Accuracy of scanning laser polarimetry in the diagnosis of glaucoma

Assessment of rates of structural change in glaucoma using imaging technologies

PURPOSE

To review the ability of current imaging technologies to provide estimates of rates of structural change in glaucoma patients.

PATIENTS AND METHODS

Review of literature.

RESULTS

Imaging technologies, such as confocal scanning laser ophthalmoscopy (CSLO), scanning laser polarimetry (SLP), and optical coherence tomography (OCT), provide quantifiable and reproducible measurements of the optic disc and parapapillary retinal nerve fibre layer (RNFL). Rates of change as quantified by the rim area (RA) (for CSLO) and RNFL thickness (for SLP and OCT) are related to glaucoma progression as detected by conventional methods (eg, visual fields and optic disc photography). Evidence shows that rates of RNFL and RA loss are significantly faster in progressing compared with non-progressing glaucoma patients.

CONCLUSION

Measurements of rates of optic disc and RNFL change are becoming increasingly precise and individualized. Currently available imaging technologies have the ability to detect and quantify progression in glaucoma, and their measurements may be suitable end points in glaucoma clinical trials.

Prevalence of Glaucoma in the Wroclaw Population. The Wroclaw Epidemiological Study

PURPOSE

Primarily to determine the prevalence of various types of glaucoma and ocular hypertension in Wroclaw inhabitants aged 40-79 years. The second aim of the study was to determine the number of undiagnosed glaucoma cases in this population.

METHODS

A representative group of the Wroclaw population (4853 people aged from 40 to 79 years) was recruited by a proportional simple random sampling selection with stratification. All participants underwent the first, screening-stage examination, which included a medical history interview, intraocular pressure (IOP) measurement, anterior chamber depth assessment by the Van Herrick technique, and optic nerve head (ONH) assessment by means of indirect ophthalmoscopy (Volk's lens), confocal scanning laser ophthalmoscopy with a Heidelberg Retinal Tomograph (HRT) and scanning laser polarimetry by the GDx Nerve Fiber Analyzer (GDx). The second stage, in glaucoma-suspect patients only, included best corrected visual acuity, static perimetry, 24-hour monitoring of IOP, gonioscopy, and full eye examination with mydriasis. Glaucoma was diagnosed by the presence of any two of the following: characteristic morphological changes in the optic disc, glaucomatous visual field abnormalities, and intraocular pressure greater than 21 mmHg.

RESULTS

The overall prevalence of glaucoma was 1.6% (79 subjects). The prevalence increased with age from 0.4% in subjects belonging to the age group 40-49 years to 4.6% in people aged between 70 and 79 years. The prevalence of definite primary open-angle glaucoma was 1.0% (49 subjects). Normal-pressure glaucoma was diagnosed in 13 subjects (0.3%). Ocular hypertension was diagnosed in 92 subjects (1.9%).

CONCLUSION

The prevalence of the different types of glaucoma was similar to that found in other white populations. Among the subjects examined, 79 had various forms of glaucoma and 71% of them had not previously been diagnosed. Undiagnosed glaucoma is a serious public health problem in Poland.

Evaluating the Optic Disc and Retinal Nerve Fiber Layer in Glaucoma II: Optical Image Analysis

Glaucoma is a widespread, blindness-causing disease that is characterized in part by specific and sometimes subtle changes in optic disc and retinal nerve fiber layer topography. Several recently developed computer-based optical imaging techniques allow objective evaluation of the optic disc and retinal nerve fiber layer. These techniques use different optical properties and different properties of the retina to provide micron scale measurements of many aspects of optic disc and retinal nerve fiber layer structure. This article describes and evaluates 3 of these techniques: confocal scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography.

Measurement of retinal nerve fiber layer thickness in normal and glaucomatous Cocker Spaniels by scanning laser polarimetry

OBJECTIVE

To measure changes in the thickness of the retinal nerve fiber layer in normal and early glaucomatous dogs with scanning laser polarimetry.

ANIMALS STUDIED

A total of 45 eyes, 32 normal and 13 glaucomatous eyes, of American Cocker Spaniels with primary glaucoma were used. All eyes were evaluated through a complete neuro-ophthalmic examination, tonometry, gonioscopy, slit-lamp biomicroscopy, and indirect ophthalmoscopy prior to enucleation.

METHODS

The retinal nerve fiber layer thickness was measured in anesthetized animals with scanning laser polarimetry (Nerve fiber analyzer, GDx; Laser Diagnostic Technologies, LTD, San Diego, CA, USA). Glaucomatous eyes retained some vision at the time of this study.

