Chancellery Research - Research Publications

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Author: Bedggood, Phillip × Author: McKendrick, Allison × Author: Turpin, Andrew × End date: 2017 × Type: Journal Article ×

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    Orientation of the Temporal Nerve Fiber Raphe in Healthy and in Glaucomatous Eyes
    Bedggood, P ; Nguyen, B ; Lakkis, G ; Turpin, A ; McKendrick, AM (ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2017-08)
    PURPOSE: To determine the normal variation in orientation of the temporal nerve fiber raphe, and the accuracy with which it may be predicted or approximated in lieu of direct measurement. METHODS: We previously described an algorithm for automatic measurement of raphe orientation from optical coherence tomography, using the intensity of vertically oriented macular cubes. Here this method was applied in 49 healthy participants (age 19-81 years) and 51 participants with primary open angle glaucoma (age 51-80 years). RESULTS: Mean fovea-disc-raphe angle was 173.5° ± 3.2° (range = 166°-182°) and 174.2° ± 3.4° (range = 166°-184°) in healthy and glaucoma patients, respectively. Differences between groups were not significant. Fovea-disc-raphe angle was not correlated with age or axial length (P > 0.4), showed some symmetry between eyes in glaucoma (R2 = 0.31, P < 0.001), and little symmetry in the healthy group (P = 0.06). Fovea-disc angle was correlated with fovea-raphe angle (R2 = 0.27, P = 0.0001), but was not a good predictor for raphe orientation (average error = 6.8°). The horizontal axis was a better predictor (average error = 3.2°; maximum error = 9.6°), but still gave approximately twice the error previously reported for direct measurement from macular cubes. CONCLUSIONS: There is substantial natural variation in temporal nerve fiber raphe orientation, which cannot be predicted from age, axial length, relative geometry of the disc and fovea, or the contralateral eye. For applications to which the orientation of the raphe is considered important, it should be measured directly.
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    Automatic identification of the temporal retinal nerve fiber raphe from macular cube data
    Bedggood, P ; Tanabe, F ; McKendrick, AM ; Turpin, A (OPTICAL SOC AMER, 2016-10-01)
    We evaluated several approaches for automatic location of the temporal nerve fiber raphe from standard macular cubes acquired on a Heidelberg Spectralis OCT. Macular cubes with B-scan separation of 96-122 µm were acquired from 15 healthy participants, and "high density" cubes with scan separation of 11 µm were acquired from the same eyes. These latter scans were assigned to experienced graders for subjective location of the raphe, providing the ground truth by which to compare methods operating on the lower density data. A variety of OCT scan parameters and image processing strategies were trialed. Vertically oriented scans, purposeful misalignment of the pupil to avoid reflective artifacts, and the use of intensity as opposed to thickness of the nerve fiber layer were all critical to minimize error. The best performing approach "cFan" involved projection of a fan of lines from each of several locations across the foveal pit; in each fan the line of least average intensity was identified. The centroid of the crossing points of these lines provided the raphe orientation with an average error of 1.5° (max = 4.1°) relative to the human graders. The disc-fovea-raphe angle was 172.4 ± 2.3° (range = 168.5-176.2°), which agrees well with other published estimates.