Oct in post seg disorders

Oct in post seg disorders

1. Uses of oct in posterior segment diseases Dr.m.dinesh

2. OCT is an invivo diagnostic imaging technique non contact non invasive that enables cross-sectional study of retina in Micron resolution & correlates very well with the retinal histology With the currently available machine the resolution is of 7- 10 microns, which allows imaging of the neurosensory retina, the retinal pigment epithelium (RPE) and the choriocapillaris . Carmen Puliafito described the concept of Optical coherence tomography (OCT) in 1995 for ocular imaging. He described OCT as the first optoelectronic eye imaging system.

3. OCT advantages: rapid, easy (very short learning curve), non-contact, non-invasive, sensitive (7-10 microns resolution) and Highly reproducible and repeatable. OCT software facilitates qualitative and quantitative analysis; comparison of scans during subsequent follow-up examination. It allows detection and measurement of: Morphological changes in retina Retinal thickness Retinal volume Retinal nerve fiber layer thickness (RNFL) Various parameters of the optic nerve head (ONH)

4. Limitations of OCT difficulty in scanning in presence of corneal edema , significant lens opacity, vitreous opacity and haemorrhage exploration is limited to the posterior pole.

5. Optical Principles Imaging with OCT is based on Michelson interferometer and includes complex analysis of reflections of low coherence light from the ocular tissue (low coherence interferometry). Michelson Interferometer A beam of light passes through a semi-transparent mirror that splits the beam into two. These two beams of light are then thrown on two equidistant mirrors; reflected light from these mirrors is then picked up and summed up by a detector. The equidistant mirrors reflect the light wave in same phase

6. If one of the mirrors is moved by a distance less than the wavelength of the incident light, the reflected lights from the two mirrors will then possess a phase difference. This phase difference then produces an interference pattern at the level of the detector

7. OCT Machine uses a low-coherence infrared (830 nm) light coupled to a fiber optic system. Light passing through the eye is reflected by structures in different retinal tissue layers. The distance between the beam splitter and reference mirror is continuously varied. When the distance between the light source and retinal tissue is equal to the distance between the light source and reference mirror, the reflected light from the retinal tissue and reference mirror interacts to produce an interference pattern. The interference pattern is detected and then processed into a signal.

8. The signal is analogous to that obtained by A-scan ultrasonography. A two-dimensional image is built as the light source is moved across the retina and then a series of stacked and aligned A-scans produce a 2-D cross-sectional retinal image resembling histologic section An infrared-sensitive charge-coupled device video camera documents the position of the scanning beam on the retina. The OCT image can be displayed on a gray scale where more highly reflected light is brighter than less highly reflected light. Alternatively, it can be displayed in color

9. OCT operates like a fundus camera but resolves like a USG machine. Has +78 D condensing lens images retina & infrared image with field 30 USG OCT Source Sound waves Infra red light waves Resolution 150 microns 10 microns Patient contact Needed Not needed

10. TD – OCT ( time domain) FD - OCT / SD – OCT ( Fourier / spectral) • Reference mirror moves • Reference mirror stationary • Interference not detected by special interferogram • Interference detected by special interferogram • No Fourier transformation • Interference pattern Fourier transformed • 1 pixel at a time • 2048 pixels at a time • Slow • Rapid • Motion artifacts present • No motion artifacts • Less sharp images • Sharper and clear images Types of oct

11. Scan Protocol Types • Line • Circle • Radial Lines

12. The "line" scan simply scans in a single, straight line. The length of the line can be changed as well as the scan angle. The "circle" scans in a circle instead of a line

13. The "radial lines" scans 6 consecutive line scans in a star pattern Other protocols The "fast" scan protocols - reduce the time needed for multiple scans Raster lines – multiple line scans in a rectangular region to cover the areas of pathology – eg : CNVM Repeat scan – repeats previously saved scans 3D scan- 3D volumetric analysis

14. The OCT System • Fundus viewing unit • Interferometric unit • Computer display • Control Panel • Color inkjet printer

15. Types of machine scans • posterior segment scan • macular scan • optic disc scan • glaucoma RNFL thickness analysis scan • anterior segment scan

16. Technique : In the presence of clear media and cooperative patients an OCT can acquire quality images even with a 3 mm pupil The patient is seated comfortably in front of the OCT machine with chin positioned on the chin rest. He is asked to fixate on the fixation target(green color light) Those patients who are unable to fixate with macula can focus with the opposite eye on an external target. After Fixation the operator selects the desired scan and aligns the instrument so that fundus image and scan beam is displayed on the screen

