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Biomedical subjects

David F Garway-Heath

Publications and source records attributed to David F Garway-Heath.

At least 19 recordsLinked to original sources
PubMed2007

Monitoring glaucomatous visual field progression: the effect of a novel spatial filter.

PURPOSE: To assess the impact of a novel visual field spatial filtering technique on the detection of glaucomatous progression. METHODS: One hundred ninety-eight ocular hypertensive (OHT) and 21 control subjects were examined prospectively (1994-2001) with regular full-threshold Humphrey visual field (VF) testing. VF progression was assessed by point-wise linear regression (PLR) of sensitivity/time in Progressor for Windows software modified to include a novel spatial filter. Standard progression criteria (slope > -1 dB/year, P < 0.01) were applied to both "raw" (unfiltered) and "filtered" VF series. Three-omitting confirmatory VF criteria were also applied to unfiltered VF series. Specificity was estimated as the proportion of progressing control subjects and as the proportion of significantly improving subjects (both OHT and control) at the end of the study period. RESULTS: Applying standard PLR, specificity was estimated at 91.8% to 97.5% using unfiltered standard PLR, compared with 93.5% to 98.4% using filtered standard PLR and 95.4% to 99.3% using unfiltered three-omitting PLR. The rate of identified VF progression in the OHT cohort was 32.3% with unfiltered standard PLR, 28.7% with filtered standard PLR, and 18.6% with unfiltered three-omitting PLR. There was no significant difference in time to detected progression between filtered and unfiltered standard PLR. CONCLUSIONS: The use of confirmatory tests resulted in improved specificity using unfiltered data; however, application of the spatial filter resulted in similar specificity but with a higher rate of detected progression. This filter may therefore be useful in the monitoring of glaucomatous progression as it may reduce the dependence on confirmatory testing, although it has yet to be applied to longitudinal SITA data.

Adult↗
PubMed2006

Development and evaluation of a linear staircase strategy for the measurement of perimetric sensitivity.

Perimetric sensitivity of patients with glaucoma has traditionally been measured in logarithmic (dB) units, but linear sensitivity correlates better with conventional structural measures of glaucomatous damage. Monte Carlo simulations of perimetric algorithms were used to assess potential effects of logarithmic steps on bias and variability when perimetric sensitivity was represented in linear units, and to assess the potential benefits of algorithms using linear steps. Simulations predicted that linear staircases could reduce the sensitivity-dependence of bias, variability and efficiency. These predictions were supported by a perimetric study of 21 patients with glaucoma and 20 age-similar controls who made repeat visits over several weeks.

Aged↗
PubMed2006

Optic nerve atrophy and retinal nerve fibre layer thinning following optic neuritis: evidence that axonal loss is a substrate of MRI-detected atrophy.

Magnetic resonance imaging (MRI) measures of brain atrophy are often considered to be a marker of axonal loss in multiple sclerosis (MS) but evidence is limited. Optic neuritis is a common manifestation of MS and results in optic nerve atrophy. Retinal nerve fibre layer (RNFL) imaging is a non-invasive way of detecting axonal loss following optic neuritis. We hypothesise that if the optic nerve atrophy that develops following optic neuritis is contributed to by axonal loss, it will correlate with thinning of the RNFL. Twenty-five patients were studied at least 1 year after a single unilateral attack of optic neuritis without recurrence, with a selection bias towards incomplete recovery. They had MR quantification of optic nerve cross-sectional area and optic nerve lesion length, as well as optical coherence tomography (OCT) measurement of mean RNFL thickness and macular volume, quantitative visual testing, and visual evoked potentials (VEPs). Fifteen controls were also studied. Significant optic nerve atrophy (mean decrease 30% versus controls), RNFL thinning (mean decrease 33% versus controls), and macular volume loss occurred in patients' affected eyes when compared with patients' unaffected eyes and healthy controls. The optic nerve atrophy was correlated with the RNFL thinning, macular volume loss, visual acuity, visual field mean deviation, and whole field VEP amplitude but not latency. These findings suggest that axonal loss contributes to optic nerve atrophy following a single attack of optic neuritis. By inference, axonal loss due to other post-inflammatory brain lesions is likely to contribute to the global MRI measure of brain atrophy in multiple sclerosis.

