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R Daniel Ferguson, Mircea Mujat, Ankit Patel, Nicusor V Iftimia; Adaptive Optics Line-scan Ophthalmoscope (AO-LSO) using a Time-domain Integration (TDI) Camera. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1598.
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© ARVO (1962-2015); The Authors (2016-present)
To compare two imaging modalities of the compact multimodal AO-LSO: the basic confocal mode with a CCD line camera vs. variable confocal aperture and/or offset line imaging with a time domain integration (TDI) camera.
Line cameras in the line-confocal AO-LSO operate at or below the width of the incident line illumination’s line-spread-function width. This degree of confocality is ideal for high contrast imaging the bright photoreceptor/RPE layers of the eye. However, when imaging dimmer structures of the inner retina, unlike the flying spot AOSLO that can simply employ larger confocal apertures (pinholes), light collection efficiency of the line-camera cannot be increased; the detector’s pixels and the confocal apertures are one and the same. A larger strip must be imaged to improve light collection without degrading resolution. This has been demonstrated with time-domain integration (TDI) line camera technology for the first time. Furthermore, due the enhanced light collection capabilities of the TDI AO-LSO, the focused line beam image may be displaced from the active TDI camera stages (the programmable number of lines integrating and transferring charge to the read-out line) to reduce direct back-scatter and enable the line-confocal analog to “dark field” AOSLO imaging, recently demonstrated by AO imaging researchers. Both of these imaging methods have been tested in four normal adult volunteers, with videos/images acquired in a number of regions and depths in the retina defined by an IRB-approved imaging protocol.
The first variable-confocal and offset aperture TDI AO-LSO images are directly compared to standard confocal AO-LSO in these subjects. The TDI approach could be regarded as a hybrid of line confocal imaging with area imaging; the variable staging of the TDI camera allow the imager transition smoothly from line confocal to area imaging mode, while collecting more light with finer resolution. Photoreceptor resolution was limited by eye motion due to the longer TDI integration time. As expected, measured contrast of the TDI AO-LSO is reduced compared to the line confocal AO-SLO, however, dark field offset-line imaging increases contrast for refracting/diffracting objects in the inner retina such as microvasculature, which is not possible with area imagers.
AO-LSO with TDI camera technology is a novel addition to the growing array of AO imagers.
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