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George Timberlake, Warren Ward; Optical attachment for binocular imaging with the Scanning Laser Ophthalmoscope (SLO). Invest. Ophthalmol. Vis. Sci. 2013;54(15):2182.
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© ARVO (1962-2015); The Authors (2016-present)
Our objective was to develop a binocular optical system that attaches to the SLO for imaging the retinas of both eyes. Such a system may help answer questions as to how (or if) individuals with bilateral macular scotomas use Preferred Retinal Loci (PRLs) in both eyes when viewing an object.
We designed and constructed an electro-optical system that alternately images the left and right retinas at 15 Hz. A linear motor moves two small, offset orthogonal mirrors up and down, reflecting the SLO light path left or right. The optical system is adjusted in position so that the focal point of the converging laser-beam scan from the SLO is imaged at the intersection of the two moving orthogonal mirrors. Additional mirrors reflect the left and right beams toward the subject. Relay lens pairs mounted in rotating eyepieces allow for inter-pupillary distance adjustment. Electronic circuits synchronize the mirror movement with the SLO 30 Hz video output. The retina is imaged in infrared (780 nm) and visual stimuli are presented in the SLO’s HeNe (632 nm) laser-beam raster. Video output can be recorded continuously and later separated into left and right eye frames using standard software, or left and right retinas can be presented on separate monitors.
Initial tests with model eyes produced alternating video images of the model eye “retinas” at 15 Hz. Analysis of recorded SLO video showed the “retina” of each model eye imaged on every other 30 Hz video frame. Retinas of two visually-normal subjects were imaged in the same way. When following a moving disk in the SLO raster, the image of the disk was placed on the fovea of both eyes. The present binocular system has some loss of field due to optical constraints. In addition, magnification is somewhat greater than the SLO alone. The 15 Hz alternating rate produces noticeable flicker for the observer, but it does not seriously interfere with binocular viewing and tracking.
Presently, only eye-tracking techniques are available for investigating how both eyes are used together by those with macular scotomas. Such techniques cannot determine what retinal area(s) are used to inspect visual stimuli. We believe that the binocular SLO attachment will be useful for investigating how individuals with bilateral macular scotomas use PRLs in both eyes to look at objects.
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