Getting to know oct presentation 2016
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A lecture on the use and understanding of OCT scans and how to interpret the results. There is a look at some basic pathology as well as progressive tissue changes to diagnose eye diseases like glaucoma.
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Getting to know oct presentation 2016
- 1. GETTING TO KNOW OCT Jason Higginbotham Bsc (Hons) MCOptom FBDO
- 2. OCT uses principles of reflectometry and interferometry to provide micron resolution scans of semi transparent media, such as living tissue. Basically, light (often infra red laser) is sent through a beam splitter. Some of the light goes to a sensor and the rest to the patients eye. The reflected / back scattered light from the eye then comes back to another sensor. The intensity and time delay of the reflected beam is compared to the reference beam. Light from different depths within the tissue will be effected in different ways.
- 3. Clinical Value: • Earlier detection of pathology, such as Glaucoma. • Progression analysis of tissue change over time. • Peace of mind at finding more conditions that may otherwise not be found. • Better understanding of pathophysiology and improved understanding of patient symptoms and needs. • More????
- 4. Commercial Value: • Extra revenue stream via direct charging and more NHS funding. • Indirect revenue growth through increased patient loyalty and more footfall if marketed well. • Adds a more professional and modern aspect to the practice in patient’s opinion. • Patients feel the ‘added value’ and will often be happier to spend at the practice. • Professionals CHARGE FOR THEIR EXPERTISE.
- 5. 26000 to 200000 A-Scans per second. These build a B-Scan.
- 6. The OCT also produces what is called a Phase Fundus image which provides C-scan image similar to that seen on a Fundus Camera; only not in colour.
- 11. 12 mm (approx.) 0.3 mm! Posterior Hyaloid Face Bursa Premacularis Area of Martigiani
- 20. Angles: (degrees vs Van Herrick) 35 to 45 Open (4) 25 to 35 Open (3) 10 to 25 Narrowing (2) <10 Very Narrow (1) 0 Closed Angle Anterior Chamber Angle Claudio Campa, Luisa Pierro, Paolo Bettin and Francesco Bandello Department of Ophthalmology, University Vita-Salute, Scientific Institute San Raffaele Milan,
- 21. As can be seen here, the Phase Fundus image has been overlaid with a thickness map. The colour relates to retinal thickness. Greens and blues are thinnest , yellows are moderately thicker and reds are thickest.
- 22. The ETDRS (Early Treatment Diabetic Retinopathy Screening) 9 Sector Map is an internationally recognised map of the Macula area. The numbers in each sector represent the average thickness of the whole Retina (in microns) in that sector.
- 23. Normative Scales
- 24. With the added ‘G Chart’, Ganglion Cell Complex thickness can be assessed against the normative data. Notice that now the scale only represents half a bell curve. Where the GCC is thicker, this is represented in white as there is no known pathology of GCC hyperplasia. G Chart
- 26. Other Maps
- 27. • Spotting Glaucoma early is one of the most important uses of OCT and is certainly one area where Optometrists come into their own within Primary care and also in Community Ophthalmology and Secondary care. • We can use the software to analyse if there is any progression in loss of Ganglion Cell Complex (GCC) at the Macula or Retinal Near Fibre Layer (RNFL) thickness at the Optic Nerve Head (ONH). • Superior / Inferior step analysis as well as R/L comparison are always important too.
- 28. GCC Progression R Eye
- 29. RNFL Progression R Eye ONH
- 32. Top – Normal FAF images OU. Normal Colour Fundus Image.
- 33. Geographic Atrophy GA is major cause of visual loss in the elderly, and usually the fovea is the last area involved. Fundus Auto Fluorescence (FAF) is considered the best imaging modality to evaluate the atrophic area and its extension.
- 34. Stargardt’s Disease Stargardt’s disease is one of the most common inherited juvenile macular degeneration. FAF shows hypo-fluorescent areas in the macular region corresponding to large macular atrophy.
- 35. Cone Dystrophy This can be visualized only with green-FAF as it would be completely covered by the central dark spot typical of blue-FAF. Cone dystrophy is a general term used to describe a group of rare eye disorders affecting the cones. It is always bilateral.
