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O3A 6 Vergence
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crossed disparity
when you are fixating on a distant object
near object will have crossed disparity
What is uncrossed disparity?
when you are fixating on a near object
dx object will have uncrssed disparity
What is a measure of vergence?
metre angle
how do you calculate metre angle?
1/dx in metres
object at 50cm? need 2 MA
Vergence demand formula?
pd (cm)X100 / d+2.7
How is gradient AC/A ratio calculated?
phoria 1 - phoria 2 / lens 2 - lens 1
exo
: add negative
Eso
: positive
What is AC/A?
amount that vergence changes for a specific change in accommodation
What is the calculated AC/A?
change in vergence that results per dioptric change in fixation dx
change due to both accommodation and proximal cues
What are the 4 vergence components of the Maddox model?
tonic
accom verg
proximal
fusional
assumes all 4 are additive
ignores convergence stimulating accom
gradient vs calculated AC/A ratio?
gradient measured both at 40cm so proximal vergence is the same
calculated is measured at dx and near so proximal is affection one reading
How to calculate CALCULATED AC/A?
CHANGE IN VERGENCE / CHANGE IN ACC DEMAND
CHANGE IN VERGENCE: Vd - phoria dx + phoria near
CHANGE IN ACC: Near - dx
What to prescribe: ortho at 6m, 10 eso at 40cm
CHANGE IN VERGENCE/CHANGE IN ACC
15 - 0 + 10 / 2.5 - 0
25/2.5= 10:1
+1.00D required plus lens because of eso
PRA NRA
keeps accomm stable
once vergence runs out
use accom
blurs
Author:
sookylala
ID:
225079
Card Set:
O3A 6 Vergence
Updated:
2013-06-26 11:30:56
Tags:
vergence
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Description:
vergence
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