GDx Parameters Research Articles

Optic nerve head and fibre layer imaging for diagnosing glaucoma.

The diagnosis of glaucoma is traditionally based on the finding of optic nerve head (ONH) damage assessed subjectively by ophthalmoscopy or photography or by corresponding damage to the visual field assessed by automated perimetry, or both. Diagnostic assessments are usually required when ophthalmologists or primary eye care professionals find elevated intraocular pressure (IOP) or a suspect appearance of the ONH. Imaging tests such as confocal scanning laser ophthalmoscopy (HRT), optical coherence tomography (OCT) and scanning laser polarimetry (SLP, as used by the GDx instrument), provide an objective measure of the structural changes of retinal nerve fibre layer (RNFL) thickness and ONH parameters occurring in glaucoma. To determine the diagnostic accuracy of HRT, OCT and GDx for diagnosing manifest glaucoma by detecting ONH and RNFL damage. We searched several databases for this review. The most recent searches were on 19 February 2015. We included prospective and retrospective cohort studies and case-control studies that evaluated the accuracy of OCT, HRT or the GDx for diagnosing glaucoma. We excluded population-based screening studies, since we planned to consider studies on self-referred people or participants in whom a risk factor for glaucoma had already been identified in primary care, such as elevated IOP or a family history of glaucoma. We only considered recent commercial versions of the tests: spectral domain OCT, HRT III and GDx VCC or ECC. We adopted standard Cochrane methods. We fitted a hierarchical summary ROC (HSROC) model using the METADAS macro in SAS software. After studies were selected, we decided to use 2 x 2 data at 0.95 specificity or closer in meta-analyses, since this was the most commonly-reported level. We included 106 studies in this review, which analysed 16,260 eyes (8353 cases, 7907 controls) in total. Forty studies (5574 participants) assessed GDx, 18 studies (3550 participants) HRT, and 63 (9390 participants) OCT, with 12 of these studies comparing two or three tests. Regarding study quality, a case-control design in 103 studies raised concerns as it can overestimate accuracy and reduce the applicability of the results to daily practice. Twenty-four studies were sponsored by the manufacturer, and in 15 the potential conflict of interest was unclear.Comparisons made within each test were more reliable than those between tests, as they were mostly based on direct comparisons within each study.The Nerve Fibre Indicator yielded the highest accuracy (estimate, 95% confidence interval (CI)) among GDx parameters (sensitivity: 0.67, 0.55 to 0.77; specificity: 0.94, 0.92 to 0.95). For HRT measures, the Vertical Cup/Disc (C/D) ratio (sensitivity: 0.72, 0.60 to 0.68; specificity: 0.94, 0.92 to 0.95) was no different from other parameters. With OCT, the accuracy of average RNFL retinal thickness was similar to the inferior sector (0.72, 0.65 to 0.77; specificity: 0.93, 0.92 to 0.95) and, in different studies, to the vertical C/D ratio.Comparing the parameters with the highest diagnostic odds ratio (DOR) for each device in a single HSROC model, the performance of GDx, HRT and OCT was remarkably similar. At a sensitivity of 0.70 and a high specificity close to 0.95 as in most of these studies, in 1000 people referred by primary eye care, of whom 200 have manifest glaucoma, such as in those who have already undergone some functional or anatomic testing by optometrists, the best measures of GDx, HRT and OCT would miss about 60 cases out of the 200 patients with glaucoma, and would incorrectly refer 50 out of 800 patients without glaucoma. If prevalence were 5%, e.g. such as in people referred only because of family history of glaucoma, the corresponding figures would be 15 patients missed out of 50 with manifest glaucoma, avoiding referral of about 890 out of 950 non-glaucomatous people.Heterogeneity investigations found that sensitivity estimate was higher for studies with more severe glaucoma, expressed as worse average mean deviation (MD): 0.79 (0.74 to 0.83) for MD < -6 db versus 0.64 (0.60 to 0.69) for MD ≥ -6 db, at a similar summary specificity (0.93, 95% CI 0.92 to 0.94 and, respectively, 0.94; 95% CI 0.93 to 0.95; P < 0.0001 for the difference in relative DOR). The accuracy of imaging tests for detecting manifest glaucoma was variable across studies, but overall similar for different devices. Accuracy may have been overestimated due to the case-control design, which is a serious limitation of the current evidence base.We recommend that further diagnostic accuracy studies are carried out on patients selected consecutively at a defined step of the clinical pathway, providing a description of risk factors leading to referral and bearing in mind the consequences of false positives and false negatives in the setting in which the diagnostic question is made. Future research should report accuracy for each threshold of these continuous measures, or publish raw data.

