30 - BV vergence

Question 1

What’s a Decompensating phoria?

Answer 1

Previously had BSV, now breaking down due to tropia caused by issue.

Question 2

What’s an Intermittent strabismus?

Answer 2

Large deviations at all distances, sometimes has bifoveal fixation, sometimes tropia.

Question 3

What’s Convergence/Divergence Insufficiency/Excess?

Answer 3

• Insufficiency = not enough, excess = too much.
• Convergence = converging response when looking at near, divergence = diverging response when switching to distance.

E.g.
- Convergence insufficiency means not enough convergence at near
- Divergence excess means large exophoria (too much divergence) at distance.

Question 4

1) STC = ?
2) Vergence response =?
3) STA?
4) Accommodative demand?
5) Accommodation response?

Answer 4

1) Stimulus to convergence. How much fusion is required at this distance.
2) How much vergence observer produces given the distance.
3-4) Stimulus to accommodation. How much accommodation they need.
5) How much they actually accommodate (accounting lag/lead)

Question 5

AC/A vs CA/C ratio?

Answer 5

• AC/A = Accommodative convergence/Accommodation ratio. How much vergence chances for every unit of accommodation change. E.g. 4 prism diopters/1 diopter. Measured via calculated or gradient.
• CA/C = Convergence accommodation/Convergence ratio. How much accommodation changes per unit of convergence. E.g. 0.2 diopters/1 prism diopter.

Question 6

Describe the modern clinical working model.

Answer 6

Basal = doesn’t change (unless altered by e.g. drugs, no sleep).
- Measured w/ CT, dissociated phoria tests

Reflex fusional reserves (<Panum’s sized retinal disparities).
- Measured w/ fusional reserves (blur/break)

Reflex accommodation (Retinal defocus = accom -> verge)
- Measured w/ AC/A

Voluntary vergence (large binocular disaprities = verge -> accom)
- Measured w/ CT recovery, fusional reserve (recovery), NPC/DPD (recovery)

Question 7

Describe DPD
Purpose:
Equipment/target:
Method:

Answer 7

Purpose: Find distance where vergence stops working. For patients with phoria at near and tropia at distance (divergence excess/insufficiency)
Equipment/target: Beads on string, pentorch, etc… + tape measure.
Method: Start target at near and move away from patient until break. