Comparison of confocal and non-confocal split-detection cone photoreceptor imaging

Abstract

Quadrant reflectance confocal and non-confocal scanning light ophthalmoscope images of the photoreceptor mosaic were recorded in a subject with congenital achromatopsia (ACHM) and a normal control. These images, captured with various circular and annular apertures, were used to calculate split-detection images, revealing two cone photoreceptor contrast mechanisms. The first contrast mechanism, maximal in the non-confocal 5.5-10 Airy disk diameter annular region, is unrelated to the cone reflectivity in confocal or flood illumination imaging. The second mechanism, maximal for confocal split-detection, is related to the cone reflectivity in confocal or flood illumination imaging that originates from the ellipsoid zone and/or inner-outer segment junction. Seeking to maximize image contrast, split-detection images were generated using various quadrant detector combinations, with opposite (diagonal) quadrant detectors producing the highest contrast. Split-detection generated with the addition of adjacent quadrant detector pairs, shows lower contrast, while azimuthal split-detection images, calculated from adjacent quadrant detectors, showed the lowest contrast. Finally, the integration of image pairs with orthogonal split directions was used to produce images in which the photoreceptor contrast does not change with direction.

Minimum intensity projection of embossed quadrant-detection images for improved photoreceptor mosaic visualisation

“…Their centres are 118.75 mm offset from the centre of the confocal pinhole. The image sequences of these four quadrants were mathematically combined similarly to that of split-detection, i.e., "legacy" vertical (90°) direction ( 8), whereas we also calculated the horizontal (0°), 45°, and 135°quadrant-detection images, which is afforded by dividing light into four rather than two detectors (Figure 2, black solid lines).The detection implementation is described in detail elsewhere (7). Photo-multiplier tube control voltages were adjusted by the operator throughout acquisition to maintain balanced mean pixel values across all quadrant detectors.…”

Insights into Sickle Cell Disease through the Retinal Microvasculature

“…[17][18][19][20][21][22][23][24] Backscattered light in AOSLO can be separated into confocal and non-confocal components. 25 Confocal AOSLO FA and reflectance imaging using singly scattered light have been used to visualize decreased macular microvascular density in eyes with sickle cell retinopathy (SCR). 26 Non-confocal imaging techniques using multiply scattered light have been shown to enhance edge contrast, improving the ability of AOSLO to reveal retinal vessel wall and blood flow features.…”

“…Non-confocal detection schemes include using offset detection, 22,27 splitdetection with the annular detection area split into two halves, 28 quadrant-detection with the annular detection area split into four sections, 25 or multi-offset detection. 22,[29][30][31] An important limitation of these techniques for a given image is that edge contrast enhancement is limited to the respective detector's direction, leading to sub-optimal visualization of edges that run parallel to the detector's direction.…”

“…9 The OCTA full vascular slab was segmented, extending from the inner limiting membrane to 9µm below the posterior boundary of the outer plexiform layer. The 10 25 During imaging, each participant's head was stabilized using a customized bite bar. Participants were instructed to direct their gaze to a green internal fixation target.…”

Imaging the structure and dynamic activity of retinal microglia and macrophage-like cells in the living human eye

“…Rossi et al showed that the non-confocal light distribution could be further sub-divided and similarly combined by using an offset aperture sequentially positioned at multiple points across the retinal conjugate focal to improve the contrast of weakly scattering cells, such as retinal ganglion cells 8,19 and microglia 8 . Recently, it was shown that adding an additional orthogonal split to the split-detection setup to achieve 4 quadrant detection 20 combined with an emboss filtering approach, could reveal a specific class of retinal microglia, the vitreous cortex hyalocytes, and the dynamics of their processes with high contrast. 9 An optical model has been proposed that suggests that these methods enhance contrast by exploiting spatial variations in the refractive index in a similar way to phase contrast microscopy 21 .…”