Article

Thinning of the Papillomacular Bundle in the Glaucomatous Eye and its Influence on the Reference Plane of the Heidelberg Retinal Tomography

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Abstract

To measure the thickness of the papillomacular bundle in glaucomatous eyes with good visual acuity and to evaluate the influence of an adjusted reference plane on the Heidelberg retinal tomography result. The thickness of the papillomacular bundle was measured with optical coherence tomography in both eyes of eight patients with asymmetric glaucoma. The eye with less glaucomatous damage with normal visual field served as the control. The difference in the thickness of the papillomacular bundle between the control eye and the glaucomatous eye was used to correct the reference plane of Heidelberg retinal tomography. The thickness of the papillomacular bundle in glaucomatous eyes was reduced (P = 0.00037) and was 33.9 +/- 16.5 microm thinner than control eyes. A corrected reference plane in Heidelberg retinal tomography caused an increased classification value (-0.683 +/- 0.164), implying that more glaucoma damage was detected after the correction. In one case the value was shifted from normal to glaucomatous after an adjustment of the reference plane. The thickness of the papillomacular bundle is decreased in glaucomatous eyes, though these eyes have good visual acuity. Evaluation of glaucoma with Heidelberg retinal tomography using the standard reference plane may underestimate the glaucoma damage.

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... Researchers have traditionally sought to position reference planes by landmarks presumed to be relatively unchanged by glaucoma, although whether such landmarks remain truly unchanged by disease has been debated (Chen et al, 2001). ...
... It is postulated that the standard and 320p.m reference planes are positioned relative to regions that are relatively unchanged in glaucoma, namely the papillomacular nerve fibre layer bundle and far peripapillary retina respectively (Heidelberg Engineering, 1993;Burk et al, 2000). This has been challenged, however (Chen et al, 2001), and it is possible that changes in these regions could cause the reference plane to shift unpredictably relative to the optic nerve head. Alternatively, the deteriorating optic nerve head could itself shift relative to regions by which the reference plane is fixed so that the reference plane becomes more superficial in the optic nerve head with advancing damage, as illustrated by Figure 9.12. ...
... For instance, lOP is suggested to affect the compliance and position of the optic nerve head and lamina cribrosa (Burgoyne et al, 1995a;Zeimer and Ogura, 1989; influence the reference plane's position in three-dimensional space and relative to the optic nerve head. Chen et al (2001) have suggested that the standard reference plane may shift with topographical change due to glaucoma; the author's own studies show that fluctuation from test to test in the position of the optic nerve head, reference plane or both can itself affect measurement (Chapters 7, 8 and 9). ...
Thesis
Analysis of sequential scanning laser tomography of the optic nerve head must be able to tell disease-induced change from measurement variability if it is to be useful for identifying glaucoma progression. Variability in neuroretinal rim area measurement was found to differ between optic nerves and between regions within each nerve, and was influenced by glaucomatous morphology, varying test conditions and different reference planes. Up to 95% of this variability could be explained by fluctuation in the height between the nerve surface and reference plane, and of the nerve head's centre of gravity along the z-axis. Such fluctuation, whether due to image variability or progressive disease, affects the position of conventional reference planes and limits their usefulness as absolute measures of change. A novel reference plane was designed that is customised to each optic nerve head, lies at a depth compatible with least variability, and stays in position despite glaucomatous damage. Its position in any nerve is calculated from surface height at the nerve margin in multiple topography images, and kept constant throughout each image series. It was found that the reference plane's description of neuroretinal rim was more reproducible and corresponded more closely with actual rim appearance compared with conventional reference planes. An analytical approach was devised to identify change based on this new reference plane. Variability in each 30degree sector of rim area in each nerve was estimated by modelling variability within images from all time-points of any nerve's image series. Confidence limits of variability represented variability in each sector, and only change repeatedly exceeding these limits in two of three tests was attributed to disease. Assessed by 90% and 95% limits of variability, progression was identified with a sensitivity and false positive rate of 90% and 6%, and 83% and 3% respectively in ocular hypertension converter eyes with unambiguous glaucomatous visual field change and unchanging eyes of normal controls. When tested in various presentations of suspected and manifest normal-pressure and high-pressure glaucoma, progression was detected in glaucoma suspect eyes without visual field defects, eyes that progressed to develop field defects, and eyes with established and more severe glaucoma.
