Márta Tóth

Comparison of repeatability of retinal nerve fiber layer thickness measurement made using the rtvue fourier-domain optical coherence tomograph and the gdx scanning laser polarimeter with variable or enhanced corneal compensation

PurposeTo compare repeatability of measurements of peripapillary retinal nerve fiber layer thickness (RNFLT) made using the RTVue-100 Fourier-domain optical coherence tomograph against repeatability of those made using scanning laser polarimetry with variable corneal compensation or enhanced corneal compensation (GDx-VCC and GDx-ECC, respectively). MethodsOne eye of each of 37 participants (14 normal and ocular hypertensive subjects, 11 patients with moderate, and 12 with severe glaucoma; groups 1, 2, and 3, respectively) was imaged using the RTVue Optic Nerve Head Map scan, GDx-VCC, and GDx-ECC, each 5 times on the same day. The coefficient of variation (CV) were compared. The P values <1% were considered as significant. ResultsFor average RNFLT CV was significantly lower with RTVue (2.11%) than with GDx-ECC (3.22%, P=0.004), for all participants. For temporal quadrant RNFLT in all participants, and group 1, CV with RTVue (4.88% and 3.30%) was significantly lower than with GDx-ECC (7.40% and 5.88%; P=0.004), and tended to be lower than with GDx-VCC (6.81% and 5.80%; P=0.011 and 0.016, respectively). For all participants, CV for inferior quadrant RNFLT was significantly lower with RTVue (3.49%) than with GDx-VCC (5.20%, P=0.002). No other difference was seen for any other parameter in any subject group. ConclusionsRepeatability characterized by CV of RNFLT measurement with the RTVue Optic Nerve Head Map scan and GDx-VCC/GDx-ECC was similar, and sufficient for clinical purposes, both in normal subjects and in glaucoma patients with different disease severity. For average peripapillary RNFLT and temporal quadrant RNFLT, repeatability of RTVue was better than that of GDx-ECC, and tended to be better than that of GDx-VCC.

Accuracy of combined GDx-VCC and matrix FDT in a glaucoma screening trial

PurposeTo assess the advantage in glaucoma screening of the use of scanning laser polarimetry with customized cornea compensation (GDx-VCC) combined with Matrix Frequency Doubling Technology (M-FDT) testing. MethodsIn a nonpopulation-based prepublicized trial, self-recruited white participants were screened for glaucoma with GDx-VCC, with M-FDT, and by independent clinical examination. Cases with possible glaucoma as found with any of the screening methods underwent a detailed clinical investigation to verify or exclude glaucoma. Sensitivity, specificity, accuracy, likelihood ratios, and predictive values were calculated using different threshold criteria for GDx-VCC alone, M-FDT alone, and for various combinations. ResultsOf the 233 attendees, 181 participants (345 eyes) successfully underwent the GDx-VCC and M-FDT measurements. Thirty-nine eyes of 24 participants had glaucoma (11.3% prevalence among eyes tested successfully). All but 2 of the glaucomatous eyes had only early damage. Evaluated separately, the criterion GDx-VCC NFI (normal threshold ≤30) performed best, with 97.0% specificity, 88.8% accuracy, and 25.6% sensitivity; but with only 8.5 positive likelihood ratio (PLR). For paired criteria, the best combination of GDx-VCC-screening test with M-FDT-screening test provided 99.6% specificity, 91.3% accuracy, and 28.6 PLR. For NFI combined with GDx-VCC nerve fiber bundle defect criterion, specificity was 99.0%, accuracy 89.6%, and PLR 18.0. However, the sensitivities in the 2 cases fell to 12.0% and 18.0%. For a triple combination of M-FDT-screening test with the latter pair of criteria, sensitivity increased to 41.7% and PLR (13.6) still remained clinically useful. ConclusionsIn a self-recruited white population with relatively high risk for mild glaucomatous damage, a combination of GDx-VCC together with M-FDT could usefully be employed for mass glaucoma screening.