- 36. Retinitis Pigmentosa Green FAF showing bilateral Retinitis Pigmentosa, with symmetrical changes. Hypo-fluorescent areas represent lack of RPE cells. On the other hand dark areas along the vessels in the periphery are bones.
- 37. B Scan shows subtle changes. Colour Fundus Image is not very informative FAF image is extremely beneficial in showing how much damage has been done to the Retinal Pigment Epithelium.
- 38. • Not to be mistaken with C-Scan or Phase Fundus images. En Face analysis registers the curved layers of the retina with reference to each patients eye. Some OCT’s have this functionality. • We can look face on at different layers of the retina and even the vitreous face and inner choroid to better understand pathology within or near to these layers.
- 40. • Glaucoma (advanced) • CSR (Central Serous Retinopathy) • Wet AMD • Anterior Scan Examples
- 41. This 44 year old patient attended a clinic. They had evident disc cupping in both eyes with some palour. Our suspicions would already be aroused by the discs, but the IOP’s were not raised.
- 42. • The right visual field shows an arcuate scotoma, with blind spot enlargement in the left eye.
- 43. The field loss becomes more obvious when we look at the RNFL layer thickness deviation maps against the normative data. You can see the evidence of loss of RNFL particularly in the Right Eye which corresponds perfectly with the field plot on the previous page. R L
- 44. The ETDRS chart shows minor thinning of the retina inferior to the Macula in the right eye. The G Chart, however, shows considerable inferior thinning and loss of the Ganglion Cell Complex across the inferior Macula. The shape from the deviation map is typically arcuate and matches the field loss very closely.
- 45. This patient presented with reduced VA and metamorphopsia in the Left eye. There was a typical Hyperopic shift in the Left spectacle Rx too. Amsler shows a large area of visual distortion in the LE. LE Fundus image shows evident oedematous change at the Macula.
- 46. Here, the ETDRS map shows a large increase in central Macula thickness. The shape of the deviation map is remarkably close to the Amsler drawing.
- 47. RE B Scan LE B Scan
- 48. LE Colour Fundus LE Phase Fundus or C Scan
- 50. 3D images can be particularly good for demonstrating to patients what is happening in their eyes. They can be good educational tools for patients.
- 51. Angles: (degrees vs Van Herrick) 35 to 45 Open (4) 25 to 35 Open (3) 10 to 25 Narrowing (2) <10 Very Narrow (1) 0 Closed Angle Anterior Chamber Angle Claudio Campa, Luisa Pierro, Paolo Bettin and Francesco Bandello Department of Ophthalmology, University Vita-Salute, Scientific Institute San Raffaele Milan,
- 53. OCT’s have digital callipers as seen above.
- 55. PKP
Editor's Notes
- Based on the principle of Optical Reflectometry and Low Coherence Interferometry. Looks at the reflections / back scattering of light from transparent and semi transparent media, such as in the human body. First used in Vascular and Cardiac medicine. Discovered accidentally at MIT in the late 1980’s whilst trying to find a way of measuring excimer laser corneal ablation in real time. Found by James Fujimoto, Carmen Puliafito, Joel Schuman, David Huang, Eric Swanson and Mike Hee. Two main methods: Time Domain and Fourier Domain (split into Spectral domain and Swept source).
- Often, Optometrists suggest OCT ‘opens a can of worms’. Certainly, without knowledge, understanding and a robust clinical approach to scans, this might be a valid comment. However, with good interpretation skills and a common sense approach, OCT should really ‘close the can of worms’!
- Often, Optometrists suggest OCT ‘opens a can of worms’. Certainly, without knowledge, understanding and a robust clinical approach to scans, this might be a valid comment. However, with good interpretation skills and a common sense approach, OCT should really ‘close the can of worms’! Some clinicians feel charging extra for their time and the use of expensive equipment is some how taboo. For me, this is quite the reverse. If a dentist suggested you need an X-ray, you would accept it and pay for it.