... The special feature of the papillomacular bundle area has been noted by other researchers. Chen et al. [54] reported a reduction in papillomacular bundle thickness on the time-domain OCT in glaucoma patients even when the visual acuity remained good. Later Kita et al. [55] found that the RNFL thickness calculated in a sector corresponding to the papillomacular bundle was spared in early glaucoma. ...
Article
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PURPOSE: To correlate multifocal electroretinogram (mfERG) findings in the macular area of glaucoma patients with automated perimetry (visual fields) and with optical coherence tomography (OCT). METHODS: A two-global flash mfERG (VERIS™) was recorded in 20 eyes with primary open-angle glaucoma. The root mean square was calculated, and three response epochs were analysed: the direct component (15-45 ms) and two induced components (IC-1 at 45-75 ms and IC-2 at 75-105 ms). The central 10° of the mfERG was compared to the central 10° of the OCT and of the visual field. Responses grouped in a superior and in an inferior semicircle, extending between 10° and 20°, were also compared to the corresponding areas of the OCT and of the visual fields. In addition, the area of the papillomacular bundle was also analysed separately. RESULTS: In glaucoma patients, mfERG responses showed a significant positive association with retinal thickness in the central 10° for IC2 (p = 0.001) and a trend for IC1 (p = 0.066). A significant association was found between the central IC1 and IC2 of the mfERG and corresponding perimetric sensitivities expressed in linear units (p < 0.01). The OCT showed a positive association with visual field sensitivities (p < 0.05) in all areas examined (p < 0.05). Separation of the papillomacular bundle area did not improve structure-function association further. CONCLUSIONS: In our study, mfERG showed a statistically significant correlation with perimetric sensitivity measured in linear units and with structural macular changes detected with time-domain OCT.
... IOP is suggested to affect the compliance and position of the optic disc and lamina cribrosa, [14][15][16][17][18] and its effect on topography could unpredictably influence the reference plane's position in three-dimensional space and relative to the optic disc. The standard reference plane may shift with topographical changes due to glaucoma 19 or test variability. 20 Analysis of reversal of cupping in the present study was by the experimental reference plane, which is positioned and customized to each eye to maintain an unchanging height relationship with the optic disc, which should help minimize possible measurement artifact caused by IOP variation. ...
Article
To identify and characterize 'reversal' of optic nerve cupping following intraocular pressure (IOP) lowering in scanning laser tomography (SLT) longitudinal image series. Modification was made to a previously described analytical approach to longitudinally study putatively increased rim area following IOP lowering. Sustained IOP reduction of 25% was by topical medication. Forty SLT image series with equivalent follow up were assessed: 10 with ocular hypertension (OHT), 10 with primary open angle glaucoma (POAG), and as controls, 20 normal. Reproducible rim area reversal was identified by sector and its time-course over 1 year examined. By a 2-of-3 reproducibility criterion, reversal following IOP lowering was confirmed in about a third of treated eyes (POAG and OHT) but not in any controls. Rim sectors showing reversal were mostly nasal, with a few occurring superotemporally. Reversal in a fifth of treated eyes persisted for at least 1 year; all these were in the nasal half of the disc. The number of sectors with persisting reversal affected less than 6% of all treated eyes' rim sectors. Rim area is not uncommonly increased after IOP lowering and this 'reversal' may persist for at least a year. Within topically treated eyes having IOP lowering of at least 25%, the proportion of rim sectors with persistent reversal appears small. Nevertheless, the effects of IOP reduction on topography, especially in the short term, should be considered when longitudinally assessing progressive rim loss in SLT images.
... Reference planes have usually been positioned by landmarks presumed to be relatively unaffected by glaucoma, although whether this is true has been debated. 17 The experimental reference plane differs in being positioned by a landmark that is expected to change in glaucoma. But there are reasons that this position is useful. ...
Article
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To describe and evaluate a new experimental reference plane for measuring rim area in scanning laser tomography. The experimental reference plane was positioned so that (1) it always lay entirely below the margin of the optic nerve head (ONH), (2) it remained at a set z-axis distance below the ONH in images of each eye, and (3) it was at a level where variability in rim area is least. Twenty normal control subjects and 20 patients with glaucoma underwent test-retest scanning laser tomographic imaging by same and different operators during same and separate visits. Control subjects had image series spanning at least 3 years. The effect of the positioning of the reference plane on global and regional rim area variability was assessed in intra- and intervisit test-retest images and longitudinal image series and compared with the standard and 320- microm reference planes. Variability in the experimental reference plane was less in test-retest images and longitudinal data (P < 0.05) and more uniform around the ONH than with other reference planes. Variability in the former was not appreciably affected by testing involving different operators and visits, or by the presence of glaucoma. Variability in rim area by the experimental reference plane was significantly less, more uniform around the ONH, not affected by different operators and visits, and less affected by glaucomatous morphology than other reference planes. This difference was pronounced in sequential data and has implications for detecting progression of glaucoma.