RESULTS

The mean +/- SD of the retinal nerve fiber layer thickness was 141.69 +/- 18 microm for normal dogs and 105.08 +/- 23.86 microm for visual glaucomatous dogs. The average retinal nerve fiber layer thickness in the superior and inferior retinal quadrants was 148.03 +/- 8.5 and 141.06 +/- 8.73 microm, respectively, for normal dogs, and 106.61 +/- 25.77 and 107.08 +/- 24.99 microm in the superior and inferior retinal quadrants, respectively, for glaucomatous dogs. The superior to nasal retinal nerve fiber layer thickness ratio was 1.45 for normal dogs and 1.26 for visual glaucomatous dogs.

CONCLUSIONS

Using scanning laser polarimetry it was possible to detect changes in retinal nerve fiber layer thickness in glaucomatous dogs at early stages of the disease. Therefore, this instrument has the potential to improve the clinical management of canine glaucoma by detecting progressive changes to the retinal nerve fiber layer.

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.

Association between localized visual field losses and thickness deviation of the nerve fiber layer in glaucoma

PURPOSE

To perform a correlation between morphology and function by studying local perimetric field losses and thickness reduction of the nerve layer in corresponding areas.

METHOD

Forty-seven patients with "preperimetric" open-angle glaucoma, 95 patients with "perimetric" open-angle glaucoma, and 75 control subjects had perimetric (Octopus) and polarimetric measurements. Criteria for exclusion: optic discs larger than 4 mm, media opacities, polarimetric hourglass pattern in the macular image. Thickness values of the retinal nerve fiber layer were determined in 14 upper and 14 lower sectors (10 degrees each) as well as nasally and temporally (40 degrees each) as provided from the GDx (software version 4000). The healthy control subjects served to determine age-corrected thickness deviation in all sectors. Analyses were calculated in eight nerve fiber bundle related areas. Due to non-linear relationships between perimetric defects and corresponding thickness deviation non-parametric tests were used.

RESULTS

Localized visual field defects in the present perimetric patients were highest in upper and lower visual field areas abutting the nasal meridian. Thickness loss of nerve fiber layer however was highest in more circumferential upper and lower nerve fiber bundles. Correlations between local mean defects and deviation of the retinal nerve fiber layer thickness from normals showed a clear association for corresponding areas. The correlation coefficients were significant (P < 0.01) for all arcuate superior and inferior visual field zones except horizontally and not for the area of the lower nasal step.

CONCLUSION

The present correspondence map indicates that focal perimetric defects can be identified best polarimetrically if they occur in the arcuate bundles of the visual field. A lack of correspondence was observed in the area of the papillo-macular bundle.

Automated detection of wedge-shaped defects in polarimetric images of the retinal nerve fibre layer

PURPOSE

Automated glaucoma detection in images obtained by scanning laser polarimetry is currently insensitive to local abnormalities, impairing its performance. The purpose of this investigation was to test and validate a recently proposed algorithm for detecting wedge-shaped defects.

METHODS

In all, 31 eyes of healthy subjects and 37 eyes of glaucoma patients were imaged with a GDx. Each image was classified by two experts in one of four classes, depending on how clear any wedge could be identified. The detection algorithm itself aimed at detecting and combining the edges of the wedge. The performance of both the experts and the algorithm were evaluated.

RESULTS

The interobserver correlation, expressed as ICC(3,1), was 0.77. For the clearest cases, the algorithm yielded a sensitivity of 80% at a specificity of 93%, with an area under the ROC of 0.95. Including less obvious cases by the experts resulted in a sensitivity of 55% at a specificity of 95%, with an area under the ROC of 0.89.

CONCLUSIONS

It is possible to automatically detect many wedge-shaped defects at a fairly low rate of false-positives. Any detected wedge defect is presented in a user-friendly way, which may assist the clinician in making a diagnosis.

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.

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.

Retinal nerve fiber layer thickness measurements with scanning laser polarimetry predict glaucomatous visual field loss

PURPOSE

To assess whether baseline retinal nerve fiber layer (RNFL) measurements obtained with a scanning laser polarimeter, the GDx Nerve Fiber Analyzer, (Laser Diagnostic Technologies Inc., San Diego, California) are predictive of development of repeatable glaucomatous visual field damage in glaucoma suspect eyes.

DESIGN

Cohort study.

