Retinal imaging
- 1. WIDE FIELD IMAGING ULTRA WIDE FIELD IMAGING OCT-ANGIOGRAPHY AUTOFLUORESCENCE DR. ASHISH MARKAN UNIT-II
- 2. The first commercially available fundus camera(by CARL ZEISS IN 1926): 20 degree field of view Later standardized 30 degree field of view for fundus camera. Imaging angles greater than 50 degrees is termed as wide field imaging and greater than 100 degrees have been termed as ultra wide field imaging(DRCR.net) Power of the lens system has direct correlation with the field of view. Focal length of lens system has indirect correlation with the field of view. INTRODUCTION
- 3. NEED FOR WIDE FIELD IMAGING: The peripheral retina is the site of pathology in many vision- threatening eye diseases. Evaluation of the retinal periphery, therefore, is important for screening, diagnosis, monitoring, and treatment of disease manifestations. Historically, imaging of the peripheral retina has been limited and difficult to obtain; recent advancements in wide-field photography, however, have dramatically improved the ability to image the anterior retina.
- 4. VARIOUS TECHNIQUES: CLASSIC fundus camera POMERANTZEFF camera RETCAM PANORET STAURENGHI LENS SYSTEM SPECTRALIS OPTOS
- 5. 22 TYPES MECHANISM DEGREES CLASSIC FUNDUS Aspheric objective lens aligned with a 35-mm single lens reflex lens system 30-60,max 96 POMERANTZEFF Contact lens--based system that required pupillary dilation and provided illumination of the eye using fiber optic transpupillary illumination and scleral transillumination. 148 RETCAM Utilizes a contact lens with a fiberoptic cable light source connected to a computer monitor to image the peripheral retina in a digital format 130 PANORET Based on the concept used in Pomerantzeff’s camera of trans-scleral illumination, but differed in its capability of digital imaging 100 STAURENGHI Confocal SLO-based imaging platform ,consisting of two biconvex aspheric lenses and a two-element convex--concave contact lens 150
- 6. NON CONTACT LENS BASED UWF HEIDELBERG SPECTRALIS HRA Uses a noncontact removable lens that attaches onto the camera head of the Heidelberg HRA CSLO which greatly expands the viewing angle capabilities from a previous maximum of 55° to the UWF range 105 OPTOS CSLO based system that utilizes the optics of an ellipsoid mirror to create images of the peripheral retina. An ellipsoid mirror contains two focal points. The laser of the Optos is directed through one of the focal points, while the patient’s eye is positioned so that the second focal point is located inside the patient’s eye. 200 The Heidelberg module is advantageous in that it provides better superior- inferior coverage, less lash artifact, and more uniform contrast.
- 7. HEIDELBERG SPECTRALIS Heidelberg Spectralis has enhanced the role of fundus imaging by combining the spectral domain OCT with confocal SLO resulting in enhanced anatomical details, improved reproducibility and automatic rescan at same site at follow-up
- 8. Lens used with SPECTRALIS to enhance the field of imaging 105 DEGREES55 DEGREES
- 9. MULTIMODALITY IMAGING FAF(488nm-SWAF,787-Near infrared) INFRARED REFLECTANCE FFA ICG One limitation of Spectralis is that instead of true color images, pseudo color images are displayed, which may not represent the exact clinical picture.