Adult↗
PubMed2006

Exploration of the psychophysics of a motion displacement hyperacuity stimulus.

PURPOSE: To explore the summation properties of a motion-displacement hyperacuity stimulus with respect to stimulus area and luminance, with the goal of applying the results to the development of a motion-displacement test (MDT) for the detection of early glaucoma. METHODS: A computer-generated line stimulus was presented with displacements randomized between 0 and 40 minutes of arc (min arc). Displacement thresholds (50% seen) were compared for stimuli of equal area but different edge length (orthogonal to the direction of motion) at four retinal locations. Also, MDT thresholds were recorded at five values of Michelson contrast (25%-84%) for each of five line lengths (11-128 min arc) at a single nasal location (-27,3). Frequency-of-seeing (FOS) curves were generated and displacement thresholds and interquartile ranges (IQR, 25%-75% seen) determined by probit analysis. RESULTS: Equivalent displacement thresholds were found for stimuli of equal area but half the edge length. Elevations of thresholds and IQR were demonstrated as line length and contrast were reduced. Equivalent displacement thresholds were also found for stimuli of equivalent energy (stimulus area x [stimulus luminance - background luminance]), in accordance with Ricco's law. There was a linear relationship (slope -0.5) between log MDT threshold and log stimulus energy. CONCLUSIONS: Stimulus area, rather than edge length, determined displacement thresholds within the experimental conditions tested. MDT thresholds are linearly related to the square root of the total energy of the stimulus. A new law, the threshold energy-displacement (TED) law, is proposed to apply to MDT summation properties, giving the relationship T = K logE where, T is the MDT threshold, Kis the constant, and E is the stimulus energy.

Adult↗
PubMed2006

Optic disc and visual field progression in ocular hypertensive subjects: detection rates, specificity, and agreement.

PURPOSE: To examine the detection rates, specificity, and agreement between visual field (VF) progression and Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, GmbH, Heidelberg, Germany) rim area (RA) progression in subjects with ocular hypertension (OHT). METHODS: One hundred ninety-eight OHT and 21 control subjects were examined prospectively (1994-2001) with regular Humphrey VF (Carl Zeiss Meditec, Inc., Dublin, CA) and HRT testing. Point-wise linear regression (PLR) of sensitivity/time was used to assess VF progression, using standard and three-omitting (less stringent and stringent) criteria. The change in HRT-detected progression was assessed by linear regression of sectoral RA/time, defined as slope>1%/year, with significance level tailored according to series variability. Less stringent and stringent criteria were tested. Specificity was estimated by the proportions of control subjects with disease progression and significantly improving subjects (all). Agreement between disc and field progression in the subjects with OHT was assessed with specificities matched for both VF and HRT. RESULTS: Specificity for VF PLR was estimated to be 85.7% to 95.4% when standard criteria were used, and for RA/time to be 88.1% to 90.5% with the less-stringent criteria. In this comparison, 21.2% progressed by RA alone and 20.2% by VF alone, and 12.1% progressed by both RA and VF. Specificity was estimated to be 95.2% to 98.2% for both VF PLR and RA/time, using the three-omitting criteria and the stringent RA/time criteria, respectively. In this comparison, 8.6% progressed by RA alone, 15.1% by VF alone, and 3.5% by both RA and VF. CONCLUSIONS: A relatively high frequency of detected disease progression was observed with either method, with progression by VF occurring at least as frequently as progression by RA. Poor agreement between RA and VF progression was observed regardless of the specificity of the progression criteria. The results indicate that, in patients with ocular hypertension, monitoring of both VF and optic disc is necessary, as agreement between optic disc and VF progression is the exception rather than the rule.

