Binocular Vision 3/4 - Week 3

Question 1

What is the AC/A ratio?

Answer 1

The ratio of accommodative convergence (in prism diopters) to the stimulus to accommodation

Question 2

How do you test the interaction between accommodation and vergence?

Answer 2

AC/A ratio test

Question 3

What are the two types of AC/A ratio tests? Which one is considered better and why?

Answer 3

Gradient AC/A and Demand AC/A

Gradient is considered the better technique because proximal control of accommodation and vergence is constant

Question 4

With what apparatus can the gradient AC/A ratio be tested?

Answer 4

Phoropter and Von Graefe
OR
Lens flipper and Prentice Card

Question 5

Explain the procedure for Gradient AC/A ratio test

Answer 5

• First measure the phoria with habitual refraction in place
• Then repeat near phoria measurement with +1, -1, +2, and -2 lenses over both eyes
• Calculate AC/A ratio to plus lenses and AC/A ratio to minus lenses

if using trial frame, can use flippers for this technique, interval showing it must be less than 1 second

px is the one holding the prentice card. Also, record afterwards so that visual system not changed

Question 6

Explain the procedure for Demand AC/A ratio test

Answer 6

It difference between their regular near and far phoria measurements, accounting for PD and WD.

Is calculated by: AC/A = PD(cm) + WD(m) x (near ph - dist. ph)

Question 7

What is the expected value for accommodative-vergence interaction?

Answer 7

AC/A ratio 4+/-2pd/D (consider ratio to plus and minus lenses separately)