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Thread: Optical coherence tomography ( OCT)

  1. #1
    Join Date
    Oct 2017
    Riyadh, Saudi Arabia
    (Consultant Ophthalmologist at MALAZ MEDICAL GROUP)


    Default Optical coherence tomography ( OCT)

    Optical coherence tomography ( OCT)

    ✍️ high-resolution images of the neurosensory retina in a non-invasive manner.

    ✍️ analogous to ultrasonography but measures light waves, rather than sound waves.

    ✍️ OCT measurements are achieved indirectly using interferometry.

    ✍️ the combination of light reflected from a tissue of interest and light reflected from a reference path produces characteristic interference patterns

    ✍️ interference pattern dependent on the mismatch between the reflected waves.

    ✍️ Since the time delay and amplitude of one of the waves (the reference path) are known, the time delay and intensity of light returning from the sample tissue may be determined.

    ✍️ The resulting plot of light intensity versus time delay is known as an A-scan and describes the anatomy of the eye tissue at a specific point.

    ✍️ A-scans are then repeated at multiple transverse locations and mapped to a grey or false-colour scale, giving rise to two-dimensional cross-sectional (tomographic) images (termed B-scans).


    ✍️ Monitoring of response to treatment and/or disease activity in patients with chorioretinal vascular and inflammatory diseases (neovascular AMD, diabetic retinopathy, RVO, CMO).

    ✍️ Diagnosis of clinically occult macular pathology (subtle abnormalities of the vitreoretinal interface).

    ✍️ Detection of glaucomatous damage to the RNFL and/or optic nerve head.

    ✍️ Assessment and longitudinal monitoring of disc volume in disc swelling and papilloedema.


    ✍️ On OCT false-colour B-scans, highly reflective tissue is reddish white in colour, while hyporeflective tissue is blue–black in colour.

    ✍️ Alternatively, images can be shown in 256 shades of grey, corresponding to different optical reflectivities

    ✍️ The inner and outer nuclear layers and ganglion cell layer are typically hyporeflective

    ✍️ the inner and outer plexiform layers and nerve bre layer are hyperreflective.

    ✍️ larger retinal vessels are seen on OCT as circular hyperreflective foci located in the inner retina, with underlying ‘shadowing’

    ✍️ A number of hyperreflective bands may be seen in the outer retina, typically consisting of

    • the external limiting membrane
    • photoreceptor inner segment-outer segment (IS-OS) junction (ellipsoid zone)
    • RPE.

    ✍️ Using specialized scanning protocols (enhanced depth imaging) the choroid and choroidal–scleral junction may also be seen.


    ✍️ Time domain OCT ( TD/OCT) using the Stratus OCT (Carl Zeiss Meditec) acquires images at 400 axial scans/s, with an axial resolution of 10 microns.

    ✍️ Spectral (or Fourier) domain (SD/OCT) using the Spectralis HRA/OCT (heidelberg Engineering) or Cirrus HD-OCT (Carl Zeiss Meditec) scan at a rate of at least 20,000 axial scans/s, with an axial resolution typically between 3 and 8 microns.

    Quantitative image analysis

    ✍️ measure retinal thickness at multiple locations and to construct retinal thickness maps corresponding to the ETDRS subfields.

    ✍️ automated quantitative assessment of drusen and geographic atrophy in patients with AMD.

    ✍️ In patients with glaucoma

    • specialized circular OCT scanning protocols are employed
    • a single circular B-scan, centred on the optic disc and 3.4mm in diameter, is obtained.
    • Segmentation of the inner and outer boundaries of the RNFL allows assessment of peripapillary RNFL thickness.
    • The presence of glaucomatous RNFL thinning can then be determined by comparison with normative databases.

    how to comment on OCT

    Optical coherence tomography OCT) attachment.php?attachmentid=3447&d=1511425699

    As follows

     I can see the following 

    ✍️ increased retinal foveal thickness
    ✍️ disruptions of RPE layer
    ✍️ infront of the RPE , there is mild hyperreflective mass with smaller hyporeflective lacunae or spaces
    ✍️ all other layers are will differentiated with increased thickness and hyporeflective minute intervening spaces ( oedema)

    ✅ Conclusion:

    ✍️ Classic CNV picture of OCT

     Wait and follow for more descriptive posts on OCT ☝️☝️☝️☝️☝️

    Optical coherence tomography OCT) attachment.php?s=1f9ed315fe3e12fdf371357e65ca9383&attachmentid=3448&d=1511425856
     how to comment on ☝️☝️☝️☝️☝️☝️☝️

    Fundus shows

    ✍️ hard exudates

    ✍️ subretinal ring shaped hemorrhage

    FFA shows

    ✍️ hot spot with dark ring ( hyperfluorescent center with surrounding ring of hypofluoresce )

    OCT shows

    ✍️ loss of foveal contour with increased retinal foveal thickness

    ✍️PED with underlying attenuated choroid reflection due to heavy fluid or hemorrhage

    ✍️ NO OCT evidence of CNV


    ✍️ hemorrhagic PED

    Follow 

    Attached Images  
    Last edited by Reda Gomah El Garia; 12-04-2017 at 10:07 AM.

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  3. #2
    Join Date
    Oct 2017
    Riyadh, Saudi Arabia
    (Consultant Ophthalmologist at MALAZ MEDICAL GROUP)


    Default Back to OCT basics

    Back to OCT basics

    ✍️ Posterior segment evaluation with OCT allows visualization of the vitreous, retinal layers, retinal pigment epithelium (RPE) and the choroidal layers.


    ✍️ The posterior hyaloid of the vitreous can be identified on macula scans especially with spectral-domain (SD-OCT).

    ✍️ useful in the evaluation of posterior vitreous detachments, vitreomacular traction or vitreopapillary traction.

    ✍️ The instrument uses 840nm wavelength of light ( can’t penetrate denser vitreous opacities like Weiss rings or asteroid hyalosis).


    ✍️ Each distinct retinal layer is visible on the OCT and corresponds well to histological studies.

    ✍️ Certain types of retinal conditions can affect different retinal layers.

    ✍️ The retinal nerve fiber layer and retinal ganglion cell layer are affected in conditions like glaucoma.

    ✍️ The inner retinal layers show atrophy secondary to retinal vascular occlusions like retinal artery occlusions.

    ✍️ The outer retinal layers show atrophy secondary to conditions that affect the RPE ( AMD and CSR)

    ✍️ Four distinct hyperreflective lines are seen in the outer retinal layers of a SD-OCT scan on a healthy eye.

    ✍️ These four hyper-reflective lines should always be identified when evaluating a macula scan.

    ☝️ RPE (retinal pigment epithelium)
    ☝️ COST(cones outer segment tips line or IZ- interdigitation zone )
    ☝️ EPIS (ellipsoid portion of the inner segments or EZ- ellipsoid zone or IS/OS- inner segment outer segment junction line)
    ☝️ ELM(external limiting membrane)


    ✍️ The choroid can be visualized by enhanced-depth imaging (EDI) or imaging with longer wave-length OCT
    ✍️ Certain conditions that affect the choroid have been found to have an abnormally thicker choroid.

    ✍️ in CSR and PCV , the choroidal thickness is thicker with visible large dilated choroidal vessels compared to age-matched normals.
    Last edited by Reda Gomah El Garia; 12-04-2017 at 10:10 AM.

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