INTRODUCTION: ------------------------- • OCT is an optical instrument that can perform cross-sectional image of biological tissue within less than 10 micron axial resolution using light waves • Retina is easily accessible to the external light, hence it is specially suited for retinal disorder • The information provided by OCT is similar to in vivo histopathology of the retina EXAMPLE:  Zeiss stratus OCT  Topcon 3D OCT-1000 PRINCIPLE OF OCT: -------------------------------- • It is a imaging technology projected light beam (820nm) near infrared light • The beam is then split into two beam (Probe beam & Reference beam) by Beam splitter • Probe beam reach to the target tissue (retina) & reference beam reach to the reference mirror at a known distance • The echo time delay of light reflected various layer of target tissue (retina) is compared with the echo time delay of light reflected from the reference mirror • A positive interference is produced when light reflected from target tissue & reference mirror arrives simultaneously • This interference is measured by a photodetector which finally produce a range of time delays for comparison • The interferometer integrates several data points over 2mm depth to construct a tomogram of retinal structures • It is real time tomogram using false color scale & different colors represent light backscattering from the different layers of retina OCT SYSTEM CONSIST OF: ------------------------------------------ • Fundus viewing unit • Interferometer unit • Computer display • Control panel • Color inkjet printer GENERATION OF ---------------------------- • OCT- 1: o 1st generation o Transverse resolution 20 micron o Axial resolution 10 micron • OCT-2: o 2nd generation o Transverse resolution 20 micron o Axial resolution 10 micron o Better user interference • BOTH OCT-1 & OCT-2: o acquire 100 vertical scan in approximately 1.2 sec • OCT-3: o 3rd generation o Axial resolution 7-8 micron o Acquire 512 vertical scan COLOR CODING OF OCT SCAN: ------------------------------------------------ • RED-YELLOW COLORS: represents areas of maximal optical reflection & backscattering • BLUE & BLACK: Represents areas of minimal optical refelection & backscattering VARIOUS PATTERN OF B-SCAN: -------------------------------------------------- • CIRCULAR SCAN FOR THE ONH RNFL: This generates a plot of the peripapillary RNFL thickness which is important in glaucoma diagnosis & monitoring • RADIAL LINE THROUGH ONH: Consist of 6-24 slices through a common central point on the ONH • MACULAR RADIAL LINES: Used to measure retinal thickness PROCEDURE OF OCT: """"""""""""""""""""""""""""""""""" • STEP-1: PATIENTS DATA  Activation of instrument & entering patients data • STEP-2: PATIENTS PREPARATION:  Pupil dilate with mydriatics (tropicamide)  Asked to look into the internal fixation target light in the ocular lens • STEP-3: PROTOCOL FOR SCAN ACQUISITION:  Selected as per the case requirements  The scanning beam is placed on the target area and scans are obtained • STEP-4: PRODUCTION & DISPLAY IMAGE:  Several data points are integrated by the interferometer to construct a tomogram of the target area  The tomogram is displayed in either grey scale or false color on a high-resolution computer screen

• published: 03 Jun 2020
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