OCT, HRT, GDx Flashcards
Measures the reflection of laser light (similar concept to ultrasound and reflection of sound)
OCT
Directly measures the thickness of the NFL
OCT
TD-OCT
Time domain OCT
SD-OCT
Spectral domain OCT
- most common
- newer
- aka HD-OCT
Greater speed in capturing images and higher definitaiton. Also different algorithm than TD-OCT
OCT OU report: key parameters
Compared to normative data base, are displayed in table formats
Small disc
<1.5mm
Medium disc
> 1.5
<2.5
Large disc
> 2.5
Colors on OCT data
GRY based on comparison to normative database
-only for >18 yo
Gray color on OCT
Not compared to normative database
-disc area ranges from normative database
Disc area ranges from normative database
1/3 < 1.58mm
1/3 are 1.58-1.88
1/3 >1.88mm
Gray when disc area is <1.3mm OR >2.5mm
What does the table tell you on OCT
Average NFL RNFL symmetry Rim area Disc area Average CD ratio Vertical CD ratio Cup volume
White
The thickets 5% of measurements fall here
Green
90%
Yellow
5%
Red
1%
Normative data for different ages
Will be differ. Just because someone has the same numbers as someone else, it will be different based on their age
RNFL OCT report
Thickness map is a topographical display of RNFL. An hourglass Shaw of yellow and red colors is typical of normal eyes
RNFL deviation map
Shows deviation fro normal. OCT en face fundus image shows boundaries of the cup and disc and the RNFL calculation circle
Neurotrophic retinal rim thickness OCT report
It is matched to normative data
RNFL TSNIT graph
Displays patients RNFL measurements along the calculation circle, compared to normative data
RNFL quadrants an clock hour
Average thickness is matched to normative data
When looking at the pie chart on the OCYT report, what are we paying attention to
Is there a difference between each eye and between visit to visit
• worry from 7-12 numbers difference in the quads and between visit to visit
Horizontal and vertical B scans
Extracted from the data cube through the center of the disc. RPE layer and disc boundaries shown in black. ILM and cup boundaries are shown in red
RNFL calculation circle
Is automatically centered on the optic disc and extracted from the data cube
Boundaries of the RNFL layer segmentation is illustrated
OCT guided progression analysis report
Some machines will compare up to 7 exams to see if there is any changes in the patient between visits
Can choose which exams you compare to each other
Can also chose the baseline to use
Why do 2 baselines
If someone is glaucoma or suspect, its to make sure its reproducible data
RNFL thickness change maps in OCT GPA report
Demonstrates change in RNFL thickness. Up to 6 exams are automatically registered to baseline comparison. Areas of statistically significant change are color coded yellow when first noted and then red when the change is sustained over consecutive visuits
Average RNFL tivckenss in GPA reports
Values are plotted for each exam,. Yellow marker denotes change when it is first noted. Red marker denotes change sustained over consecutive visits. Rate and significance of change is shown in Text
RNFL thickness profiles
TSNIT values from exams are plotted. Areas of statistically significant change are colro coded yellow where first notes and tried when the change is sustained over consecutive visits
RNFL summary GPA report
Summarizes GPA analysis and indicates with a check mark if there is possible or likely loss of RNFL
RNFL thickness map progression best for
Focal change
RNFL thickness profiles progression best for
Broader focal change
Average RNFL thickness progression best for
Diffuse change
HFA cirrus combines report
Some companies will compile the HVF and OCT in one page to compare them together
OCT ganglion cell complex
- measures the thickness of the 3 innermost retinal cell layers that are preferentially affected in glaucoma
- compares the patients two eyes for symmetry
- asymmetry is an early sign of glaucoma
- higher correlation between asymmetry and glaucoma in ST and IT regions
Scans macular thickness-evaluating ganglion cell layer. This thins in glaucoma
What is involved int he GCC
NFL
GCL
IPL
HRT
- laser that produces 3D high resolution image of the ONH
- measure the nerve fibers damage/loss
How does HRT work
Takes 32 layer by layer pictures from the surface of the optic nerve to form 0.5mm to 4.0mm deep into the ocular structures. The computer then piles the slices together in a reconstructed paper printout that looks like a map drawn to represent the hills ands valleys of a geo area. By color coding areas of elevation and depression, the HRT provides a 2D representation of what the original, 3D, stack looks like
Limitations of HRT
- any patient movements (including moving theeye, blinking, or moving the head) will disrupt the lasers path, imparting the quality of the image
- if patient does not focus on the same location from test to test, the angle of the image will change, and that will affect the measurements greatly
- the images created by the HRT must be reproducible/identical in order to analyze and compare to the normative database and to monitor for change
Image quality and HRT
Needs to be very good quality or you cant compare from exam to exam
30 or lower
Inter-eye asymmetry on HRT
Evaluates the symmetry of the RNFL profiles between the eyes. If the correlation between eyes is good, the value will be close to 0
Glaucoma diagnosis nerve fiber analyzer (GDx)
Scanning laser polarimter measures nerve fiber layer thickness and 65,536 retinal points
Normal NFL on GDx report
No statistically significant thinning of the NFL and a nerve fiber indicator (NFI) number less than 30. The NFI ranges from 0 (thick) to 00 (severely thin NFL)
Advanced glaucoma in GDx
Characterized by statistical significance of nerve fiber layer thinning on GDx scan. Often accompanying by a nerve fiber indicator number of >30 in either eye and poor inter-eye symmetry. Both are seen in this scan of a patient with severe visual field loss secondary to advance glaucoma
Symmetry wants a ___ number
High
NFI wants a ___ #
Low
Serial analysis of GDx
Can compare from visit to visit
