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Retinal Imaging Update A. Scanning Laser Ophthalmoscope (SLO) – (Optos - Panoramic200) a. How it works i. Spinning polygon produces a rapid scan of the laser lights at 30,000 RPM. Raster ii. Mirrors reduce the scan raster from approximately a 1 meter square raster to a 1 mm square raster. They also produce a virtual image of the raster at a fixed point in front of the instrument. The image of the raster must be placed in the patient’s pupil and thus, head positioning is critical. iii. There is a red and green laser that are produced and scanned simultaneously. The green laser penetrates less (most of the information being gathered from the sensory retina to the RPE) and the red wavelength light penetrates deeper (most of the information being gathered from the RPE to the choroid). The image produced is like having to 2 color transparencies laid on top of each other to form the final image. iv. Color light detectors accept the reflected laser light (red & green) and transform it into electronic signals to the computer. Very little laser light is reflected back from the fundus and therefore, the detector are set on high sensitivity (sometimes this causes the optic disc to be overexposed). v. The computer with the propriety software transforms the electronic signals into programmed image. vi. Computer monitor produces final visible image. b. Characteristics of the Panoramic200 image i. It is able to capture 80% of the retina in one shot. ii. Steering (gaze positions) can allow a field of view further into a desired direction. iii. Pupillary dilation doesn’t increase the field of view but does may brighten the image a little. iv. Digital image that can be magnified, lightened, darkened, and emailed. c. Retinal hole d. Operculated retinal tear i. Pathophysiology ii. Clinical appearance 1. A tear is red in the base due to being able to see the choriocapillaris more easily. The margins are more likely to be ragged. The torn retina is seen as a plug above the break. iii. SLO imaging 1. The operculum can be seen adjacent to the round tear and the underlying shadow can also be seen. iv. Clinical significance 1. Operculated tears are associated with retinal detachment and again due mostly to vitreous traction. e. Flap (horseshoe) retinal tear i. Pathophysiology 1. A flap tear is caused by vitreous traction. ii. Clinical appearance 1. A tear is red in the base due to being able to see the choriocapillaris more easily. The margins are more likely to be ragged. The torn retina is seen as a plug above the break. iii. SLO imaging iv. Clinical significance 1. Flap tears are associated with retinal detachment and again due mostly to vitreous traction. Flap tears are almost always treated. f. Retinal detachment i. Pathophysiology 1. The sensory retina separates from the pigment epithelium. ii. Clinical appearance 1. Fresh detachment look whitish and longstanding are mostly clear. The choroidal detail is fuzzy under the detachment. Posterior border is almost always convex to the posterior pole. iii. Ultrasound imaging iv. SLO imaging 1. Typical appearance as seen with a BIO just much more is seen in one view. Because fresh RDs are white due to ischemic edema, it tends to saturate the green color detectors and therefore, often looks green. v. Clinical significance 1. Loss of visual field and blindness. g. Retinoschisis i. Pathophysiology 1. Vitreous traction on the peripheral thin retina causes it to split in the middle layers of the retina. Progression is usually the result of increase or continued vitreous traction. ii. Clinical appearance 1. Thin smooth bullous membrane that doesn’t move on eye movements. Red or white vessels are sometimes seen traversing the inner detached layer. The choroidal detail is fuzzy under the detachment. Posterior border convex to the posterior pole. iii. Ultrasound imaging. iv. SLO imaging 1. Smooth thin blister in the far periphery with an outer layer break and convex posterior border. v. Clinical significance 1. Retinoshises can involve the macula but is unusual for that to happen. h. Diabetic retinopathy i. Age-related macular degeneration j. Glaucoma – glaucomatous optic atrophy i. Pathophysiology ii. Clinical appearance iii. SLO imaging 1. The detectors need to be on lower contrast settings in order to view the optic disc. In most cases, the physiologic optic disc cup is the brightest structure of the fundus. High settings can saturate (over exposed or bleached out) the cup and cause it to looking larger and haze or obliterate the neural rim to cup margins. By lowering the sensitivity, the discs will have a good appearance and cupping can be more accurately assessed.. B. Optical Coherence Tomography (OCT) a. Noninvasive, noncontact transpupillary imaging technology b. Analogous to ultrasound B-wave imaging or