- 10. OPTOS ULTRAWIDE FIELD IMAGING Optos produces colour images of the retina using a green laser light (red-free light) (532 nm) and red laser light (633 nm)- PSEUDOCOLOUR IMAGE The red and green laser components of the confocal scanning ophthalmoscope can be separated. GREEN RED ANTERIOR RETINAL STRUCTURES AND VASCULATURE CHOROIDAL VASCULATURE
- 11. PRINCIPLE OF OPTOS UWF: Two galvanometer mirrors provide rapid two-dimensional raster scanning onto an ellipsoidal mirror. Ellipsoid mirror has two focal points, one of which is near the mirror and the second of which lies at approximately the pupillary plane A point source of light emitted at the first focal point will thus converge within the patient’s eye and permit a wide scanning angle even without pupillary dilation. The reflected or emitted light passes back through the confocal aperture and various filters including those necessary to detect fluorescence emission wavelengths AARON NAGIEL, MD, PHD, ROBERT A. LALANE, MD, SRINIVAS R. SADDA, MD, STEVEN D. SCHWARTZ, MD . ULTRA-WIDEFIELD FUNDUS IMAGING A Review of Clinical Applications and Future Trends. RETINA 36:660–678, 2016
- 12. Imaging capabilities with OPTOS: Wide field (200 degrees) fundus imaging Fluorescein angiography of retinal periphery (488 nm laser, barrier - 500 nm) Autofluorescent imaging of retinal periphery(532 nm for excitation and 570-780 emission filter) More recently infrared 805 nm wavelength with a barrier filter -835 nm has been added for ICGA(RETINA,2016)
- 13. ADVANTAGES: Obviates the need for contact lens Pupillary dilatation not required Fast imaging speed( A single monochromatic scan requires 0.25 sec to perform) High resolution(20 pixel resolution per degree) Customizability with various lasers and filters Permits in focus imaging from ant retina to PP and even into deep staphyloma
- 14. CLINICAL USES: Diabetic retinopathy Retinal venous occlusions Choroidal masses Uveitis Retinal vasculitis Choroidal dystrophies(Gyrate,choroideremia) Retinal detachment Pediatric retinal diseases
- 15. PRE AND POST LASER OPTOS IMAGES:
- 16. ISCHAEMIC CRVO
- 18. CYSTICERCOSIS
- 19. LIMITATIONS : Incapable of imaging ora to ora and can still miss anterior retinal pathology Fails to image superior and inferior retina more frequently than nasal and temporal Distortion and decreased resolution of peripheral retina Measurement of distance and area on the images may not correspond to the actual dimensions of the eye(Recently introduced a stereographic projection software algorithm-maintains same angular relationship at every eccentricity) Image contrast is not uniform across the fundus. Does not allow retinal view before taking the image. Artifacts produced by eyelashes, native lens,intraocular lens, pigments in the anterior segment and vitreous opacities
- 20. OCT ANGIOGRAPHY OCT Angiography is a new non-invasive, motion contrast micro- vascular imaging modality.(OCTARA algorithm by TOPCON) Based on Split Spectrum Amplitude Decorrelation Angiography (SSADA) and Motion Correction Technology (MCT)
- 21. How does SSADA works?? Takes sequential consecutive OCT scans, and then compares each OCT scan with the subsequent scan. Also uses multiple spectrums from single B-scan to improve the image quality. By looking at the changes in the pixel intensity at a particular location, generates a decorrelation value, a marker of whether there’s motion or not, which in this case would be either flow in the vessel or static tissue. Generates a flow image or a functional image of this B-scan. By taking a large number of B-scans generates a 3-D volume of retinal vasculature
- 22. Different scan sizes: SMALLER THE SCAN ,MORE DETAILED THE IMAGES
- 23. Because of SSADA algorithm, OCT –A image system can achieve high quality vascular images with lower acquisition times
- 24. EN FACE VISUALISATION En face visualization is based on the retinal anatomy. Because this is an OCT based technique, we can use the OCT data to perform segmentation on the layers of interest in the eye, and we can generate en face visualization of the vessels at different layers of anatomic interest, such as the superficial capillary and the deep capillary and the choroidal capillary.
- 25. MOTION CORRECTION The idea behind motion correction is very simple, by acquiring two complementary datasets sequentially, unavoidable saccadic artifacts can be removed afterwards using sophisticated motion correction algorithm.