... This has not been supported by retinal thickness measurements derived from optical coherence tomography (OCT) in glaucoma subjects. 25 The mean retinal nerve fibre layer thickness estimated by OCT has been used to set a novel reference plane that may be useful to detect early glaucoma, particularly in tilted optic discs. 26 It has been reported in our companion paper that there is variability in inter-test reference height and, therefore, in the height of the contour line at the temporal ONH margin. ...
Article
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To devise and test strategies for improving Heidelberg retina tomograph (HRT and HRT-II) rim area (RA) repeatability and assess the benefit of the strategies in time series of HRT images. The effect of the standard and 320 microm reference planes and image quality on RA repeatability was assessed in a test-retest HRT image dataset from 74 subjects. A longitudinal HRT image dataset from 30 ocular hypertensive subjects was analysed by linear regression of RA over time, with each of the reference planes and using a manual image alignment facility. RA variability was estimated by comparing the standard deviation of residuals (RSD) generated by each linear regression. RA repeatability was better with the 320 microm reference plane (repeatability coefficient 0.17 mm(2)), improving further with only good quality images (repeatability coefficient 0.08 mm(2)). For the longitudinal data, a significant (p<0.0001) reduction in the RSD from 0.10 to 0.05 mm(2) was obtained with the 320 microm reference plane. Manual alignment led to a further significant (p<0.0001) reduction in the RSD to 0.04 mm(2). The findings support the use of a 320 microm reference plane and manual image alignment to analyse RA over time. The estimates of RA repeatability may be used to define thresholds for glaucomatous change.
... However, an OCT study has shown that the retinal nerve fiber layer thickness at the papillomacular bundle becomes thin in glaucoma. 34 The experimental RP was designed with the purpose of overcoming the limitations of the other RPs. It always lies below the ONH margin contour line, and it does not rely on a localized region at the ONH margin for the determination of its depth position. ...
Article
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The values of Heidelberg Retinal Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany) stereometric parameters depend on the reference plane (RP), the instability of which results in parameter variability. Identification of change depends on RP stability. This study was undertaken to evaluate the influence of various RPs on rim areas (RAs) in a longitudinal image series. A longitudinal image series of 31 subjects with ocular hypertension who had reproducible visual field loss and 19 normal subjects was analyzed using five different RPs: the standard RP (HRT software version 3.1.2.0), two 320-mum RPs (software ver. 3.1.2.0 and 1.7.0), a previously described experimental RP, and a new Moorfields RP. The Moorfields RP takes the standard RP at baseline and then is fixed relative to the reference ring for subsequent images. Linear regression of RA over time was performed, and the slope and residual SD (RSD) were calculated for each RP. Comparisons between RPs were made by paired t-tests. In eyes with progressing disease, application of the standard RP resulted in significantly greater variability (as measured by the RSD) compared with other RPs (mean 0.057 mm(2) vs. 0.035-0.038 mm(2)). There was a trend toward faster RA change/time (mean, -0.0123 mm(2)/y) for the standard RP and slower (-0.0095 mm(2)/y) for the experimental RP. There was a trend for the Moorfields RP to result in the best signal-to-noise ratio (speed of RA change/variability): mean RA slope -0.0118 mm(2)/y and mean global RSD 0.037mm(2). Compared to the standard RP, the Moorfields RP has significantly lower variability and probably provides a greater facility for discriminating RA change from measurement variability in a longitudinal HRT image series.