METHODS

Participants were recruited from the UCSD longitudinal Diagnostic Innovations in Glaucoma Study (DIGS). One eye from each of 160 glaucoma suspects with normal standard automated perimetry (SAP) visual fields at baseline was studied. Study eyes were divided into convert and nonconvert groups based on the development of three consecutive glaucomatous visual fields during follow-up. SLP parameters, IOP, vertical cup disk ratio, stereophotograph assessment as glaucoma or normal, corneal thickness, and visual field indices were included in univariate and multivariate Cox proportional hazards models to determine which SLP RNFL and ocular parameters were predictive of visual field conversion.

RESULTS

Sixteen (10%) eyes developed repeatable visual field damage (converts) and 144 (90%) did not (nonconverts). Mean (95%CI) follow-up time until visual field conversion for convert eyes was 2.7 (1.7, 3.6) years. Mean total follow-up of nonconvert eyes was 3.8 (3.5, 4.1) years. Four out of thirteen examined baseline SLP parameters and baseline SAP Mean Deviation (MD), SAP Pattern Standard Deviation (PSD), and glaucomatous stereophotograph assessment were significant univariate predictors of visual field conversion. In multivariate models adjusted for age, IOP and CCT, SLP parameters inferior ratio, ellipse modulation, and UCSD linear discriminant function (LDF) were significant predictors of visual field conversion. When SAP PSD and stereophotograph assessment were also included in the multivariate model inferior ratio and UCSD LDF remained independently predictive of visual field loss.

CONCLUSIONS

Thinner baseline SLP RNFL measurements were independent predictors of visual field damage. In addition to thinner SLP RNFL measurements, higher baseline SAP PSD, and baseline glaucomatous stereophotograph assessment each contributed to an increased risk of the development of abnormal visual fields in glaucoma suspect patients. SLP RNFL measurements were independently predictive of future visual loss even when age, IOP, CCT, vertical cup disk ratio, and SAP PSD were included in the model.

The correlation between optic nerve head topographic measurements, peripapillary nerve fibre layer thickness, and visual field indices in glaucoma

AIMS

To establish whether the structural parameters provided by the Heidelberg retina tomograph (HRT) and the laser diagnostics glaucoma scanning system (GDx) can be used to reflect functional damage in the visual field.

METHODS

62 patients with primary open angle glaucoma underwent examination with the HRT, GDx, and Humphrey field analyser. The relations between the topographic parameters, retinal nerve fibre parameters, and visual field indices were analysed by scatter plot and linear regression.

RESULTS

Among the topographic parameters generated by the HRT, rim area had the best correlation with visual field indices. The "number," maximum modulation, and ellipse modulation generated by the GDx also had correlations with visual field indices. The correlations were better for the sectoral parameters than the global parameters. However, great interindividual variation was found in the association.

CONCLUSION

Although relations were found between some topographic parameters, RNFL parameters, and visual field indices, great interindividual variation limits the prediction of one parameter from the other. Therefore, both structural and functional aspects should be evaluated in order to obtain full characterisation of the glaucomatous damage for clinical judgment and treatment.

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

PURPOSE

The Number is a standard parameter of the GDx that reportedly distinguishes normal and glaucomatous eyes. The authors evaluated the sensitivity and specificity of the Number and examined whether expert clinical judgment of GDx printouts leads to a better separation.

MATERIALS AND METHODS

Two experienced observers judged 800 GDx scans on 400 randomly presented printouts from 200 glaucoma patients and 200 age-matched normal subjects. The diagnosis was based on the symmetry analysis printout and was per patient rather than per eye. The observers assessed sensitivity for all glaucoma patients together, and separately for mild, moderate, and severe glaucoma. Their specificity was determined in the group of normal subjects. The same procedure was performed for the Number, at various critical values.

RESULTS

Both observers discriminated better than the Number. At a critical value of 23, the specificity of the Number was 81.5%, which matched the lowest specificity of the 2 observers: 82.5% and 92.0% for observers 1 and 2, respectively. At these specificities, the sensitivity of the 2 observers and of the Number were 92.0%, 89.5%, and 85.5%, respectively. The sensitivity increased with the severity of glaucoma. The Kappa values for intraobserver agreement were 0.80 and 1.0.

CONCLUSIONS

The Number yielded acceptable sensitivity and specificity values at a critical value of 23 in this test population. However, the clinical judgments of the printouts by both expert observers resulted in a better separation between normal and glaucomatous eyes, particularly in the group with mild glaucoma.