- 26. Allows clinicians to identify retinal circulation using the intrinsic motion of the blood cells in the vessel using non invasive microvascular enhanced imaging. Does not require contrast dye injection Can acquire different scan sizes at disc and macula within 3 seconds(in case of Angiovue) Uses motion correction to remove the artifacts and give a sharp image ADVANTAGES
- 27. FFA OCT ANGIOGRAPHY Uses a dye Uses the movement of blood cells in a vessel Needs to be scheduled Can be taken in few minutes Cumbersome Fast and easy Highlights capillary abnormalities much better In case of CNV,fluorescein leaks too much to see the structures as distinctly The afferent core vessels and peripheral anastomoses can be seen clearly Produces much crisper images of choroidal neovascularisation CONVENTIONAL FA VS OCT-ANGIOGRAPHY
- 29. IDIOPATHIC CNV
- 30. MYOPIC CNVM
- 31. NEOVASCULAR AMD
- 32. ROLE OF OCT-A IN GLAUCOMA (BY MICHEL PEUCH) Using the AngioVue to image the optic nerve head, observed a particularly dense vascular network around the disc,which is not picked up on FA. This network is located superficially just underneath the fiber optic layer or mixed with the fibers. These vessels have a role in nourishing the fibers. Found a clinical correlation between glaucoma stage and reduction of this superficial vascular network around the disc.
- 34. Analysed the blood flow inside the disc and found reduced vascularisation inside the disc in patients with glaucoma as compared to those without glaucoma ADVANCED GLAUCOMA
- 35. Observed the lamina cribrosa using OCT-A. Better visualization of the pores due to increased resolution of this system. Observed enlarged and stretched pores in patients with glaucoma
- 36. ROLE OF OCT-A IN GLAUCOMA
- 37. AUTOFLOURESCENCE: Fundus autofluorescence (FAF) imaging is a novel imaging method that allows topographic mapping of lipofuscin distribution in the retinal pigment epithelium cell monolayer as well as of other fluorophores that may occur with disease in the outer retina and the subneurosensory space. Excessive accumulation of lipofuscin granules in the lysosomal compartment of retinal pigment epithelium cells represents a common downstream pathogenetic pathway in various hereditary and complex retinal diseases, including age-related macular degeneration.
- 38. FAF imaging has been shown to be useful with regard to understanding of Patho physiologic mechanisms Diagnostics Phenotype–genotype correlation Identification of predictive markers for disease progression Monitoring of novel therapies. FAF imaging gives information above and beyond that obtained by conventional imaging methods, such as fundus photography, fluorescein angiography, and optical coherence tomography USES OF FAF:
- 39. RPE cells have inclusions that have morphological features of phagocytosed outer segments and LF granules. (1RPE cell will phagocytose 3x109 outer segments) Autofluorescence in the RPE is dependent upon outer segment renewal and potentially is affected by a balance between accumulation and clearance. (AF is increased in RPE dysfunction and decreased when there is loss of photoreceptors.) The retinoid fluorophores that form LF have extended system of conjugated double bonds Allows the absorption of light Emission of fluorescence. These autofluorescent properties permit visualization of the accumulation of LF granules in RPE
- 40. IMAGING DEVICES FOR FAF FUNDUS SPECTROPHOTOMETER SCANNING LASER OPHTHALMOSCOPY(HRA BASED) FUNDUS CAMERA OPTOS TOPCON
- 41. CSLO BASED FUNDUS CAMERA Uses confocal optics:A focused low power laser beam is swept across the fundus in a raster pattern. The confocal nature of the optics ensures that the reflectance and fluorescence are derived from the same optical plane. Light originating in the light beam, but out of the focal plane, is greatly suppressed to a large degree Uses a single flash and images the entire retinal area at the same time. In the absence of confocal optics, the detected fluorescence signal derives from all tissue levels in the light beam with fluorescent properties, and light scattering anterior and posterior to the plane of interest can greatly influence the detected signal Excitation wavelength:488 nm Excitation wavelength:580nm(cf 535 nm) Barrier filter:500 nm Barrier filter:715 nm(cf 615nm) Using shorter wavelength contributes to lens AF signals so increased the wavelength
- 42. NORMAL FAF PATTERN: OPTIC NERVE HEAD Appears dark in the absence of RPE and its retinoid based LF RETINAL VESSELS Reduced FAF signal because of absorption by blood FOVEA Reduced FAF signal because of absorption by luteal pigments PARAFOVEA Signal tends to be higher but still exhibits decreased intensity because of increased melanin absorption and low density of LF granules in central RPE cells
- 43. Relative spatial distribution of auto fluorescent intensities: von Ru¨ckmann A, Fitzke FW, Bird AC. Distribution of fundus autofluorescence with a scanning laser ophthalmoscope. Br J Ophthalmol 1995;79:407–412.
