Week 2.04 Ocular Imaging Flashcards
Retinal photography
Automatic stereo pairs
Can piece them together to get panoramic view
Why do we use red free filter
Red free filter (green) - anything red looks black (haemorrhages, microaneurysms)
Improves contrast of RED things
Improved contrast of any RNFL defects
Shorter wavelength reflected
Why do we do retinal photography
Record keeping
Quick - digital
Indirect - less affected by media
Patient education
Digital img transfer
Diabetic retinal screening service
NICE guidelines for management of type 2 diabetes
“All adults diabetic px should have their eyes screened at time of diagnosis and at least annually thereafter”
Screening = dilated fungus photography taken by a technician and graded centrally by an accredited grader
Fluorescein fundus angiography
- Px injected with fluorescein
- Normal retinal vessels have tight junctions therefore no leakage
- Choroidal capillaries are fenestrated therefore NaFl leaks freely but does not penetrate RPE
Time stamps for fluorescein angiography
1 sec arterial phase
15-20sec capillary phase
20-25 secs venous phase
10-15 mins - late phase
What’s the difference between neovascularisation and collaterals
A collateral vessel is a vessel u didn’t see before but its now suddenly being used because of different vessels blocked
Collateral vessels don’t leak whereas neovasc vessels do
What kind of things can we see on FFA
Geographic atrophy - dry AMD
Choroidal neovascularisation
Haemorrhages
Microaneurysms
Leaky parafoveal vessels
Indocyanine green angiography
- Absorbed 600-900nm, emits 750-950 (infrared)
- Possible better resolution that FFA
- E.g. Choroidal neovasc, Choroidal melanoma
- Good penetration through overlying blood/pigment
Fundus autofluorescence
Lipofuscin is present in RPE cells due to phagocytosis of photoreceptor outer segments
Hyperfluorescence - Lipofuscin accumulation due to defective RPE’s age or oxidative damage
RPE cell death = hyperfluorescence
Scanning laser polarimetry
- Relies on polarised light
- made up of lot of fibres
- RNFL & cornea are birefringent (made up of lots of fibres)
Optomap
- uses a red laser
- then a green laser
- low magnification
- can preform FFA and autofluorescence by using layers at fluorescein/ Lipofuscin peak absorption
What’s confocal microscopy
Convex lens focuses light source on certain layer of the cornea
Pinhole at confocal plane of lens - only allows light from focal length to be sensed
Narrow depth of focus
What is confocal microscopy used for
Herpes simplex keratitis - presence of dendriform cells
Diabetic neuropathy - changes in nerve fibres
Ocular surface disease e.g. dry eye - track macrophage
Confocal scanning laser ophthalmoscope
Combines scanning laser to confocal microscopy
Heidelberg retinal tomography
Calculates rim area, rim volume, cup area, cup volume, cup to disc ratio, mean RNFL thickness and RNFL cross sectional area
Pentacam
Like an Optic section
Corneal thickness
Keratoconus
Inferior steepening
AC depth
Lenticular pacification
Ultrasound
Cataract surgery pre-assessment
Which filter can be used with retinal photography to improve visibility of neovascularisation
Red free
Which colour filter will penetrate deepest layers
Red