Effect of individualized compensation for anterior segment birefringence on retinal nerve fiber layer assessments as determined by scanning laser polarimetry

PURPOSE

Scanning laser polarimetry estimates retinal nerve fiber layer (RNFL) thickness through measurement of retardation of a polarized laser light passing through the naturally birefringent RNFL and cornea. The commercial instrument, the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, Inc., San Diego, CA), uses an anterior segment compensator of fixed magnitude and slow polarization axis to eliminate the contribution of the cornea to the total signal. Previous studies have shown up to 30% of patients are not adequately compensated by this method. The aim of this study was to determine the effect of individualized anterior segment compensation using a newly designed variable compensator on estimates of retinal nerve fiber layer thickness compared with those as determined with the fixed compensator in the commercial device.

DESIGN

Comparative, observational case series.

PARTICIPANTS

Twenty-eight eyes from 14 normal participants and 24 eyes from 12 patients with bilateral glaucoma.

METHODS

Using information derived from a scan of the macula, a newly designed variable anterior segment compensator for the GDx was set to neutralize anterior segment birefringence. Normal participants and patients with glaucoma underwent RNFL measurements using the standard (fixed) compensator and the variable compensator. The results were compared using Hotelling's generalized means test and Bonferroni's adjustment for multiple comparisons.

MAIN OUTCOME MEASURES

Standard GDx modulation and thickness parameters as determined with the fixed and variable compensators.

RESULTS

All thickness values were statistically significantly lower as determined with the variable compensator, with no discernible differences in any of the modulation parameters.

CONCLUSIONS

Individualized anterior segment compensation lowers the RNFL thickness values as determined by scanning laser polarimetry compared with those determined with the standard fixed compensator. This may narrow the normal range and increase the discriminating ability of scanning laser polarimetry between normal and disease. However, modulation is less affected, and the modulation parameters may thus prove more useful for distinguishing between normal and glaucoma.

Comparison of algorithms for detection of localised nerve fibre layer defects using scanning laser polarimetry

AIMS

To evaluate different algorithms used to analyse retinal nerve fibre layer thickness (RNFL) data obtained by scanning laser polarimetry, in order to compare their relative abilities to discriminate between patients with glaucomatous localised nerve fibre layer defects and normal subjects.

METHODS

48 eyes of 48 glaucomatous patients with localised RNFL defects and 53 eyes of 53 healthy subjects were included in this study. The localised RNFL defects were identified by RNFL photography and/or slit lamp biomicroscopic examination. All patients were submitted to RNFL examination using scanning laser polarimetry (GDx nerve fibre analyser, Laser Diagnostic Technologies, Inc, San Diego, CA, USA). Three methods of analysis of polarimetry data were used: GDx software provided parameters; RNFL thickness measurements in 16 equal sectors around the optic disc (sectoral analysis); and Fourier analysis of the curve of distribution of RNFL thickness measurements. Linear discriminant functions were developed to assess sensitivity and specificity of the sectoral based analysis and Fourier analysis and were compared to the GDx parameters. In addition, areas under the receiver operating characteristic (ROC) curves were compared.

RESULTS

At a fixed specificity of 91%, the sensitivity of the linear discriminant function from sectoral data (LDF sectoral) was 81%, with an area under the ROC curve of 0.93. The linear discriminant function from Fourier measures had a comparable performance, with an area under the ROC curve of 0.93, and sensitivity of 71% for specificity at 91%. At the same specificity, the sensitivities of the GDx software provided parameters ranged from 15% to 40%. The areas under the ROC curves for the LDF sectoral and LDF Fourier were significantly greater than the ROC curve area for the single best GDx parameter.

CONCLUSION

The sectoral based analysis and the Fourier analysis of RNFL polarimetry data resulted in an improved detection of eyes with glaucomatous localised nerve fibre layer defects compared to the GDx software provided parameters.

Combined use of frequency doubling perimetry and polarimetric measurements of retinal nerve fiber layer in glaucoma detection

PURPOSE

The aim of this study was to evaluate the diagnostic usefulness of the combined use of frequency-doubling technology (FDT) perimetry and polarimetry of the retinal nerve fiber layer.

DESIGN

Cross-sectional study.

METHODS

Seventy ocular hypertensive patients (normal optic disk and standard perimetry, elevated intraocular pressure [>21 mm Hg]), 59 patients with "preperimetric" open-angle glaucoma (glaucomatous optic disk atrophy, elevated intraocular pressure [>21 mm Hg], no visual field defect in standard perimetry), 105 patients with "perimetric" open-angle glaucoma (glaucomatous optic disk atrophy and clearly marked visual field defect), and 73 control subjects had FDT screening (protocol: C-20-5) and polarimetric measurements (GDx). Criteria for exclusion: optic disks larger than 4 mm(2), media opacities, patients younger than 33 years or older than 66 years. None of the subjects had earlier FDT perimetry. One eye of each patient and control subject entered the statistical evaluation. Database and statistical software were used for case-wise recalculation of all missed localized probability levels to create a FDT screening score.

