Sensitivity and specificity of the GDx: clinical judgment of standard printouts versus the number

[Screening method for angle closure and angle closure glaucoma using scanning laser polarimeter GDxVCC and photodynamic gonioscopy in a darkened room. One-year outcomes of systematic peripheral iridotomy]

INTRODUCTION

Angle closure glaucoma, a recognized major world health issue disproportionately affecting women and Asians, is not often considered in our European populations, normotensive subjects, myopic patients, or subjects with a deep anterior chamber. Early diagnosis is worthwhile, as laser peripheral iridotomy (LPI) is an effective one-step treatment of the causal mechanism.

PATIENTS AND METHODS

We have performed a retrospective study of patients who underwent an LPI, the indication for which was based on "photodynamic" gonioscopy in a darkened room showing iridotrabecular contact in darkness. Such photodynamic gonioscopy was motivated by the presence of even minute defects in the nerve fiber layer as seen on the GDxVCC or the presence of a Van Herick sign (narrow limbal anterior chamber depth).

RESULTS

One hundred and three eyes of 103 patients underwent LPI and a minimum 1-year follow-up (mean follow-up almost 2 years). Mean age was 63.7±11.8 years, and women accounted for 63.1% of cases. The vast majority (78.6%) of patients had neither glaucoma nor ocular hypertension. There were 60.1% hyperopes and 39.9% myopes. Over half (57%) had a deep or a very deep anterior chamber. After LPI, there was immediate deepening of the limbal depth of the anterior chamber in 100% of cases. The aqueous humor that flowed forward was almost always viscous-looking. After 1 year, the IOP was 1.3mm Hg±2.4 lower (P<.001) (t test). All patients who had experienced morning headaches (44% of patients) were relieved of this symptom. GDxVCC after 1 year was clearly improved in 18% of cases, slightly improved in 20%, stable in 50%, slightly worse in 11% of cases, and clearly worse in 1%. Cases treated at an earlier stage had a better improvement in GDxVCC.

DISCUSSION

Our study shows frequent chronic angle closure in our European population even with deep anterior chambers. Absence of a Van Herick sign does not rule out angle closure at night. A photodynamic gonioscopy with the Goldmann three-lens mirror (to avoid unintentional indentation with the small diameter lenses in these normotensive eyes) should be performed in a darkened room. LPI is an effective one-step treatment of the underlying cause, that is particularly beneficial if performed early.

[GDx-VCC NFI analysis in Lebanese glaucoma patients]

PURPOSE

To describe the Nerve Fiber Indicator (Nerve Fiber Index; NFI) parameter findings and progression in Lebanese glaucoma patients or suspects.

STUDY DESIGN

Retrospective, observational study.

PATIENTS AND METHODS

A review was conducted of the GDx VCC examinations performed between January 2003 and December 2008 in an ophthalmological diagnostic center, in 1063 Lebanese subjects referred for this testing by their ophthalmologists. This group of subjects included confirmed glaucoma patients and glaucoma suspects. GDx VCC examination was repeated one or more times, at a one-year interval, in only 136 patients. Since we only had access to their GDx VCC examinations, the number of subjects in each category was unknown prior to the exam. After GDx VCC examination, we divided the subjects into three categories according to their NFI score. Subjects were considered to be normal when the NFI score was below 30, glaucoma suspects when the score was between 30 and 40, and confirmed glaucoma patients when the score was above 40.

RESULTS

Among the 1063 patients studied, 525 were female and 538 male, with a mean age of 56.8 ± 14.2 years at the time of examination. The mean NFI score was 27.01 ± 14.23, higher in males than females in the various age groups, and higher in older than in younger subjects, the greatest difference being between the 11- to 20-year and the 81- to 90-year age groups (P=0.015). Eight hundred and eighty patients had an NFI score within normal limits, the score was consistent with glaucoma suspect in 280 patients and with confirmed glaucoma in 103 patients. Among the 136 patients who underwent multiple GDx VCC examinations, 69 were initially classified as normal. Upon repeat GDx VCC examinations over a five year period, 24 of these 69 patients (34.78%) presented with scores consistent with glaucoma suspect or confirmed glaucoma.

CONCLUSION

This study demonstrates that glaucoma was detected or suspected in at least one of three subjects referred for GDx VCC examination (383/1063). NFI scores were higher in males than females and in older compared to younger subjects.

[Contribution of GDx-VCC in ocular hypertensive patients: a complement to blue-on-yellow perimetry and FDT matrix?]