Adult↗
PubMed2006

Structure and function in glaucoma: The relationship between a functional visual field map and an anatomic retinal map.

PURPOSE: To examine the relationship between an anatomic map relating the retinal nerve fiber layer (RNFL) distribution to the optic nerve head and a functional map derived from the interpoint correlation of raw sensitivities in visual field (VF) testing. METHODS: Previously, interpoint correlations were generated for all possible pairs of VF test points in a dataset of 98,821 Humphrey VF test results taken from the Moorfields Eye Hospital archive. The relationship between these correlations and the physical distance between the VF test point pairs was evaluated by Pearson's correlation coefficient and multiple regression analysis. The distance between the pairs of VF test points was calculated in two ways. First, the anatomic map was used to estimate the angular distance at the optic nerve head (ONH), between the RNFL bundles corresponding to the VF test points in each pair (ONHd). Second, the retinal distance between pairs of test points was calculated from the Humphrey VF template (RETd). A best-fit model for predicting functional correlation (FC) from ONHd and RETd was constructed and used to formulate a filter incorporating the anatomic-functional correlation data. RESULTS: All scatterplots showed a negative association between interpoint retinal sensitivity correlation values and distance between points: ONHd (R2 = 0.60) and RETd (R2 = 0.33). The raw sensitivity correlation values could be predicted from a multiple regression model using ONHd, RETd, and a combined interaction of ONHd and RETd (R2 = 0.75, P < 0.00001). The construction of a new filter was based on the equation FC = 0.9325 - (0.0029 . ONHd) - (0.0077 . RETd) + (0.0001 . ONHd . RETd). CONCLUSIONS: A good level of association was observed between the strength of correlation between points in the VF and the relative location of those test points in the peripheral retina and in corresponding RNFL bundles at the ONH. These results help to validate the relationship between structure and function and may be of use in the further refinement of physiologically derived VF filters to reduce measurement noise.

Glaucoma, Open-Angle↗
PubMed2006

Measurement variability in Heidelberg Retina Tomograph imaging of neuroretinal rim area.

PURPOSE: To investigate the optimal frequency of imaging during follow-up to detect glaucoma progression by characterizing variability (noise) in neuroretinal rim area (RA) measured by Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany). METHODS: RA noise was estimated from patient data and characterized by fitting theoretical distributions to the observed data. Multilevel regression was used to determine factors that significantly affect noise. Computer simulations of disease progression were performed by adding noise generated from the distribution derived from the observed data to the average rate of loss in RA estimated from longitudinal data. Rates of detection of disease progression were investigated for various progression rates, follow-up periods, and rates of imaging. RESULTS: Noise was not normally distributed and was best characterized by the hyperbolic distribution, which fit averages well while allowing for extreme values. Noise was greatly influenced by image quality, but age did not have a significant effect. Rates of detection improved for more frequent imaging, better quality images, and faster rates of disease progression. CONCLUSIONS: Noise in HRT measurement of RA is well characterized by the hyperbolic distribution. Sensitivity of detection improves with more frequent testing, but if consistently poor-quality images are yielded for a patient, the probability of detection is low. Results from this work could be used to tailor individual follow-up patterns for patients with different rates of RA loss and image quality, especially in a clinical trial setting.

Cross-Sectional Studies↗
PubMed2006

Improving the repeatability of topographic height measurements in confocal scanning laser imaging using maximum-likelihood deconvolution.

