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Volumetric multiple wavelength ultrahigh resolution
imaging in glaucomatous retina
Marilyn Puah
Biomedical Imaging Group, School of Optometry and Vision Sciences
What is OCT?
•Ultrahigh resolution optical coherence tomography (UHR OCT) is an
upcoming new technology that allows non-invasive, optical medical
diagnostic imaging.
•Analogue to ultrasound but it allows real-time in situ imaging with
higher resolution of 1 to 15 microns.
•It enables a three-dimensional in vivo direct visualization of the
microstructure of the retina, allowing both qualitative and quantitative
changes to be seen which are beneficial in diagnosing optical diseases
especially in early stages.
•OCT measures by echo time delay and intensity of back reflected light
Principle of OCT
•Measures time delay and magnitude of optical echoes at different
transverse positions
•Dimensions of structures at different depths are based on “echo” time
for light to be backscattered
•By scanning optical beam in the transverse direction and performing
successive axial scan measurements, cross sectional image is produced
•A 2D grey scale or false colour image is produced
Eye
•Retina of eye consists of 10 layers
•Nerve fibres in the eye exit via the optic nerve head to the brain
•A flat disc or disc or shallow depth is indication of a healthy optic nerve
head
Transverse Scanning
Backscattered Intensity
Axial Position
(Depth)
1 mm
Standard
Clinical
RESOLUTION (log)
ULTRASOUND
Figure 5. Cross section of the eye, optic nerve head and retina
100 mm
Specimen
Figure 2. How OCT generates images
High
Frequency
10 mm
OPTICAL COHERENCE
TOMOGRAPHY
1 mm
CONFOCAL
MICROSCOPY
100 mm
1 mm
2D Grey Scale or False Color Image
1 cm
10 cm
IMAGE PENETRATION (log)
Figure 1. Comparison of OCT with various imaging techniques
Comparison with other imaging techniques
•Ultrasound allows increased penetration depth for imaging with higher
frequency sound waves
•But resolution is reduced due to increased ultrasonic attenuation
•Confocal microscopy allows submicron resolution
•But image penetration is limited
•OCT strikes a balance between confocal microscopy and ultrasound
imaging
•OCT allows image penetration up to 2-3mm and resolution ranging from
15 to 1µm which is dependent on bandwidth of light source
Methods
•In vitro measurements of glaucomatous animal retinas were taken with
microscope OCT
•Allows three-dimensional imaging and visualisation of the morphological
changes of the optic nerve head
•Images’ intraretinal contrast were then compared to histology
•Allows the improvement of OCT system in regards to resolution, contrast
and penetration depth for future studies
•3 pairs of tree shrews’ eyes and 5 pairs of rats’ eyes were imaged
•Glaucoma introduced in the left eye and right eye as a control
•All retinas were processed using ImageJ
•Best 3 pairs of eyes were chosen for this presentation
What is glaucoma?
•Glaucoma is one common disease of the eye in human
•Characterized by increase in intraocular pressure and atrophy in the
optic nerve head with corresponding visual field loss which is usually not
noticeable by patient until a late stage
•Optic atrophy results in a larger cup disc size and depth, which is seen as
a dip from the cross section of the optic nerve head.
•Several studies done have proposed that structural changes of the optic
nerve head and nerve fibre layer will precede before visual field loss
appear.
•Therefore it is crucial to detect it early so that appropriate treatment can
be done to prevent further damage to the optic nerves.
Figure 6. Progression of glaucomatous optic
nerve head
Figure 3. Microscopy OCT
Figure
7.
Visual
field
loss
corresponding to glaucomatous optic
nerve head
Figure 4. Components of OCT
Results
Tree shrew CTS1 normal RE
Rat CR312 normal RE
Rat CR337 normal RE
Tree shrew glaucomatous LE
Rat CR312 glaucomatous LE
Rat CR337 glaucomatous LE
Discussion
•Glaucoma introduced in left eye
•Optic atrophy and morphological changes seen in left eye
•Tree shrews’ and rats’ retinas differ
•Hyaloid artery interfere with ONH imaging in tree shrews
•Orbital fats caused a layer oil film, disrupting images
•Careful handling of retinas required
•Hyaloid artery interferes with imaging
•Detection of glaucoma in animals’ retina correspond to that in human
Limitations of OCT
•Optical imaging restricted to surface tissues but not affected in the eye
•Less penetration than ultrasound
•Optical artefacts interfere with quality of images
Future outlook
•Visualise structure without sacrificing animal
•Extend knowledge to human
•Beneficial in early detection of glaucoma
•Pick up other ocular diseases due to early morphological changes
•Applies to other areas of biomedical research
Acknowledgements
•I would like to thank Prof Wolfgang, Dr Boris Povazay and the OCT team
for their help and guidance throughout the 6 weeks of the placement
which made the experience amazing
•I would also like to extend my upmost gratitude to CUROP and Cardiff
University for funding me during the 6 weeks of placement
Reflections
•Provide an insight to research work
•Exposed to new technology
•Rewarding, fruitful experience
•Allowed to be part of a promising research team
References
Figure
5
taken
from
http://www.healthyeyes.org.uk/uploads/pics/Eye-1.jpg
sunbear.com/images/glopticnerve.jpg
http://www.answersingenesis.org/Home/Area/Magazines/tj/images/v13n1retina3.gif
Figure 6 taken from http://www.meei.harvard.edu/patient/images/optic-nerve-head.jpg
Figure 7 taken from http://www.intecheye.com/Upload/glaucoma1.jpg
and
http://www.eand