- 44. DECREASED AF SIGNAL INCREASED AF SIGNAL Absence or reduction in RPE lipofuscin density Excessive RPE lipofuscin accumulation Lipofuscinopathies including Stargardt disease, Best disease, and adult vitelliform macular dystrophy RPE loss or atrophy (e.g., geographic atrophy) Age-related macular degeneration (e.g., RPE in the junctional zone preceding enlargement of occurrence of geographic atrophy) Hereditary retinal dystrophies (e.g., RPE65 mutations) Subretinal fluid leading to separation of the outer segments of the photoreceptors from the underlying RPE, which leads to improper outer segment turnover Increased RPE melanin content (e.g., RPE hypertrophy) Macrophages containing lipofuscin in the subretinal space (choroidal tumors such as nevi and melanomas) Intraretinal and subretinal lipid Drusen in the sub–pigment epithelial space Fibrosis, scar tissue, or borders of laser scars Choroidal vessel in the presence of RPE and choriocapillaris atrophy (e.g., in the center of laser scars or within patches of RPE atrophy) Retinal vessels Luteal pigment (lutein and zeaxanthin) Media opacities (vitreous, lens, anterior chamber, or cornea) Depletion of luteal pigment (e.g., in idiopathic macular telangiectasia type 2) Displacement of luteal pigment (e.g., cystoid macular edema) Optic nerve head drusen
- 45. DISEASE FAF PATTERN BEST DISEASE High levels of FAF in area of pseudohypopyon RETINITIS PIGMENTOSA Parafoveal ring of increased FAF STARGARDT DISEASE Focal areas of increased intensity correlating with flecks seen on fundus imaging GEOGRAPHIC ATROPHY Low FAF signal in area of RPE atrophy
- 46. FAF IMAGING IN BEST DISEASE
- 47. FAF IN GEOGRAPHIC ATROPHY IN AMD
- 48. FAF TO PREDICT PROGRESSION IN GEOGRAPHIC ATROPY Specific pattern of FAF abnormalities at baseline outside the atrophic patches. It has been shown that the extension of areas of increased auto fluorescence surrounding atrophy patches correlates with atrophy progression over time FAF patterm mm2/year Banded 1.81 Diffuse 1.77 Diffuse trickling pattern 3.02 Focal 0.81 No FAF pattern 0.38 Schmitz-Valckenberg S, Bindewald-Wittich A, Dolar- Szczasny J, et al. Correlation between the area of increased autofluorescence surrounding geographic atrophy and disease progression in patients with AMD. Invest Ophthalmol Vis Sci 2006;47:2648–2654.
- 50. FAF IN CSR ACUTE: Minimal abnormalities other than slight increase in autofluorescence in areas of serous detachment CHRONIC: Usually a/w with RPE atrophy and thus decreased autofluorescence 3 MONTHS LATER 4 MONTHS LATER ACUTE CSR Spaide RF, Klancnik JM Jr. Fundus autofluorescence and central serous chorioretinopathy. Ophthalmology 2005;112: 825–833
- 51. Functional correlate of FAF abnormalities Severe decreased autofluorescence is observed over areas with RPE atrophy such as in advanced atrophic AMD, over areas with melanin pigment migration, or in the presence of fibrotic scar tissue. Indicates severe damage to the RPE, leading to compromised photoreceptor function. Microperimetry and visual field testing confirm that no measurable local retinal function can be detected over these lesions. Decreased FAF intensity correlate with an absolute scotoma for the patient. Areas of increased FAF, which often have no visible correlate shown by fundus biomicroscopy or fluorescein angiography Increased accumulation of autofluorescent material may occur before cell loss Because normal photoreceptor function is dependent on normal RPE function,, a negative feedback mechanism could also be proposed, whereby cells with LF-loaded secondary lysosomes would phagocytose less shed photoreceptor outer segments subsequently leading to impaired retinal sensitivity. Combining FAF imaging with fundus perimetry has shown that retinal sensitivity is significantly reduced over areas with increased FAF intensities(rodes more than cones in AMD)
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