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Scanning
Laser Ophthalmoscope (SLO) - Rodenstock, Germany
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The Scanning Laser Ophthalmoscope (SLO) was invented by Webb, Pomeranzeff, and Hughes in 1979. It used a very narrow moving beam of light which could bypass most ocular media opacities (i.e. corneal scars, cataracts, vitreous hemorrhage) to reach the surface of the retina and record its surface detail. A live video image of the retina was displayed on a computer monitor and test results were digitally recorded. Several diagnostic tests were possible with this machine.
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How SLO Image is Recorded
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SLO Image of Macula with
Drusen
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Tests Performed on the Scanning Laser Ophthalmoscope
Scanning
Laser Acuity Potential (SLAP) Test
The letter E corresponding to different levels of visual acuity (ranging from 20/1000 to 20/60) was projected directly on the patient’s retina. The examiner could direct the test letters to foveal and/or extrafoveal locations within the macula, and determine a subject’s potential visual acuity.
This was especially helpful in individuals who have lost central fixation but who could still possess significant eccentric vision. It was also useful in separating out the component of retinal function from anterior segment contributions to overall visual dysfunction when contemplating surgical interventions.
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SLO image showing the different stimulus sizes
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Sample Results of SLAP Test
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Microperimetry
/ Scotometry
The SLO could visualize a particular area of the retina and test its sensitivity to visual stimuli, thereby generating a map of the seeing and non-seeing areas. If central vision was lost, the patient could potentially be trained to use an adjacent retinal site to substitute for central visual function.
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SLO image depicting where test was performed
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Sample result of Microperimetry test
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Hi-Speed FA
/
ICG
Fluorescein and Indocyanine Green Angiography
(FA/ICG) performed using the SLO is recorded at 30 images per second, producing a real-time video sequence of the ocular blood flow. The standard fundus camera sequence is limited by flash recycling to 1-2 frames per second, and is unreliable in its ability to document details of choroidal filling which occur over a 1-2 second span of time.
The higher speed of image acquisition more completely captured the chorioretinal filling sequence, and could be used to accurately identify the choroidal feeder vessels of neovascular membranes. Guided by high-speed FA/ICG results, laser treatment of sight-threatening diseases like Exudative Age-Related Macular Degeneration (AMD) could be carried out with pinpoint accuracy.
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ICG image highlighting area of neovascularization.
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