INTRODUCTION

Evaluate the importance of GDx-VCC results compared with FDT Matrix and blue-on-yellow perimetry in a population of ocular hypertensive patients.

METHODS

Prospective study including 135 eyes of 135 patients. All had normal standard achromatic perimetry and intraocular pressure greater than 21 mmHg without medication. They underwent short wavelength automated perimetry (SWAP) 24-2 FASTPAC, FDT Matrix 24-2 Threshold strategy, and retinal nerve fiber layer (RNFL) analysis with GDx-VCC.

RESULTS

Fifty two patients had neither structural (GDx-VCC) nor functional (SWAP and Matrix) optic nerve injury. Eighty-three patients had preperimetric glaucoma (at least one of the tests showed pathologic results). We found isolated functional defects (38% cases), isolated structural lesions (31% cases), or mixed injury (31% cases). When GDx-VCC revealed structural damage, Matrix was abnormal in 30%, as was SWAP in 8% of cases. Both functional and structural evaluation revealed identical defects for 12% of patients. RNFL loss could be either diffused or compatible with typical glaucomatous topography. Most temporal damage was detected by FDT Matrix, whereas SWAP performed better for nasal defects. The results of GDx analyses correlated better with Matrix than with SWAP.

CONCLUSION

When associated with automated perimetry, GDx-VCC is a valuable tool to evaluate optic nerve damage and detect preperimetric glaucoma. Clinical evaluation of the optic nerve head remains essential. We found a good correlation between visual field defects and structural injuries.

Thickness of the retinal nerve fibre layer estimated with the scanning laser polarimeter in healthy children

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

The GDx VCC examination is reproducible in children. The present RNFL results should represent useful reference values in the evaluation of pediatric glaucoma.

Scanning laser polarimetry - a review

Glaucoma is a leading cause of irreversible blindness worldwide. Retinal ganglion cells and their axons represent the selective target of the disease. When visual function is still intact on standard automated perimetry and optic disc appearance is suspicious, an early diagnosis may be supported by the identification of a retinal nerve fibre layer (RNFL) defect in the peripapillary area. At present days, computer-based, real-time imaging of the peripapillary RNFL is available through instruments of easy use and with high levels of accuracy and reproducibility. Scanning laser polarimetry is performed by a confocal scanning laser ophthalmoscope with an integrated polarimeter (GDx-VCC). There is a considerable amount of scientific evidence about the role of this imaging technique for glaucoma diagnosis. The aim of this review is to describe the principles of operation, the examination procedure, the clinical role, the results of main diagnostic studies and the future development of the software for the scanning laser polarimetry.

Error in refractive correction and its impact on scanning laser polarimetry

PURPOSE

The GDx VCC is a scanning laser polarimeter which measures thickness of the retinal nerve fiber layer (RNFL). A perpendicular incident laser beam in the RNFL is a prerequisite of a correct measurement of the thickness of this layer. An error in refractive correction could cause an obliqueness of the laser beam and consequently a deviation of the RNFL thickness reading. The present study investigated the influence of error in refractive correction on the estimation of the RNFL thickness and the nerve fiber index (NFI).

METHODS

Totally 32 persons were included in this study, 17 without ocular diseases and 15 with glaucoma. The measurement of the RNFL was carried out first routinely with correction of the spherical equivalent refractive error. Then the measurement was repeated 4 times with excessive refractive correction of +1, +2, -1, or -2 D, respectively. The deviation in RNFL thickness and NFI caused by each overcorrection was calculated. An univariate ANOVA analysis was applied to analyze the influence of the error in refractive correction on the result of thickness of RNFL and the NFI.

RESULTS

The error in refractive correction caused a significant deviation in the RNFL thickness reading and the NFI in both the group without ocular diseases and the group with glaucoma. The influence was different between these 2 groups.

CONCLUSION

A careful correction of refractive error is important for glaucoma diagnosis and follow-up with GDx VCC.

Study of patients with ocular hypertension with scanning laser polarimetry and short-wavelength automatic perimetry

AIMS

To compare and correlate retinal nerve fiber layer (RNFL) measurements obtained by scanning laser polarimetry (SLP) with defects detected by short-wavelength automatic perimetry (SWAP) in eyes with ocular hypertension (OHT).

METHODS

SLP and SWAP were performed in 96 eyes of 48 consecutive patients with OHT.