radar except light is used instead of acoustic or radio waves c. Can image retinal structures in vivo with a resolution of 10 μ d. The retinal detail provided is liken to an "optical biopsy" to provide 2- and 3-dimensional cross-sectional images of tissue microstructure, by collecting backscattering of light reflected from the fundus and related structures e. How It works: i. Cross-sectional images of the retinal are produced using the optical backscattering of light ii. The anatomic layers within the retina can be differentiated and retinal thickness can be measured iii. Utilizes spatially uniform, low-coherent light that is generated by a superluminescent diode laser 1. Low coherent light allows for a propagation speed nearly 1 million times faster than sound 2. This allows for the high resolution images iv. Transmitted to the eye via fiber optic delivery 1. Similar to using 78D lens 2. Mounted on a slit lamp delivery system v. 2 Galvanometer-driven mirrors are used allows for scanning light across the retina in approx 2.5 seconds 1. Can be done with visible or IR Videoscopy vi. The temporal information contained in the resulting interference pattern is the basis for constructing the images vii. Received light is converted into electric signal by a photodiode and then processed by a computer f. Provides cross-sectional images of retinal structures i. Allows for clinical correlation ii. Better anatomic perspective iii. Supplements other diagnostic testing g. Provides better understanding of vitreomacular interactions and related diseases i. Has redefined our understanding of the pathogenesis of full thickness macular holes. 1. It is now understood that 'perifoveal' vitreous detachment and not tangential traction leads to the development of stages of macular hole ii. Has helped understand the expanding spectrum of vitreomacular syndrome b/c of better visualization of vitreoretinal interactions h. Instrumental in understanding in new retinal diseases. i. Has help define the disease Retinal Angiomatous Proliferation (RAP) i. Provides important diagnostic and management information post treatment j. Emerging technology for optic nerve evaluation i. ON head and NFL evaluated via circular scans around the nerve or radial scan through the nerve ii. Cross sectional circle around the ON is produced 1. Provides “cylinder” of information 2. Cylinder is unfolded -> looked at in cross-section iii. Especially good for glaucoma suspects and OHT iv. Average NFL thickness maybe most useful in monitoring glaucoma v. Multiple studies show that OCT has the ability to detect early glaucoma change by measuring NFL thickness 1. Particularly inferior quadrant 2. Often before VF loss vi. Studies also show that nasal side of ON is affected earlier and more than what is usually considered vii. The Ave & quadrant NFL thickness have good correlation with MD an HVF C. Retinal Thickness Analyzer (RTA) a. Produces a color-coded 2D and 3D thickness and topography map of the retina, allowing accurate measurement of retinal thickness. b. Can also provide deviation probability maps from a normative database and quantitative numerical values. c. Uses a computerized slit lamp to measure retinal thickness at the central 20 degrees of the macula and overlays a map of measurements on the patient’s retinal image. d. In 3-5 minutes 5-13 scans are acquired, up to 208 optical cross sections are analyzed by a thickness algorithm at the posterior pole and peripapillary area, and topography algorithm for optic disc is measured. e. Can detect as little as 34m of macular edema f. Serial RTA studies can be used to monitor progression macular thickening as DME in response to treatment. g. It can be used to monitor progression of NFL thinning in glaucoma h. Technique i. A thin laser slit beam is projected obliquely through a dilated pupil onto the retina ii. Viewed at an angle in a similar manner to that of slit-lamp biomicroscopy. iii. The reflected images are recorded by a video camera and digitized. iv. Laser slit intersects with the interface between the vitreous and the retina before intersecting with the interface between the retina and the choroid. v. Because the laser is projected at an angle, this results in two separate reflections. vi. The images are analyzed by an automated, operator-free software algorithm, which detects the different reflections and uses this to produce a map showing the distance between the interfaces. vii. Sensitive mapping allows quantitation of height and area of thickening. viii. The high-speed cross-sectional imaging of the retina may be useful for identifying, monitoring and quantitatively assessing macular diseases, and detecting macular edema and subretinal fluid in common retinal diseases such as diabetic retinopathy and AMD ix. Can also be used for optic nerve evaluation and to follow glaucoma