Posterior segment imaging Flashcards
What are 4 types of posterior segment imaging?
- Colour fundus photography
- Ultra-widefield imaging
- Fundus autofluorescence (FAF)
- Monochromatic and multicolour SLO
What are 4 indications for colour fundus photography?
- screening for posterior segment disease e.g. diabetic retinopathy
- diagnosis and monitoring of posterior segment disease
- assessment of anatomic end points in clinical trials (e.g. Early Treatment Diabetic Retinopathy Study)
- Evaluation of disease risk factors in epidemiological studies e.g. Beaver Dam Eye Study
What are the basic principles of colour fundus photography?
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
What are 3 refinements that commercial fundus cameras have undergone since their introduction?
- optimisation for non-mydriatic images
- stereoscopic image acquisition
- transition from analogue to digital image capture
What are 2 examples of commonly used fundus cameras?
- Topcon TRC-50DX
- Zeiss FF450plus
How are retinal cameras typically described and what form is most commonly used?
by their optical field of view - most commonly use angle of 30 or 35 degrees
What benefit is conferred by ultra-widefield imaging over conventional fundus imaging?
peripheral retina is captured
What is an example of an ultra-widefield optical camera?
Optos 200 Tx system
What principle does the Optos ultra-widefield camera use?
scanning laser ophthalmoscopy, in combination with large ellipsoid mirror
What field of view in an undilated pupil is achieved with ultra-widefield imaging?
200 degrees
What feature allows autofluorescence and angiographic imaging with ultrawidefield imaging?
the use of appropriate light filters
What are 4 types of laser wavelengths used in ultra widefield imaging?
- Green 532nm
- Red laser 633nm
- Infrared 802nm
- Blue 488nm
Which filter is used with ultrawidefield imaging for fluorescein angiography?
blue 488nm filter
What are 3 indications for ultra widefield imaging?
- Assessment of peripheral non-perfusion in retinal vascular diseases e.g. diabetic retinopathy
- Assessment of patients with uveitis demonstrating scattering inflammatory foci
- Assessment of patients with posterior segment pathology e.g. vitreous detachment, retinal tears, and retinal detachments
What is meant by fundus autofluorescence (FAF)?
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)
What are 3 indications for FAF?
- diagnosis and monitoring of geographic atrophy progression in patients with age-related macular degeneration
- assessment of patients with inherited retinal degenerative disese
- screening and assessment of patients with toxic retinopathies
What are the basic principles of how FAF images are obtained?
incorporating appropriate light filters, FAF images can be obtained with either fundus cameras or scanning laser ophthalmoscopy (SLO) devices
What are FAF properties dependent on?
wavelengths of light used - blue or green vs near-infrared
What are the uses of FAF with blue or green light?
highlights lipofuscin - byproduct of outer segment degradation that accumulates in retinal pigment epithelium cells
What structure is highlighted by near-infrared when used with FAF?
melanin
How is lens autofluorescence reduced with FAF imaging?
fundus camera and longer-wavelength filters used
What are 2 examples of SLO devices commonly used for FAF imaging?
- Spectralis Bluepeak autofluorescence system (blue excitation wavelength 488nm)
- Optos autofluorescence system (green excitation wavelength 532nm)
What are 5 indications for monochromatic and multicolour scanning laser ophthalmoscopy (SLO)?
- Red-free imaging
- Blue light reflectance imaging
- Green light
- Near-infrared reflectance imaging
- Monochromatic images for pseudocolour images
What is red-free imaging with monochromatic and multicolour SLO used to assess?
preretinal, intraretinal, and subretinal haemorrhage
What are 4 things that can be assessed with blue light reflectance imaging in monochromatic and multicolour SLO?
- RNFL defects in glaucoma
- Epiretinal membranes (ERMs)
- Capillary non-perfusion in retinal vascular disease
- Abnormally increased reflectance in macular telangiectasia (MacTel)
What is green light in monochromatic and multicolour SLO used for?
best for looking at the intermediate retinal structure; particularly useful for looking at intraretinal haemorrhage
What is near-infrared reflectance imaging in monochromatic and multicolour SLO useful for? What 2 things can it visualise?
imaging of deep retinal and choroidal structures;
1. visualisation of reticular drusen **
2. diagnosis of acute macular neuroretinopathy**
What can be monochromatic images be combined to form?
pseudocolour iamges of the ocular fundus
What is the basic principle of how monochromatic/multicolour SLOs work?
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
What is an example of a monochromatic/multicolour SLO device?
Spectralis
Multicolor HRA-OCT
How does the Spectralis
Multicolor HRA-OCT work for monochromatic/multicolour SLO?
combines reflectance images from 3 monochromatic laser sources: blue (488nm), green (515nm) and infrared (820nm) reflectance
What are 3 advantages of monochromatic/multicolour SLO imaging?
- able to image through the undilated pupil
- visualisation and discrimination of pathology between retinal/choroidal layers
- combining with different modalities e.g. OCT in the same platform