RESULTS

Twenty-five eyes (26%) had SWAP visual field defects. Twenty-seven eyes (28.1%) had abnormal RNFL evaluation defined by the GDx neural network ('number' > 29). Fourteen eyes of 10 patients (14.5%) had abnormal RNFL evaluation and SWAP visual field defects. RNFL thickness measurements were significantly reduced in eyes with abnormal SWAP. A weak but statistically significant correlation between the 'number' and pattern standard deviation (r = 0.3, p = 0.006) and the corrected pattern standard deviation (r = 0.3, p = 0.007) in SWAP was found. Areas of abnormal RNFL thickness corresponded to the localization of the SWAP visual field defects in corrected pattern deviation plots in 10 of the 14 eyes with defects in both tests.

CONCLUSIONS

SWAP visual field defects frequently coexist and correspond with abnormalities of RNFL detected by SLP in eyes with OHT. In certain eyes, however, the two methods detect different glaucoma properties.

Evaluation of Screening versus Regular Polarimetry

PURPOSE

The purpose of this study is to evaluate a new screening program for the GDx VCC (variable corneal compensation) retinal nerve fiber layer analyzer. This new method uses a fast screening approach to detect retinal nerve fiber layer loss associated with glaucoma. The study evaluates the sensitivity and specificity of the screening program and compares the results with those from the GDx VCC full examination.

METHODS

One hundred seventeen eyes from 60 subjects with a mean age of 60.65 years (range, 41-79 years old) were analyzed. Subjects were divided into a normal or glaucoma group based on an ophthalmic examination. Each individual underwent a GDx VCC screening examination, GDx full examination, Humphrey HFA II 24-2 SITA Standard visual field, intraocular pressure assessment, and dilated optic nerve examination. The outcome for the GDx screening examination was within normal limits, borderline, or outside normal limits and compared with the GDx full examination results.

RESULTS

The sensitivity and specificity for the GDx full examination were 73% and 79%, respectively. The sensitivity and specificity for the screening method were 67% and 91%, respectively. The full examination was more sensitive; however, the screening examination was more specific.

CONCLUSION

The screening examination is more conservative than the full examination algorithm and may miss some individuals with glaucomatous damage that the full examination may identify. However, the number of false-positives for the screening examination is less than the full examination method.

Glaucomes. Imagerie de la structure : HRT, GDx et OCT

Confocal scanning laser tomography (HRT), scanning laser polarimetry (GDx VCC), and optical coherence tomography provide quantitative data of the retinal fiber layer and optic nerve head. They have become good complementary evaluation tools for glaucomatous optic neuropathy and their results should be analyzed with clinical data. Good knowledge of the parameters they analyze and their limitations are indispensable. To monitor progression of structural involvement, the analysis programs used need to be validated with prospective clinical studies.

Discrimination between normal and early glaucomatous eyes with scanning laser polarimeter with fixed and variable corneal compensator settings

PURPOSE

To evaluate the ability of scanning laser polarimetry (SLP) with a fixed corneal polarization compensator (GDx-FCC Nerve Fiber Analyzer) compared to one with a variable one (GDx-VCC) in the discrimination between healthy and early glaucomatous eyes.

METHODS

Forty patients with early glaucomatous visual field defects, having a mean deviation of 3.1-/+1.6 dB and a pattern standard deviation of 3.1-/+0.9 dB, and 40 controls underwent both GDx-FCC and GDx-VCC. One eye per patient was considered. The cut-off point, taken as the value dividing healthy from glaucomatous eyes with highest probability, was determined for each GDx parameter. Linear discriminant functions (LDFs) were separately developed for GDx-FCC and GDx-VCC parameters. Sensitivity, specificity, and area under the receiver operating characteristic curve (AROC) for discriminating between healthy and glaucomatous eyes were calculated for each GDx parameter, both according to the GDx normative database and after the selection of new cut-off points, and for the LDFs.

RESULTS

All software-provided parameters showed low sensitivity and high specificity. The selection of new cut-off points improved the performance of all GDx parameters: VCC parameters performed better than FCC parameters; the largest AROCs were associated with the superior/nasal ratio for the GDx-FCC (0.86) and with the Number for the GDx-VCC (0.87). The LDFs provided an AROC of 0.89 with both the GDx-FCC and the GDx-VCC parameters.

CONCLUSIONS

The GDx-VCC showed a higher ability in the early diagnosis of glaucoma when compared with the GDx-FCC. The individuation of the right cut-off point of selected parameters with both GDx settings performed better than the software-provided parameters, and comparably to the GDx parameters-based LDFs.

