Toolbox In Glaucoma Flashcards
Where do you need to obtain data with pachymetry
As central as possible
What should you do for pachymetry to increase your reproducibility of data in pachymetry
Greater number of measurements
Always use the lowest data
Why always use the lowest data in pachymetry
Perpendicular measurements are lowest or smallest in value
What does pachymetry measure
CCT
Why do we not use the average data for pachymetry?
Lowest is the most accurate and helps decrease error
Do all pachymeters give us the same measurements?
No
Values vary basis of
-velocity of ultrasound used in algorithm
-MHz of probe
Ultrasound velocity for pachymetry
Usually 1620 or 1640 MHz
20MHz +/- 3um accuracy
50MHz +/-1um accuracy
Which is more accurate, 20MHz or 50MHz pachymetry
50
Anterior segment OCT
Can get pachymetry this way but its not billable
Difference between OCT and optical techniques and ultrasound pachymetry
OCT will measure about 20um lower
How to sue CCT data in glaucoma management
- error in IOP measurements
- OHTN patients
- thinner cornea at greater risk of developing glaucoma
Thicker cornea and IOP
False high IOP
Thin cornea and IOP
False low IOP
The STAR calculator
- OHTS and EGPS data
- intended for use only in untreated OHT patients
- age (30-80)
- IOP 20-32 mmHg
- CCT 475 to 650 microns
- PSD 0.50 to 3.00 dB
- C/S ratio vertical o.oo to o.8
Probability of conversion in 5 years
<55=% observe and monitor
5-15% consider treatment
>15% treat
Ultrasound biomicroscope
- uses 35MHz probe
- can work well through opaque media-OCT does not work well
Thin or thick cornea has higher risk of glaucoma
Thinner
Pneumotonometer
- IOP:200/sec
- up to 20 seconds
- measures 7 pulses and selects 5 best to calculate IOP and POBF
- also gives pulse amplitude and calculates pulse volume
Pulsatile ocular blood flow
- a calculated value
- suggested that could be indicative of a disease
- large range of normality and is derived making numerous assumptions
Good for seeing plateau iris syndrome or pupillary block
Ultrasound biomicroscope
Problem with POBF
Different systems of pneumotonometry give different values
Ethnicity and POBF
Someone living in a hot environment, the choroid is pumping blood more and increasing the flow so they will have a higher number
Pascal tonometer
- similar yo poneumotonometry
- 100/sec
- doesn’t calculate the blood flow but gives the amplitude (diff between min aand max)
OPA
Difference between systole and diastole
OHT and OPA
Higher
-better blood flow, could be protective
NTG and OPA
Lower
-decreased blood flow, enhanced damage even though normal pressure
Positive predictive value and OPA
Less than 2mmHg increases chance of NTG
Lower OPA increase chance of
Glaucoma
Conclusion on OPA
Reduced in normal tension and POAG patients compared with healthy controls. OPA is influences by IOP but not by corneal thickness
Cannon laser blood flowmeter
Uses two lasers
- one measures blood velocity
- second laser measures vessel diamter
Unit is a fundus camera
Large artery or vein is selected
Unit measured at a specific site
Blood flow is calculated
Principles of cannon laser blood flowmeter
- based on Doppler principles
- blood vessels gives back some frequency because it is stationary-not Doppler shifted
- moving blood is Doppler shifted
- light from these two reflective sources-interference pattern is produced
- this interference pattern moves
- thus blood flow is calculated
Heidelberg retinal flowmeter
-combines confocal scanning laser technology and Doppler principles
Summary of measuring blood flow to eye
- no gold clinical standard where ocular blood flow measurement is concerned
- expensive
- noise in measurement is high thus making it difficult to obtain data consistently
How does angiovue work
- uses motion contrast to detect blood flow
- rapidly acquire multiple cross-sectional images from a single location on the retina
- flow is the diffenve between two sequential scenes
- flow=frame #1-frame #2
Info you can get from angiography
Stureucre and function of optic nerve and retina
Plus side of angiography
- non invasive, dye free and fast
- no injection, no NaFL
- order test as needed to more closely monitor disease progression and treatment repsosne
- image acquisition in less than 3 seconds
- total time in room appx 10 minutes
Motion correction technology
Minimizes saccadic motion to enhance image intensity
Angiomontage
Provides a wider field of view
Angiodisc
Gives you a calculation for amount of capillaries that have dropped out (i think that’s what he said)
How many caps are working in that region
Can see how changing treatment can change the caps
SWEPT source
Calculates 100,000 scans per second and very cleat from top to bottoms
- fast
- multimodal imaging
- signal to noise roll off characteristics in tissue
- scanning light Is not visible to the patients to decrease eye movements during scan
- uniform image quality over depth
- vitreous can be seen much better
- invisible OCT scanning light and high imaging speed of 100,000 A scans/sec reduce effect of eye movements and allows more data to be collected per scan
