O3A 6 Vergence
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- 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?
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?
- accom verg
- 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
+1.00D required plus lens because of eso
- keeps accomm stable
- once vergence runs out
- use accom
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