The Groningen Longitudinal Glaucoma Study. I. Baseline sensitivity and specificity of the frequency doubling perimeter and the GDx nerve fibre analyser

PURPOSE

To describe the baseline data of a large cohort of patients included for follow-up with perimetry using the frequency doubling technique (FDT) and with quantification of the retinal nerve fibre layer as assessed by GDx, and to calculate the sensitivity and specificity of both devices from these baseline data.

METHODS

Regular visitors to our glaucoma service were included. All subjects were followed for at least 4 years with FDT in full-threshold mode, GDx and conventional perimetry. Patients were classified as having either glaucoma or suspect glaucoma, according to baseline perimetry results. In addition, a group of healthy subjects was recruited outside the hospital.

RESULTS

A total of 452 glaucoma patients, 423 glaucoma suspects and 237 healthy subjects were incorporated into the analyses. Sensitivities for both FDT and GDx were fixed at 0.90. For the group as a whole, the specificity was 0.81 for FDT, using number of depressed test-points p < 0.01 in the total deviation probability plot with a cut-off point > 1, and 0.78 for GDx, using the Number, with a cut-off point > 29. The area under the receiver operating characteristic (ROC) curve was 0.92 for FDT and 0.94 for GDx. Of the subjects with suspect glaucoma, 75% showed normal FDT test results and 52% showed normal GDx results. Unlike FDT, GDx failed to detect some moderate/severe glaucoma cases.

CONCLUSIONS

The performances of FDT and GDx are approximately equivalent in terms of sensitivity, specificity and area under the ROC curve. In glaucoma suspects, GDx in particular yielded a rather high percentage of positive test results. The majority of these positive test results are presumably false-positive results rather than results indicating preperimetric glaucoma.

Macular and retinal nerve fiber layer analysis of normal and glaucomatous eyes in children using optical coherence tomography

PURPOSE

To evaluate macular and nerve fiber layer (NFL) thickness in normal and glaucomatous eyes of children 3 to 17 years old using optical coherence tomography (OCT-3).

DESIGN

Observational cross-sectional study.

METHODS

One hundred fifty-six eyes of 79 patients were enrolled in this institutional study. Fifty-two eyes (33.3%) met criteria for glaucoma and 104 (66.7%) were normal. There were 44 female (55.6%) and 35 male (44.3%) subjects whose ages ranged from 3 to 17 years old (mean 9.5 years, standard deviation 3.5 years, median 9 years). The OCT-3 (Carl Zeiss Meditec, Dublin, California) was used to obtain a fast macular thickness map as well as a fast retinal NFL map of each eye. Data from specific locations around the macula, as well as total macular volume, was analyzed. Similarly, the retinal NFL scan reports average NFL thickness from specific locations around the optic nerve. Data from the superior temporal and inferior temporal sections was analyzed.

RESULTS

There was a statistically significant difference in macular thickness and NFL thickness when normal eyes were compared against those with glaucoma, in all quadrants studied (all P values <or=.001). Mean macular volume was 7.01 +/- 0.42 mm(3) vs 6.57 +/- 0.85 mm(3) for normal vs glaucomatous eyes, respectively (P < .001).

CONCLUSIONS

OCT may prove valuable in the early diagnosis of glaucoma. We have found a difference between normal and glaucomatous eyes in children, similar to that reported in adult studies. Further investigation of OCT testing in children should be considered.

Les lasers diagnostiques dans le glaucome : la polarimétrie à balayage laser (GDx VCC) et la tomographie confocale par balayage laser (HRT)

Automated structural measurements of retinal nerve fibers and optic nerve head are possible with new lasers providing objective and reproductible data for analysis. Scanning laser polarimetry (GDx VCC), based on retardation of polarized light, assesses peripapillary nerve fiber layer thickness. Confocal scanning laser tomography yields precise topographic maps of the optic disc and peripapillary retina. The advantages, applications for glaucoma detection, both in a screening setting as well as for monitoring progression, limitations and pitfalls need to be well known and results should be analyzed with clinical data.

Image analysis of optic nerve disease

Existing methodologies for imaging the optic nerve head surface topography and measuring the retinal nerve fibre layer thickness include confocal scanning laser ophthalmoscopy (Heidelberg retinal tomograph), optical coherence tomography, and scanning laser polarimetry. For cross-sectional screening of patient populations, all three approaches have achieved sensitivities and specificities within the 60-80th percentile in various studies, with occasional specificities greater than 90% in select populations. Nevertheless, these methods are not likely to provide useful assistance for the experienced examiner at their present level of performance. For longitudinal change detection in individual patients, strategies for clinically specific change detection have been rigorously evaluated for confocal scanning laser tomography only. While these initial studies are encouraging, applying these algorithms in larger numbers of patients is now necessary. Future directions for these technologies are likely to include ultra-high resolution optical coherence tomography, the use of neural network/machine learning classifiers to improve clinical decision-making, and the ability to evaluate the susceptibility of individual optic nerve heads to potential damage from a given level of intraocular pressure or systemic blood pressure.