17. Normal retinal scan: The posterior hyaloid -very faint, fine and slightly reflective line The fovea shows a characteristic depression on the macular scan. Internal limiting membrane is clearly defined in the OCT scans due to contrast between the reflective retina and non-reflective vitreous. The outer retina is bounded by a highly reflective band (70 µ thick) that represents RPE

18. The NFL and RPE highly reflective than the other layers of the retina RNFL – thicker on nasal side of macula( side due to the density of papillomacular bundle .) ONL – thickest portion The plexiform layers are hyperreflective than the nuclear layers. The photoreceptors form a poorly reflective band immediately anterior to the RPE, (d/t its vertical orientation)

19. Normal retina in oct

20. Highly reflective structures are shown in bright colours ( white and red) . • Those with low reflectivity are represented by dark colours (black and blue ). • Intermediate reflectivity is shown Green

21. The Bruchs ’ membrane and the choriocapillaris are generally seen as a single less reflective structure but in some scans the choriocapillaris may be visible separate from the RPE and the Bruchs ’ membrane. The larger retinal vessels are located indirectly by the shadow cone that they form on the posterior layers. Scan analysis has both qualitative and quantitative aspects. Qualitative analysis includes morphological & reflectivity study. Morphological changes include addressing changes in contour, changes in retinal layers and location of changes ( preretinal , intraretinal , subretinal )

22. Qualitative Reflectivity changes include identifying increased or decreased reflectivity or shadowing and noting its location (Superficial, intraretinal and deep). Quantitative analysis can be performed with regard to thickness, volume and surface mapping. The color codes used depict varying thickness Blue 150-210 microns, green 210-270 microns, Yellow 270-320 microns, orange 320-350 microns, red 350- 470 microns and white greater than 470 microns.

23. Patterns of Abnormalities Increased thickness: Retinal edema is the main cause of increase in macular thickness. Focal or diffuse spongy edema and cystoid edema Vitreoretinal traction may also result in retinal deformation and intraretinal edema Decreased thickness: retinal atrophy secondary to laser, trauma or inflammations.

24. High reflectivity Superficial: Epiretinal or vitreal membranes, subhyaloid /sub-internal limiting membrane hemorrhage , cotton wool spots and Myelinated nerve fibers Intraretinal : Hard exudates, intraretinal hemorrhages , fibrosis and scarring Deep: RPE hyperplasia, drusen , scarring, atrophy, subretinal neovascular membranes, deep pigmented lesions like nevus.

25. Low reflectivity Gross separation of cellular elements and fluid present either in form of cystoid space, neurosensory detachment or retinal pigment epithelium detachment Impending macular holes (cystic appearance) Usually the cystic spaces are optically clear but slight haze can be created by accumulation of cells, fibrin, blood and inflammatory exudates. Shadowing Dense highly reflective elements produce a kind of blockage of light waves by attenuation that appears as a shadow which conceals the elements lying behind it. Eg : hemorrhages , cotton wool spots, large hard exudates, dense pigmented lesion or scar and retained foreign body

26. Clinical applications of posterior segment scan Vitreoretinal Interface Disorders Idiopathic epiretinal membranes (ERMs), a layer of fibrotic tissue develops on the surface of the retina, usually after a posterior vitreous detachment. vitreomacular traction (VMT) syndrome or idiopathic macular hole, there are abnormal attachments between the vitreous and the retina ,resulting traction exerted on the retina causes anatomical alteration and subsequent visual loss.

27. Vitreomacular adhesion is defined on OCT as “ perifoveal vitreous separation with remaining vitreomacular attachment and undistorted foveal morphologic features.” Vitreomacular traction is defined by “anomalous posterior vitreous detachment accompanied by anatomic distortion of the fovea.” Pseudocysts, cystoid macular edema , macular schisis , and subretinal fluid are typical fndings of VMT.

28. PVD Vitreomacular adhesion

29. Vitreo –macula traction syndrome

30. Epiretinal Membrane Most idiopathic ERMs are thought to result from fibroglial proliferation on the inner surface of the retina secondary to a break in ILM occurring during posterior vitreous detachment. Secondary ERMs result from an already-existing ocular pathology such as CRVO/BRVO , diabetic retinopathy, uveitis, and retinal breaks with or without detachment. Glial cells, RPE cells, and myofibroblasts are shown to be mostly involved in ERM formation. ERM may lead to loss of normal retinal anatomy, with the patient experiencing metamorphopsia , micropsia, monocular diplopia, and decreased visual acuity.

