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A novel retinal imaging tool combining confocal scanning laser ophthalmoscopy (cSLO) with high-resolution spectral-domain optical coherence tomography (SD-OCT) allows for the first time simultaneous imaging with cSLO (including angiography and autofluorescence) and SD-OCT.
Frank G. Holz, MD, and colleagues at the University of Bonn in Germany described the features of the technology and presented images acquired using the dual platform in patients with various macular pathologies, including early, atrophic, and exudative age-related macular degeneration (AMD) and retinal vascular occlusions.
The device offers five cSLO imaging modes: fluorescein angiography, indocyanine green angiography, fundus autofluorescence, infrared, and redfree, any of which can be combined with simultaneous SD-OCT. The SD-OCT acquires 40,000 A-scans/second with a 7-µm depth and 14-µm lateral resolution. B-scans obtained with the SD-OCT system encompass an angle of 30° at a scan width of 1.536 (or 768) A-scans, lateral resolution of 6 (or 11) µm/pixel digital at a scan rate of 26 (or 50) B-scans/sec. The system also incorporates automated eye-tracking to adjust for any eye movement.
"With its high speed, the SD-OCT affords more comprehensive coverage of the retina, can generate 3-D images, and allows testing to be completed more quickly with reduced sampling errors from motion artifact," Dr. Holz said. "The high-transverse pixel density images acquired allow visualization of retinal ultrastructure from the internal limiting membrane to the retinal pigment epithelium cell/choriocapillaris. Such finely detailed images enable precise localization of intraretinal diseases and visualization of specific pathologic features."
Images presented in the poster depicted the clarity of vessel microarchitecture in an eye with exudative AMD and showed how the anatomic pathology correlated with leakage on fluorescein angiography.
"The instrument also allows for exact alignment of images obtained at different time points and, therefore, serial measurements of retinal thickness in SD-OCT cross-sections at precisely the same anatomic locations," Dr. Holz said. "In comparison with previous OCT techniques without the possibility of alignment, this feature will help clinicians to decide whether or not a reinjection is necessary in a patient treated with an intravitreal anti-VEGF agent."
In an eye with early AMD, the subconfluent soft drusen could be seen clearly in the SD-OCT image beneath the hyperreflective retinal pigment epithelium, and corresponding alterations on fundus autofluorescence were visualized on simultaneously acquired cSLO frames. In another example, the morphologic substrates of well-defined increased fundus autofluorescence signals in the junctional zone of areas with geographic atrophy were visualized at outer retinal layers.
A cSLO fundus autofluorescence image obtained in a patient with a recent branch retinal artery occlusion showed a decreased autofluorescence signal that correlated with features visible on funduscopy. Hyperreflectivity and swelling of the inner neurosensory retinal layers with a shadowing effect of posterior structures could be seen in an SD-OCT image. In a cross-section SD-OCT scan, the impacted calcified embolus in the retinal vessel could be visualized as a hyperreflective structure.