understanding and comparing confocal scanning lasers to optical coherence tomography for optic nerve...
TRANSCRIPT
![Page 1: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/1.jpg)
Understanding and Comparing Confocal Scanning Lasers to
Optical Coherence Tomography for Optic Nerve Head Analysis (ONH)
A presentation courtesy of Zeiss
![Page 2: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/2.jpg)
Third Generation Products• LDT abandoned
TopSS in 1999 to continue develop-ment of GDx Access
• HDT released their HRT II instrument, which is smaller, faster, easier and cheaper
![Page 3: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/3.jpg)
How they Work• A 670-780nm LASER light source plus (2) Pinhole (20-25
micron) apertures detect light reflected off the retina
LASER
DETECTOR
PINHOLEAPERTURE
FOCALPOINT
![Page 4: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/4.jpg)
Signal
• Confocal Scanning Lasers sense the shape of the surface of the Hyloid Face or the Vitreous to Internal Limiting Membrane interface.
• At this point the peak reflection is recorded
• Difficulties with some common conditions as PVD can cause artifacts.
• Have excellent “X-Y” resolution, but coarse “Z” resolution.
![Page 5: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/5.jpg)
Scanning Lasers make Slices• Typically 32
“Slices” are acquired over a 4mm depth.
• Each slice has a depth of 25 microns.
• A non sampled gap of 100 microns is between slices.
Y
X
Z
![Page 6: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/6.jpg)
Scanning• Typically a 6mm
by 6mm area of retinal surface is scanned.
• Each slice is about 20 –25 microns thick.
• Each gap between slices is about 100 microns thick.
• Only a few slices fall on the ONH.
![Page 7: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/7.jpg)
Examples of Data• Two of the 32 slices
are displayed at the right.
• Lets plot the paths of light of the 3 data-points.
• At different areas on the disk in slice 14 of 32 notice:– Yellow is on a blood
Vessel
– Green is on the rim
– Purple is in the cup
Slice 14 of
32
Slice 18 of
32
![Page 8: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/8.jpg)
How the slices determine topography• A graph illustrates
REFLECTANCE for the same location at each of the 32 slices. Since the Yellow curve peaked before the Green or Purple curve, a RELATIVE difference in Topography can be calculated.
0
10
20
30
40
50
60
1 5 9 13 17 21 25 29
Slice
Re
fle
ctio
n In
ten
sity
Vessel
Rim
Cup
![Page 9: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/9.jpg)
Establishing a Reference Plane• A Publication by
Weinreb et al shows the Papilomacular bundle as an area adjacent to the rim showing the least amount of change. So these instruments use this area and other areas as a peripheral band concentric around the disk to manufacture “ZERO” or a reference plane.
![Page 10: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/10.jpg)
Volumetric Analysis• The operator must
draw the outline of the disk.
• This is not easy as the image is not taken in white light.
• Notice how two different operators outline the same disk with different shapes.
• Volumetric parameters are operator dependent.
![Page 11: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/11.jpg)
Optical Coherence Tomography• To scan the ONH,
Optical Coherence Tomography acquires (6) 4mm long by 2mm deep “Slices” in the X-Z axis.
• Datapoints are sampled every 2 microns providing excellent resolution in the Z axis.
• Confocal Scanning Lasers typically sample every 100 microns. Z
X
Y
![Page 12: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/12.jpg)
Image Analysis• Using a proprietary algorithm, OCT identifies the
Retina Pigment Epithelium and places a marker.
![Page 13: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/13.jpg)
• The markers show the boundaries of the disk in each individual slice. The next slide shows all six slices.
![Page 14: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/14.jpg)
ONH Tomography ExamplesSlice 1
Slice 2
Slice 3
Slice 4
Slice 5
Slice 6
![Page 15: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/15.jpg)
ONH Analysis• Using the algorithm
OCT objectively finds the margin of the disk.
• OCT objectively finds the cup by using an offset value of 150 microns up from the RPE.
• No reference plane is required.
![Page 16: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/16.jpg)
OCT Printout• Details volumetric analysis of cup and Disk.
• Provides Direct Cross Section of anatomy.
![Page 17: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/17.jpg)
“Z” Dimension Datapoints
Confocal Scanning
Lasers acquire 32 datapoints
over 4mm
Optical Coherence
Tomography acquire 1024 datapoints over 2mm
![Page 18: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/18.jpg)
Datapoint Comparrison• Confocal
Scanning Lasers have 100 micron gaps between datapoints in “Z” dimension.
• Optical Coherence Tomography has only 2 micron gap.
150 Micron
s
100 Micron
Gap
![Page 19: Understanding and Comparing Confocal Scanning Lasers to Optical Coherence Tomography for Optic Nerve Head Analysis (ONH) A presentation courtesy of Zeiss](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cca5503460f949921e2/html5/thumbnails/19.jpg)
Conclusion• Confocal Scanning Laser Technology is not capable
of seeing small changes in the ONH.
• Glaucomatous change occurs very slowly.
• Progression may not be observed with sampling points with 100 micron gaps.
• OCT with higher “Z” resolution is more likely to see glaucomatous progression.
• Objective placement of Cup and Disk insures accuracy between operators.
• Viewing the anatomy confirms ONH Analysis from artifacts seen in confocal scanning lasers.