RESULTS

At a predefined specificity of 94.5% in control eyes, discrimination between "perimetric" glaucoma and normal subjects is superior using the FDT perimetry (sensitivity = 84.8%) in comparison to polarimetry (sensitivity = 63.8%), whereas sensitivity is similar with both methods in "preperimetric" patients (GDx, FDT: 25.4%). In several cases, patients classified as glaucomatous by the GDx are not the same patients as identified by the FDT perimetry. Therefore, a two-dimensional discrimination analysis can increase correct positive classification. Using a linear combination of the present FDT screening score and polarimetry ("the number"), 92.4% of "perimetric" glaucoma eyes and 44.1% of "preperimetric" glaucoma eyes have been classified as glaucomatous.

CONCLUSION

Joint usage of polarimetry and FDT perimetry indicate that a combination of different techniques which can uncover different glaucoma properties, might be helpful in early glaucoma detection.

GDx in glaucoma

The purpose of this paper is to review the clinical applications of GDx in the diagnosis and follow-up of glaucoma. The limits and potential of GDx technology are discussed.

Quantitative analysis of axonal loss in band atrophy of the optic nerve using scanning laser polarimetry

AIMS

To measure axonal loss in patients with band atrophy from optic chiasm compression using scanning laser polarimetry (GDx, Laser Diagnostic Technologies, Inc, San Diego, CA, USA) and to evaluate the ability of this instrument to identify this pattern of retinal nerve fibre layer (RNFL) loss.

METHODS

19 eyes from 17 consecutive patients with band atrophy of the optic nerve and permanent temporal hemianopia due to chiasmal compression, and 19 eyes from an age and sex matched control group of 17 healthy individuals were prospectively studied. All patients were submitted to an ophthalmic examination including Goldmann perimetry and evaluation of the RNFL using scanning laser polarimetry. Mean RNFL thickness around the optic disc were compared between the two groups. The diagnostic performance of the deviation from normal analysis provided by the GDx software was also assessed.

RESULTS

The peripapillary RNFL thickness (mean (SD)) of eyes with band atrophy was 47.9 (7.63) micro m, 37.1 (8.48) micro m, 57.0 (9.31) micro m, and 37.2 (8.86) micro m in the superior, temporal, inferior, and nasal regions, respectively. The total average was 43.7 (12.0) micro m. In the control group, the corresponding values were 71.1 (12.2) micro m, 40.4 (10.9) micro m, 85.4 (14.0) micro m, and 49.8 (10.1) micro m. The total average measured 67.9 (11.2) micro m. The measurements from eyes with optic atrophy were significantly different from those in the control group in all regions but the temporal. The deviation from normal analysis provided by the GDx software failed to identify the majority of abnormalities in the temporal and nasal regions of patients with band atrophy.

CONCLUSIONS

Scanning laser polarimetry was able to identify axonal loss in the superior, inferior, and nasal regions, but failed to detect it in the temporal region of the optic disc, despite the fact that this area was clearly altered in eyes with band atrophy. This examination also showed poor sensitivity to detect axonal loss in the nasal region when GDx software analysis was used. The results of this study emphasise that RNFL evaluation using scanning laser polarimetry should be interpreted with caution in the study of eye diseases that lead to axonal loss predominantly in the nasal and temporal areas of the optic disc.

Change in retinal nerve fiber layer thickness after laser in situ keratomileusis

PURPOSE

To determine the effect of laser in situ keratomileusis (LASIK) on retinal nerve fiber layer (RNFL) dropout.

SETTING

Nevyas Eye Associates, Philadelphia, Pennsylvania, USA.

METHODS

This prospective consecutive study comprised 120 eyes. The GDx((R)) nerve fiber analyzer (Laser Diagnostic Technologies, Inc.) was used to measure RNFL thickness, an early indicator of glaucomatous damage, preoperatively and 1 week to 4 months and 6 months postoperatively to determine whether any change in apparent RNFL thickness was due to corneal change or to actual RNFL damage and to determine whether apoptotic cascade caused ongoing RNFL dropout. Humphrey visual fields were done in eyes with an abnormal GDx (increase of 20 in GDx number).

RESULTS

The GDx was normal in 89 eyes, including 6 eyes with tilted discs, an abnormal number, and a normal image and 15 eyes with a nonprogressive increase in the GDx number. Three eyes, normal at the interim, were abnormal at 6 months but had a normal visual field. Eleven eyes had a significant increase in the number at 6 months, including 1 eye that showed a possible glaucomatous visual field defect at 9 months and a normal visual field at 14 months.