Chapter
The Heidelberg retina tomograph (HRT) is a confocal laser scanning system designed to acquire and analyse three-dimensional images of the posterior segment of the eye. The topography is presented as a colour-coded map, with darker colours representing more superficial structures and lighter colours representing deeper structures. Clinical evaluation of the ONH is mainly based on HRT parameters and their formulas such as the Moorfields regression analysis (MRA) and the various linear discriminant functions. No commercially available imaging device is able to discriminate perfectly between normal and glaucomatous eyes – there is an overlap in measurements between the two; however, when an eye with glaucoma will be classified as ‘borderline’ or ‘outside normal limits’, the final decision as to whether an eye is glaucomatous or not is a clinical judgement, based on all available clinical data. A potentially important clinical application of the HRT is the detection of glaucomatous progression from a baseline image. Topographic change analysis (TCA) is a statistical method to compare the topographic height values in discrete areas of the image. The analysis requires the mean of a set of three topographic images at each point in time, so that each pixel in the image will have three height values. The key determinant in the TCA is the variability in topographic height values within the superpixel over the two sets of three images for each comparison (three at baseline, three at follow-up).
Article
Background: To monitor the efficiency of glaucoma therapy it is necessary to detect progression of the disease as soon as possible. This survey presents the results on functional and morphological approaches to detect glaucoma progression. Material and Methods: Risk factors identified in the therapeutic intervention studies should be used to evaluate the possible risk for progression. The functional test approaches of standard achromatic perimetry (SAP), short wavelength automated perimetry (SWAP) and frequency doubling technology (FDT) are described. Furthermore, morphologic changes are described by means of optic nerve head and nerve fiber photography, optic nerve head tomography, optic coherence tomography and nerve fiber polarimetry. Results: The risk factors identified in the interventional studies were as follows: 1. higher intraocular pressure, 2. worse mean deviation (MD), 3. older age, and 4. frequent disc hemorrhages. Additionally, in patients with normal pressure glaucoma, migraine headaches were identified. Patients with ocular hypertension showed a higher risk of conversion into open angle glaucoma in case of higher pattern standard deviation (PSD), thinner central corneal thickness and larger vertical cup-to-disc ratio. The optic nerve head photography was the standard procedure of morphological monitoring in the interventional studies. A direct comparison of the available techniques on nerve fiber thickness and optic nerve head morphology is not yet available. SAP represents the functional methodology with the most validated results. SWAP and FDT showed that progression in early glaucoma can be detected before SAP damage occurs. Conclusion: Glaucoma patients should be regularly tested with SAP and optic nerve head photography. Automated nerve fiber or optic nerve head morphology measuring techniques might be favourable to complete the diagnostic monitoring. In patients without glaucomatous damage SWAP and FDT may be able to detect changes earlier than SAP. The results of a review of the literature are presented and discussed for each technology.
Article
Hintergrund: Die Grenzziehung zwischen frühen glaukomatösen Schäden und Normalbefunden, aber auch die Verlaufsbeobachtung von Glaukompatienten bereiten noch immer häufig Probleme. In den letzten Jahren wurden zahlreiche neue Untersuchungsmethoden für Glaukom erprobt und teilweise bereits am Markt eingeführt. Methoden: Die vorliegende Zusammenfassung gibt einen Überblick über die Ziele apparativer Untersuchungen bei Glaukom und Glaukomverdacht. Die für einen breiteren Einsatz in der ophthalmologischen Praxis infrage kommenden Untersuchungsmethoden werden bezüglich ihrer Eignung für die Ziele der Frühdiagnose, objektiver Diagnostik, Progressionsanalyse und Screeningeinsatz beurteilt. Schlussfolgerungen: Bislang haben die neuen apparativen Methoden das diagnostische Vorgehen nur gering beeinflusst. Dies liegt im Wesentlichen daran, dass gerade bei den problematischen Glaukomgrenzfällen auch diese Methoden nur über eine limitierte Aussagekraft verfügen oder noch nicht ausreichend untersucht wurden. Dennoch können hier der Heidelberger Retina Tomograph (HRT), der Nervenfaseranalysator GDx, die Blau/gelb-Perimetrie sowie der Frequenzverdopplungstest (FDT) eine gewisse Rolle spielen. Zur Therapiekontrolle haben sich der HRT und das GDx vor allem in frühen Krankheitsstadien bewährt. Der FDT eignet sich durch sehr kurze Untersuchungsdauer, gepaart mit guter Spezifität, gut als Screeningtest.