Novel Fractal Feature-Based Multiclass Glaucoma Detection and Progression Prediction

We investigate the use of fractal analysis (FA) as the basis of a system for multiclass prediction of the progression of glaucoma. FA is applied to pseudo 2-D images converted from 1-D retinal nerve fiber layer data obtained from the eyes of normal subjects, and from subjects with progressive and nonprogressive glaucoma. FA features are obtained using a box-counting method and a multifractional Brownian motion method that incorporates texture and multiresolution analyses. Both features are used for Gaussian kernel-based multiclass classification. Sensitivity, specificity, and area under receiver operating characteristic curve (AUROC) are computed for the FA features and for metrics obtained using wavelet-Fourier analysis (WFA) and fast-Fourier analysis (FFA). The AUROCs that predict progressors from nonprogressors based on classifiers trained using a dataset comprised of nonprogressors and ocular normal subjects are 0.70, 0.71, and 0.82 for WFA, FFA, and FA, respectively. The correct multiclass classification rates among progressors, nonprogressors, and ocular normal subjects are 0.82, 0.86, and 0.88 for WFA, FFA, and FA, respectively. Simultaneous multiclass classification among progressors, nonprogressors, and ocular normal subjects has not been previously described. The novel FA-based features achieve better performance with fewer features and less computational complexity than WFA and FFA.

Influence of selective laser trabeculoplasty on 24-hour diurnal intraocular pressure fluctuation in primary open-angle glaucoma: a pilot study.

BACKGROUND AND OBJECTIVE To investigate the influence of selective laser trabeculoplasty on mean diurnal intraocular pressure (IOP) and diurnal IOP fluctuation in primary open-angle glaucoma. PATIENTS AND METHODS After washout from intraocular pressure-lowering drugs, a baseline diurnal IOP curve was obtained for 26 eyes of 13 patients before selective laser trabeculoplasty. The IOP curve was repeated at 3 and 6 months. RESULTS In five eyes, office time (8:00 a.m. to 12:00 p.m.) IOP decreased by 20% or more. No similar decrease was seen in mean diurnal IOP in any case. IOP-lowering drugs were required for 11 eyes before the 3-month visit. Baseline diurnal IOP was higher for these eyes than for the others (P = .002). Compared with baseline values, a significant decrease was seen in mean IOP at the 6-month visit (P = .017) and in IOP fluctuation at both visits (P < .001 and P = .004, respectively) for the eyes without drug treatment. CONCLUSION Although no eyes showed mean diurnal IOP reduction of 20% or more, selective laser trabeculoplasty resulted in a significant decrease in the amplitude of diurnal IOP fluctuation.

Increased Long-term measurement variability with scanning laser polarimetry employing enhanced corneal compensation: an early sign of glaucoma progression.

PurposeTo investigate whether the intervisit standard deviation (ISD) of various scanning laser polarimetry parameters is increased, in progressing glaucoma. MethodsGDx-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. ResultsBaseline 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. ConclusionsWith 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.

Accuracy of scanning laser polarimetry, scanning laser tomography, and their combination in a glaucoma screening trial.

PurposeTo compare the usefulness in glaucoma screening of scanning laser polarimetry (GDx-VCC), scanning laser tomography [Heidelberg retina tomograph II (HRT II)], and their combined evaluation. MethodsIn a nonpopulation-based prepublicized trial, self-recruited white participants were screened for glaucoma with GDx-VCC, HRT II, and by independent clinical examination. Cases with possible glaucoma as found with any of the screening methods underwent a detailed clinical investigation to verify or exclude glaucoma. ResultsOf the 136 attendees 118 participants (218 eyes) successfully underwent the GDx-VCC and HRT II measurements. Twenty-three eyes (11%) of 13 participants had glaucoma. Seventeen of these glaucomatous eyes (74%) had early damage. Evaluated separately, the GDx-VCC screening test (borderline cases grouped with the normal cases) performed best with 96.8% specificity, 89.5% accuracy, 7.5 positive likelihood ratio (PLR), but with only 23.8% sensitivity. Accuracy and PLR for all HRT parameters were <86.4% and <3.7, respectively. Combining different threshold criteria, for GDx-VCC accuracy increased to 90.3% to 90.8% and PLR to 14.0 to 17.7; but for HRT no useful increase was seen (accuracy <86.4% and PLR<4.7 for all combinations). Combination of the best HRT and GDx-VCC criteria resulted in a PLR which was increased compared with the HRT combinations, but decreased compared with the GDx-VCC combinations (PLR<12.7 for all combinations). ConclusionsIn this white screening population with relatively high risk for mild glaucomatous damage, a combination of different GDx-VCC criteria was useful for glaucoma screening; but combinations of HRT criteria or combinations of GDx-VCC criteria with HRT criteria were less good for this purpose.

