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OPTICAL COHERENCE TOMOGRAPHY PART-1

OPTOM FASLU MUHAMMED

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Optical: relating or involving light and optics

Coherence: Constant phase difference in 2 or more waves overtime

Tomography: imaging by sectioning or slicing

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INTRODUCTION OCT 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

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PRINCIPLE interferometry and low coherence light in

near infrared range (820nm) probe beam Reflected light from each structures are

according to their optical property Based on interferometry

involves interference between the reflected light and the reference beam

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L.S

REFERENSE MIRROR

BEAM SPLITTER

DETECTORE

EYE

REFLECTED MEASSUREMENT BEAM

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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.

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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.

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OCT SYSTEM COMPRISES Fundus viewing unit Interferometry unit Computer display Control panel Color printer

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• Resolution 10 m

• 2 dimensional images

• Low coherence interferometry

using fixed wavelength

• Lower speed Upto 512 A scan/sec

• Resolution 3m

• 2 or 3 dimensional images

• Low coherence interferometry• using broad wavelenth spectrum

• High speed – • Upto 16000A scan/sec

TIME DOMAIN OCT

SPECTRAL DOMAIN OCT

2 TYPE OCT

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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

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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.

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AdvantagesDisadvantages

Non contact Media clarity

Easy tolerance skill of operator

Quantitative retinal pt. cooperationInformation

Teaching tool non-centered scans-inaccurate

measurements.

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NORMAL OCT SCAN OF RETINA The OCT scan of retina allows cross-sectional

study of the macular ,peripapillary region including RNFL and ONH region

PHOTORECEPTORSRPECHORIOCAPILLARIS

NFLFOVEOLA

GCL

ELM

ONL

OPL

INLIPL

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NORMAL OCT

•High reflective (Red) - NFL & RPE• Medium reflective (yellow / Green) - Plexiform >Nuclear• Low reflective (Blue-Black) - photoreceptors• Photoreceptor layer - thickest at fovea• NFL- increased thickness nasally

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OCT SCANS Line scan: It gives an option of acquiring multiple line

scans without returning to main window. . Default angle is 0* and length of scan is

5mm The length of the scan and angle can be

altered to acquire multiple scans of different parameter.

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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.

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Macular thickness map ; same as radial lines except that the aiming circle

has a fixed diameter of 6mm . protocol helps in measuring macular thickness Fast macular thickness map a quick protocol that takes only 1.92 seconds to

acquire six scan of 6mm length each , when done in both the eyes

used for comparative retinal thickness / volume analysis

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EMM5 (MACULAR THICKNESS SCAN)

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THICKNESS MAP

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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 disease

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RASTER LINE SCAN

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CROSS LINE SCAN

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Optic disc scan: Consits of equally placed line scans 4 mm

length ,at 30* intervals and centered on disc Accurate assessment of size ,area ,C:D

ratio ,volume of cup can be meassured

RNFL scan: Circular scan of 1.34mm radius centered on ONH The mean RNFL Thickness meassured using age

adjusted RNFL thickness average analysis protocol

In case of glaucoma progression, neuro ophthalmic diseases.

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OCT SCANS

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TO BE CONTINUED…

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ANY DOUBTS ????

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REFERENCE Ophthalmology investigation and

examination techniques –bruce james larry benjamin-pg no.232-239

RTVue users manual OF OCT Diabeticeye disease-Alejandro espaillat-pg.75 www.opsm.com

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PROFICIENCY TEST

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1.BASIC PRINCIPLE OF OCT ?A. SCATTERINGB. POLARIZATIONC. INTERFERENCED. DIFFRACTION

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2.IN NORMAL OCT ,NERVE FIBER LAYER INCREASED THICKNESS AT WHICH AREA?A. NASALLYB. TEMPORALC. SUPERIORD. INFERIOR

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3. RNFL SCAN CIRCULAR SCAN OF ………..RADIUS CENTERED ON ONH

A. 3.5 mmB. 2mmC. 3mmD. 1.34mm

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4.RADIAL LINE CONSISTS OF EQUALLY SPACED LINE SCANS OF ……….A. 6-24 line scanB. 1-20 line scanC. 1-6 line scanD. None of the above

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5.IDENTIFY THE SCAN?

A.Line scanB.Cross line

scanC.RNFL ScanD.None of the

above

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THANK UUUUU…