Chapter
Measuring disease progression is vital in the management of patients with glaucoma and ocular hypertension. Progression may be assessed by structure (optic disc photography or semi-automated imaging devices) and function (perimetry). Progression strategies may be subdivided into “event analyses” (progression requires a predetermined threshold to be exceeded) and “trend analyses” (the behaviour of the parameter over time is monitored). Stereophotographic examination is prone to high inter-observer variability. Amongst imaging devices, the HRT has the most published longitudinal data, as it has been commercially available for the longest time and its software is “backward compatible”. Two progression algorithms are currently available in the HRT software: “trend analysis” and “topographical change analysis”. To date there are no statistically supported progression algorithms in the OCT or GDx-VCC operational software. There is poor concordance between HRT and visual field progression. The reasons for this remain unclear.
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The Heidelberg Retina Tomograph (HRT) is a commercially available instrument for the detection of glaucomatous damage by analysis of optic nerve head topography. The main purpose of the study was to investigate the ability of HRT to detect changes in optic disc topography indicating progression of optic neuropathy in eyes with open-angle glaucoma or, in eyes with ocular hypertension, conversion to open-angle glaucoma. Fifty-nine subjects (34 with ocular hypertension, 25 with glaucoma) from the glaucoma service at Sahlgrenska University Hospital were included in this study. One eye of each patient was selected. All participants underwent thorough clinical examination, including HRT, high-pass resolution perimetry (HRP), and optic disk photography. After a mean follow-up time of 50 months, patients were re-examined. Based on analyses of optic disc photographs and HRP, eyes were classified into one of two groups: progressive or stable. The differences between baseline and follow-up HRT parameters in the two groups were analysed. The topographic HRT change images were also compared after digital image processing. A pixel ratio was calculated defined as the ratio between the area of pixels representing deepening of the disc surface and the total disc area. Receiver operating characteristic (ROC) curves for HRT parameters and pixel ratio were compared. In the group judged to have progressive optic neuropathy, a statistically significant change between baseline and follow-up examination was found for the following HRT parameters: cup shape measurement, classification index, the third moment in contour, cup/disc ratio, cup area, rim area, and area below reference). In the stable group no HRT parameters had changed significantly. A well-defined distinction between the two groups was found by comparing digitally processed HRT change images. The area under the ROC curve was larger for pixel ratio than for any of the HRT parameters. The HRT is a useful tool for long-term follow-up of glaucomatous optic neuropathy. Digital image processing of HRT change images could facilitate the detection of progressive change.
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To determine the relationship between optical coherence tomography (OCT) images of the retina and retinal substructure in vitro and in vivo. In vitro, OCT images of human and bovine retina were acquired after sequential excimer laser ablation of the inner retinal layers. Measurements of bands in the OCT images were compared with measurements of retinal layers on histology of the ablated specimens. In vivo, OCT images were acquired of retinal lesions in which there was a displacement of pigmented retinal pigment epithelial (RPE) cells: retinitis pigmentosa and laser photocoagulation (eight eyes each). The mean thickness of human inner OCT bands (131 microm; 95% confidence interval [CI], 122-140 microm) was 7.3 times that of the retinal nerve fiber layer (RNFL). This band persisted despite ablation greater than 140 microm. The inner aspect of the outer OCT band corresponded to the apical RPE, but the mean thickness of this band in human tissue (55 microm; 95% CI, 48-62 microm) was 2.6 times the thickness of the RPE-choriocapillaris complex. OCT measurement of total retinal thickness was accurate (coefficient of variance, 0.05) and precise (coefficient of correlation with light microscopy, 0.98). Hyperpigmented lesions gave rise to high signal, attenuating deeper signal; hypopigmented lesions had the opposite effect on deeper signal. The inner band is not RNFL specific, partly consisting of a surface-related signal. The location, not thickness, of the outer band corresponds to RPE melanin. Given the additional effect of polarization settings, precise OCT measurement of specific retinal layers is currently precluded.
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Objective: To determine whether diabeteslike lesions associated with the proliferative stage of diabetic retinopathy develop in galactose-fed dogs, since studies designed to define the complex biochemical effects of prolonged hyperglycemia on retinal vessels have been hampered by the lack of an animal model that mirrors both the early and advanced stages of diabetic retinopathy.Methods: Eyes from 9-month-old male beagles fed a daily diet containing either 30% nonnutrient filler (control diet) or 30% galactose (galactose diet) for up to 84 months were enucleated and histologically examined.Results: Retinal vessel changes associated with the proliferative stage were observed in two of nine galactose-fed dogs while the remainder demonstrated retinal changes that included the appearance of microaneurysms, acellular capillary beds associated with areas of nonperfusion, and intraretinal microvascular abnormalities. Proliferative changes were evidenced by the formation of preretinal fibrous membranes and the appearance of fibrovascular membranes on the retinal surface and on the posterior hyaloid membrane. No retinal lesions were observed in similar dogs fed a control diet for up to 84 months.Conclusion: The galactose-fed dog appears to be the first animal model that can develop diabeteslike retinal vessel changes associated with both the early and advanced stages of retinopathy, including the proliferative stage.
