Lec 5 Ocular Imaging

Question 1

What’s interferometry

Answer 1

Technique of superimposing 2 or more waves to detect differences between them

• works as waves with same freq and phase add but opposite phase will subtract

Question 2

What are the major forms of OCT

Answer 2

Time domain OCT

Frequency domain OCT

• spectral domain ICT
• swept source OCT

Doppler OCT

Question 3

How does a time domain OCT work

Answer 3

Optical path length of the reference mirror is translated longitudinally in time

Question 4

How does a spectral domain OCT work

Answer 4

Extracts special info by distributing different optical frequencies onto a detector stripe
(line array CCD or CMOS)

Question 5

How does a swept source OCT work

Answer 5

Light source emits different freq of light sequentially and a spectrum of responses is acquired.

Spectral components are encoded in time creating a spectrum to be processed by four or transformation

Question 6

How does a Doppler OCT work

Answer 6

Measures blood flow per volume using the Doppler effect

Question 7

Differences between TD OCT and SD OCT

Answer 7

TD makes A scan one pixel at a time VS SD makes a whole A scan in one go based on Fourier transformation

TD moving reference mirror VS SD stationary

TD 400scans/sec and low res VS SD 26000scans/sec and high res

TD slower than eye movement VS SD faster than eye movement

Question 8

What’s the advantage of swept source OCT

Answer 8

2x speed of SD OCT

Scans deeper in choroid

Better scans though media opacities

100,000 scans/sec

Invisible line scans

Question 9

In an OCT what lesions are hyper reflective (WHITE)

Answer 9

Hard exudates

Blood

Scars

Question 10

In an OCT what lesions are hyporeflective (BLACK)

Answer 10

Serous fluid

Hypopigmented lesions of RPE