Final - Davey Flashcards
Ultrasound pachymetry
- always use which data
- why
Lowest
Perpencicular = lowest value
Diff pachymeters values vary on the basis of
Velocity of ultrasound: lower vel = less accuracy
20MHz +/- 3 microns accuracy
50MHz +/- 1 micron accuracy
Why don’t we commonly use OCT for measuring CCT
Cannot bill for it
Tend to get ~20 microns lower value with optical techniques vs ultrasound
Uses for CCT data in glaucoma management
Error in IOP measures
Ocular HTN pts (thinner K at incr risk for developing glaucoma)
STAR II calculator
Intended for use only in untreated OHT pts
Calculates probability of conversion to glauc with age, IOP, CCT, PSD, C/D
<5% observe/monitor
5-15% consider tx
>15% tx
Ultrasound biomicroscope
Uses 35MHz probe
Works well thru opaque media - OCT does not
Pneumotonometer
Blood flow analyzer
IOP 200/sec
Up to 20 sec
Measures 7 pulses and selects best 5 to calc IOP & POBF*
Incl amp and pulse volume
*pulsatile ocular blood flow
Pulsatile ocular blood flow (POBF)
Calculated value
Could be indicative of a disease
Large range of normal, derived making numerous assumptions
2 flows to the eye
Pulsatile inflow
Steady outflow
Fluctuation of eye pressure
Should not fluctuate minute to minute
Will fluctuate thru-out the day
Ocular pulse amplitude (OPA)
Reduced in NTG & POAG pts compared to healthy controls
(I.e. low OPA related to glaucoma)
Influenced by IOP, but not CCT
Measure w/ PASCAL tonometer
Cannon laser blood flowmeter
- describe machine/unit
- how/what it measures
2 lasers: one measures blood velocity, the other vessel diameter
Unit = fundus camera
Large artery or vein selected
Unit measures at a specific site
BF is calculated
Cannon laser blood flowmeter
-principles
Based on Doppler principles
Moving blood is Doppler shifted, stationary vessel is not
Heidelberg retinal flowmeter
Combines confocal scanning laser technology and Doppler principles
Ocular blood flow problems/limitations
No gold clinical standard
Expensive
Noise is high = difficult to obtain consistent data