PURPOSE: To evaluate maximum likelihood (ML) blind deconvolution as a technique for improving the repeatability of topographic height measurements obtained from scanning laser tomography (Heidelberg Retinal Tomograph [HRT]; Heidelberg Engineering, Heidelberg, Germany). METHODS: ML blind deconvolution is an image-processing technique that estimates the original scene from a degraded image. This technique has been used in confocal scanning laser microscopy to remove "out-of-focus" haze in three-dimensional confocal image stacks. ML blind deconvolution requires no prior estimation of the point-spread function (PSF), as opposed to classic linear deconvolution methods. Instead, the algorithm estimates an initial PSF based on the optical setup of the confocal scanning device and optics of the eye and iteratively proceeds to a solution. The improvement in repeatability of height measurements from mean topography images within scan (intrascan) and between scans (interscan) afforded by ML deconvolution was evaluated in a test-retest series of HRT images from 40 ocular hypertensive and glaucomatous patients with varying degrees of media opacity. RESULTS: There was an improvement in intrascan repeatability in 38 out of the 40 mean topography images (median improvement 2.5 microm, inter-quartile range 2.19, P < 0.001), and an improvement in interscan repeatability in 33 of the 40 mean topographies (median improvement, 1.0 microm, interquartile range 3.49, P < 0.001). There was a positive association between the magnitude of the improvement in repeatability and the level of mean pixel height standard deviation (MPHSD), intrascan (P = 0.004) and interscan (P = 0.002). CONCLUSIONS: ML blind deconvolution algorithm improves the repeatability of topographic height measurements from the HRT. This improvement was greater in patients with poorer quality images.

Algorithms↗
PubMed2006

Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer.

PURPOSE: The Ocular Response Analyzer (ORA) is a new instrument that measures the corneal biomechanical response (corneal hysteresis, CH) to rapid indentation by an air jet. CH is the difference in applanation pressures (P1, P2) between the rising and falling phases of the air jet. The investigation had two parts: a characterization study and a validation study. In the characterization study, the purposes were to investigate the intraocular pressure (IOP)-dependence of CH and to characterize the performance of the ORA. In the validation study, the purposes were to investigate the association between CH and both age and central corneal thickness (CCT) and the agreement between ORA and Goldmann applanation tonometer (GAT) IOP measurements. METHODS: For the characterization study, data were collected from 105 untreated subjects (45 ocular hypertensive patients and 60 normal subjects; mean age, 60 years, range, 26-82). GAT and ORA measurements were performed before and after IOP lowering of one randomly selected eye with apraclonidine drops. The change in P1 and P2 (arbitrary units) in relation to change in GAT IOP was analyzed to calibrate the instrument. The relation between P1, P2, and CCT was explored and ORA IOP was derived from the analyses. For the validation study, ORA and GAT IOP and CCT were measured in 144 eyes of 144 untreated subjects (mean age, 58 years; range, 19-83). The characterization calculations were applied to the dataset and values of CH and ORA IOP were calculated. The relationship between CH and both subject age and CCT was determined. The associations between CH and CCT and between ORA and GAT IOPs, were investigated by linear regression analysis. The agreement between measuring devices was calculated. RESULTS: In the characterization study, P1 changed by 6.41 arbitrary units for every 1-mm Hg change in GAT IOP. CH (P1 - P2) changed by -1.60 arbitrary units for every 1-mm Hg change in GAT IOP. For each unit change in P2, P1 changed by 1.27 units. From this association a new IOP-independent corneal factor was derived [P1 - (P2/1.27)] and is termed the corneal constant factor (CCF; mm Hg). ORA IOP normalized for CCF was defined as P2 - CCF (mm Hg). The CCF (mm Hg) was associated with CCT (micrometers) and with age: CCF = [(0.036 . CCT) - (0.028 . age)] + 1.06 (adjusted r2 = 0.34; P < 0.0001 for CCT, P = 0.007 for age). Normalized ORA IOP measurements were not associated with CCT. GAT IOP was associated with CCT and CCF-more strongly with the latter: GAT IOP = (0.03 . CCT)+1.52 (r2 = 0.06, P = 0.002); GAT IOP = (0.65 . CCF) + 4.5 (r2 = 0.13, P < 0.0001). The mean difference (95% limits of agreement) between GAT and normalized ORA IOP was 0.1 (-6.6 to +6.8) mm Hg. CONCLUSIONS: The CCF describes an IOP-independent biomechanical property of the cornea that increases with thicker CCT and decreases with greater age. It is moderately strongly associated with CCT and yet explains more of the interindividual variation in GAT IOP than does CCT. Normalized ORA IOP measurements are not associated with CCT.