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The Heidleberg Retina Tomograph provides rapid, reproducible measurements of optic disc topography as well as calculations of disc parameters. We used a stepwise discriminant analysis to determine which parameters were most useful in detecting individuals with early glaucomatous visual field loss. We studied one eye in each of 45 normal individuals and one eye in each of 46 individuals with early glaucomatous visual field loss. The appearance of the optic disc was not used for classification purposes so as not to bias the diagnostic determination obtained by the instrument. The data were analyzed using the reference plane of the software version 1.10 and using a method incorporating the height of the papillomacular bundle as reference level with and without age correction. We obtained an 89% sensitivity and 78% specificity for the detection of early visual field loss using the standard reference level. The jackknife classification revealed lower sensitivity of 87% and an unchanged specificity of 78%. With the method incorporating the height of the papillomacular bundle as reference level, the sensitivity was 87% and the specificity was 84% for detecting early visual field loss. The jackknife classification revealed a sensitivity of 87% and a specificity of 82%. With the age correction, the sensitivity was 87%, specificity 84% with regular and jackknife classification. With the standard reference level, the important parameters were the third moment and the maximum depth, with the papillomacular bundle reference level volume above reference level added as important, and with age correction, height variation in contour replaced maximum depth in the analysis. Three significant shape parameters of the optic disc can be used to detect early glaucomatous visual field loss.
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The authors evaluated the accuracy of topographic measurements with the laser tomographic scanner using a model eye. Diameter, depth, and shape at different axial lengths of four sample holes that simulated optic nerve heads in phakic and aphakic conditions were determined by confocal imaging. The computer-generated cross-section profiles of the simulated optic nerve heads corresponded well with the actual contours as photographed by scanning electron microscopy. The average relative error in diameter was 2.0% (range: 0.3-2.9%) for the phakic model eye and 3.6% (range: 0.6-8.2%) for the aphakic model eye. The average relative error in depth was 11.7% (range: 1.2-20.1%) for the phakic model eye and 10.1% (range: 1.7-22.6%) for the aphakic model.
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We acquired five independent topographic images of the optic nerve head of eight normal eyes and eight eyes with primary open-angle glaucoma with a laser tomographic scanner. Each image had a field of view of 15 x 15 degrees with a resolution of 256 x 256 pixels. The pixel size was approximately 15 x 15 microns. The value of a pixel of a topographic image represented the height at this position. The mean height and the standard deviation over the five topographic images were calculated for each of the 65,536 pixel positions. The standard deviation of a single height measurement in normal eyes was 38.7 microns (range, 23.4 to 62.2 microns) for areas in the peripapillary retina and 42.6 microns (range, 24.4 to 53.7 microns) for measurements within the optic nerve head area. In glaucomatous eyes, the standard deviation was 41.2 microns (range, 23.2 to 59.6 microns) in the peripapillary retina and 49.4 microns (range, 28.1 to 72.8 microns) within the optic nerve head. There was no significant difference between the standard deviation of a single height measurement in normal and glaucomatous eyes (P = .34 within the optic nerve head area; P = .57 on peripapillary retina). No correlation was found between standard deviation of the measurements and pupil size or age of the subject.
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We describe the use of a laser tomographic scanner to objectively measure optic nerve head topography. A laser beam is focused on the optic disc using confocal imaging. Reflected light is detected only if it originates from a small region around the focal place of the special optics. Optic disc parameters are calculated from the measured values of confocal reflected light. In five glaucomatous eyes, maximum cup depth was between 0.33 mm and 0.58 mm. Cup volume was between 0.10 mm3 and 0.65 mm3; it correlated well with ophthalmoscopy. Compared with conventional imaging systems, the laser tomographic scanner has certain advantages: 1) images can be obtained with miotic pupils; 2) clarity of media is not important; 3) low light intensity is employed; and 4) a real time image is obtained.