- A cross sectional view is known as a B-scan, whereas a scan from the front to the back of the eye is called an A-scan. OCT uses lots of A-scans to build B-scan images and uses B-scans to produce 3D Maps or Cubes with lots of data. For example, the Retina Scan Duo takes up to 53000 A-scans per second to produce B-scans. It can then use up to 1024 vertical and horizontal B-scans to make a 3D map.
- Sometimes, lesions not visible on the Colour Fundus image can become more apparent with the C Scan images.
- We are commonly taught there are ten layers to the retina. With OCT, we usually see an eleventh layer, called the External Limiting Membrane. This is the top of the Muller cells, which support the photoreceptors. Notice that the outer segments of the photoreceptors are a dark band. This band thickens around the Foveola, where there are only Cones and the outer segments of these become longer towards the centre. This slight bulge is perfectly normal. Note also that the Outer Nuclear layer is thickened around the Fovea and Foveola as there is a ‘one to one’ connection between the Cones and their associated Bipolar, Amacrine, Horizontal and Ganglion cells. This is anatomically normal and is why we see so well at the Fovea. Note that although the Fovea is thinner and the inner layers are pushed to the side, in about 10% of patients, some of the inner layers are still more present centrally without any detriment to the patients vision.
- Positive Black and White.
- Negative Black and White.
- False Colour.
- Looking at this image, the scan width is approximately 12mm. It is important to remember that OCT images are massively vertically stretched. Notice also there are some Vitreal areas which can sometimes be confused for Posterior Vitreous Face Detachments (PVD’s). The dark ‘hollow’ are above the Macula is quite commonly seen and is known as the Bursa Premacularis and is a normal physiological feature. Just above the disc is a similar ‘void’ called the Area of Martigiani; again this is physiologically normal.
- Here, you can see that Drusen are always based at the outer most layers of the Retina; the RPE and Bruch’s membrane complex. Usually, they appear to commence at Bruchs (between the RPE and Bruch’s), though sometimes they can appear to start within the RPE. They can vary in size and may sometimes rupture inner layers. When interpreting OCT scans, the key things to look out for are Reflectivity, Thickness or Thinning, Brightness, Shadows, Artefacts and understanding normal features. Here, we can see that Drusen appear very much like the RPE and BM in terms of their brightness. They don’t case shadows and they are not hyper or hypo reflective in relation to the RPE/BM. The nearest layers, the Outer segments (OS) and Inner segments (IS) of the photoreceptors are distorted, but inner layers tend to be unaffected and the overall retinal thickness is rarely changed noticeably.
- Here, we can see several important features about Exudate. Firstly, they tend to appear around the Inner Plexiform (IPL) and Inner Nuclear (INL) Layers or sometimes into the Outer Plexiform Layer (OPL). Secondly, they are Hyper Reflective and appear bright white on Positive, or red on False Colour. Thirdly, they cast a shadow on the scan image where much of the infra red laser has been reflected back or scattered rather than passing through to the outer layers and into the choroid.
- Serous or clear fluid appears as a hollow area or dark area within or between tissue layers. In the above case, it is between the neuro sensory Retina and the RPE. It is generally completely dark and casts no shadow at all. Where blood or blood related leakage is found, it casts a shadow and is Hypo Reflective. Blood Vessels also cast slight shadows, but it is actually the blood within the vessels rather than the vessel walls that is hypo reflective.
- Poor Image due to Cataracts. Notice the Hypo Reflectivity of some of the cystic spaces and the shadowing.
- Reverse Shadowing (window defect) occurs when the Hyper reflective layers, such as the RPE / pigment are not present as in the above case. This is a Cone Dystrophy where the RPE layer and the central photoreceptor layers are absent. The infra red laser undergoes far less backscatter and reflection and so the increased intensity reaching the choroid becomes visible as a brighter choroidal reflection. Most commonly seen in geographic atrophy, but also in full thickness macula holes and photoreceptor disease.
- Here, it is clear that the shadows are present through all the Retinal layers. This is caused by vitreal floaters, lens opacities, corneal opacities or other such phenomena that backscatter the light / infra red laser before it even reaches the Retina.