Efficacy of fractal analysis in identifying glaucomatous damage

In this work, we propose a novel fractal-based technique to analyze pseudo 2D representation of 1D retinal nerve fiber layer (RNFL) thickness measurement data vector set for early detection of glaucoma. In our proposed technique, we first convert the 1D RNFL data vector sets into pseudo 2D images and then exploit 2D fractal analysis (FA) technique to obtain the representative features. These 2D fractal-based features are further processed using principal component analysis (PCA) and the final classification between normal and glaucomatous eyes is obtained using Fischers linear discriminant analysis (LDA). An independent dataset is used for training and testing the classifier. The technique is used on randomly selected GDx variable corneal compensator (VCC) eye data from 227 study participants (116 patients with glaucoma and 111 patients with healthy eyes). We compute sensitivity, specificity and area under receiver operating curve (AUROC) for statistical performance comparison with other known techniques. Our classification performance shows that fractal-based technique is superior to the standard machine classifier Nerve Fiber Indicator (NFI).

Atypical retardation pattern: can performance of classification be improved?

Purpose. (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. Methods. 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. Results. 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). Conclusion. Although the WFA and FFA classification performance was greater than NFI as assessed by ROC area the difference was not statistically significant.

Feature-based glaucomatous progression prediction using scanning laser polarimetry (SLP) data

In this work, we investigate the effectiveness of a novel fractal feature-based technique in predicting glaucomatous progression using the retinal nerve fiber layer (RNFL) thickness measurement data. The technique is used to analyze GDx variable corneal compensator (GDx-VCC) scanning laser polarimeter (SLP) data from one eye of 96 study participants (14 progressors, 45 non-progressors, and 37 ocular normal patients). The novel feature is obtained by using a 2D box-counting (BC) method, which utilizes pseudo 2D images from 1D temporal, superior, nasal, inferior, temporal (TSNIT) RNFL data. For statistical performance evaluation and comparison, we compute sensitivity, specificity and area under receiver operating curve (AUROC) for fractal analysis (FA) and other existing feature-based techniques such as fast Fourier analysis (FFA) and wavelet-Fourier analysis (WFA). The AUROCs indicating discrimination between progressors and non-progressors using the classifiers with the selected FA, WFA, and FFA features are 0.82, 0.78 and 0.82 respectively for 6 months prior to progression and 0.63, 0.69 and 0.73 respectively 18 months prior to progression. We then use the same classifiers to compute specificity in ocular normal patients. The corresponding specificities for ocular normal patients are 0.86, 0.76 and 0.86 for FFA, WFA and FA methods, respectively.

Influence of pupil dilation on repeatability of scanning laser polarimetry with variable and enhanced corneal compensation in different stages of glaucoma

PurposeTo evaluate the influence of pupil dilation on repeatability of scanning laser polarimetry with variable (GDx-VCC) and enhanced (GDx-ECC) corneal compensation, in different stages of glaucoma. MethodsOne eye of each of 37 Caucasian participants [14 healthy and ocular hypertensive subjects with mean deviation (MD) <2 dB, 11 glaucoma patients with MD 6 to 12 dB, and 12 glaucoma patients with MD >15 dB] was imaged 5 times with both GDx-VCC and GDx-ECC, before and after pupil dilation. ResultsNo statistically significant alteration was found for any parameter or most coefficients of variation in any group, or in the total study population, due to pupil dilation. Intraclass correlation was similar with both compensation techniques: it varied between 98.5% and 99.2% before, and 97.3% and 99.1% after pupil dilation for all participants. Intrasession variability was below 6 μm for all parameters and all groups irrespective of corneal compensation and pupil dilation. By using GDx-ECC, a statistically significant trend for higher coefficient of variation values in more severe stages of glaucoma was found, irrespective of pupil dilation (Jonckheere-Terpstra test, P<0.026, for all parameters). With GDx-VCC this trend was not seen for 2 of the 3 parameters before pupil dilation, but did appear for all parameters in mydriasis (P<0.002). ConclusionsRepeatability of GDx-VCC and GDx-ECC is similar, and is satisfactory for clinical purposes; it is only minimally influenced by pharmacological mydriasis. However, repeatability of the measurement decreases with increasing severity of glaucoma. This characteristic is better detectable with GDx-ECC than with GDx-VCC.