive threshold algorithm (SITA) Standard], optic nerve stereoscopic photographs, red-free digital RNFL photographs and GDx VCC examination. Group S included 283 normal eyes and 39 preperimetric glaucoma eyes with RNFL superior or diffuse defects in the fiber layer photographs. Group I included 324 normal subjects and 24 with preperimetric glaucoma eyes with RNFL inferior or diffuse defects in fiber layer photographs. RESULTS: Mean values of the area under the curve (AUC) for receiver operating characteristic analysis for inferior average (Inf Avg), temporal-superior-nasal-inferior temporal average (TSNIT Avg), superior average (Sup Avg), and the nerve fiber indicator were significantly less in the eyes with RNFL defects than the control group compared with the AUC for thickness at hour 12 and at hour 6 calculated from the RNFL sector density. The AUC for receiver operating characteristic analysis of the new parameters improved by 12% with respect to the best GDx VCC standard values. CONCLUSIONS: Our results confirm that the 12 sector divisions of the GDx VCC have better diagnostic reliability in preperimetric glaucoma, and are able to improve the discrimination capability between normal and early damaged RNFLs.     

Relación entre la perimetría automatizada convencional y los parámetros de la capa de fibras nerviosas de la retina obtenidos con la polarimetría láser

PurposeTo determine the relationship between the structural parameters of the retinal nerve fiber layer (RNFL) obtained by using the scanning laser polarimetry with variable corneal compensation (GDx VCC) and the results of standard automated perimetry (SAP), in normal, ocular hypertensive, preperimetric glaucomas and glaucoma subjects.MethodsA total of 423 eyes of 423 consecutive subjects were prospectively included in the study and classified depending on the basal intraocular pressure, optic nerve head appearance and SAP results into four groups: 87 normal eyes, 192 ocular hypertensive eyes, 70 preperimetric glaucomas and 74 glaucomatous eyes. Pearson's correlation coefficients, between mean deviation (MD), pattern standard deviation, number of points altered in each quadrant, and number of points altered at different probability levels of SAP and structural parameters of RNFL obtained by using GDx VCC, were calculated in the different diagnostic groups. In the glaucoma group correlations between the 52 points tested by 24-2 SITA standard and GDx parameters were also calculated. Regression curves were plotted for the strongest correlations.ResultsWeak or non-significant correlations were found in the normal, ocular hypertensive and preperimetric glaucoma groups. However, the glaucoma group presented weak to moderate correlations between several GDx VCC parameters and the SAP variables analysed. The strongest correlation was observed between the standard deviation TSNIT and the MD (0.460).ConclusionsRNFL parameters measured with the GDx VCC presented weak to moderate correlations with the visual field indices and the number of altered points in the glaucoma group.     

Optic disk and nerve fiber layer imaging to detect glaucoma

PURPOSE: To compare optic disk and retinal nerve fiber layer (RNFL) imaging methods to discriminate eyes with early glaucoma from normal eyes. DESIGN: Retrospective, cross-sectional study. METHODS: In a tertiary care academic glaucoma center, 92 eyes of 92 subjects (46 with early perimetric open-angle glaucoma and 46 controls) were studied. Diagnostic performance of optical coherence tomography (StratusOCT; Carl Zeiss Meditec, Dublin, California, USA), scanning laser polarimetry (GDx VCC; Laser Diagnostic Technologies, San Diego, California, USA), confocal laser ophthalmoscopy (Heidelberg Retinal Tomograph [HRT] III; Heidelberg Engineering GmbH, Heidelberg, Germany), and qualitative assessment of stereoscopic optic disk photographs were compared. Outcome measures were areas under receiver operator characteristic curves (AUCs) and sensitivities at fixed specificities. Classification and regression tree (CART) analysis was used to evaluate combinations of quantitative parameters. RESULTS: The average (+/- standard deviation) visual field mean deviation for glaucomatous eyes was -4.0 +/- 2.5 dB (decibels). Parameters with largest AUCs (+/- standard error) were: average RNFL thickness for StratusOCT (0.96 +/- 0.02), nerve fiber indicator for GDx VCC (0.92 +/- 0.03), Frederick S. Mikelberg (FSM) discriminant function for HRT III (0.91 +/- 0.03), and 0.97 +/- 0.02 for disk photograph evaluation. At 95% specificity, sensitivity of disk photograph evaluation (90%) was greater than GDx VCC (P = .05) and HRT III (P = .002) results, but not significantly different than those of StratusOCT (P > .05). The combination of StratusOCT average RNFL thickness and HRT III cup-to-disk area with CART produced a sensitivity of 91% and specificity of 96%. CONCLUSIONS: StratusOCT, GDx VCC, and HRT III performed as well as, but not better than, qualitative evaluation of optic disk stereophotographs for detection of early perimetric glaucoma. The combination of StratusOCT average RNFL thickness and HRT III cup-to-disk area ratio provided a high diagnostic precision.     

Comparison of retinal nerve fibre layer thickness and visual field loss between different glaucoma groups

BACKGROUND/AIMS: Scanning laser polarimetry (SLP) uses a confocal scanning laser ophthalmoscope with an integrated polarimeter to evaluate the thickness of the retinal nerve fibre layer (RNFL). The aim of this study was to verify the ability of the SLP to detect differences in RNFL thickness between normal and glaucomatous eyes and between glaucomatous eyes subdivided in groups by the severity of visual field damage. METHODS: This was a cross sectional retrospective study. The charts of 40 healthy subjects and 68 glaucoma patients who underwent complete ophthalmological examination, optic disc stereophotography, peripapillary, and macular SLP imaging were reviewed. The right eye of subjects eligible for the study was enrolled. Only eyes with SLP examinations indicating a minimised effect of anterior segment birefringence based on macular image were included. The ability of retardation parameters to discriminate between healthy and glaucomatous eyes was evaluated. Based on visual field loss, glaucoma patients were subdivided in three subgroups (early, moderate, and severe). RNFL thickness between healthy control group and glaucoma subgroups was compared. RNFL thickness and visual field loss correlation was evaluated. RESULTS: There was a significant difference in superior and inferior maximum RNFL thickness between normal and glaucomatous eyes (p<0.001). With these two parameters, the area under receiver operator characteristic curve was 0.75 and 0.74, respectively. Superior and inferior RNFL thickness was significantly different between healthy control group and all glaucoma subgroups (p<0.001) and between glaucoma subgroups (p<0.05), except for early and moderate glaucoma subgroups (p>0.05). Linear regression showed a weak correlation between RNFL thickness and visual field loss. CONCLUSION: These results suggest that once visual field loss is established, smaller reductions in the RNFL thickness detected by SLP are necessary for a given reduction of mean defect value.     

Comparative study of retinal nerve fiber layer measurement by StratusOCT and GDx VCC, I: correlation analysis in glaucoma

PURPOSE: To evaluate the average and regional correlations of retinal nerve fiber layer (RNFL) thickness measured by StratusOCT (optical coherence tomography; Carl Zeiss Meditec, Inc., Dublin, CA) and GDx VCC (Laser Diagnostic Technologies, Inc., San Diego, CA). METHODS: Eighty-nine subjects-27 normal, 21 with suspected glaucoma, and 41 with glaucoma-were included in this cross-sectional study. The total average and the mean 12-clock-hour RNFL thickness were measured with the StratusOCT and GDx VCC. The discriminating powers of the two techniques for detection of suspected glaucoma and glaucoma were compared by the area under the receiver operating characteristic curves (AUC). Correspondence between StratusOCT and GDx VCC RNFL measurements in each clock hour was examined with linear regression analysis. RESULTS: The average RNFL thickness in the normal group was measured at 101.38 +/- 7.73 and 55.26 +/- 4.32 mum by StratusOCT and GDx VCC, respectively. Both nerve fiber analyzers demonstrated a double-hump pattern in the RNFL profiles with maximum RNFL thickness located at the inferotemporal and superotemporal clock hours by the StratusOCT and the superior and inferior clock hours by the GDx VCC. Significant differences were found in the total average and the individual clock-hour RNFL thickness between StratusOCT and GDx VCC RNFL measurements in both the normal and the suspected glaucoma/glaucoma groups. The GDx VCC superior RNFL measurement demonstrated the largest AUC (0.909) for detection of suspected glaucoma and glaucoma, whereas the largest AUC (0.901) in StratusOCT was found over the inferotemporal clock hour. The total average RNFL thickness measured with StratusOCT and GDx VCC correlated highly with each other (r = 0.852). When the respective clock-hour RNFL measurements were compared, the correlation coefficient varied with the position around the optic nerve head, with the highest correlation found over the superior and inferior clock hours (11, 12, 1, 6, and 7 o'clock; all with r > 0.700) and the lowest located at the temporal clock hour (9 o'clock; r = 0.277). CONCLUSIONS: Despite the substantial differences in the values of RNFL thickness, significant correlations were observed between StratusOCT and GDx VCC RNFL measurements. The variations of the correlation coefficient around the optic nerve head suggested that GDx VCC RNFL measurement does not have a fixed relationship with that of StratusOCT and the use of site-specific RNFL birefringences may improve the estimation of RNFL thickness by the GDx VCC. Nevertheless, the GDx VCC was found to be as effective as the StratusOCT in detecting the loss of RNFL in glaucoma.     

糖尿病患者视网膜神经纤维层厚度的测定及相关因素分析

目的用GDx神经纤维分析仪（GDxVCC）测定眼底表现正常的2型糖尿病患者双眼视网膜神经纤维层（RNFL）,了解有无早期RNFL变薄,分析危险因素与RNFL厚度的相关性。方法收集42例2型糖尿病患者相关病例资料。眼科常规检查后,用GDxVCC仪强化角膜补偿（ECC）和可变角膜补偿（VCC）测定双眼颞侧、上方、鼻侧、下方、颞侧曲线平均（TSNIT平均）、上方平均、下方平均、TSNIT标准差和神经纤维指数（NFI）5项值。分析糖尿病组的ECC、VCC5项检测值在诊断能力上的差异,即受试工作者曲线下面积（ROC）;糖尿病组5项检测值的最大值、最小值和均数;血糖水平与糖尿病组检测值的相关性;糖尿病组中ECC与VCC5项检测值的差异比较;糖尿病组与对照组5个检测指标的差异;建立年龄与NFI值的线性回归方程。结果NFI值的ROC最大;ECC和VCC的NFI值均约为20;血糖与RNFL延迟量间无明显相关性。糖尿病组ECC与VCC5项指标的NFI值的差异无统计学意义（t=1．787,P=0．072）;年龄对糖尿病患者NFI值的影响远远大于其对正常人NFI值的影响。结论NFI值为反映RNFL厚度的主要参考指标,年龄对糖尿病患者RNFL厚度存在较大影响;眼底表现正常的糖尿病患者存在早期RNFL变薄;ECC和VCC模式检测的NFI值无明显差异。糖尿病组2个测量模式间TSNIT标准差差异有统计学意义。     

Comparison of the GDx VCC scanning laser polarimeter and the stratus optical coherence tomograph in the detection of band atrophy of the optic nerve

AIM: To compare the ability of scanning laser polarimeter (SLP) with variable corneal compensation (GDx VCC) and optical coherence tomograph (Stratus OCT) to discriminate between eyes with band atrophy (BA) of the optic nerve and healthy eyes. METHODS: The study included 37 eyes with BA and temporal visual field (VF) defects from chiasmal compression, and 29 normal eyes. Subjects underwent standard automated perimetry (SAP) and retinal nerve fibre layer (RNFL) scans using GDx VCC and Stratus OCT. The severity of the VF defects was evaluated by the temporal mean defect (TMD), calculated as the average of 22 values of the temporal total deviation plot on SAP. Receiver operating characteristic (ROC) curves were calculated. Pearson's correlation coefficients were used to evaluate the relationship between RNFL thickness parameters and the TMD. RESULTS: No significant difference was found between the ROC curves areas (AUCs) for the GDx VCC and Stratus OCT with regard to average RNFL thickness (0.98 and 0.99, respectively) and the superior (0.94; 0.95), inferior (0.96; 0.97), and nasal (0.92; 0.96) quadrants. However, the AUC in the temporal quadrant (0.77) was significantly smaller (P<0.001) with GDx VCC than with Stratus OCT (0.98). Lower TMD values were associated with smaller RNFL thickness in most parameters from both equipments. CONCLUSION: Adding VCC resulted in improved performance in SLP when evaluating eyes with BA, and both technologies are sensitive in detecting average, superior, inferior, and nasal quadrant RNFL loss. However, GDx VCC still poorly discriminates RNFL loss in the temporal quadrant when compared with Stratus OCT.     

Fourier analysis of scanning laser polarimetry measurements with variable corneal compensation in glaucoma

PURPOSE: To apply Fourier analysis to the retinal nerve fiber layer (RNFL) thickness measurements obtained with scanning laser polarimetry (SLP), by using variable corneal compensation, and to evaluate the ability of this method to discriminate glaucomatous from normal eyes. METHODS: The study included one eye each of 55 patients with glaucoma and 52 healthy subjects. RNFL thickness measurements were obtained with a modified commercial scanning laser polarimeter (GDx Nerve Fiber Analyzer; Laser Diagnostic Technologies, Inc., San Diego, CA) so that corneal birefringence could be corrected on a subject-specific variable basis. The shape of the RNFL thickness double-hump pattern was analyzed by Fourier analysis of polarimetry data. Fourier coefficients and GDx parameters were compared between the two groups. A linear discriminant function was developed to identify and combine the most useful Fourier coefficients to separate the two groups. Receiver operating characteristic (ROC) curves were obtained for each measurement, and sensitivity values (at fixed specificities) were calculated. RESULTS: The Fourier-based linear discriminant function (LDF Fourier) resulted in a sensitivity of 84% for a specificity set at 92%. For similar specificity, the GDx software-provided parameters had sensitivities ranging from 24% to 69%. The area under ROC curve for the LDF Fourier was 0.949, significantly larger than the ROC curve area for the single best GDx software-provided parameter, superior average (0.870). CONCLUSIONS: The combination of Fourier RNFL thickness measures in an LDF, obtained using SLP with variable corneal compensation, improved the ability to discriminate glaucomatous from healthy eyes, compared with the GDx software-provided parameters.     

Specificity and sensitivity of glaucoma detection in the Japanese population using scanning laser polarimetry.

AIMS: To investigate the usefulness of the scanning laser polarimeter (GDx; GDx Nerve Fiber Analyzer) for glaucoma detection in the Japanese population, and to investigate the difference in the thickness of retinal nerve fibre layer (RNFL) between normal tension glaucoma (NTG) and primary open angle glaucoma (POAG). METHODS: 69 eyes of 69 normal subjects and 115 eyes of 115 chronic open angle glaucoma patients (60 NTG and 55 POAG patients) were studied. The thickness of RNFL was measured with GDx. An eye was diagnosed as glaucomatous, if at least one original GDx variable showed p <5%. The difference in thickness of RNFL between the NTG and POAG groups was then investigated. RESULTS: 46 normal eyes (66.7%) were diagnosed as not glaucomatous (no variables showing p <5%), and 93 glaucomatous eyes (46 NTG and 47 POAG eyes) (80.9%) were diagnosed as glaucomatous. Actual values of average thickness, ellipse average, superior average, and superior integral were significantly lower in the POAG group than those in the NTG group. CONCLUSIONS: New variables which elucidate focal RNFL defects or early changes are needed to improve the moderate detection ability found in this present study. The pattern of the change in RNFL may differ in NTG and POAG groups.     

Comparing glaucomatous optic neuropathy in primary open angle and primary angle closure glaucoma eyes by scanning laser polarimetry-variable corneal compensation

PURPOSE: To study the retinal nerve fiber layer thickness difference between high-tension primary open angle glaucoma (HT-POAG) and primary angle closure glaucoma (PACG) eyes using scanning laser polarimetry-variable corneal compensation (GDx VCC) in Taiwan-Chinese population; to evaluate the usefulness of the GDx VCC for detecting POAG and PACG eyes in Taiwan-Chinese population. PATIENTS AND METHODS: The study comprised 88 early to moderate glaucomatous eyes (one randomly selected eye from 47 HT-POAG patients and 41 PACG patients) and the control group consisted of 45 age-matched eyes from 45 normal individuals. Each subject underwent retinal nerve fiber layer thickness measurement by GDx VCC and Humphrey Field Analyzer visual field testing. Measured GDx VCC parameters were compared among groups. We also calculated the area under the receive operator characteristic (AROC) curve, corresponding sensitivity/specificity and best cut off value for each parameter in differentiating normal from POAG and PACG eyes. RESULTS: There was no significant difference between HT-POAG and PACG eyes in each parameter. The parameter with the best AROC curve for differentiating normal from POAG eye was nerve fiber indicator (AROC, 0.779; sensitivity=57.4%, specificity=100%; best cut off value >27). The parameter with the best AROC curves for differentiating normal from PACG eyes was temporal-superior-nasal-inferior-temporal average (AROC, 0.829; sensitivity=46.3%, specificity=100%, best cut off value <51.7). CONCLUSIONS: There was no significant difference between the HT-POAG and PACG eyes as far as the various parameters were concerned. GDx VCC shows fair discriminating ability in distinguishing normal from POAG and PACG eyes in Taiwan Chinese population.     

Detection of glaucoma using scanning laser polarimetry with enhanced corneal compensation

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Structure-function relationship is stronger with enhanced corneal compensation than with variable corneal compensation in scanning laser polarimetry

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Enhanced imaging algorithm for scanning laser polarimetry with variable corneal compensation

PURPOSE: To describe and investigate a method of improving assessment of retinal nerve fiber layer (RNFL) morphology with scanning laser polarimetry (SLP) with variable corneal compensation (VCC). METHODS: By neutralizing anterior segment birefringence with a variable compensator, the current VCC method allows direct measurement of RNFL retardation. In the new method, enhanced corneal compensation (ECC), the variable compensator was set to introduce a "bias" birefringence. This bias was removed mathematically for each individual pixel to produce the RNFL image. In 177 eyes of healthy subjects, patients with glaucoma, and subjects with ocular hypertension, retardation images were obtained with both VCC and ECC. RESULTS: In the tested eyes, images obtained with ECC showed the expected RNFL appearance better than those obtained with VCC. In addition, the typical scan score, which quantifies the amount of atypia, was higher with ECC than with VCC. The amount of residual anterior segment birefringence dropped significantly with ECC in the various groups. Measurements of peripapillary RNFL retardation showed reduced temporal and nasal values with ECC, whereas superior and inferior values were not significantly different between VCC and ECC. The dynamic range appeared to have increased with ECC. The accuracy of the TSNIT (temporal, superior, nasal, inferior, temporal) average and inferior average for detecting glaucoma was higher with ECC than with VCC. CONCLUSIONS: RNFL morphology may be better assessed with the presented ECC method than with standard VCC. ECC may be implemented in the current VCC systems by means of a software upgrade. It may enhance the clinical utility of the GDx VCC in glaucoma management.     

Correlation between frequency doubling technology perimetry and scanning laser polarimetry in glaucoma suspects and glaucomatous eyes

The aim of this study was to determine the relationship between the frequency doubling technology (FDT) screening algorithm and parapapillary retinal nerve fiber layer (RNFL) thickness in the eyes of glaucoma suspects and patients with open angle glaucoma. FDT C20-1 screening program and a scanning laser polarimetry (SLP) system (GDx-NFA) was used to assess 53 glaucomatous eyes, 53 glaucoma suspects and 36 normal control eyes. In glaucomatous eyes, there were correlations between the FDT the screening algorithm and RNFL retardation values in several polarimetric indices, most significantly "inferior thickness" (r = -0.321, P = 0.029). In the eyes of glaucoma suspects, however, we observed no correlation between the FDT results and RNFL retardation values (r = 0.080, P > 0.05, "inferior thickness"). In glaucomatous eyes, the abnormal scores obtained with FDT screening program correlated negatively with RNFL retardation values, as measured by SLP. Despite poor correlation between the FDT abnormal score and RNFL retardation value in glaucoma suspects, detection of abnormality using the FDT screening protocol may aid in the assessment of early glaucomatous structural damage.