retinal imaging

Question 1

retinal photography
filters

Answer 1

red free filters
make red objects appear blacker, can see blood vessels clearer
work better in black and white images

Question 2

retinal photography

Answer 2

angiography
- sodium fluorescein dye injected into blood
- passes through eye
- camera used to capture path of NAFL
- wheb illuminated by light molecules within NAFL excited to higher energy state and then emit light at higher wavelength
- blue filter placed over camera illumination to excite molecules and further blue-green filter allows only the higher wavelength to enter camera

Question 3

retinal photography
angiography interpretation
causes of hypofluorescence
causes of hyperfluorescence

Answer 3

hypo- transmition defect eg blood, pigment

hyper- leakage of dye , staining of dye, pooling of dye

Question 4

alternative to sodium fluorescein

Answer 4

idocyanine green ICG
doesn’t leak out of blood vessels

Question 5

retinal photography
angiography
adv and disadv

Answer 5

adv- assesses ocular vasculature
fluorescein- retinal
ICG- choroid
detects presence of oedema (leakage)

disadv- invasive
side effects such as skin discolouration and light sensitivity

Question 6

retinal photography
stereo photography
how to view
adv and disadv

Answer 6

taking two pics of same spot in eye from diff angles to get 3d image
how to view?
- red green spectacles
- polarised spectacles

adv- allows appreciation of depth
disadv- requires dedicated cameras and requires pupil dilation drops

Question 7

scanning laser opthalmoscopy SLO

Answer 7

-laser scanned across retina
-at each point reflectivity is measured
-image formed from individual reflectivity measurements at each retinal location
-allows high resolution images as not affected by pupil size and aberrations

Question 8

SLO
wild field of view- optomap

Answer 8

scanning laser opthalmoscopy
uses special ellipsoidal mirror to allow very wide field of view without collaging or dilation

Question 9

SLO
how are images in colour?

Answer 9

green laser- operated at 532nm reflected from sensory retina, increases contrast of vasculature like red free filter

red laser- operates at 633nm
reflected from RPE and choroid
increases contrast of pigmented lesions

Question 10

SLO
optomap
adv and disadv

Answer 10

adv- wild field of view
no dilation required

disadv- no depth
difficult to align some patients

Question 11

optical coherence tomography OCT

Answer 11

topcon triton SS-oct
heidelberg engineering spectrails OCT
carl zeiss cirrus HD-OCT

-depth measured by echo time delay (time taken for sound to travel)
-reflectivity measured by size of amplitude of echo (amount of sound reflected)

Question 12

OCT IMAGES

Answer 12

axial- a scan 1D
represents both depth and reflectivity in a single location

cross section- b scan 2D
series of adjacent scans that combine to form cross sectional image

cube section- c scan 3D
by combing multiple adjacent b scans it’s possible to produce 3D image

Question 13

oct angiography

Answer 13

• detects blood flow through blood vessels via comparison of consecutive images OCT
• keep taking pictures to analyse blood flow and monitor any abnormalities such as leaks
• no dye needed and non invasive
• helps detect diabetes and neurovascular amd

Question 14

oct
adv and disadv

Answer 14

adv
- 3d images can see the layers of retina
- no need for dilation

disadv
- no colour rep
- image formation difficult through going parts of the eye eg if it’s cloudy like cataracts
- better at making images for central retina than the edges(periphery)