Diagnostic accuracy of the GDx VCC for glaucoma

PURPOSE

To determine the diagnostic accuracy of the GDx VCC in the diagnosis of glaucoma.

DESIGN

Prospective, comparative, observational, clinic-based case series.

PARTICIPANTS

One eye each of 77 healthy subjects and 162 patients with primary open-angle glaucoma of Caucasian racial origin. Healthy subjects had normal visual fields (VFs), healthy-looking optic discs, and intraocular pressures of < or =21 mmHg in both eyes. Glaucoma patients had a reproducible glaucomatous VF defect and a glaucomatous appearance of the optic disc in at least one eye.

METHODS

All subjects were measured with the GDx VCC with an automated variable corneal compensator. We constructed receiver operating characteristic (ROC) curves for all available parameters. Subsequently, we calculated sensitivity, specificity, and multilevel likelihood ratios for the best discriminating parameter in the entire group. In addition, we calculated sensitivity and specificity in patients with mild, moderate, and severe glaucomatous damage separately.

MAIN OUTCOME MEASURES

Software-derived parameters TSNIT (temporal, superior, nasal, inferior, temporal) Average, Superior Average, Inferior Average, TSNIT Std. Dev. (standard deviation), and Nerve Fiber Indicator (NFI).

RESULTS

The areas under the ROC curve for TSNIT Average, Superior Average, Inferior Average, TSNIT Std. Dev., and NFI were 0.93, 0.94, 0.90, 0.92, and 0.98, respectively. For the best discriminating parameter NFI, the sensitivity and specificity with a cutoff point of > or =40 were 89.0% and 95.9%, respectively. The multilevel likelihood ratios for glaucoma were 0.07 at NFI values of <35, 1.30 at values between 35 and 44, and 61.50 at values of > or =44. At the cutoff level of > or =40, the sensitivities of the NFI for correctly identifying glaucoma patients with mild, moderate, and severe damage were 83.8%, 92.9%, and 90.1%, respectively.

CONCLUSIONS

The GDx VCC allowed easy, rapid, and accurate discrimination between healthy and glaucomatous eyes. The NFI was the best discriminating parameter. The GDx VCC seems to fulfill criteria for a glaucoma screening device.

Sensitivity and specificity of scanning laser polarimetry using the GDx

BACKGROUND/AIMS

To determine the sensitivity and the specificity of the GDx in the detection of (1) advanced glaucoma, (2) early glaucoma, and (3) nerve fibre bundle defects (NFBD).

METHODS

Group A comprised 20 eyes with reproducible glaucomatous visual field defects confirmed by octopus perimetry, group B consisted of 10 eyes with normal visual fields but either glaucomatous NFBD or deterioration of the disc over time clearly visible upon flicker comparison, and group C included 16 eyes with glaucomatous or non-glaucomatous NFBD clearly visible on red free photographs. Forty four eyes of 22 healthy volunteers served as controls. The GDx printouts of all subjects were evaluated by three independent observers in a masked fashion and without the clinical picture of the optic disc. Two of the three observers (SK, UH) were GDx experts, one (KUL) was an untrained GDx user.

RESULTS

Among the GDx experts, sensitivity/specificity was 100%/100% (SK) and 90%/100% (UH) in detecting advanced glaucoma, and 100%/100% (SK) and 90%/100% (UH) in detecting early glaucoma. The sensitivity in detecting NFBD was only 37.5% (SK and UH). For the untrained GDx user the corresponding values were 50%/100% (group A), 20%/100% (group B), and 12.5%/91% (group C).

CONCLUSION

Detection of (early) glaucoma damage by the GDx, evaluated by trained experts, can be extremely high. To optimise its benefit in clinical routine training in interpreting GDx printouts is highly recommended. Detection of localised NFBD is crucial, even for experts.

Imaging in glaucoma

Structural assessment using the imaging technologies discussed herein provides reproducible quantitative measurements of posterior segment ocular structures. These measurements have been found to provide useful data for glaucoma detection in various regions of the posterior segment. Further studies are needed to evaluate the utility of these technologies for pre-perimetric glaucoma detection and for monitoring glaucoma progression over an extended period.