OPTICAL COHERENCE TOMOGRAPHY
OPTICAL COHERENCE TOMOGRAPHY PART-1OPTOM FASLU MUHAMMED1
Optical: relating or involving light and optics
Coherence: Constant phase difference in 2 or more waves overtime
Tomography: imaging by sectioning or slicing2
INTRODUCTIONOCT is the new diagnostic tool that can perform cross- sectional images of biological tissues within less than 10 micron axial resolution.
It provide non contact, real time, high resolution, cross- sectional imaging of the eye
PRINCIPLEinterferometry and low coherence light in near infrared range (820nm)probe beamReflected light from each structures are according to their optical propertyBased on interferometryinvolves interference between the reflected light and the reference beam4
5L.SREFERENSE MIRRORBEAM SPLITTER
EYEREFLECTED MEASSUREMENT BEAM
The echo time delay of the light reflected from various layers of retina is compared with echo time delay of the light reflected form the reference mirror
positive interference - light reflected from the retina and the reference mirror- within short coherence length of each other.
photo detector -range of time delays for comparison Different colors represent light backscattering from different depths of retina.The low- coherence light source determines the axial resolution.
Oct system comprisesFundus viewing unitInterferometry unitComputer displayControl panelColor printer
Resolution 10 m
2 dimensional images
Low coherence interferometry using fixed wavelength
Lower speed Upto 512 A scan/sec
9 Resolution 3m
2 or 3 dimensional images
Low coherence interferometry using broad wavelenth spectrum
High speed Upto 16000A scan/sec
TIME DOMAIN OCTSPECTRAL DOMAIN OCT2 TYPE OCT
spectral Domain OCT Advantages High speed reduces eye motion artifacts present in time domain OCT High resolution provides precise detail, allows more structures to visualized Layer by layer assessment Larger scanning areas allow data rich maps 3-D scanning improves clinical utility
PROCEDUREActivation of the machine and entering of patient data is the first step.
Patient position: Patient is asked to look in to the internal fixation target light.
Protocol for scan is selected as per the case requirement. The scanning beam is placed on the area of interest and scans are obtained.
Non contactMedia clarity
Easy tolerance skill of operator
Quantitative retinal pt. cooperationInformation
Teaching toolnon-centered scans-inaccurate measurements.
NORMAL OCT SCAN OF RETINAThe OCT scan of retina allows cross-sectional study of the macular ,peripapillary region including RNFL and ONH region13
15High reflective (Red) - NFL & RPE Medium reflective (yellow / Green) - Plexiform >Nuclear Low reflective (Blue-Black) - photoreceptors Photoreceptor layer - thickest at fovea NFL- increased thickness nasally
OCT SCANSLine scan:It gives an option of acquiring multiple line scans without returning to main window.. Default angle is 0* and length of scan is 5mmThe length of the scan and angle can be altered to acquire multiple scans of different parameter.
Radial line:Consists 6-24 equally spaced line scans that pass through a central common axis; the length of these line scans can be changed by adjusting the size of aiming circle
The radial lines are useful for acquiring macular scan and retinal thickness /volume analysis.
Macular thickness map ;same as radial lines except that the aiming circle has a fixed diameter of 6mm .protocol helps in measuring macular thicknessFast macular thickness mapa quick protocol that takes only 1.92 seconds to acquire six scan of 6mm length each , when done in both the eyesused for comparative retinal thickness / volume analysis
EMM5 (MACULAR THICKNESS SCAN)
Raster lines ; it provides options of acquiring series of lines that are parallel , equally spaced and are 6-24 in number
This scan is especially useful in choroidal neovascular membrane where one wishes to obtain scan at multiple level.
Not only CNVM to scan ,all macular disease23
Raster line scan
Cross line scan
Optic disc scan:Consits of equally placed line scans 4 mm length ,at 30* intervals and centered on discAccurate assessment of size ,area ,C:D ratio ,volume of cup can be meassured
RNFL scan:Circular scan of 1.34mm radius centered on ONHThe mean RNFL Thickness meassured using age adjusted RNFL thickness average analysis protocolIn case of glaucoma progression, neuro ophthalmic diseases.26
TO BE CONTINUED
ANY DOUBTS ????29
REFERENCE Ophthalmology investigation and examination techniques bruce james larry benjamin-pg no.232-239RTVue users manual OF OCTDiabeticeye disease-Alejandro espaillat-pg.75www.opsm.com
1.BASIC PRINCIPLE OF OCT ?
2.In normal OCT ,Nerve fiber layer increased thickness at which area?NASALLYTEMPORALSUPERIORINFERIOR
3. RNFL scan Circular scan of ..radius centered on ONH
4.Radial line consists of equally spaced line scans of .6-24 line scan1-20 line scan1-6 line scanNone of the above35
5.Identify the scan?
36Line scanCross line scanRNFL ScanNone of the above