31. Epiretinal membrane Oct features Epiretinal membranes are seen as linear, increased reflectivity structures located anterior to retina. loss of the normal foveal contour, increased retinal thickness, and the presence of cystoid changes

32. Macular hole : is partial or full thickness dissolution of retinal tissue at the foveal region. It may occur following blunt trauma, long-standing macular edema or as an idiopathic condition. OCT has become the gold standard in diagnosing and monitoring macular holes. OCT has been instrumental in the classification of macular hole development, following the sequence of events from antero-posterior vitreofoveal traction to full-thickness macular hole (FTMH)

33. Macular hole, Stage-1 Foveolar detachment with yellow spot. Stage I: OCT shows reduced or absent foveal pit (a cystoid space occupying the inner part of the foveal tissue.)

34. Macular hole stage II Partial break in the retinal surface with small full-thickness loss of retinal tissue with cystic spaces in the retina ( Full thickness eccentric defect with operculum )

35. Macular hole, Stage III Full thickness macular hole with or without operculum. OCT shows a central full thickness macular hole with detached posterior vitreous

36. Macular hole stage-IV stage III hole with a complete PVD macular hole with surrounding narrow cuff of subretinal fluid, cystoid changes at the edges with pigment deposit at the base of macular hole

37. Pseudo-macular hole Macular ‘ pseudohole ’ is a result of anterior and central displacement of the perifoveolar retina during contraction of epiretinal membrane Oct findings include wrinkling of the inner retinal surface surrounding the hole, apparent retinal tissue in the base of the pseudohole (an intact photoreceptors layer ) absence of yellow RPE deposits overlying operculum or pseudo-operculum.

38. Pseudo-macular hole

39. Lamellar -macular hole The four characteristics of a lamellar hole on OCT include: an irregular foveal contour a break in the inner fovea separation of the inner from the outer foveal retinal layers absence of a full-thickness foveal defect with intact foveal photoreceptors

40. Central serous chorioretinopathy is a noninflammatory, idiopathic serous detachment of the macula with or without associated retinal pigment epithelial detachment OCT – method of choice to detect subtle serous detachments of the macula The serous detachment appears as a hypo-reflective, shallow separation of the neurosensory retina from the retinal pigment epithelium margins have a gradual slope compared to pigment epithelial detachments. Overlying neurosensory retina may be thickened in the acute phases.

41. Central serous chorioretinopathy

42. Central serous chorioretinopathy Retinal pigment epithelial detachment appears as a well defined, dome shaped hypo-reflective elevation of the RPE with cystic hypo-reflectivity. Such detachments may be present within the area of serous detachment or in an adjacent area

43. Oct is more sensitive for detection of early retinal thickening compared to slit-lamp biomicroscopy . Hard exudates ,nerve fiber layer microinfarcts (soft exudates) and intraretinal hemorrhages have characteristic features. All three are hyper-reflective on OCT and may show posterior shadowing. Thickening of the retina with no evident cystoid changes and affecting a significant area of the retina gives rise to a ‘spongy’ pattern of edema The spongy areas are thought to represent altered Mueller cells. Thickening with cystoid changes are thought to denote necrosis of Mueller cells from chronic edema .These changes may also be associated with foveolar detachment Diabetic macular edema (CSME)

44. Diabetic macular edema , CME Type

45. Diabetic macular edema: CME with NSD

46. (A) Fundus photograph showing clinically significant macular edema , (B) OCT line scan shows loss of macular contour due to spongy macular edema with hyporeflective thickening of the retina and small areas of increased reflectivity denoting hard exudates

47. Diabetic macular edema with taut posterior hyaloid

48. CRAO OCT Features Fresh cases show diffuse thickening of the neurosensory retina Increased reflectivity is seen in the inner retinal layers with decreased reflectivity of the photoreceptor layers and the RPE secondary to the shadowing effect . Involvement of macular may have appearance of cystoid changes in the macular area with loss of the macular contour In old cases decrease in macular thickness is noted

