Development of a novel reference plane for the Heidelberg retina tomograph with optical coherence tomography measurements

Symmetry of optic nerve head parameters measured by the heidelberg retina tomograph 3 in healthy eyes: the Blue Mountains Eye study

PURPOSE

To assess the symmetry of optic nerve head parameters measured by the Heidelberg Retina Tomograph 3 (HRT 3) between fellow eyes in a normal elderly population.

DESIGN

Cross-sectional population-based study.

METHODS

Participants of the Blue Mountains Eye Study 10-year follow-up who did not have optic disc disease, including glaucoma, were included. Optic nerve head parameters measured by HRT 3 were compared between fellow eyes. The normal range of interocular asymmetry (larger disc minus smaller disc) was determined by the 2.5th and 97.5th percentiles.

RESULTS

A total of 1276 eligible participants had HRT scans of both eyes. HRT measurements in right eyes differed slightly in rim steepness and rim volume from those in left eyes (P < .05). The 2.5th and 97.5th percentile of interocular asymmetry limits were -0.41 and 0.45 for cup-to-disc ratio and -0.19 and 0.22 for cup-to-disc area ratio, respectively. The highest interocular correlation was found in disc area and cup area (r ranged from 0.74-0.76), whereas mean cup depth, cup volume, and retinal nerve fiber layer thickness had the poorest correlation (r ≤ 0.07). Greater optic disc area asymmetry was associated with a larger interocular difference in the other optic nerve head parameters.

CONCLUSIONS

There was minimal interocular difference and substantial interocular correlation in optic nerve head parameters measured by HRT 3. Interocular asymmetry greater than 0.2 for cup-to-disc area ratio was considered outside the normal range.

Correlation between morphology of optic disc determined by Heidelberg Retina Tomograph II and visual function in eyes with open-angle glaucoma

Purpose:

To investigate the correlation between the morphology of the optic disc and the visual function of eyes with open-angle glaucoma (OAG).

Patients and Methods:

One hundred and three eyes of 76 patients with OAG were studied. The baseline optic disc morphology was used to classify the eyes into four types: focal ischemic type (FI), myopic glaucomatous type (MY), senile sclerotic type (SS), and generalized enlargement type (GE). The morphological parameters of the disc were determined by the Heidelberg Retina Tomograph II (HRT-II) and the visual function by the mean deviation (MD) of the Humphrey field analyzer.

Results:

Fourteen eyes were classified as the FI type; 52 as the MY type; 17 as the SS type; and 20 as the GE type. The highest correlation coefficients of HRT-II parameters to the MDs was the cup/disc area ratio (r = −0.27) for all groups, the vertical cup/disc ratio (r = −0.42) in the MY group, the maximum cup depth (r = 0.49) in the SS group, and the cup area (r = −0.70) in the GE group. However, none of the parameters was correlated in the FI group.

Conclusions:

The correlation between the HRT-II parameters and MDs was different for the four disc types. These findings suggest that a classification of optic disc morphology had a benefit for interpreting the measured values of HRT-II.

Tilted optic disks

Tilted optic disks are a common finding in the general population. An expression of anomalous human development, the tilted disk appears rotated and tilted along its axes. Visual sequelae described with tilted optic disks include myopia, astigmatism, visual field loss, deficient color vision, and retinal abnormalities. Although the natural course of tilted optic disks is nonprogressive, the anomaly can be mistaken for tumors of the anterior visual pathway, edema of the optic nerve head, or glaucoma. A thorough examination of patients with tilted disk includes refraction, dilated fundus examination, and visual field testing. At times, neuroimaging may be necessary to arrive at the correct diagnosis. Until normative data are validated for tilted disks, the role of new imaging technologies for the optic nerve head is limited. Familiarity with the spectrum of ophthalmoscopic appearance and the clinical manifestations of tilted disks may be the most critical factors in avoiding misdiagnosis.

Detection of optic nerve head neural canal opening within histomorphometric and spectral domain optical coherence tomography data sets

PURPOSE

To assess the ability to detect the neural canal opening (NCO) and its characteristics within three-dimensional (3-D) histomorphometric and 3-D spectral domain optical coherence tomography (SD-OCT) reconstructions of the optic nerve head from nonhuman primate (NHP) eyes.

