Advanced Primary Care Optometry (10328) Lecture Notes PDF

Advanced Primary Care Optometry (10328) Optical coherence tomography of the posterior eye Dr Agnes Choi and Dr Vicki Evans  Acknowledgement of Country We acknowledge and pay respect to the traditional owners of the land on which we meet – the Ngunnawal Peop...

Advanced Primary Care Optometry (10328) Optical coherence tomography of the posterior eye Dr Agnes Choi and Dr Vicki Evans  Acknowledgement of Country We acknowledge and pay respect to the traditional owners of the land on which we meet – the Ngunnawal Peoples. It is upon their ancestral lands that the University of Canberra is built. ​ We wish to acknowledge and respect their continuing culture and contribution they make to the life of Canberra and the region. We also acknowledge all other First Nations Peoples on whose land we gather.  Respond NOW via myUC student portal Tell us… We value your feedback… So let your voice be heard We are seeking feedback on your It can help us improve your Your responses are anonymous to experience as a student in this learning experience; make your the teaching staff in the unit, and unit feedback constructive, specific, faculty staff respectful and actionable Provide comments so we understand the context behind your ratings Prescribed Reading Ly A et al. An evidence-based approach to the routine use of optical coherence tomography. Clin Exp Optom 2019; 102:242-259  Pop Quiz preview Explain the optical principles of OCT imaging What is the difference between and A-scan, B-scan and volume scan? What are the key retinal segmentations applied in OCT? What are the main types of scan you can use with an OCT and why would you use each one? What is red disease and green disease? What are the post-hoc analysis indices commonly used in OCT and how are they applied? Compare and contrast the report format of three main types of OCT images If using GPA, what are you measuring? Identify and describe how to correct common artifacts in OCT imaging Describe OCT-A and a clinical indication for OCT-A  Learning Objectives What is optical coherence tomography How to do it When to use it Watch out for artifacts OCT-Angiography in a nutshell  What is it Technology basics  OCT has much higher resolution than ultrasound, MRI, CT or cSLO Comparison of resolution in axial and lateral direction between some medical imaging techniques for different body parts. Skin/cornea: reflectance confocal microscopy (RCM). Retina: confocal scanning laser ophthalmoscopy (cSLO), adaptive optics scanning laser ophthalmoscopy (AOSLO) , optical coherence tomography (OCT), adaptive optics optical coherence tomography (AO-OCT). General: magnetic resonance imaging (MRI), computed tomography (CT), medical ultrasound Aumann, S., Donner, S., Fischer, J., Müller, F. (2019). Optical Coherence Tomography (OCT): Principle and Technical Realization. In: Bille, J. (eds) High Resolution Imaging in Microscopy and Ophthalmology. Springer, Cham. https://doi.org/10.1007/978-3-030-16638-0_3 Cross sectional view. A beam of light typically 800-1400 nm near infrared is scanned across the tissue sample. Measured time of flight delay. Superficial layer has shorter propagation delay than deeper layers. Costa et al 2006 Prog Retin Eye Res  A-scans Amplitude can be plotted against the time of flight delay in the axial plane. This reveals changes in amplitude of tissue reflectivity over the depth of the retinal. Amplitude of reflection or A-scan (similar to ultrasound). Costa et al 2006 Prog Retin Eye Res  B-scans Many A-scans (red lines) are combined to provide a B-scan cross sectional image through one line Costa et al 2006 Prog Retin Eye Res Costa et al 2006 Prog Retin Eye Res  Volume scans Many B-scans are combined to provide a volume scan. This creates a cube of information and the surface of the cube is called the enface plane. This allows calculation of thickness over an area or region. Aumann S., Donner S., Fischer J., Müller F. (2019) Optical Coherence Tomography (OCT): Principle and Technical Realization. In: Bille J. (eds) High Resolution Imaging in Microscopy and Ophthalmology. Springer, Cham. https://doi.org/10.1007/978-3-030-16638-0_3  Basic principles of Interferometry Non-invasive technique for examining ocular structure by cross sectional imaging. Allows real-time viewing of tissues. Interferometry techniques used a photo-detector to collect back- scattered light from a scanning near infrared source. Source light is split into two separate paths by the interferometer