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Pathophysiology

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Oxy/deoxy Hemoglobin Enhanced Maps

Oxy/Deoxy hemoglobin enhanced maps can highlight critical pathologies as they relate to blood flow and oxygenation, including providing increased visibility of choroidal neovascular membranes (CNVM) and indications of perfusion, both of which are normally detected using invasive fluorescein angiography.

The hemoglobin absorption spectra for a range of oxygenation values are shown in Figure 1 below. These spectra form the basis for the oxy/deoxy hemoglobin maps which represent the ratio of oxygenated hemoglobin to deoxygenated hemoglobin in the retinal and choroidal vessels.

Figure 1

The image below (Figure 2) shows the oxy/deoxy hemoglobin enhanced image of a healthy eye created by processing the appropriate multi-spectral image data generated by the RHA system; the arteries which carry oxygenated blood are bright while the veins appear dark.

Figure 2

Figure 3 (a) below highlights a CNVM and the associated vascular net as well as the absence of vessels in a region inferior to the macula. Figure 3 (b) shows the same eye with a processed MSI multi-wavelength composite image, while Figure 3 (c) is a view of the CNVM using a 5 Line Raster OCT. These features, which typically were identified using invasive intravenous fluorescein angiography (IVFA) may now be identified using the non-invasive RHA system oxy/deoxy hemoglobin enhanced image map.

Figure 3 (a)

Figure 3 (b)

Figure 3 (c)

Stereo Imaging

Stereo imaging of the retina and the optic nerve head using anaglyphs allows clinicians to clearly visualize retinal topography, including pigment epithelial detachments (PED), edema and changes in the cup contour.

The light management capabilities of the RHA allow for stereo images to be collected without the camera or the patient changing position. Figure 4 below shows stereo images of a PED taken with a narrow band red illumination which is clearly visible as a 'blister', inferior to the macula. The stereo image is presented in an anaglyph form and can be viewed using a pair of glasses with a cyan lens over the right eye and a red lens over the left.

Figure 4 - Stereo Anaglyph Image

Figure 5 shows a second stereo example of a patient who experienced facial trauma as the result of  an automobile airbag injury.  The raised optic nerve head and peripapillary edema can clearly be seen in these images.

Figure 5 - Stereo Anaglyph Image

The stereo viewing feature is particularly useful for evaluating the optic nerve head, particularly cup shape and rim erosion.

Figure 6 - Left

Figure 6 - Right