Objective Assessment of Progression after Acute Primary Angle Closure Using HRT and GDx

Irreversible damage to the optic nerve can follow the rapid increase of IOP during an Acute Primary Angle Closure (APAC). Despite the development of advanced imaging technology, there is still a lack of good longitudinal studies assessing patients after an acute attack. The aim of this study was to assess the progression of patients using different objective optic nerve head and retinal imaging parameters following APAC. Twenty patients with a single attack of APAC, were retrospectively assessed in this study. Patients were assessed with the Heidelberg Retinal Tomography (HRT3) and Scanning Laser Polarimeter (GDx-VCC) as well as Humphrey Visual Field (HVF) repeatedly up to eighteen months after the acute attack. Progression for each imaging modality was assessed with multiple parameters. All patients showed Retinal Nerve Fibre Layer (RNFL) and optic disc changes over time. At 18 months, 67% of patients showed progression in 4/5 GDx parameters, and 33% in all 5. HRT analysis similarly showed progression in 4/5 parameters in 70% of patients, and 30% in all 5. This study shows that structural progressive changes to RNFL and ONH occur following APAC confirming that APAC patients need long-term follow-up after the acute attack.

Retinal Nerve Fiber Layer Thickness, Brain Atrophy, and Disability in Multiple Sclerosis Patients

To study the relationship between retinal nerve fiber layer (RNFL) thickness and brain atrophy using magnetic resonance imaging (MRI) with bicaudate ratio (BCR) in patients with multiple sclerosis (MS) with different levels of disease severity. We also assessed whether RNFL thickness correlated with Expanded Disability Status Scale (EDSS) score. The participants consisted of 88 patients with MS and 59 age- and sex-matched healthy control subjects. Eleven patients had clinically isolated syndrome (CIS), 68 patients had relapsing-remitting MS (RR-MS), and 9 patients had secondary progressive MS. Patients and controls were evaluated using optical coherence tomography (OCT, Cirrus) and scanning laser polarimetry with variable corneal compensation (GDx VCC). Patients underwent the same brain MRI scanning protocol. Disability was evaluated according to the EDSS. The BCR was calculated by dividing the minimum intercaudate distance by brain width along the same level. The BCR was higher in patients with MS (0.12 ± 0.03) than in controls (0.08 ± 0.009) (P < 0.001). OCT average RNFL thickness in patients with MS was significantly lower (84.51 ± 14.27 μm) than in control subjects (98.44 ± 6.83 μm). BCR was correlated with OCT average RNFL thickness (r = -0.48, P = 0.002) in patients with MS without optic neuritis. Significant correlations were found between average RNFL thickness and EDSS (r = -0.43, P = 0.003). Additionally, there were correlations between BCR with GDx parameters in patients with MS without optic neuritis. This study shows that RNFL thickness correlates with BCR and with MS subtypes. Additionally, our study indicates that OCT is better suited for MS assessment than GDx. We conclude that the damage of retinal axons appears related to brain damage in patients with MS.

Relationship between the retinal nerve fibre layer (RNFL) parameters and visual field loss in established glaucoma patients in South Indian population

Purpose: Optical coherence tomography (OCT) and Scanning LASER polarimetry (GDX-VCC) are newer techniques to analyse retinal nerve fibre loss in glaucoma. This study aims to evaluate the relationship between the Retinal Nerve Fibre Layer(RNFL) parameters measured using Stratus-OCT and GDx-VCC and visual field loss by Octopus interzeag perimetry in established glaucoma patients in South Indian Population. Materials and methods: Prospectively planned cross sectional study of 67 eyes of 34 established glaucoma patients on medical management. The mean age of patients was 46.911 years (SD+13.531). A complete ophthalmic examination, automated perimetry with octopus interzeag 1-2-3 perimeter, retinal nerve fibre analysis with GDx VCC and Stratus OCT was done. The differences between the mean RNFL parameters in the presence or absence of field defects were evaluated. Results: The data analysed were mean deviation, loss variance, OCT total average nerve fibre thickness, GDX VCC- TSNIT average and Nerve fibre indicator (NFI).The data were split into two subgroups on the basis of presence or absence of visual field defect and analysed. The difference between the mean value of NFI between the subgroups was highly significant with a p value < 0.01.The OCT parameter Total average nerve fiber layer thickness differed significantly between the two subgroups (p value <0.05). The mean GDx TSNIT average did not differ significantly between the two subgroups. Conclusion: The total average nerve fibre thickness by OCT correlated better with visual field loss than the GDX TSNIT average .Among the GDx parameters, the NFI was found to be a better indicator of visual field damage than the average thickness.

Retinal nerve fiber thickness is reduced in sleep apnea syndrome

To investigate the prevalence of glaucoma, visual field abnormalities, as well as changes in retinal nerve fiber layer in patients with obstructive sleep apnea syndrome (OSAS). In this cross-sectional study, 51 patients with OSAS were included. Based on apnea hypopnea index (AHI), there were 26, 6 and 19 cases of severe (AHI⩾30), moderate (15⩽AHI<30), and mild (5⩽AHI<15) OSAS, respectively. The control group was matched for age, sex and body mass index. Prevalence of glaucoma and ocular hypertension as well as the following values were assessed and compared between two groups: best-corrected visual acuity, intraocular pressure, central corneal thickness (CCT), cup:disk ratio, mean deviation (MD), pattern standard deviation, and retinal nerve fiber layer (RNFL) parameters using glaucoma diagnosis measurement (GDx). Seven eyes (6.7%) had intraocular pressure (IOP)>21mmHg; of these, four eyes (3.9%) had glaucoma. No significant difference was detected in CCT between the two groups. IOP was significantly higher in the OSAS group before (p<0.001) and after (p<0.001) correcting for CCT. There was a significant difference between groups in MD and most GDx parameters including DISK (temporal-superior-nasal-inferior-temporal) average (p=0.002), superior average (p=0.05) and nerve fiber indicator (NFI) (p=0.03), where those in the patient group showed lower values. There was a significant positive correlation between AHI and both IOP and NFI. OSAS patients had a higher prevalence of glaucoma and ocular hypertension. OSAS patients also had higher IOP, worse visual field indices, and lower RNFL parameters compared with the control group.

THE COMPARISON OF TSNIT STANDARD DEVIATION VALUES IN GLAUCOMATOUS PATIENTS WITH MYOPIA AND MYOPIC PATIENTS MEASURED WITH GDx VCC

Introduction. The objective thickness measurement of retinal nerve fiber layer (RNFL) is now possible with scanning laser polarimetry (GDx VCC). The TSNIT (temporal-superior-nasal-inferior-temporal) parameters are: TSNIT Average, Superior Average, Inferior Average, TSNIT Standard Deviation, Inter-eye-Symmetry and nerve fiber indicator (NFI). TSNIT Standard Deviation captures the modulation (peak to trough difference) of the double-hump pattern. A normal eye will have high modulation in the double-hump RNFL pattern, while a glaucoma eye will typically have low modulation in the double-hump pattern. As a result, high modulation will have a high TSNIT Standard Deviation value while low modulation will have low TSNIT Standard Deviation value. Objective. Our research aim was to evaluate and to compare the TSNIT Average and TSNIT Standard Deviation in glaucomatous patients with myopiс refraction and patients with myopia. Materials and methods. We examined two matched patient groups: basic - myopic patients with open-angle glaucoma 79 subjects (112 eyes) and control group 21 patients with myopia (39 eyes). All patients underwent imaging with the scanning laser polarimeter with variable corneal compensation GDx VCC. GDx parameters were TSNIT Average and TSNIT Standard Deviation. The Kruskal-Wallis test, the Mann-Whitney U-test and Spearman's rank correlation coefficient was applies for comparing groups and assessing the correlation. P values of P 0,05). The study demonstrated also a significant negative correlation of myopia grade and TSNIT Standard Deviation (rs = -0,3; P = 0,002) and a significant inverse correlation between the open-angle glaucoma stage and TSNIT Standard Deviation (rs = - 0,3; P = 0,03).

3-T Diffusion tensor imaging of the optic nerve in subjects with glaucoma: correlation with GDx-VCC, HRT-III and Stratus optical coherence tomography findings

ObjectivesTo correlate diffusion-tensor imaging (DTI) of the optic nerve with morphological indices obtained by scanning laser polarimetry (GDx-VCC); confocal scanning laser ophthalmoscopy (Heidelberg III retinal tomograph; HRT-III) and optical coherence...

Structure/Function Studies and the Effects of Memantine in Monkeys with Experimental Glaucoma

Purpose. The scanning laser polarimetry with variable corneal compensation (GDx VCC) methodology was established and verified in monkeys with experimental glaucoma (ExpG). Terminal GDx parameters were correlated with axon counts and electrophysiologic measures. The effects of memantine on these parameters were investigated. Methods. ExpG was induced in monkeys and intraocular pressure monitored weekly. Some monkeys received memantine in their diet before and after ExpG induction (1-10 months). GDx VCC scans, stereophotographs, and multifocal visual evoked potential (mfVEP) data were collected at baseline and every 6 to 8 weeks until euthanasia. Optic nerves were prepared for axon counting and other morphologic analysis. Results. There was no difference in IOP elevation exposure between memantine-treated and no-memantine-treated monkeys. The percentage of the optic nerve area composed of connective tissue septa was significantly greater in ExpG eyes than in Fellow eyes. There was a strong positive correlation between axon counts and terminal GDx parameter measures. Animals not receiving memantine exhibited significantly lower mfVEP amplitudes in ExpG eyes compared with the ipsilateral baseline or the final value in the Fellow eye. ExpG eyes from memantine-treated animals had higher overall mean amplitudes that were not significantly different relative to the ipsilateral baseline and final amplitudes in the Fellow eye. Conclusions. The authors' studies confirm that GDx VCC can be utilized in monkey ExpG studies to detect early retinal structural changes and that these changes are highly correlated with optic nerve axon counts. These structural changes may or may not lead to central functional changes as shown by the mfVEP in response to investigational therapies.

Comparison of retinal nerve fibre layer thickness with visual evoked potential and visual field in patients with multiple sclerosis

To evaluate retinal nerve fibre layer thickness and to compare results with visual evoked potentials and visual field in patients with multiple sclerosis. A prospective, case-control study, university hospital setting. Seventy-three eyes of 37 multiple sclerosis patients and 74 eyes of 37 healthy subjects. All patients underwent a complete neurological and ophthalmological examination and peri-papillary retinal nerve fibre layer thickness was evaluated using scanning laser polarimetry (GDx). Furthermore, visual evoked potential and visual field testing were performed. The χ(2) test, Student's t-test, Mann-Whitney U-test and Pearson's correlation coefficient analysis of the GDx, visual evoked potential and visual field testing parameters. GDx measurements showed significantly more retinal nerve fibre layer damage in the patients than in the control groups. Comparison of the GDx parameters between patients with optic neuritis and non-optic neuritis demonstrated a statistically significant difference in symmetry (P = 0.046) and superior/nasal parameters (P = 0.009). A correlation was found between the number, superior and inferior ratio parameters, and P100 amplitude obtained with visual evoked potential in patients with non-optic neuritis. Additionally, there was a correlation between the number, inferior ratio and superior/nasal parameters, and the mean deviation of visual field in the non-optic neuritis group. For retinal nerve fibre layer thickness measurements in multiple sclerosis patients, the GDx, along with other techniques, such as visual evoked potential, can be used as a diagnostic and follow-up criterion, particularly in patients without optic neuritis.

Evaluation of GDx parameters by using information theory

To evaluate the performance of GDx parameters in the diagnosis of glaucoma by using information theory and compare the results obtained using receiver operating characteristic (ROC) curve analysis, which is a traditional method. Materials and methods: Retinal nerve fiber layer thickness was measured in 270 eyes with glaucoma and 81 normal eyes with scanning laser polarimeter (NFA GDx version, 1.0.08), and 14 GDx parameters were calculated. Both ROC curve analysis and information theory were used to determine the best GDx parameters. The best cut-off points of these parameters were obtained using information theory for glaucoma prevalence (Pr) of 1%, 2%, and 5%. Results: The parameters having the maximum information content and discriminatory power are The Number, Ellipse modulation, and Maximum modulation, respectively. The best cut-off points associated with these parameters are 32.08, 1.65, and 1.20 for specified Pr values considered, respectively. The best cut-off value for inferior ratio is 1.95 when Pr is 1% or 2%, whereas the best cut-off point of the parameter is 2.11 when Pr is 5%. Conclusion: Although ROC curve analysis can be used for evaluating the performance of the diagnostic test, it cannot determine the best cut-off point for certain prevalence. Information theory approach seems to be more superior to the traditional ROC curve analysis for tackling this problem.

Comparison of Optical Coherence Tomography and Scanning Laser Polarimetry Measurements in Patients with Multiple Sclerosis

To compare optical coherence tomography (OCT) and scanning laser polarimetry (GDx) measurements of the retinal nerve fiber layer (RNFL) in multiple sclerosis (MS) patients with and without optic neuritis (ON). OCT and GDx were performed on 68 MS patients. Qualifying eyes were divided into two groups: 51 eyes with an ON history > or =6 months before (ON eyes) and 65 eyes with no history of ON (non-ON eyes). Several GDx and OCT parameters and criteria were used to define an eye as abnormal, for example, GDx nerve fiber indicator (NFI) >20 or 30, OCT average RNFL thickness, and GDx temporal-superior-nasal-inferior-temporal average (TSNIT) below 5 or 1% of the normative database of the instruments. Agreement between OCT and GDx parameters was reported as percent of observed agreement, along with the AC1 statistic. Linear regression analyses were used to examine the relationship between OCT average RNFL thickness and GDx NFI and TSNIT. All OCT and GDx measurements showed significantly more RNFL damage in ON than in non-ON eyes. Agreement between OCT and GDx parameters ranged from 69 to 90% (AC1 0.37 to 0.81) in ON eyes and 52 to 91% (AC1 = 0.21 to 0.90) in non-ON eyes. Best agreement was observed between OCT average RNFL thickness (p < 0.01) and NFI (>30) in ON eyes (90%, AC1 = 0.81) and between OCT average RNFL thickness (p < 0.01) and GDx TSNIT average (p < 0.01) in non-ON eyes (91%, AC1 = 0.90). In ON eyes, the OCT average RNFL thickness showed good linear correlation with NFI (R = 0.69, p < 0.0001) and TSNIT (R = 0.55, p < 0.0001). OCT and GDx show good agreement and can be useful in detecting RNFL loss in MS/ON eyes.

Diagnostic Validity of Optic Disc and Retinal Nerve Fiber Layer Evaluations in Detecting Structural Changes after Optic Neuritis

To assess the diagnostic validity of morphometric examination of the optic disc and retinal nerve fiber layer (RNFL) thickness to detect permanent structural changes after retrobulbar optic neuritis (ON). Evaluation of a diagnostic test. Twenty-five patients with a history of retrobulbar ON and 29 disease-free controls. The optic discs were evaluated by means of confocal scanning laser ophthalmoscopy (Heidelberg Retinal Tomograph [HRT III]), and RNFL thickness by means of scanning laser polarimetry (GDx), and optical coherence tomography (OCT). Vision function was assessed in all subjects by testing visual acuity, contrast sensitivity, color vision, visual field (VF), and visual evoked potentials (VEPs). Statistical comparisons were made between the affected (ON) and unaffected eyes (non-ON) of the patients with ON, and between these eyes and control eyes (Mann-Whitney test and Wilcoxon's test). Receiver operating characteristic (ROC) curves, and sensitivity and specificity in discriminating ON from control eyes, were calculated for the significant parameters. Correlations between the tests were calculated by means of Spearman's correlation coefficient. We compared OCT, GDx, HRT, and visual testing results in ON eyes versus control eyes. All of the visual function test parameters and RNFL thickness (GDx and OCT) were significantly different between the ON eyes and both the non-ON and control eyes (P<0.01), and there were significant differences in some GDx parameters between the non-ON and control eyes. There were no significant differences in the HRT parameters. The ROC curves indicated that the greatest diagnostic validity was associated with the GDx nerve fiber indicator (AUC, 0.92; sensitivity, 0.80; specificity, 0.97 using a cutoff point of 20.5 between ON and non-ON eyes), and OCT temporal thickness (AUC, 0.92; sensitivity, 0.72; specificity, 0.95 using a cutoff point of 51.5 microm). When investigating permanent damage after ON, RNFL thickness is a promising biomarker. The GDx and OCT are reliable, noninvasive, user-friendly devices; both show good diagnostic validity and good correlations with functional tests in discriminating affected from unaffected eyes. Retinal nerve fiber layer thinning in non-ON eyes should be further studied as a possible subclinical indicator of disease.

Retinal Nerve Fiber Layer Thickness in Patients with Exfoliation, Exfoliative Glaucoma, and Primary Open Angle Glaucoma

to evaluate the retinal nerve fiber layer(RNFL) profile of healthy controls, persons with exfoliation syndrome (XFS), and patients with exfoliation glaucoma (XFG) and primary open angle glaucoma(POAG). One eye from each of 269 participants was analyzed. Fifty eyes were normal , 45 eyes had XFS, 89 eyes had POAG, and 89 had XFG. Glaucoma patients were divided according to the severity of the disease into mild and advanced groups. All participants underwent imaging with the GDx-VCC device. Measurements of the parameters TSNIT average, TSNIT SD, and nerve fiber indicator (NFI) were performed. Polametric RNFL thickness values were compared by means of Bonferroni-corrected t-tests. Regarding control and glaucoma groups, statistically significant differences were identified in all GDx parameters. RNFL thickness values of the control group differed significantly from the values of the XFS group. There was no statistically significant difference between RNFL thickness values for the mild POAG and mild XFG groups or for the advanced POAG and advanced XFG groups. Polarimetry-determined RNFL in eyes with XFS is thinner than that of healthy eyes. No differences in RNFL thickness were found when eyes with POAG and XFG of similar severity were compared.

Relationship between standard automated perimetry and retinal nerve fiber layer parameters measured with laser polarimetry

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.

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

Purpose To 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. Methods A 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. Results Weak 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). Conclusions RNFL 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.

Sub‐clinical atrophy of the retinal nerve fibre layer in multiple sclerosis

This study aimed to evaluate the presence of abnormalities in the retinal nerve fibre layer (RNFL) in multiple sclerosis (MS) patients with normal ophthalmic examination, and to compare the ability of optical coherence tomography (OCT) and scanning laser polarimetry (GDx) to detect axonal loss. Patients with MS and disease-free controls were invited to enrol in the study from 1 February 2007 to 30 June 2008. Ophthalmic examination, including evaluation of visual acuity (VA) and visual field (VF), showed normal results in all subjects. Retinal nerve fibre layer properties were measured by means of OCT and GDx. Visual evoked potentials (VEPs) were also recorded. Forty eyes of 40 MS patients and 20 eyes of age- and sex-matched controls were included in the study. Despite normal VA and VF results, significant differences between the two groups were observed in VF mean deviation (MD), most of the RNFL measurements provided by OCT and GDx, and VEP P100 latency and amplitude. There was a significant correlation between OCT and GDx parameters, and between these parameters and VEP results. Nineteen MS eyes (35.7%) showed RNFL abnormalities detected either by OCT or GDx. Sub-clinical ganglion cell loss can be detected in MS patients with normal visual function. Both OCT and GDx are useful complementary tools with which to identify this damage.

Increased Long-term Measurement Variability With Scanning Laser Polarimetry Employing Enhanced Corneal Compensation

To investigate whether the intervisit standard deviation (ISD) of various scanning laser polarimetry parameters is increased, in progressing glaucoma. GDx-variable corneal compensation (VCC) and GDx-enhanced corneal compensation (ECC) measurements, and Octopus G2 visual field tests, were performed at 6-month intervals on 27 healthy subjects and 52 consecutive glaucoma patients. One eye per participant was analyzed. Fifteen patients progressed (on the basis of visual field criteria) and 37 remained stable, during the 2.6+/-0.4 years follow-up. Baseline visual field indices and the stage of glaucoma did not differ between the glaucoma groups. No regression with time was found for any GDx parameter in any group. The ISD of GDx-ECC nerve fiber indicator (NFI), but not GDx-VCC NFI, was significantly higher in progression than in the stable glaucoma group (Mann-Whitney U test with Bonferroni correction, P=0.028). Also, several other ISD values tended to increase in the progressing group. Logistic regression analysis revealed that ISD of NFI [odds ratio (OR)=1.22, P=0.013], inferior average (OR=1.80, P=0.035), and average thickness along the measuring ellipse (OR=2.00, P=0.042), as determined with GDx-ECC (but not with GDx-VCC), all associated with visual field progression, independently of patient age. With GDx-ECC, increase of ISD is an early sign of glaucoma progression, precedes the development of detectable parameter changes, and is associated with visual field progression.

Retinal Nerve Fiber Layer Measurements Before and After Photorefractive Keratectomy

Purpose To determine whether the nerve fiber analyzer GDx with the new variable corneal compensation (VCC) device allows measurements of retinal nerve fiber layer parameters independent from birefringence changes of the cornea after photorefractive keratectomy (PRK). Methods Retinal nerve fiber layers of 32 eyes in 32 myopic patients undergoing PRK were analyzed using the GDx-VCC. Photorefractive keratectomy was performed using a NIDEK EC-5000 excimer laser. Measurements were obtained before and after PRK without dilating the pupil. To evaluate birefringence changes, GDx-VCC macular images also were taken before and after PRK. Results After PRK, superior and inferior ratios, superior/nasal max modulation, and temporal-superiornasal-inferior-temporal average changed significantly ( P &lt;.001) when corneal birefringence correction was not applied. When corneal birefringence correction was applied, only temporal-superior-nasal-inferior-temporal average and superior maximum improved significantly. Furthermore, a comparison of the postoperative data without polarization correction to the data with corrected corneal polarization demonstrated significant changes in superior ratio ( P =.004), superior/nasal ( P &lt;.001), ellipse modulation ( P =.007), and temporal-superiornasal-inferior-temporal standard deviation ( P =.009). Conclusions Our results show the VCC algorithm is able to compensate for most of the changes in corneal birefringence induced by corneal refractive surgery if the polarization has been re-calculated. Because mild changes in GDx parameters could affect the interpretation of the results in some patients, a new postoperative baseline macular image should be acquired. [ J Refract Surg . 2008;24:639–644.]

Retinal Nerve Fiber Layer Images Captured by GDx-VCC in Early Diagnosis of Glaucoma

Objectives: To compare differences in retinal nerve fiber layer (RNFL) parameters between normal subjects and patients with various degrees of glaucoma, evaluate the sensitivity and specificity of GDx-VCC parameters, and determine the capability of GDx-VCC parameters and the most valuable indicators for the diagnosis of early glaucoma. Methods: GDx-VCC was used to measure RNFL in 80 patients with early glaucoma (130 eyes), 70 patients with advanced glaucoma (90 eyes) and 40 normal controls (80 eyes). All glaucoma patients were divided into an early glaucoma group and an advanced glaucoma group, according to the mean defect of the visual field. RNFL parameters were compared between normal subjects and patients with various degrees of glaucoma. Receiver operating characteristic (ROC) curves of GDx parameters were drawn to determine the most valuable GDx parameters for the diagnosis of early glaucoma. Results: The RNFLs were significantly thinner in patients with early glaucoma than those in normal subjects; they were also significantly thinner in patients with advanced glaucoma than those in patients with early glaucoma. The differences in all parameters reached statistical significance (p < 0.001). The mean defect of the visual field was significantly correlated with all RNFL parameters (p < 0.001). The areas under the ROC curves were >0.7 for all parameters, which could effectively differentiate early glaucoma from normal subjects. The areas under the ROC curves were 0.81 for nerve fiber indicator and inferior average with better differentiation capability. Conclusions: GDx-VCC can provide quantitative measurements of RNFL thickness for clinical use, which can effectively differentiate patients with early glaucoma from normal subjects, and will be clinically very helpful for the early diagnosis of glaucoma. Nerve fiber indicator and inferior average are the most effective indicators for the early diagnosis of glaucoma.

Análisis del espesor de la capa de fibras nerviosas en niños de 6 a 9 años

To establish a database of scanning laser polarimetry (GDx) parameters for children between 6 and 9 years of age and compare the results at each age. The retinal nerve layer thickness of 116 children from one school was evaluated with GDx and the results were analyzed for each age and for the entire group to determinate the normal range for that population. In the global analysis of the software-derived GDx parameters, we obtained a TSNIT average of 59.43 (IC95% 58.41-60.45), a superior average of 71.35 (IC95% 69.99-72.70), an inferior average of 70.08 (IC95% 68.71-71.45), and a TSNIT Std. Deviation of 25.11 (IC95% 24.36-25.86). The results from the analysis for age were similar to the global results. Given the low level of cooperation required, GDx can be used without problem to study the retinal nerve fiber layer in 6-9-year-old children. GDx could provide objective information about the state of development of the retinal nerve fiber layer during this period of life.