Posterior segment imaging

Question 1

What are 4 types of posterior segment imaging?

Answer 1

1. Colour fundus photography
2. Ultra-widefield imaging
3. Fundus autofluorescence (FAF)
4. Monochromatic and multicolour SLO

Question 2

What are 4 indications for colour fundus photography?

Answer 2

1. screening for posterior segment disease e.g. diabetic retinopathy
2. diagnosis and monitoring of posterior segment disease
3. assessment of anatomic end points in clinical trials (e.g. Early Treatment Diabetic Retinopathy Study)
4. Evaluation of disease risk factors in epidemiological studies e.g. Beaver Dam Eye Study

Question 3

What are the basic principles of colour fundus photography?

Answer 3

specially modified cameras may be used to acquire photographs of the ocular fundus; bright ring of white light illuminates fundus, light reflected is captured on pixel array of a charge-coupled device (CCD) and digital image generated

Question 4

What are 3 refinements that commercial fundus cameras have undergone since their introduction?

Answer 4

1. optimisation for non-mydriatic images
2. stereoscopic image acquisition
3. transition from analogue to digital image capture

Question 5

What are 2 examples of commonly used fundus cameras?

Answer 5

1. Topcon TRC-50DX
2. Zeiss FF450plus

Question 6

How are retinal cameras typically described and what form is most commonly used?

Answer 6

by their optical field of view - most commonly use angle of 30 or 35 degrees

Question 7

What benefit is conferred by ultra-widefield imaging over conventional fundus imaging?

Answer 7

peripheral retina is captured

Question 8

What is an example of an ultra-widefield optical camera?

Answer 8

Optos 200 Tx system

Question 9

What principle does the Optos ultra-widefield camera use?

Answer 9

scanning laser ophthalmoscopy, in combination with large ellipsoid mirror

Question 10

What field of view in an undilated pupil is achieved with ultra-widefield imaging?

Answer 10

200 degrees

Question 11

What feature allows autofluorescence and angiographic imaging with ultrawidefield imaging?

Answer 11

the use of appropriate light filters

Question 12

What are 4 types of laser wavelengths used in ultra widefield imaging?

Answer 12

1. Green 532nm
2. Red laser 633nm
3. Infrared 802nm
4. Blue 488nm

Question 13

Which filter is used with ultrawidefield imaging for fluorescein angiography?

Answer 13

blue 488nm filter

Question 14

What are 3 indications for ultra widefield imaging?

Answer 14

1. Assessment of peripheral non-perfusion in retinal vascular diseases e.g. diabetic retinopathy
2. Assessment of patients with uveitis demonstrating scattering inflammatory foci
3. Assessment of patients with posterior segment pathology e.g. vitreous detachment, retinal tears, and retinal detachments

Question 15

What is meant by fundus autofluorescence (FAF)?

Answer 15

many structures in posterior segment have innate fluorescent properties - when stimualted by light of a specific wavelength, they emit light of a longer wavelength (even in absence of fluorescent contrast agent)

Question 16

What are 3 indications for FAF?

Answer 16

1. diagnosis and monitoring of geographic atrophy progression in patients with age-related macular degeneration
2. assessment of patients with inherited retinal degenerative disese
3. screening and assessment of patients with toxic retinopathies

Question 17

What are the basic principles of how FAF images are obtained?

Answer 17

incorporating appropriate light filters, FAF images can be obtained with either fundus cameras or scanning laser ophthalmoscopy (SLO) devices

Question 18

What are FAF properties dependent on?

Answer 18

wavelengths of light used - blue or green vs near-infrared

Question 19

What are the uses of FAF with blue or green light?

Answer 19

highlights lipofuscin - byproduct of outer segment degradation that accumulates in retinal pigment epithelium cells

Question 20

What structure is highlighted by near-infrared when used with FAF?

Answer 20

melanin

Question 21

How is lens autofluorescence reduced with FAF imaging?

Answer 21

fundus camera and longer-wavelength filters used

Question 22

What are 2 examples of SLO devices commonly used for FAF imaging?

Answer 22

1. Spectralis Bluepeak autofluorescence system (blue excitation wavelength 488nm)
2. Optos autofluorescence system (green excitation wavelength 532nm)

Question 23

What are 5 indications for monochromatic and multicolour scanning laser ophthalmoscopy (SLO)?

Answer 23

1. Red-free imaging
2. Blue light reflectance imaging
3. Green light
4. Near-infrared reflectance imaging
5. Monochromatic images for pseudocolour images

Question 24

What is red-free imaging with monochromatic and multicolour SLO used to assess?

Answer 24

preretinal, intraretinal, and subretinal haemorrhage

Question 25

What are 4 things that can be assessed with blue light reflectance imaging in monochromatic and multicolour SLO?

Answer 25

1. RNFL defects in glaucoma 2. Epiretinal membranes (ERMs) 3. Capillary non-perfusion in retinal vascular disease 4. Abnormally increased reflectance in macular telangiectasia (MacTel)

Question 26

What is green light in monochromatic and multicolour SLO used for?

Answer 26

best for looking at the intermediate retinal structure; particularly useful for looking at intraretinal haemorrhage

Question 27

What is near-infrared reflectance imaging in monochromatic and multicolour SLO useful for? What 2 things can it visualise?

Answer 27

imaging of deep retinal and choroidal structures; 1. visualisation of **reticular drusen ** 2. diagnosis of a**cute macular neuroretinopathy**

Question 28

What can be monochromatic images be combined to form?

Answer 28

pseudocolour iamges of the ocular fundus

Question 29

What is the basic principle of how monochromatic/multicolour SLOs work?

Answer 29

uses monochromatic light filters; longer wavelengths of light (near-infrared) penetrate more deeply for visualisation of subretinal and choroidal structures; shorter wavelengths (blue light) allow imaging of superficial retinal structures

Question 30

What is an example of a monochromatic/multicolour SLO device?

Answer 30

Spectralis Multicolor HRA-OCT

Question 31

How does the Spectralis Multicolor HRA-OCT work for monochromatic/multicolour SLO?

Answer 31

combines reflectance images from 3 monochromatic laser sources: blue (488nm), green (515nm) and infrared (820nm) reflectance

Question 32

What are 3 advantages of monochromatic/multicolour SLO imaging?

Answer 32

1. able to image through the undilated pupil 2. visualisation and discrimination of pathology between retinal/choroidal layers 3. combining with different modalities e.g. OCT in the same platform