AC/A And CA/C

Question 1

Describe Gradient AC/A.

Answer 1

Most common clinically
Change in phoria as a function of change in accommodative stimulus
By dissociating patient, change in AC does not lead to change in disparity vergence (fusional)
By keeping target at fixed distance proximal vergence should remain constant (present but constant)

Question 2

How is gradient represented on a graph?

Answer 2

Near phoria (y)/ accommodative stimulus (x)

3 or more

Question 3

What is calculated AC/A?

Answer 3

Change in vergence response/change in accommodative stimulus

Compares the distance and near phorias
Change in vergence response represents accommodative and proximal.

Question 4

What is an alternative equation for calculated AC/A? What can proximal vergence be estimated by?

Answer 4

(AV+PV) / AS

Proximal vergence response can be estimated by calculated AC/A-gradient AC/A (gradient= AV/AS)

Question 5

What does the change in vergence response represent for calculated AC/A?

Answer 5

Change in accommodative vergence and proximal vergence

Question 6

How can proximal vergence be calculated from calculated and gradient AC/A?

Answer 6

Calculated - Gradient

Question 7

What is the approximation of the relationship between AR and AS ac/a’s?

Answer 7

Response AC/A = Stimulus AC/A x 1.08
Or about 10% larger

Question 8

How do we calculate required ADD using AC/A and phoria?

Answer 8

Required ADD= phoria/ AC/A ratio

Question 9

When do we use ADDs vs prisms?

Answer 9

ADDs for eso patient with high AC/A ratios
Base out prism for eso patients with low AC/A
Base in for exo