METHODS

NCO was delineated within 40 radial, sagittal sections of 3-D histomorphometric reconstructions of 44 normal eyes of 38 NHPs, each perfusion fixed at IOP 10 mm Hg, and 3-D SD-OCT (Spectralis; Heidelberg Engineering, Heidelberg, Germany) volumes acquired in vivo from a separate group of 33 normal eyes of 24 NHPs. Within all reconstructions, a least-squares ellipse was fitted to the 80 NCO points. For each eye, the dimensions and plane error (a gauge of planarity) of the fitted ellipse were calculated.

RESULTS

The NCO was successfully delineated within every section of each histomorphometric and SD-OCT reconstruction. Median plane error was similar within histomorphometric and SD-OCT volumes (8 microm, range 4-19, histomorphometry, and 10 microm, range 4-26, SD-OCT) and was small relative to the size of the ellipse. Median histomorphometric ellipse dimensions were 1453 mum (major axis, range 1218-1737) and 1066 microm (minor axis, range 808-1263). Median SD-OCT ellipse dimensions were 1512 microm (major axis, range 1191-1865) and 1060 microm (minor axis, range 772-1248).

CONCLUSIONS

The NCO is biologically continuous and relatively planar within all 3-D histomorphometric and SD-OCT reconstructions. These characteristics support its further evaluation as a reference plane for cross-sectional and longitudinal measurement of optic nerve head structures using 3-D SD-OCT.

Comparison of optic disc margin identified by color disc photography and high-speed ultrahigh-resolution optical coherence tomography

OBJECTIVE

To determine the correspondence between optic disc margins evaluated using disc photography (DP) and optical coherence tomography (OCT).

METHODS

From May 1, 2005, through November 10, 2005, 17 healthy volunteers (17 eyes) had raster scans (180 frames, 501 samplings per frame) centered on the optic disc taken with stereo-optic DP and high-speed ultrahigh-resolution OCT (hsUHR-OCT). Two image outputs were derived from the hsUHR-OCT data set: an en face hsUHR-OCT fundus image and a set of 180 frames of cross-sectional images. Three ophthalmologists independently and in a masked, randomized fashion marked the disc margin on the DP, hsUHR-OCT fundus, and cross-sectional images using custom software. Disc size (area and horizontal and vertical diameters) and location of the geometric disc center were compared among the 3 types of images.

RESULTS

The hsUHR-OCT fundus image definition showed a significantly smaller disc size than the DP definition (P <.001, mixed-effects analysis). The hsUHR-OCT cross-sectional image definition showed a significantly larger disc size than the DP definition (P <.001). The geometric disc center location was similar among the 3 types of images except for the y-coordinate, which was significantly smaller in the hsUHR-OCT fundus images than in the DP images.

CONCLUSION

The optic disc margin as defined by hsUHR-OCT was significantly different than the margin defined by DP.

Logistic Regression Analysis for Glaucoma Diagnosis Using Stratus Optical Coherence Tomography

PURPOSES

The purposes of this study are to investigate the diagnostic performance of logistic regression analysis (LRA) applied to multidimensional information on glaucoma disease and to determine the area under receiver operator characteristic curves (AROCs) for differentiating between normal and glaucomatous eyes in the Taiwan Chinese population based on the summary data from the Stratus Optical Coherence Tomography (OCT).

METHODS

One randomly selected eye from each of the 89 patients with glaucoma and from each of the 88 age- and gender-matched normal individuals were included in the study. Nine glaucomatous eyes and eight normal eyes were excluded as a result of poor OCT scans. Finally, 80 normal eyes and 80 glaucomatous eyes (mean deviation, -4.5 +/- 4.12 dB) were analyzed. The whole dataset was split into four equal sets. Each set combines 20 patients with glaucoma and 20 normal individuals. Fourfold crossvalidation was conducted. Retinal nerve fiber layer thickness and optic nerve head were measured by Stratus OCT in each patient. Twenty-five OCT parameters were included in a LRA method to determine the best combination of parameters for discriminating between glaucomatous and healthy eyes based on AROCs.

RESULTS

With the LRA method, the AROC for glaucoma detection was 0.911 with sensitivity at 80% and 90% specificity were 83.7% and 80.0%, respectively.

CONCLUSIONS

Compared with the OCT-provided parameters, the LRA method improved the ability to differentiate between normal and glaucomatous eyes in the Taiwan Chinese population.

Improving the repeatability of Heidelberg retina tomograph and Heidelberg retina tomograph II rim area measurements

AIMS

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Glaucoma follow-up by the Heidelberg retina tomograph--new graphical analysis of optic disc topography changes

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Imaging in glaucoma

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