Adrenergic alpha-Agonists↗
PubMed2005

Retinal nerve fiber layer axonal loss and visual dysfunction in optic neuritis.

Axonal loss is thought to be a likely cause of persistent disability after a multiple sclerosis relapse; therefore, noninvasive in vivo markers specific for axonal loss are needed. We used optic neuritis as a model of multiple sclerosis relapse to quantify axonal loss of the retinal nerve fiber layer (RNFL) and secondary retinal ganglion cell loss in the macula with optical coherence tomography. We studied 25 patients who had a previous single episode of optic neuritis with a recruitment bias to those with incomplete recovery and 15 control subjects. Optical coherence tomography measurement of RNFL thickness and macular volume, quantitative visual testing, and electrophysiological examination were performed. There were highly significant reductions (p < 0.001) of RNFL thickness and macular volume in affected patient eyes compared with control eyes and clinically unaffected fellow eyes. There were significant relationships among RNFL thickness and visual acuity, visual field, color vision, and visual-evoked potential amplitude. This study has demonstrated functionally relevant changes indicative of axonal loss and retinal ganglion cell loss in the RNFL and macula, respectively, after optic neuritis. This noninvasive RNFL imaging technique could be used in trials of experimental treatments that aim to protect optic nerves from axonal loss.

Adult↗
PubMed2005

A new statistical approach for quantifying change in series of retinal and optic nerve head topography images.

PURPOSE: To describe and evaluate new statistical techniques for detecting topographic changes in series of retinal and optic nerve head images acquired by scanning laser tomography (Heidelberg Retinal Tomograph [HRT]; Heidelberg Engineering, Heidelberg, Germany). METHODS: Proven quantitative techniques, collectively referred to as statistic image mapping (SIM), are widely used in neuroimaging. These techniques are applied to HRT images. A pixel-by-pixel analysis of topographic height over time yields a statistic image that is generated by using permutation testing, derives significance limits for change wholly from the patient's own data, and removes the need for reference data sets. These novel techniques were compared to the Topographic Change Analysis (TCA super-pixel analysis) available in the current HRT software, by means of an extensive series of computer experiments. The SIM and TCA techniques were further tested and compared to linear regression of rim area (RA) against time, in real longitudinal HRT series of eyes of 20 normal subjects and 30 ocular hypertensive (OHT) patients that were known to have converted to glaucoma, on the basis of visual field criteria. RESULTS: Computer simulation indicated that SIM has better diagnostic precision at detecting change. In the real longitudinal series, SIM flagged false-positive structural progression in two (10%) of normal subjects, whereas TCA identified three (15%), and linear regression of RA against time identified two (10%). SIM identified 22 (73%) of the OHT converters as having structural progression, whereas the TCA and linear regression of RA against time each identified 16 (53%) over the course of the follow-up. CONCLUSIONS: SIM has better diagnostic precision in detecting change in series of HRT images when compared to current quantitative techniques. The clinical utility of these techniques will be established on further longitudinal data sets.

Adult↗
PubMed2004

Variable corneal compensation improves discrimination between normal and glaucomatous eyes with the scanning laser polarimeter.

