Summary Background: the recommended contour line (CL) location with the Heidelberg Retina Tomograph (HRT) is on the inner edge of Elschnig's scleral ring. This study investigated HRT parameter reproducibility when: (i) the CL size is altered relative to Elschnig's ring; (ii) the CL is either redrawn or imported between images. Methods: using the HRT, seven 10° images were acquired for 10 normal volunteers and 10 primary open angle glaucoma (POAG) subjects. A CL was drawn on one image for each subject using Elschnig's scleral ring for reference and imported into subsequent images. The CL diameter was then (a) increased by 50 μm; (b) increased by 100 μm; and (c) decreased by 50 μm. To investigate the effect of the method of contour line transfer between images a CL was: (1) defined for one image and imported to 6 subsequent images; (2) drawn separately for each image. Results: parameter variability improved as the size of the CL increased for the normal group relative to Elschnig's ring but was unchanged in the POAG group. The export/import function (method 1) resulted in better parameter reproducibility than the redrawing method for both groups. Conclusions: the exporting and importing function resulted in better parameter variability for both subject groups and should be used for transferring CLs across images for the same subject. Increasing the overall CL size relative to Elschnig's scleral ring improved the reproducibility of the measured parameters in the normal group. No significant difference in parameter variability was observed for the POAG group. This suggests that the reproducibility of HRT images are affected more by the variation in topography between images than change in CL definition.

PURPOSE:Although glaucomatous visual field defects are more common in the superior field than in the inferior field, microaneurysms are more frequent in the superior than in the inferior retina in diabetic retinopathy. The authors hypothesized that differences in vascular hemodynamics in the two areas might contribute to these phenomena.METHODS:The blood flow response to hyperoxia and hypercapnia was evaluated in peripapillary retinal tissue superior and inferior to the optic nerve head using confocal scanning laser Doppler flowmetry. In 14 young, healthy persons, blood flow was measured while breathing room air and during isocapnic hyperoxia (100% O2 breathing) and isoxic hypercapnia (PCO2 increased 15% above baseline). Histograms were generated from pixel-by-pixel analysis of retinal portions of superior and inferior temporal quadrants of the entire image.RESULTS:Baseline blood flow in the inferior temporal quadrant was significantly greater than in the superior temporal quadrant (P < 0.05). However, the inferior region failed to increase in perfusion during hypercapnia and experienced significant mean blood flow reduction; flow reduction in the pixels at the 25th, 50th, 75th, and 90th percentile of flow; and an increased percentage of pixels without measurable flow, during hyperoxia (each P < 0.05). In contrast, in the superior temporal region, hyperoxia failed to reduce blood volume, velocity, or flow, whereas hypercapnia significantly increased mean flow; increased flow in the pixels at the 25th, 50th, 75th, and 90th percentile of flow; and reduced the percentage of pixels without measurable flow (each P < 0.05).CONCLUSIONS:The inferior temporal quadrant of the peripapillary retina is, in comparison with the superior temporas region, less responsive to vasodilation and more responsive to vasoconstriction. These differences could contribute to different susceptibility to visual field defect or vascular dysfunction in the superior and inferior retina.

Purpose: To investigate whether topographical measurements of the optic nerve head are more reproducible when the contour line is redrawn for each image as opposed to imported using the Heidelberg Retina Tomograph (HRT). Introduction: Optic nerve head topography can be measured in vivo using Confocal Scanning Laser Ophthalmoscopes such as the HRT. Image analysis requires that the area of the optic disc is defined by subjectively drawing a contour line around Elschnig's ring. The HRT software can export this contour line between images for a subject, or the contour line can be redrawn. Method: Ten eyes of ten normal volunteers (40–60 years) were analysed with the HRT. Seven 10° images of the optic disc were taken by one observer for each randomly selected eye. Focus and scan depth settings were kept constant. All available stereometric parameters were analysed using three methods: (1) with a separately drawn contour line for each individual image, (2) with a contour line imported from the first image into subsequent images of the series, (3) by repeatedly redrawing the contour line for a single image from each eye. All contour lines were drawn by one observer. Mean co‐efficients of variation were calculated for each parameter for the three methods. Results: The mean co‐efficient of variation for the parameters ranged from 1.7–23.4% (method 1), 0–20% (method 2) and 1.6–13.4% (method 3). Conclusion: These results show that redrawn contour lines increase variability. Topographical measurements of the optic nerve head are more reproducible if the contour line is imported across subsequent images rather than redrawn for each individual image.