CONCLUSIONS

There was no evidence of RNFL thinning or glaucomatous damage. A new baseline GDx should be established post LASIK to correct for corneal change.

Scanning laser polarimetry in monkey eyes using variable corneal polarization compensation

PURPOSE

To determine if scanning laser polarimetry (SLP) using variable anterior segment birefringence compensation can provide meaningful retinal nerve fiber layer (RNFL) thickness measurements in monkey eyes.

METHODS

A scanning laser polarimeter (GDx; Laser Diagnostic Technologies, San Diego, CA) was modified so that anterior segment birefringence could be compensated on an eye-specific basis. Six eyes of three adult Cynomolgus (Macaca fascicularis) monkeys were imaged. The authors determined the corneal polarization magnitude (CPM) and corneal polarization axis (CPA) in these eyes, and compared them with the fixed values in the commercial scanning laser polarimeter. Individually compensated RNFL images, using eye-specific CPM and CPA, were then obtained to determine if the resulting retardation profiles reflected the expected RNFL appearance observed with stereoscopic optic disc photographs. Two of the imaged monkeys had experimental glaucoma of the right eye, which allowed comparison of RNFL thickness measures between healthy eyes and those damaged by experimental glaucoma.

RESULTS

The CPM was small in each of the six eyes examined, ranging from 5.7 to 8.7 nm. The CPA ranged from -62 degrees to 78.7 degrees (nasally upward CPA values were recorded as negative; nasally downward CPA values were recorded as positive). These values are different from the values assumed by the commercially available fixed-compensator GDx. When eye-specific compensation was used, RNFL retardation profiles mimicked the expected appearance of the RNFL in all eyes. The authors also observed a substantial decrease in retardation in experimental glaucoma eyes compared with healthy fellow eyes.

CONCLUSIONS

Scanning laser polarimetry using eye-specific corneal polarization compensation can provide meaningful RNFL thickness measurements in monkey eyes. Observed differences in retardation between healthy and experimental glaucoma eyes suggest that SLP may be useful for detecting and monitoring RNFL loss in experimental primate glaucoma.

Scanning laser polarimetric analysis of retinal nerve fiber layer thickness in Turkish patients with glaucoma and ocular hypertension

PURPOSE

To assess the thickness of the retinal nerve fiber layer (RNFL) in patients with different stages of glaucoma, in comparison with ocular hypertensive (OHT) and healthy subjects in a Turkish population.

METHODS

Scanning laser polarimetry was done with a GDx Nerve Fiber Analyzer (NFA, GDx version, 1.0.08) on 270 eyes with glaucoma, 52 OHT eyes, and 81 normal eyes. The eyes were classified as having early (146 eyes), moderate (66 eyes) and severe (58 eyes) glaucoma based on the Humphrey Visual Field indices. We compared 14 NFA parameters by analysis of variance (ANOVA) and Scheffe multiple comparison analysis. Receiver operator characteristic curves (ROC) and Fisher linear discriminant analysis (LDF) were used to measure the sensitivity and specificity of the NFA parameters.

RESULTS

Except for symmetry, all NFA parameters showed significant differences between the groups (p<0.05). The eyes with glaucoma had significantly thinner RNFL than healthy eyes (p<0.01). The RNFL retardation measurements of OHT eyes were lower than controls, but higher than the early glaucoma group. The sensitivity and specificity of the GDx System were 87% and 72.8%, respectively. Applying LDF, the group with the highest sensitivity and specificity (85.9% and 74.1%) was determined as inferior ratio, superior/nasal ratio, superior maximum and the Number.

CONCLUSIONS

Assessment of RNFL thickness with scanning laser polarimetry can distinguish glaucoma, OHT and normal subjects with relatively high sensitivity and specificity.

Visual field defects and neural losses from experimental glaucoma

Glaucoma is a relatively common disease in which the death of retinal ganglion cells causes a progressive loss of sight, often leading to blindness. Typically, the degree of a patient's visual dysfunction is assessed by clinical perimetry, involving subjective measurements of light-sense thresholds across the visual field, but the relationship between visual and neural losses is inexact. Therefore, to better understand of the effects of glaucoma on the visual system, a series of investigations involving psychophysics, electrophysiology, anatomy, and histochemistry were conducted on experimental glaucoma in monkeys. The principal results of the studies showed that, (1) the depth of visual defects with standard clinical perimetry are predicted by a loss of probability summation among retinal detection mechanisms, (2) glaucomatous optic atrophy causes a non-selective reduction of metabolism of neurons in the afferent visual pathway, and (3) objective electrophysiological methods can be as sensitive as standard clinical perimetry in assessing the neural losses from glaucoma. These experimental findings from glaucoma in monkeys provide fundamental data that should be applicable to improving methods for assessing glaucomatous optic neuropathy in patients.