- These are some examples of scan types. Different OCT devices have a variety of scan types, but most are very similar to the above. Sometimes the Maps are also called cubes, volume scans or mesh scans for example.
- Some OCT’s also come with anterior scan patterns. The above shows a Corneal Radial scan with a pachymetry map and also an ACA (Anterior Chamber Angle) Line Scan at the Limbus. Such scans are very useful for checking Corneal health. They can also check Corneal thickness and the Chamber Angle; particularly helpful with Glaucoma assessments.
- Open versus Closed Angles. Very evident without having to use digital callipers, but these can be used. Find also a useful conversion from ACA in degrees to Van Herrick's.
- Sometimes on these thickness temperature maps, the superior and inferior disc margins will be off the scale and will appear white. This is quite common. Most devices allow you to alter the scale if necessary. Often, lesions can be quite obvious just by looking at these maps (see later).
- With the ‘Traffic Light System’, OCT’s help to provide a comparison of the patient’s Retinal thickness or some other layer or multi layer thickness with a Normative Database. The colour system has long been established. Green represents the thickness of the Retina found in 5 to 95% of the Normal Population (‘Green is Good’). The bright yellow represents the first standard deviation thinner, where 1 to 5% of the Normal Population would have a Retina that thin. Red is the second standard deviation thinner, where 0 to1% of the Normal Population would have a Retina that thin. There are, of course, conditions where the Retina is too thick, such as Oedema. Here, the lemon represents the first standard deviation thicker, where 1 to 5% of the Normal Population would have a Retina that thick and Pink where 0 to1% of the Normal Population would have a Retina that thick.
- Imagine a Bell curve coming out of the page / screen based on the colour scale above. The top of the bellis the centre of the Green on the Normative Database Scale. It is important to note that even if the map is all red, it could still be normal for that patient. However, it is less likely that it is normal where the map is all red. Of course, there may be cases where despite being all green, the patient is still abnormal as well. However, this is unlikely.
- The Ganglion Cell Complex is a clinically recognised ‘layer’ of the Retina. It represents the innermost five layers of the Retina. These are the ILM (Inner Limiting Membrane), the RNFL (Retinal Nerve Fibre Layer), the GCL (Ganglion Cell Layer), the IPL (Inner Plexiform Layer) and the INL (Inner Nuclear Layer). The GCC has been clinically proven to be the only layers of the Retina affected by Glaucoma and so some devices measure this against Normative data. Other OCT’s try to measure the GCL alone or the GCL and IPL together to assess Glaucoma risk. Note also the Superior / Inferior comparison. This is useful as no RNFL fibres cross the midline, and usually, the inferior GCC is thicker than the superior. This also allows us to assess symmetry WITHIN the eye. If there is a considerable asymmetry between superior and inferior areas, this can be a sign of pathology. Symmetry is an important differential diagnostic tool on many occasions. It is important to remember that the IPL, GCL and RNFL are in fact all part of the same large cells, whose Nuclei lie within the Ganglion Cell Layer. Damage to the cell body tends to occur first and thus the GCC starts to reduce in thickness at the Macula first. Often, the axons of the Ganglion Cells (the RNFL) remain intact within the RNFL at the disc for some time after the cell body has died within the GCL. Hence, the RNFL at the disc can take longer to show loss of tissue than found within the GCC at the Macula.
- As well as comparing Retinal thickness and GCC with a normative database, OCT’s also compare RNFL thickness with normative data. There are several ways in which this can be assessed. On the right we have what is often referred to as a Disc Circle Scan. This is a 360 degree panoramic scan around a 3.4 mm circumference circle around the ONH (Optic Nerve Head). The OCT compares the RNFL thickness at all points around this circle to normative data and produces what is often called a TSNIT or ONH Profile map. The black line represents the patients RNFL ONH profile and this is overlaid over normative profiles. The same normal distribution and standard deviations apply and once again, there is no known condition where there is too much RNFL, so we only have colours for thinning of RNFL and white for anything thicker. We can also measure average RNFL thickness across the whole Optic Disc compared to normative data or to the Superior and Inferior Bundles, the ISNT rule (TSNIT) or even Clock hour for more refined analysis (for notching for example). OCT’s will always measure the CD ratio’s higher than clinicians do. This is because the OCT can see where Bruchs Membrane ends and we cannot. We see the disc edges and these are wider than the gap in Bruchs that the OCT measures. This means the is always bigger in relation to the gap in Bruchs.