Article
Topographic analysis and measurement of the optic nerve head is important for the diagnosis and follow-up of glaucoma. To quantify structures of the optic nerve head the new technique of laser tomographic scanning was used. A laser beam was focused onto the surface of the optic nerve head and the reflected light was detected in a confocal detection unit. The consequent change of focus produced a tomographic scanning series and allowed measurement of three-dimensional structures. To analyze the reproducibility of optic cup measurements the authors did ten recordings of one eye of eight normal volunteers. The mean standard deviation of the measurements was +/- 0.015 mm3 and the mean coefficient of variation was 9.5%. Confocal laser tomographic scanning is a safe, effective, convenient method to measure and document the topography of the optic nerve head and should be a valuable technique for follow-up of glaucoma patients.
Article
To determine whether diabeteslike lesions associated with the proliferative stage of diabetic retinopathy develop in galactose-fed dogs, since studies designed to define the complex biochemical effects of prolonged hyperglycemia on retinal vessels have been hampered by the lack of an animal model that mirrors both the early and advanced stages of diabetic retinopathy. Eyes from 9-month-old male beagles fed a daily diet containing either 30% nonnutrient filler (control diet) or 30% galactose (galactose diet) for up to 84 months were enucleated and histologically examined. Retinal vessel changes associated with the proliferative stage were observed in two of nine galactose-fed dogs while the remainder demonstrated retinal changes that included the appearance of microaneurysms, acellular capillary beds associated with areas of nonperfusion, and intraretinal microvascular abnormalities. Proliferative changes were evidenced by the formation of preretinal fibrous membranes and the appearance of fibrovascular membranes on the retinal surface and on the posterior hyaloid membrane. No retinal lesions were observed in similar dogs fed a control diet for up to 84 months. The galactose-fed dog appears to be the first animal model that can develop diabeteslike retinal vessel changes associated with both the early and advanced stages of retinopathy, including the proliferative stage.
Article
The objective of this article was to evaluate whether a new method for analysis of optic nerve topography, the ranked-segment distribution (RSD) curve, can differentiate between normal and glaucoma eyes. Topographic optic nerve parameters of 39 normal subjects aged 50-79 years were measured using a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Disc parameters were determined from the mean topography of three images of each eye obtained with a 15 degrees field of view. Rim area and retinal nerve fiber layer cross-section area were measured in 36 segments (each of 10 degrees) around the disc margin. For each parameter, the 36 segments were ranked in descending order and graphically depicted as the RSD curve. In normal eyes, the fifth percentile values for each of the ranked segments were calculated and graphed to compare with glaucoma eyes within the same age group. Evaluation of RSD curves was done automatically with a computer program using predefined criteria. Three primary open-angle glaucoma cases are presented to demonstrate the RSD curve method. In these three glaucoma eyes, RSD curves demonstrated defects more consistently than stereoscopic disc photography, nerve fiber layer photography, and computerized visual field testing. In two cases, RSD curves differentiated between diffuse and localized defect as well as demonstrated the locations of the defects. The RSD curve technique may assist in the interpretation of topographic optic nerve parameters and in the detection of glaucomatous optic neuropathy.
Article
Optic nerve head drusen often make evaluation of the nerve head difficult to interpret. In addition, visual field defects are known to occur in patients with optic disk drusen, resembling glaucomatous damage. The authors report two cases of coincident optic nerve head drusen and glaucoma, in which the use of optical coherence tomography (OCT) in evaluating the nerve fiber layer was beneficial. Two patients with both optic nerve head drusen and glaucoma, one with primary open angle glaucoma, the other with pseudoexfoliation glaucoma were evaluated. Both patients had asymmetric optic disk drusen, with clinically visible drusen only in one eye. Ophthalmologic examination, color and red-free photography, automated Humphrey visual field testing and OCT were performed. Nerve fiber layer loss as measured by OCT was found to be greater than expected by the appearance of the optic nerve head and red-free photography, with visual fields consistent with findings in case 1. In case 2, visual fields were full, despite nerve fiber layer thinning seen by OCT and red-free photography. There can be significant nerve fiber layer thinning in patients with both glaucoma and optic disk drusen, despite the appearance of the optic nerve head in these patients. The cup margin may be obscured by the drusen, giving rise to a falsely full-appearing disk. In such cases, OCT may provide a useful means to quantitatively measure the nerve fiber layer thickness and to aid in the management of these patients by detecting nerve fiber layer thinning earlier than would otherwise be possible.