ABV_Test1 Flashcards
What is the AC/A ratio formula?
PD(cm) + target distance (m) x (near phoria - distance phoria)
What sign do you use for esophorias?
Plus
What sign do you use for exophorias?
Minus
What is the same value for AC/A ratio when you contain the same measurement for phorias at distance and near?
Distance PD
List the three ways in getting AC/A ratio?
Calculated method
Gradient
Modified Thorington
What is the standard measurement taking when measuring CA/C ratio?
6 prism diopters per 1 meter.
What are two ways to get CA/C ratio?
BCC & placing 6pd in eye
Wessin Fixation disparity card.
What does DOG stand for?
Difference of Gaussian card
What is the norm for CA/C ratio?
0.50D/6 pd
What is the Morgan norm for NRA?
+2.00 to +2.50D
What is the Morgan norm for PRA?
‐2.37 up to ‐4.00
Why does blur occur during NRA testing?
Blur.
- Accommodation can no longer relax
- PRV can no longer be stimulated
How do you test if vergence system or accommodative system is to blame for NRA?
Cover one eye.
If target is clear from the blur, then vergence is to blame.
Which ptx will have trouble with NRA testing?
- Those who cannot relax their accommodation
2. Those who have trouble converging
What does it mean if the endpoint is double for NRA?
Ptx is highly exophoric with low PRV values
What does a low NRA value mean?
- Ptx has difficulty relaxing accommodation
2. Highly exophoric with low PFV reserves
What does a high NRA value mean?
Ptx has latent hyperopia with a big lag of accommodation.
What can cause a big lag of accommodation
Over-minusing a ptx
Underplussing a ptx.
Are NRA/PRA an accommodative test or vergence test?
Accommodative test; however u cannot ignore the effects of the vergence system
What happens if vergence is allowed to move with accommodation during NRA or PRA testing?
Diplopia!
What is the cause of blur during PRA testing?
- Accommodation can no longer be stimulated
2. NRV cannot be stimulated any further “independent” of accommodation
What’s the cause if endpoint is diplopia durng PRA testing?
Ptx is higly esophoric at near with low NRV values
What test are you doing if ptx is suppressing an eye during PRA test?
Minus to blur amplitude of accommodation
Give me two reasons a ptx may have low PRA values?
- Ptx has problems stimulating accommodation
2. Ptx may have high esophoria at near, thus hard to diverge eyes.
Caleb, refer to examples on pg 12 of Core concepts
Si senor
T/F?
There is no change in accommodation from the uncorrected to corrected sate for a myope.
True
NRV testing is specific for what?
The point just before the blur.
Why may blur result for NRV testing?
- Low divergence reserves like in esophoria
2. Accommodation not being stimulated