- Where we use the ETDRS, GCC or RNFL maps, we consider a round and limited area to compare with Normative Data. Most OCT’s actually measure a 6 x 6mm area for Normative data (some go to 9 x 9mm). Over the disc, most OCT’s use a 5 x 5 or 6 x 6mm cube compared to normative data. Above, we can see the full cube map as a colour code compared to normative data for the Macula. The Normative Database Map speaks for itself. The Deviation Map is a colour coded measure of how different from the Normative data each point on the map is. The ‘hotter’ colours show thicker that norm, green is similar to norm and the ‘cooler’ colours are thinner that the norm. This may allow us to quickly assess how far from the normal a patients Retina actually is.
- Such analysis is also useful for assessing if there is any progressive loss or increase in overall Retinal thickness at the posterior pole. This may help in assessing the rate of progress of Ischaemic Retinopathies, Macula Oedema or the effect of Lucentis treatment for example. Most software for OCT’s allows complex analysis over time of tissue thickness change. Most software carries out statistical analysis over time to measure if change is due to pathology, age or isn’t significant at all (i.e. within the normal repeatability limits of the device).
- Glaucoma Progression Macula. Notice the progressive loss of Ganglion Cell Layer / GCC in this patients Right Eye. The graph produced by the OCT helps us determine if change is occurring and there is obvious loss of tissue. Notice the very evident Inferior / Superior difference. This progression may help us to decide upon a correct course of referral if this were only over a short period. In this particular case, this is from a Px already under Treatment and the progression will help the Ophthalmologist direct a more aggressive treatment protocol to try and prevent further tissue loss.
- Glaucoma Progression Disc. This is the same eye! Notice there is less dramatic loss of RNFL tissue initially, but latterly the same Superior / Inferior difference can be seen. This is because recent studies have shown that loss of the Ganglion Cell Complex (ILM, RNFL, GCL, IPL and INL) can pre-date ONH RNFL loss by several years and can be an excellent pre-clinical sign of Glaucomatous change and can help us to avoid field loss by starting Glaucoma treatment prior to this taking place. GCL / RNFL loss can help identify Glaucoma up to eight years before clinical signs such as field loss manifest. A Px can lose 50% of the GCC Superiorly and Inferiorly and 40% of the Papillo-Macula Bundle before this might manifest as a field loss! Diagnosing Glaucoma via field screening means we are often rescuing what is left of the Optic Nerve when we start treatment, where as with OCT, we can help to prevent or slow the field loss from occurring.
- This is an image of the Right and Left Macula Maps shown together as many OCT’s will allow. This comparison is important when looking for symmetry / asymmetry between the eyes. We mentioned symmetry / asymmetry within the eye earlier. It is just as useful to understand the symmetry between the eyes. In the above example, the marked difference between Right and Left scans is more likely to indicate pathology in the Right eye than bilateral pathology, even if both scans looked like the Right eye.
- In An average 80 year old, each RPE cell is also 80 years old. It is estimated that each Macula RPE cell will have recycled some 3billion pigment discs over that time scale! Most cells build up Lipofuscin, but RPE in particular do this. Where there is hypoxic or metabolic stress to the RPE, either due to age or other changes, then Lipofuscin can build up to an excessive level. Where this occurs, the Lipofuscin will Hyper-fluoresce (shine brightly) with FAF. Where RPE cells have actually died (causing death to the photo-receptors they support), then Lipofuscin is no longer present and subsequently, there will be areas of Hypo-fluorescence on FAF in these circumstances. This allows us to understand more of the Function of the RPE as opposed to just the form.
