Posterior Segment Imaging Flashcards
What is the nyquist limit
60
What happens to the nyquist limit if you get rid of optics
It doubles to 120
After the nyquist is at 120, what is the limiting factor
Neural
Three major conventional retinal imaging tools
- fundus camera
- scanning laser ophthalmoscope (SLO)
- optical coherence tomography (OCT)
What is the problem with ground based terelcsopes
Atmospheric turbulence
How do you get around atmospheric turbulence without putting the telescope into satellite
AO based telescope
How does AO based telescope bypass the atmospheric turbulence
Shack hartman sends WF to deformable mirror and the mirror will deform its surface and can take the shape of the deformed wavefront and give us a plane wavefront that has not aberrations
The ability to image cones at high resultion with AO opened a window for what
To examine both normal and abnormal processes in the retina
What happens when you correct higher order aberrations
Produced a modest improvement in VA and contrast sensitivity in the normal eye
What does using an adaptive optics imagin system do when looking at the back of the eye
Can learn where the rods and cones are/are not and where they are dense or not
How do you tell the color cones apart
Bleach them
L cones
Red
M cones
Green
S cones
Blue
How can individual cones be characterized by their sensitivity to long, medium, or short wavelength light, according to the cone opsin it contains
By combining AO imaging with retina densitometry
When look at an image of rods and cones, which ones are green cones (M cones)
Brighter looking ones
When looking at an image of the rods and cones, what are the darker cones
Blue cones
Ratio of L and M cones across individuals
Highly variable without affecting VAs
Proportion of S cones amongst individuals
The proportion of S cones is relatively constant across eyes (3.9-6.6%)
Why cone opsin is constant across individuals
S cones
What opened a crucial window to examine both normal and abnormal processes in the retina
The ability to image cones at high resolution with AO
Cone mosaics of single gene dichromats
Appear completely normal despite the fact that they have two instead of the usual three cone photopigments
What happens when someone has no L cons
M cones try to occupy the space, sometimes its just left unoccupied
When a dichromat is missing 1/3 of their foveal cones, how does this affect VA
They are normal, indicating that adaptive optics imaging can detect retinal degeneration well before conventional clinical tests
Where are the PR larger, in the center or peripheral
Peripheral
What is the main advantage afforded by the SLO over traditional imaging
- improved efficiency in light collection (through the use of more sensitive detectors)
- video rate imaging capabilities
Benefit of confocal detection is 2 fold
- resulting images have higher contrast
- through axial scanning of the foca spot, axial slices of the retina can be obtained with 300mm resolution
AOSLO images of retinal vasculature
AO combined with fluorescein angiography allows imaging of even the fine structure of the retinal cap bed
What does AOSLO images of retinal vasculature detect
Direction of blood flow and the velocity within the caps
The retinal image is conveyed to the brain through an array of
17 or more parallel ganglion cell pathways
diabetic retinopathy and adaptive optics
Can see how the vessels are leaking
Imaging RPE with adaptive optics
- maintains the photoreceptors
- ARMD, RP, Stargardts
- AO reflectance imaging makes it possible to image the RPE mosaic in living human eyes in which the PR layer is instant, by taking advantage of the autoflourescence properties of lipofuschin in the RPE
AO OCT
Lateral and axial resolution
-can go to each layer and look at subcellular layer
Applications of AO-OCT
- ARMD
- glaucoma
- diabetic retinopathy
- stem cell treatment of degenerative disorders of the retina