49. Acute CRAO showing opacification of retina and a cherry red spot; OCTshowing increase reflectivity on the inner retinal layers and hypo-reflectivity in the outer retinal layers, increased thickness of neurosensory retina, loss of normal macular contour with cystoid changes in the macular area,

50. CRVO OCT Features Retinal thickening and Cystoid Macular Edema (CME) Increase in retinal thickness is seen as loss of macular contour on OCT. In the area of retinal edema , presence of cystoid spaces with reduced reflectivity depicts CME Intraretinal and subretinal hemorrhages are seen as focal areas with bright and high reflectivity with back scattering. Area of shadowing appears as black spaces in the RPE & choriocapillaris layer

51. CRVO

52. BRVO

53. Nonexudative ARMD Drusens Drusenoid PED Outer retinal atrophy/degeneration(Geographic atrophy) Pigment migration in drusenoid PED Outer retinal tubulation Pseudocyst

54. Nonexudative ARMD

55. Non-exudative AMD with large drusen .  Mild disruption of the EZ line is visible.  No signs of subretinal fluid or CNVM.  Foveal contour is intact.

56. Drusenoid pigment epithelial detachment (DPED) Well-defined drusen at least 350 microns in the narrowest diameter and appears elevated on stereoscopic fundus photographs.  Has a high rate of progression to both geographic atrophy (GA) and neovascular AMD.

57. Drusenoid pigment epithelial detachment (DPED) with RPE migration

58. Geographic atrophy As non- exduative AMD progresses in more advanced stages, the outer retinal layers become disrupted and develops atrophy.  Drusen is reabsorbed and geographic atrophy develops that corresponds to decrease in central vision.  SD-OCT scans of geographic atrophy reveals RPE thinning, loss of EZ and IZ lines, depression of the inner retinal layers as the outer layers are loss, and increase visibility of Bruch's membrane and the choroid.

59. Outer retinal tubulation

60. Pseudocysts in a patient with nonexduative age-related macular degeneration.  The hyporeflective space does not indicate a CNVM but a degenerative process

61. Exudative age-related macular degeneration  

62. Exudative age-related macular degeneration  

63. Retinal Angiomatous Proliferation Occult CNV associated with proliferation of intraretinal capillaries in the paramacular area and a contiguous telangiectatic response that has a progressive vasogenic sequence. Six distinctive findings of OCT included drusen (100%), inner retinal cyst (80%), outer retinal cyst (68%), fibrovascular PED (84%), serous retinal detachment (40%), and PED (68%).

64. Stage I: intraretinal neovascularization.   Stage II: subretinal neovascularization with a retinal-retinal anastomosis. Stage II: subretinal neovascularization with a serous PED Stage III: Choroidal neovascularization with a vascularized PED and a retinal-retinal anastomosis.

65. minimally reflective spcae in NSR sourrounded by hyperreflective dot like structures Retinal Angiomatous Proliferation

66. OCT: Hyper-reflective tissue with, SRF and cystoid changes in NSR Retinal Angiomatous Proliferation

67. Fundus photograph shows shallow retinal detachment with involvement of macula OCT scan confirms macular detachment with increased thickness of detachment macula. Retinal detachment

68. THAN Q References : Retina ryan 6 th ed Yanoff 4 th ed Step by Step Optical Coherence Tomography Parul Sony (RP centre )

69. Section 1: Patient related data, examination date, list and signal strength • Section 2: Indicates whether the scan is related to macula with its pixel strength (as in this • picture) or optic disc cube (It also displays the laterality of the eye: OD • (right eye), OS (left eye). • Section 3: Fundus image with scan cube overlay. 3A: Color code for thickness overlays. • Section 4: OCT fundus image in grey shade. • Section 5: The circular map shows overall average thickness in nine sectors. It has three • concentric circles representing diameters of 1 mm, 3 mm and 6 mm, and except for the • central circle, is divided into superior, nasal, inferior and temporal quadrants. The central • circle has a radius of 500 micrometers . • Section 6: Slice through cube front. Temporal – nasal (left to right). • Section 7: Slice through cube side. Inferior – superior (left to right). • Section 8: Thickness between Internal limiting membrane (ILM) to retinal pigment • epithelium (RPE) thickness map. 8A: Anterior layer (ILM). 8B: Posterior layer (RPE). All • these are 3-D surface maps. • Section 9: Normative database uses color code to indicate normal distribution percentiles. • Section 10: Numerical average thickness and volume measurements.

70. SD- OCT