PURPOSE: The presently available scanning laser polarimeter (SLP) has a fixed corneal compensator (FCC) that neutralizes corneal birefringence only in eyes with birefringence that matches the population mode. A prototype variable corneal compensator (VCC) provides neutralization of individual corneal birefringence based on individual macular retardation patterns. The aim of this study was to evaluate the relative ability of the SLP with the FCC and with the VCC to discriminate between normal and glaucomatous eyes. DESIGN: Prospective, nonrandomized, comparative case series. PARTICIPANTS: Algorithm-generating set consisting of 56 normal eyes and 55 glaucomatous eyes and an independent data set consisting of 83 normal eyes and 56 glaucomatous eyes. TESTING: Sixteen retardation measurements were obtained with the SLP with the FCC and the VCC from all subjects. MAIN OUTCOME MEASURES: Dependency of parameters on age, gender, ethnic origin, and eye side was sought. Logistic regression was used to evaluate how well the various parameters could detect glaucoma. Discriminant functions were generated, and the area under the receiver operating characteristic (ROC) curve was determined. RESULTS: Discrimination between normal and glaucomatous eyes on the basis of single parameters was significantly better with the VCC than with the FCC for 6 retardation parameters: nasal average (P = 0.0003), superior maximum (P = 0.0003), ellipse average (P = 0.002), average thickness (P = 0.003), superior average (P = 0.010), and inferior average (P = 0.010). Discriminant analysis identified the optimal combination of parameters for the FCC and for the VCC. When the discriminant functions were applied to the independent data set, areas under the ROC curve were 0.84 for the FCC and 0.90 for the VCC (P<0.021). When the discriminant functions were applied to a subset of patients with early visual field loss, areas under the ROC curve were 0.82 for the FCC and 0.90 for the VCC (P<0.016). CONCLUSION: Individual correction for corneal birefringence with the VCC significantly improved the ability of the SLP to distinguish between normal and glaucomatous eyes and enabled detection of patients with early glaucoma.

Adult↗
PubMed2004

Relationship between visual field sensitivity and retinal nerve fiber layer thickness as measured by scanning laser polarimetry.

PURPOSE: To evaluate the strength and pattern of the relationship between visual field (VF) sensitivity and retinal nerve fiber layer (RNFL) thickness measurements by scanning laser polarimetry (SLP). METHODS: Fifty-four eyes of 54 normal subjects (age, 42 +/- 15 years; VF mean deviation [MD], -0.69 +/- 1.01 dB) and 51 eyes of 51 glaucoma patients (age, 66 +/- 14 years; VF MD, -6.92 +/- 5.43 dB) were imaged with an SLP using fixed corneal compensation (FCC) and variable corneal compensation (VCC). VF sensitivity was recorded in the dB and the 1/L scales. Linear and logarithmic relationships were sought globally and in six VF sectors. Relationships of VF and RNFL thickness with age were sought in normal subjects. RESULTS: Both VF sensitivity and RNFL thickness declined with age (as determined by the regression slope): -0.13% (P = 0.0005) and -0.64% (P = 0.0001) per year for dB and 1/L VF sensitivity, respectively, and -0.25% (P = 0.003) per year for VCC RNFL thickness. FCC RNFL thickness was not statistically significantly related to age. The relationship of VF sensitivity to VCC global (R(2) = 0.49) and sectoral (R(2) = 0.00-0.47) RNFL thickness was greater than for FCC global (R(2) = 0.12) and sectoral (R(2) = 0.00-0.21) RNFL thickness. Relationships were curvilinear with the dB scale, with logarithmic regression of dB VF sensitivity against RNFL thickness being significantly better than linear regression. Logarithmic regression of 1/L VF sensitivity against RNFL thickness was no better than linear regression for all sectors. There was no relationship between VF sensitivity and RNFL thickness in the temporal peripapillary RNFL sector. CONCLUSIONS: The strength of the structure/function relationships compare well with previous reports in the literature. The relationships were curvilinear with the dB scale and linear with the 1/L scale, and were much stronger with VCC than with FCC RNFL thickness measurements.

Adult↗
PubMed2003

Influence of cataract surgery with implantation of different intraocular lenses on scanning laser tomography and polarimetry.

