Qualitatively, beam tilt has a layer-specific influence on retinal eAC.
<p>A: To illustrate the anatomic location of OCT images, we here provide a T<sub>1</sub>-weighted magnetic resonance image of a mouse eye (axial resolution 21.875 μm; collected as part of a study [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217...
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| منشور في: |
2025
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| الملخص: | <p>A: To illustrate the anatomic location of OCT images, we here provide a T<sub>1</sub>-weighted magnetic resonance image of a mouse eye (axial resolution 21.875 μm; collected as part of a study [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref014" target="_blank">14</a>] in Dr. Bruce Berkowitz’s lab). Blue and red marks are placed in the retina ±625 µm from the optic nerve head, measured along the retina-choroid border. The contour of that border approximates a circle whose geometric center is marked with a white star, and is very near the optical rear nodal point for the whole eye (green star; ~ 1.62 mm interior to the corneal surface [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref015" target="_blank">15</a>] for a mouse with an axial length of ~3.35 mm). B-D: Estimated attenuation coefficient (eAC) OCT images of the same retina, captured at different beam tilts. Retinal data were sampled 175−625 µm (measured along CC) from the center of the optic nerve head in both the temporal (figure left; blue lines) and nasal (figure right; red lines) retina. The path of the OCT beam is vertical (purple arrow). Retinal layers are marked in panel C; retinal nerve fiber layer (RNFL), ganglion cell layer and inner plexiform layer (GCL & IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), external limiting membrane (ELM), the “ellipsoid zone” (ELIP), the outer segment tips at the “interdigitation layer” (INT), the retinal pigment epithelium (RPE), and choriocapillaris (CC). The anatomical correlate of a hyporeflecting band “X” between INT and RPE is controversial [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref016" target="_blank">16</a>]. B: The retina appears rotated clockwise because the OCT beam entered the pupil temporal to the optical axis of the eye. Path length to the temporal retina is reduced – it appears closer to the camera and higher in the image – compared to the path length to the nasal retina. Equivalently, the beam is tilted relative to anatomical borders, and the magnitude of beam tilt is derived from the apparent angle of tissue borders. By convention [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref004" target="_blank">4</a>], negative angles indicate an apparent clockwise rotation of the retina, and therefore a beam that is aimed in the temporal-to-nasal direction. Prior efforts [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref003" target="_blank">3</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref004" target="_blank">4</a>] assigned a single angle measurement per OCT image, but this was inadequate for the current dataset, as exemplified by variation at the temporal retina’s RNFL (−38° at 175 µm from the optic nerve, and −24° at 625 µm), and by the variation in RNFL signal within the nasal retina: When the retina-vitreous border is angled < −20° (right yellow arrowhead) the RNFL is darker than the adjacent retinal layers. At less-severe tilts (closer to 0°; left yellow arrowhead) the RNFL is brighter than the GCL & IPL. Note that ELIP and INT in the temporal retina is more reflective (higher eAC) than in the nasal retina. This pattern is also present in group-average data (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.g002" target="_blank">Fig 2</a>, top), and changes as beam tilt varies. C: When beam tilt is near-zero, the nasal and temporal retina look similar. Still, much of the outer retina (including ELIP and INT) appears slightly <i>less</i> reflective (darker grayscale; lower eAC) in the temporal retina compared to the nasal retina. Orange angled marks (\\\ and///) depict the ~ 14° tilt of photoreceptor inner and outer segments expected in the central retina [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0325217#pone.0325217.ref013" target="_blank">13</a>]. D: The OCT beam is aimed nasal-to-temporal, causing an apparent counter-clockwise rotation of the retina (beam tilt > 0°). Now, temporal/nasal differences in ELIP and INT reflectivity are reversed compared to panel B, presumably because the long axes of nasal photoreceptors are now well-aligned with the OCT beam. Lines perpendicular to CC are used to digitally linearize the retina for later processing. Along those lines – like the left-most blue line – beam tilt at the retina-vitreous border (+17°) need not match the beam tilt measured at CC (+13°). We use measurements at those two locations to assign a unique beam tilt to each location in the retina: Along that far left blue line, for instance, at depths one quarter, one half, and three-quarters into the retina, the assigned tilts are respectively +16°, + 15°, and +14°.</p> |
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