- Normal Colour Fundus and normal FAF image. Lipofuscin creates normal fluorescence. Hyper-fluorescence is build up of Lipofuscin, hypo is loss of RPE. Can measure stress and cell death. Form versus Function.
- Cone dystrophies can be classified into 2 sub-groups: stationary and progressive The stationary form tends to remain stable over time and is usually present at birth or develops in early childhood. The progressive form continuously evolves over time. Color fundus and FAF pictures are valuable tools to visualize the changes in the affected area.
- Some OCT’s can recognise the curved interfaces between different layers, which is dependent on progress in Software design.
- En Face. The ILM can highlight things like Epiretinal Membranes, Macula Holes, Pseudo Macula Holes and Vitreal Haemorrhages The IPL/INL interface can highlight Exudate, intra retinal haemorrhages (such as in DR) and cystoid oedema. The RPE/BM interface can highlight Drusen (AMD), Serous fluid as in CSR for example. The RPE/BM offset shows us the inner Choroid and can highlight the small vessel plexus which may highlight CNV, Choroidal haemorrhages, Naevi and other changes.
- Notice the Asymmetry WITHIN the eye, showing loss inferiorly only. With Glaucoma, we can see that only the GCC is affected initially. The overall Retinal thickness, even in later stages of GCC loss is relatively unchanged in thickness as outer layers are unaffected. Thus, if a patient has considerable loss of total Retinal thickness, the pathology may be less likely to be linked to Glaucoma or Optic Neuropathy. However, note that two conditions may co exist in some cases and there may be loss of total Retinal thickness as well as independent loss of GCC thickness in the same eye.
- The white area on the colour temperature map immediately lets us know the central macula is thick. The ETDRS tells us that 0 to1% of the normal population would have a Retina this thick. The Normative Database map, covering 9 x 9mm, shows the true extent of where the thickness is ‘abnormal’ and the deviation map shows just how much thicker than normal the Right macula is.
- The B-Scan image of the RE shows extensive elevation of the sensory retina away from the RPE. Note the tiny area of RPE detachment present as well. The LE scan also shows a minor full retinal lift with a fluid filled space beneath. This is early CSCR, which is rare to be bilateral. Chronic cases may benefit from Photodynamic Therapy (PDT).
- It is evident from the Fundus image that some form of Maculopathy exists in this patient. There are no drusen present, but the patients vision will be <6/120 and very distorted. The SLO / phase fundus image is similar and perhaps misses some of the obvious oedema and haemorrhage. On the next slide, the horizontal line scan image is more conclusive.
- The B-Scan above, however, shows us the true extent of the considerable damage that is present. Notice the cystoid nature of the inner oedema and the break in Bruch's membrane with evident detachment of the sensory retina and central PED detachment.
- The 3D map is extremely valuable in fully highlighting the degree of oedema and detachment. The colour temperature map below is off the scale.
- Open versus Closed Angles. Very evident without having to use digital callipers, but these can be used. Note the conversion between degrees and Van Herrick’s as mentioned earlier.
- R / L Comparison. Notice thinning R eye, but normal cross section. L Eye cross section is Conical in nature. Normally, the thinnest point of the Cornea is displaced infero-nasally in KC. However, in this case, it is displaced infero-temporally.
- KCC. Inferior thinning. Conical cross section. Looking along the radial scan that corresponds with the thinnest point.
- Corneal Oedema. Digital callipers show extreme thickening of the Cornea. There is notable distortion of the Endothelium, showing it’s importance for fluid regulation; the Endothelial pump.
- Penetrating Keratoplasty. This patient has undergone Corneal transplant, using Penetrating Keratoplasty. Notice the large difference in thickness between the original Ectatic Cornea and the transplanted Cornea. Oedema is present at the wound / graft site too.
- Herpetic Keratitis. This Px had an old Dendritic Ulcer. The OCT allows us to better understand how deep the scar penetrates into the Cornea and if is has broken through Bowman’s Layer. This might affect healing, scarring and the treatment protocols in the hospital.