Intro to OCT

Question 1

what does OCT stand for

Answer 1

optical coherence tomography

Question 2

what is OCT

Answer 2

a non-invasive imaging technique that allows very detailed information to be acquired about living structures within the eye

Question 3

what are the advantages of OCT

Answer 3

non-contact, fast, reliable, usually does not require mydriasis, using non-ionising radiation, aids recognition and monitoring of very subtle changes to eye structures.

Question 4

what is the difference between OCT and ultrasound

Answer 4

OCT uses reflective sound rather than reflective light

Question 5

what is an A-scan

Answer 5

produces a 1D image of the eye , used to measure axial length

Question 6

what is a B-scan

Answer 6

constructed from multiple A-scans taken across various planes

Question 7

how does OCT work

Answer 7

uses low coherence infrared light. light split into two beams, one beam goes to a reference mirror, the other to the tissue being imaged, back-scattered light from both surfaces combine, interference occurs and an image generated.

Question 8

what are the two types of OCT scanners

Answer 8

time domain OCT and spectral (Fourier) domain OCT

Question 9

what is time domain OCT

Answer 9

reference mirror is moved to detect reflection from various layers one depth at a time to produce axial A-scan.

Question 10

what are the disadvantages

Answer 10

Inefficient as depends on how fast the mirror can move

Question 11

what is spectral (Fourier) domain

Answer 11

the reference mirror is kept stationary and reflections from all layers/depths are detected simultaneously as spectrum to produce an A-scan

Question 12

what are the advantages of Spectral (fourier) domain

Answer 12

faster and provides higher resolution with fewer motion artefacts

Question 13

what structure allows all layers of the eye to be identified

Answer 13

spectrometer

Question 14

how can you create a 3D image

Answer 14

combining multiple B-scans

Question 15

what is the resolution that OCT works at

Answer 15

3-10um

Question 16

what is the resolution of MRI

Answer 16

1um

Question 17

What is the resolution of CT

Answer 17

500um

Question 18

what is the resolution of ultrasound

Answer 18

150um

Question 19

what orientation does an OCT scan usually show the vitreous

Answer 19

superiorly

Question 20

how is the foveal identified

Answer 20

by the depression and reduced retinal thickness

Question 21

what does the seudo colour light show

Answer 21

the backscattered light

Question 22

what happens in OCT

Answer 22

changes in optical density are identified

Question 23

what do bright colours or light grey correspond to

Answer 23

features with highly reflectivity

Question 24

what are examples of highly reflective structures

Answer 24

retinal nerve fibre layer, plexiform layers, retinal pigment epithelium and choroid.
adjacent structures with large differences in RI too.

Question 25

what do dark colours and blue represent

Answer 25

little or no reflectivity

Question 26

what is the photoreceptor integrity line

Answer 26

boundary of the inner segment and outer segment

Question 27

what are the reasons for poor quality OCT

Answer 27

blinking, poor fixation or nystagmus, media opacities and dry eye

Question 28

what colour does the vitreous usually appear

Answer 28

black

Question 29

what could you find on the vitreous

Answer 29

floaters or clouding

Question 30

what does PVD stand for

Answer 30

posterior vitreous detachment

Question 31

what is asteroid hylosis

Answer 31

accumulation of calcium or lipids

Question 32

what are we looking for when scanning the retina

Answer 32

areas of hyper or hypo-reflectivity , intra or sub-retina fluid, specific layers that may be involved, the thickness and distribution of individual layers

Question 33

true or false, retinal blood vessels block the reflections from the RPE and choriocapillaris

Answer 33

true