PURPOSE: To describe the influence of cataract surgery with implantation of different intraocular lenses on scanning laser tomography (SLT) and scanning laser polarimetry (SLP) and to measure the birefringent properties of intraocular lenses in a laboratory setting. DESIGN: Prospective cohort study. METHODS: The influence of phacoemulsification cataract surgery with intraocular lens implantation (56 polymethylmethacrylate [PMMA; 31 Pharmacia/Upjohn 811 B and 25 Domilens Flex 60]; 25 hydroxyethylmethacrylate/methylmethacrylate (HEMA/MMA) [Technomed, Memory Lens]; 32 silicone [Allergan Si40]; 25 acrylic [Storz Hydroview]) on SLP and SLT measurements was evaluated preoperatively and 3 to 4 weeks postoperatively in 138 eyes of otherwise healthy patients. Lens opacities were classified according to the Lens Opacities Classification System III (LOCS III). Imaging was performed with TopSS and GDx (Laser Diagnostic Technologies, San Diego, California, USA) for SLT and SLP, respectively. Additionally, birefringent properties of intraocular lenses were measured in a laboratory setting. RESULTS: Our results show that imaging with SLT and SLP is possible with lens opacity-induced visual acuity reductions down to 0.2 and 0.16, respectively. There were no significant differences in the topographic parameters assessed before and after cataract surgery with SLT. However, standard deviations between three within-session single measurements were smaller postoperatively. Nerve fiber layer patterns were similar before and after cataract surgery with SLP, whereas certain total nerve fiber layer thickness values were significantly higher postoperatively. As a consequence, "the number" is significantly lower in the Domilens Flex 60 group (P =.01) and in the Storz Hydroview group (P =.02), and with a tendency also in the other groups as well. Measurements with a high-resolution optical bench revealed no birefringent properties of the implanted lenses. CONCLUSIONS: Our results indicate that after cataract surgery with intraocular lens implantation some SLP values are altered significantly, whereas SLT parameters are not influenced. These findings are of clinical interest, especially in the follow-up of glaucoma patients.

Acrylic Resins↗
PubMed2003

Reasons for rim area variability in scanning laser tomography.

PURPOSE: To determine reasons for rim area variability in scanning laser tomography. METHODS: Regional rim area variability from testing in same and different visits and by same and different observers was characterized in 30 normal and 42 glaucomatous eyes. Variations in (1) optic nerve head (ONH) surface geometry (center of gravity: X, Y, Z), (2) image tilting (horizontally and vertically), and (3) position of the reference plane in relation to the ONH (REF) were analyzed by multiple regression analysis. Whether and how much these factors explain rim area variability was studied in cross-sectional and longitudinal data by using two different reference planes. RESULTS: Variability was higher in glaucoma and in testing by different observers in separate visits. Across a range of eyes, approximately 40% of variability in single-topography images and 60% of variability in mean-topography images was explained. In individual image series, a median 85% of variability was explained, exceeding 90% in at least 25% of eyes. The most frequent contributors to rim area variability were REF (in > or =95%) and Z (in > or =80%); they also usually explained more variability than other factors. The nature of variability differed between reference planes. CONCLUSIONS: A large proportion of rim area variability was explained by variation in the topographical features studied, especially REF and Z. Reference plane definition also influenced variability. Variation in the position of the reference plane in relation to the ONH can affect rim area measurements and should be considered when evaluating the progression of glaucoma.

Aged↗
PubMed2002

Comparison of optic nerve imaging methods to distinguish normal eyes from those with glaucoma.