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.

Scanning laser polarimetry in a selected group of patients with glaucoma and normal controls

PURPOSE

To evaluate the ability of scanning laser polarimetry to discriminate between subjects with glaucoma with specific patterns of visual field defect and normal controls.

METHODS

This cross-sectional, prospective study in a glaucoma practice, focused on subjects with glaucoma with predefined types of visual field defect, including advanced (group A, n = 14), localized (group L, n = 46), or mixed (diffuse and localized) defects (group M, n = 22) and normal controls (n = 32). Scanning laser polarimetry was performed in one study eye per subject. Two methods of analysis were used: a subjective analysis, in which examination printouts with the image of the optic disk manually blocked were classified by two observers masked to the diagnosis, and a logistic regression analysis of the retardation parameters included in the printouts.

RESULTS

The observers correctly identified 97% of the controls and 68% of subjects with glaucoma (overall correct classification of 77%), with 93%, 70%, and 47% of patients from groups A, L, and M, respectively, being correctly identified. The best discrimination obtained with the logistic regression correctly identified 69% of controls and 94% of glaucoma subjects (overall correct classification of 87%). The performance was only slightly better for cases from group A compared with L and M.

CONCLUSIONS

Subjective assessment of the scanning laser polarimetry standard printout of single eyes might not be sensitive enough to detect cases of glaucoma with localized or milder mixed types of visual field defect. The discriminating ability of scanning laser polarimetry improves slightly when logistic regression analysis is employed.

Using optical imaging summary data to detect glaucoma

PURPOSE

To evaluate the sensitivity and specificity for discriminating between early to moderate glaucomatous and normal eyes using summary data reports from the Heidelberg Retina Tomograph (HRT), the GDx Nerve Fiber Analyzer (GDx), and the Optical Coherence Tomograph (OCT).

DESIGN

Comparative cross-sectional study

PARTICIPANTS

One eye each of 50 normal subjects and 39 glaucoma patients with early to moderate visual field damage (mean deviation, -5.04 +/- 3.32 dB; range, -0.85 to -13.2 dB).

METHODS

Three experienced graders masked to patient identity and diagnosis evaluated each summary data report from the HRT, GDx, and OCT independently.

MAIN OUTCOME MEASURES

Each summary report was classified as either normal or glaucomatous. Sensitivity and specificity are reported for each grader, and agreement between graders is reported.

RESULTS

For the HRT, sensitivity and specificity ranged from 64% to 75% and 68% to 80%, respectively. Agreement (kappa +/- standard error [SE]) between observers one and two, two and three, and one and three was 0.73 +/- 0.07, 0.77 +/- 0.07, and 0.67 +/- 0.08, respectively. For the GDx, sensitivity and specificity ranged from 72% to 82% and 56% to 82%, respectively. Agreement (kappa +/- SE) between observers one and two, two and three, and one and three was 0.66 +/- 0.08, 0.66 +/- 0.08, and 0.50 +/- 0.09, respectively. For the OCT, sensitivity and specificity ranged from 76% to 79% and 68% to 81%, respectively. Agreement (kappa +/- SE) between observers one and two, two and three, and one and three was 0.73 +/- 0.07, 0.58 +/- 0.08, and 0.51 +/- 0.09, respectively.

CONCLUSIONS

When used alone, HRT, GDx, and OCT summary data reports can differentiate between normal and glaucomatous eyes with mild to moderate visual field loss. However, none of the instruments provided sensitivity and specificity that justify summary data reports being used as a screening tool for early to moderate glaucoma.

The value of polarimetry in the evaluation of the optic nerve in glaucoma

Scanning laser polarimetry (SLP) is a technology used to measure the thickness of the human retinal nerve fiber layer (NFL) in vivo. SLP has been demonstrated to well differentiate between glaucomatous, ocular hypertensive, and normal eyes, despite overlapping data. Recently increased interest is seen in the polarizing properties of the cornea and crystalline lens that may lead to spurious measurements. Although the instruments that use SLP compensate for these anterior segment polarizing properties, recent interest has focused on the extent and effects of incomplete compensation. If well compensated in all, SLP may better separate diseased from normal eyes. Its promising role in the follow-up of glaucoma is still under investigation.