then re-combines the light coming back from the two paths at the interferometer output This reflected light is measure by the detector Time and amplitude variation is generated between structures of different depth and reflectivity. Aumann, S., Donner, S., Fischer, J., Müller, F. (2019). Optical Coherence Tomography (OCT): Principle and Technical Realization. In: Bille, J. (eds) High Resolution Imaging in Microscopy and Ophthalmology. Springer, Cham. https://doi.org/10.1007/978-3-030-16638-0_3 Super luminescent diode Interferometer Coupler measures the effect of combining two light waves. If the wavelengths are coherent (can be Converted to electrical current superimposed, or are in-phase) as they travel over time, they can add constructively (i.e. they amplify each other) or destructively (i.e. they cancel out each other) or anything in between Costa et al 2006 Prog Retin Eye Res Aumann, S., Donner, S., Fischer, J., Müller, F. (2019).  Temporal Domain OCT Light from the light source is split into the reference beam and the central beam. To record one depth profile of the sample (amplitude scan or A-scan) the reference arm needs to be scanned. This has to be repeated for each lateral scan position. Back reflected light from both arms is combined again at the fibre optic coupler and recorded by the detector. The signal processor transforms the waves into peaks of amplitude (A-scan) To create a cross-sectional image (or B-Scan), the sample beam is scanned laterally across the sample. This abbreviation originated in ultrasound imaging, where B-Scan means brightness scan. Aumann, S., Donner, S., Fischer, J., Müller, F. (2019). Optical Coherence Tomography (OCT): Principle and Technical Realization. In: Bille, J. (eds) High Resolution Imaging in Microscopy and Ophthalmology. Springer, Cham. https://doi.org/10.1007/978-3-030-16638-0_3  Comparison of technologies Time Domain Fourier Domain low coherent light source 2nd generation of OCT technology acquisition of a depth scan for every location to generate an more efficient implementation of the principle of low- A-scan coherence interferometry lateral scans required to generate B-scan uses spectral information to generate A-scans without the very slow imaging speed and poor image quality need for mechanical scanning of the optical path length noisy images impede use for clinical diagnosis Spectral Domain Swept Source Domain 3rd generation, broad wavelength spectrum light source 4th generation, the optical source rapidly sweeps a narrow captures whole depth information simultaneously line-width over a broad range of wavelengths improved image speed and quality, determined by linescan one wavelength sweep constitutes a spectral interferogram rate of camera with fringe patterns, as in SD-OCT co-localisation of fundus scan with cross-sectional OCT the interferogram contains information for all depth layers of images improves motion tracking the sample simultaneously improved usefulness for diagnosis acquisition speed is given by the sweep rate of the swept- source and subsequent AD Aumann, S., Donner, S., Fischer, J., Müller, F. (2019). Optical Coherence Tomography (OCT): Principle and Technical Realization. In: Bille, J. (eds) High Resolution Imaging in Microscopy and Ophthalmology. Springer, Cham. https://doi.org/10.1007/978-3-030-16638-0_3  Optical setup of spectrometer based OCT (SD-OCT) and swept source OCT (SS-OCT). While SD-OCT uses a spectrometer for wavelength separation, SS-OCT features a light source which sweeps the wavelength in time. Both implementations record an interference spectrum which carries the depth in formation of the sample. FFT is used to transform the interference signal into the A-scan. Aumann, S., Donner, S., Fischer, J., Müller, F. (2019). Optical Coherence Tomography (OCT): Principle and Technical Realization. In: Bille, J. (eds) High Resolution Imaging in Microscopy and Ophthalmology. Springer, Cham. https://doi.org/10.1007/978-3-030-16638-0_3 There are an ever-growing number of OCT instruments on the market OPTOMETRY AUSTRALIA OCT BUYER’S GUIDE 2018 https://www.o ptometry.org.a u/wp- content/uploa ds/Publications /Equipment/E Q-OCT-buyers- guide-2018.pdf  Spectralis Heidelberg Cirrus Zeiss RS Duo 2 Nidek Maestro 2 Topcon Spectral Domain Spectral Domain Spectral Domain Spectral Domain 40-80k A-scan/sec 27-68 A-scan/sec 53k A-scan/sec 50k A-scan/sec https://www.nidek- How to acquire the perfect image, https://www.beye.com/product/cirrus-hd- intl.com/product/ophthaloptom/diag https://topconhealthcare.com/products/ HRA+OCT Spectralis, Heidelberg oct-500 nostic/dia_retina/duo2.html maestro2/ Engineering Academy  Line scan of macula Retina and Glaucoma Imaging Platform Spectralis RPE Bruchs membrane Choroid  Line scan of macula Staurenghi et al 2014 Ophthalmol  Segmentation https://iacl.ece.jhu.edu/index.php/Retinal_layer_segmentation_of_macular_OCT_images Figure 1: (a) A typical retinal OCT image (B-scan) enlarged with the layers labeled on the right-hand side. Every B-scan consists of a set of vertical scan lines (A-scans). The fovea is characterized by a depression in the surface of the retina where the top five (inner) layers are absent. (b) A fundus image with lines overlaid representing the locations of every B- scan within a volume. The red line corresponds to the B-scan in (a).  Structure and depth Most OCTs allow simultaneous viewing of fundus (IR) with OCT scan, many now incorporate cSLO colour imaging of the fundus as well. This is incredibly useful for tracking change in clinical pathologies such as neovascular AMD and glaucoma file:///C:/Users/s437761/Downloads/303057-002_SPECTRALIS_Sales%20Tool_cSLO%20Retinal%20Modalities%20Sheet_US.pdf How to do it The main things  OCT scan pattern and examples of use You can shoose: Line – Macula – Optic nerve head Volume – Macular thickness – Ganglion cell layer thickness Circle – TSNIT graph Panda et al 2018 Comput Med Imaging Graph Line scan  Line scan of macula Staurenghi et al 2014 Ophthalmol Minimum distance between ILM and Bruch’s membrane opening around Line scan of an optic nerve the optic nerve head (BMO-MRW) head, disc margin Staurenghi et al 2014 Ophthalmol Glaucoma Module Premium Edition Spectralis Volume scan  Spectralis OCT macular scan https://www.opticianonline.net/cet-archive/123  Cirrus OCT macular scan – macular thickness analysis Cirrus HD-OCT User Manual - Models 500, 5000  Cirrus OCT macular scan – ganglion cell layer thickness analysis Bounded by purple and yellow line GCL + IPL thickness  Nidek OCT macular scan Ganglion cell complex (GCC) = RNFL + GCL + IPL Bruce 2014 Pharma March Optometry Australia Circle scan  Cirrus OCT RNFL scan https://www.ophthalmologymanagement.com/issues/2011/july-2011/the-expanding-role-of-sdoct-in-practice Spectralis OCT RNFL scan Check size of circle Check segmentation is correct Glaucoma Module Premium Edition Spectralis  Nidek OCT RNFL scan Disc margin is shortest distance from BMO to ILM https://nidek-oct.com/glaucoma-diagnostics Putting it all together  Cirrus report Neuroretinal rim thicknesses, defined as the distance between the optic disc margin and cup margin at a specific point, in a 360° circumferential area are presented as a neuroretinal rim thickness curve with Cirrus HD-OCT. (TSNIT graph.) https://www.zeiss.co.uk/content/dam/Meditec/gb/Chris/OCT%20Busin ess%20Builder/PDF%27s/1.pdf  Spectralis report Arthur, S., Smith, S., Wright, M. et al. Reproducibility and agreement in evaluating retinal nerve fibre layer thickness between Stratus and Spectralis OCT. Eye 25, 192– 200 (2011). https://doi.org/10.1038/eye.2010.178 Maestro report https://lombartinstrum ent.com/products/topc on-3d-oct-1-maestro2- spectral-domain-oct/ Topcon Maestro 2 https://www.reviewofoptometry.com/article/how-do-oct-devices-for-glaucoma-compare Glaucoma progression analysis Deviation maps When to use it Clinical applications Clinical Application 1 Glaucoma  46 y.o. Caucasian female 6/6 each eye IOP 15 mmHg each eye Gonioscopy showed open angles Pachymetry was 579 μm each eye Large cups OU (OD > OS) HFA VF showed no glaucomatous field defects each eye RNFL within normal limits each eye – circle scan Macular retinal thickness map showed an arc of thinning extending infero- temporally from the optic disc OD – volume scan Spectralis Asymmetry analysis showed the arcuate defect on the right-left comparison and the superior-inferior comparison. Asrani et al 2011 Arch Ophthalmol  56 y.o. Caucasian female OD 6/6 OS 6/9 IOP OD 19 mmHg OS 21 mmHg Sloped inferior rim OD and thin inferior rim OS HFA VF: a superior nasal step and a small superior paracentral defect OD a superior hemifield defect and an early inferior paracentral defect OS RNFL: inferotemporal thinning OD Inferior and temporal thinning OS Macular retinal thickness map: inferior defect OD highlighted in superior-inferior comparison inferior defect highlighted in superior-inferior comparison overall thinner retinal thickness OS highlighted in right-left comparison Asrani et al 2011 Arch Ophthalmol Cryer 2016 Pharma June Optometry Australia  Clinical Application 2 Optic neuropathy and papilloedema  http://webeye.ophth.uiowa.edu/eyeforum/c ases/72-optic-nerve-drusen-visual-field- loss.htm https://www.ophthalmologymanagement.com/issues/2011/july-2011/the-expanding-role-of- sdoct-in-practice https://www.ophthalmologymanagement.com/issues/2011/july-2011/the-expanding-role-of-sdoct-in-practice  Healthy Mild papilloedema Severe papilloedema Vartin et al 2012 Br J Ophthalmol Clearly visible ODD A few visible ODD Buried ODD Hamann et al 2018 Acta Ophthalmol  Clinical Application 3 Age-related macular degeneration https://www.opticianonline.net/features/macular-degeneration-case-study  Clinical Application 4 Central Serous Chorioretinopathy Pole et al 2020 Am J Ophthalmol Case Rep  Clinical Application 5 Diabetic retinopathy and macular oedema Before focal/grid laser 6 months after laser DM macular oedema Hirano et al 2014 Ophthalmic Res Chauhan 2015 Pharma September Optometry Australia OCT Artifacts  Operator- dependent artifact – Truncation Incorrect thickness measurement Asrani et al 2014 JAMA Ophthalmol  Ocular cause of artifact – epiretinal membrane Incorrect segmentation Asrani et al 2014 JAMA Ophthalmol  Ocular cause of artifact – posterior vitreous detachment Erroneous elevation in RNFL thickness because traction released Asrani et al 2014 JAMA Ophthalmol  Machine error Incorrect segmentation https://www.reviewofophthalmology.com/article/dont-be-fooled-spotting-oct-artifacts  Motion artifact Incorrect segmentation Incomplete segmentation https://www.reviewofophthalmology.com/article/dont-be-fooled-spotting-oct-artifacts  Floater Ocular cause of artifact – Floater Missing data Liu et al 2015 Am J Ophthalmol OCT-Angiography  Basic principle of OCT-A Uses the principle of “motion contrast” to detect blood flow Differing patterns of reflectance across time due to red blood cell movement within tissue. To detect motion, we must image the exact same retinal location four consecutive times. Majcher and Johnson Review of Optometry March 15, 2017. https://www.reviewofoptometry.com/article/imaging-motion-a-review-of- octa#:~:text=OCT%2DA%20imaging%20is%20based,blood%20cell%20movement%20within%20tissue.&text=To%20detect%20motion%2C%20we%20must,acquiring%20four%20macular%20cube%20scan s).  Basic principle of OCT-A Uses the principle of “motion contrast” to detect blood flow https://www.nidek-intl.com/archives/004/201902/5c763ea7a8890.pdf Majcher and Johnson Review of Optometry March 15, 2017. https://www.reviewofoptometry.com/article/imaging- motion-a-review-of- octa#:~:text=OCT%2DA%20imaging%20is%20based,blood %20cell%20movement%20within%20tissue.&text=To%20 detect%20motion%2C%20we%20must,acquiring%20four %20macular%20cube%20scans). Pole et al 2020 Am J Ophthalmol Case Rep Superficial capillary Deep capillary plexus Outer retina Choroid plexus (SCP) (DCP) https://www.nidek-intl.com/archives/004/201902/5c763ea7a8890.pdf Now it’s your turn! What can you see? Which scan will you use?  Inf temp thinning, wedge defect RNFL scan (circle) TSNIT graph Posterior pole asymmetry analysis (volume) Ganglion cell layer analysis (Cirrus, Nidek) Panda et al 2018 Comput Med Imaging Graph Asrani et al 2011 Arch Ophthalmol  OS Silver wiring, microvascular changes, beading Volume scan infero-nasal to the optic disc, px look a little to RHS Searching for Clues on OCT images, Spectralis Basics of OCT interpretation, Heidelberg Engineering Academy Ahmad and Carrim 2017 Optom Vis Sci  Retinal haemorrhage & OD drusen neovasc AMD Volume scan Px looks a little to RHS Ong and Guymer 2016 Pharma June Optometry Searching for Clues on OCT images, Spectralis Basics of OCT Australia interpretation, Heidelberg Engineering Academy Prescribed Reading Ly A et al. An evidence-based approach to the routine use of optical coherence tomography. Clin Exp Optom 2019; 102:242-259  Pop Quiz your turn Explain the optical principles of OCT imaging What is the difference between and A-scan, B-scan and volume scan? What are the key retinal segmentations applied in OCT? What are the main types of scan you can use with an OCT and why would you use each one? What is red disease and green disease? What are the post-hoc analysis indices commonly used in OCT and how are they applied? Compare and contrast the report format of three main types of OCT images If using GPA, what are you measuring? Identify and describe how to correct common artifacts in OCT imaging Describe OCT-A and a clinical indication for OCT-A Thank you!