Optical Coherence Tomography (OCT) Gella Laxmi 2009PHXF013P
Optical Coherence Tomography (OCT)
Gella Laxmi2009PHXF013P
Introduction
OCT
Determining and visualizing structure that absorb and scatter light
Noninvasive in vivo analysis of retinal tissue
1 mm 1 cm 10 cm
Penetration depth (log)
1mic
10mic
100micronm
Resolution (log)
Ultrasound
OCTConfocalmicroscopy
Standardclinical
CT and MRI
Principle
Michelson Interferometer
Beam splitter
Diode 820
Reference beam
Patients eye
DVD
OCT software
Detector
Combination of multiple A scans to produce…..
Time Domain OCT
CHORIOCAPILLARISCHORIOCAPILLARIS
NFLNFLGCLGCL
FOVEOLAFOVEOLA
IPLIPL
INLINL
OPLOPL
ONLONL
RPERPE PHOTORECEPTORSPHOTORECEPTORS ELMELM
Spectral Domain OCT
Features of SD-OCT
Better anatomic representation
High resolution (6 microns)
Fewer movement artifacts
Live cross-sectional movies of various details
High Signal to noise ratio
Scanning speed 25, 000 A-scans per second
3D imaging
Vs
Histological retina Vs SD-OCT
Retinal Structures on SD-OCT
Horizontally oriented structures – hyperreflective
Vertically oriented structures (layers containing nuclei) – hypo reflective
Choriocapillaris: Innermost limit of the
vascular layer of the eye
Thin and hyper-reflective
layer
Larger vessels of choroid
– hyporeflective
Inconsistently identified
Bruch’s membrane: Not visible on SD-OCT
VV
VVV
CCRPECCRPE
V
CCRPE
Retinal Pigment Epithelium:
RPE-CC complex divided into 3 parallel strips
2 are thick, hyperreflective separated by thin
hyporeflective line
Verhoef’s membrane
Photoreceptors:
Rods and cones contain inner and
outer parts
Inner part: nuclei (outer nuclear layer)
Outer part: inner and outer segment
Connection b/w inner and outer
segment forms a hyper-reflective strip
(result of diff in RI)
Sharply raised at the foveola
External limiting membrane
Outer plexiform layer: Visual cells connect to the bipolar cells
Horizontal axons of the horizontal cells
Hyper-reflective strip
Inner nuclear layer: Nuclei of bipolar, horizontal, muller and amacrine
cells
Hyporeflective layer
Inner plexiform layer: Synapses b/w ganglion cells and amacrine cells Hyper-reflective owing to their horizontal
structure
Ganglion cell layer Bulky cells are multilayered Hyper-reflective
Nerve fiber layer Nerve axons Very high reflective layer
RNFLGCLIPL
Internal limiting membrane
Difficult to distinguish
Hyaloid and vitreous
Various pathologic structures clearly visible
Reporting SD-OCT
Comment on each layer
Reflectivity
Morphological features
Measurements of thickness
Take-home message
Retinal anatomy and virtual histology can be
studied with the SD-OCT
The SD-OCT shows more detail at the
vitreoretinal interface, and there is better
delineation of all retinal layers
References
Bruno Lumbroso. SD-OCT Reveals Details of Posterior Segment Structures. Cataract & refractive surgery today Europe. June 2008. Pg 27-28
Wolfgang Drexler, et al. State-of-the-art retinal optical coherence tomography. Progress in retina and eye research. 2008.Jan; 27(1): 45-88
Bruno Lumbroso, et al. Understanding Spectral OCT. I.N.C Innovation-News-Communication. 2007.
Michael R. Hee, et al. Optical Coherence Tomography of the Human Retina. Arch Ophthalmol. 1995; 113: 325-332.