Screening models for glaucoma

For social and economic reasons, glaucoma screening is a useful and necessary task, with possible benefits for individuals and the health care system arising from the early diagnosis and early therapy of patients with glaucoma. Early treatment of patients with glaucoma decreases the probability that those patients will become blind and lowers the direct and indirect costs for patients with glaucoma. Most of the reported studies dealing with glaucoma screening used only one parameter (eg, intraocular pressure) to detect and to discriminate glaucoma patients from healthy subjects. Glaucoma screening devices might be combined to obtain the best specificity and sensitivity. Because the diagnosis of glaucoma is very closely associated with a morphologic change in the optic nerve head, one screening parameter should be the morphology of the papilla. To increase specificity and sensitivity, a combination of morphologic and functional testing might be useful. In this review, we report the context of glaucoma screening in terms of health economics, the testing quality of devices for functional and morphologic screening, and the results of a pilot study.

The diagnostic value of optic nerve imaging in early glaucoma

In the last decade, new imaging techniques have been added to conventional fundus photography and have been evaluated for use in early glaucoma. They all measure the loss of neuroretinal rim or retinal nerve fiber layer as a correlate to glaucomatous ganglion cell and axon loss. The value of optic disc photography, planimetry, laser scanning tomography, laser scanning polarimetry, and optical coherence tomography for the diagnosis of glaucomatous eyes in a preperimetric or early perimetric stage is analyzed on the basis of sensitivity, specificity, and receiver operating characteristics (ROC) curves. It becomes clear that all these techniques allow a more or less semi-automated evaluation of the optic disc and retinal nerve fiber layer but still have their limitations in the diagnosis of a very early, preperimetric stage of the glaucoma disease.

Diagnostic capabilities of frequency-doubling technology, scanning laser polarimetry, and nerve fiber layer photographs to distinguish glaucomatous damage

PURPOSE

To investigate the ability of three diagnostic tests: frequency-doubling technology (FDT), scanning laser polarimetry (GDx), and nerve fiber layer (NFL) photographs to distinguish normal from glaucomatous eyes.

METHODS

Data were obtained in a cross-sectional, hospital clinic-based study, including one eye from each of 253 persons older than 40 years (68 normal, 94 glaucoma suspects and 91 glaucoma patients). We performed a comprehensive ocular examination, as well as static automated perimetry (Humphrey 24-2), screening FDT, GDx, optic nerve stereoscopic photographs and high-contrast NFL photographs.

RESULTS

The following were significantly different for glaucomatous patients compared with suspects and normals: mean values of mean deviation (MD, Humphrey 24-2) and corrected pattern standard deviation (CPSD), 11 GDx indices, mean FDT testing time and missed points, and NFL graded defects (ANOVA, Mantel-Haenszel test; p = 0.0001). Using Humphrey 24-2 test results and clinical assessment as the defining features of glaucoma, we found that the optimal mix of sensitivity and specificity values were 84% and 100% for FDT (presence of any defect); 62% and 96% for GDx (The Number, cut-off value of 27); and, 95% and 82% for NFL photographs (presence of any abnormality). FDT testing took the least time to be administered.

CONCLUSIONS

The FDT had the best diagnostic performance. Neural network analysis of GDx data outperformed other elements of its software.

The effect of myelination on perimetry and retinal nerve fibre analysis

BACKGROUND: Myelinated retinal nerve fibres around the optic nerve head can lead to an enlargement of blind spot with kinetic perimetry. Presumably extensive myelination will also decrease the visual sensitivity with static perimetry. This study reports the effect of myelination on static perimetry in several patients. Scanning laser polarimetry can measure the retinal nerve fibre layer thickness around the optic nerve head in vivo. This technique was applied at the myelination to investigate its effect on retinal nerve fibre layer thickness determination. METHODS: Four eyes of three subjects with myelination around the optic nerve head were tested with Bjerrum screen at one metre to measure the blind spot size. They were followed by Humphrey Visual Field Analyser with a custom pattern to quantify the threshold level at the blind spot region. A GDx Nerve Fiber Analyser was used to measure the retinal nerve fibre layer thickness around the optic nerve head. RESULTS: All the patients demonstrated an enlargement of the blind spot, with different extents, corresponding to the area of myelination. Threshold testing revealed a depression in the myelinated regions. The results for retinal nerve fibre layer were not conclusive with two eyes demonstrating thickening and two eyes showing no effect from myelination. CONCLUSIONS: A static field test with a modern visual field analyser may help to quantify the effect of myelination on visual sensitivity. More studies on the effect of myelination on retinal nerve fibre layer thickness measurement are suggested with more subjects involved.