PURPOSE: To compare the ability of qualitative assessment of optic nerve head stereophotographs (ONHPs), confocal scanning laser ophthalmoscopy (CSLO), scanning laser polarimetry (SLP), and optical coherence tomography (OCT) to distinguish normal eyes from those with early to moderate glaucomatous visual field defects. METHODS: Eighty-nine eyes (63 normal, 63 age-matched with glaucoma) of 89 subjects more than 40 years of age were studied. Receiver operating characteristic (ROC) curves were generated from discriminant analysis of CSLO, SLP, and OCT measurements and from ONHP scores. Sensitivity at 80% and specificity at 90% were calculated. Differences between individual methods and combinations of methods were assessed for statistical significance. Agreement on categorization between methods (kappa) was assessed. RESULTS: The average visual field mean deviation (MD +/- SD) in patients with glaucoma was -3.9 +/- 2.2 dB, and the average pattern standard deviation (PSD) was 4.7 +/- 3.4 dB. In normal subjects the average MD was 0.1 +/- 0.9 dB and the average PSD was 1.5 +/- 0.3 dB. Optimal sensitivities, specificities, and areas under ROC curves were, respectively: ONHP (0.94, 0.87, 0.93), CSLO (0.84, 0.90, 0.92), SLP (0.89, 0.87, 0.94), and OCT (0.82, 0.84, 0.88). Best agreement on categorization (kappa) was between ONHPs and CSLO (0.70). The ROC area for the combination of methods was 0.99, higher than for any method alone. The ROC area for the combination of methods was significantly better than the CLSO rim area (P = 0.012) and the OCT retinal nerve fiber layer (RNFL) thickness (P = 0.002). CONCLUSIONS: The quantitative methods CSLO, SLP, and OCT were no better than qualitative assessment of disc ONHPs by experienced observers at distinguishing normal eyes from those with early to moderate glaucoma. A combination of the imaging methods significantly improves this capability.

Diagnostic Techniques, Ophthalmological↗
PubMed2002

Correction for the erroneous compensation of anterior segment birefringence with the scanning laser polarimeter for glaucoma diagnosis.

PURPOSE: To evaluate whether erroneous compensation for anterior segment retardation can be estimated and used to correct peripapillary (PP) retinal nerve fiber layer (RNFL) retardation measurements. METHODS: Retardation measurements (for the 780-nm wavelength), given as RNFL thickness by the scanning laser polarimeter, were obtained at the macula and PP retina in 45 eyes of 45 normal subjects and 53 eyes of 53 patients with early glaucoma. The correlation of macula and PP retardation was assessed. The normal range for RNFL retardation was defined as 97.5th minus 2.5th percentile (normal subjects). This was calculated for uncorrected PP RNFL retardation and for PP RNFL retardation corrected by retardation measurements taken in the macula (analysis 1) and in the temporal aspect of the PP measurement annulus (analysis 2). Further ranges were defined at different percentile cutoffs, and normal and glaucomatous eyes were classified as abnormal if retardation measurements were below each cutoff. The accuracy of classification by uncorrected and corrected measurements was assessed by receiver operating characteristic curve analysis. Uncorrected and corrected RNFL retardation was correlated with visual field mean deviation (MD). RESULTS: PP retardation correlated significantly with of macular retardation in normal (r(2) = 0.71, P < 0.000) and glaucomatous (r(2) = 0.41, P < 0.000) eyes. The normal range for uncorrected PP retardation was 25.4 degrees and for corrected retardation, 18.0 degrees (analysis 1) and 14.6 degrees (analysis 2), a reduction of 29% and 43%, respectively. For a specificity of 85%, the sensitivity to identify glaucomatous eyes of uncorrected and corrected (analyses 1 and 2) retardation was 26%, 55%, and 66%, respectively. Corrected PP retardation measurements correlated better with visual field MD (analysis 1: r(2) = 0.21; analysis 2: r(2) = 0.18) than did uncorrected measurements (r(2) = 0.05). CONCLUSIONS: Erroneously corrected anterior segment birefringence significantly affects PP RNFL retardation measurements. Retardation arising from the cornea-corneal compensator interaction can be partially estimated from the macula and temporal aspect of the PP measurement annulus, allowing correction of PP RNFL retardation. This provides a narrower normal range and greater sensitivity for glaucoma diagnosis.

Anterior Eye Segment↗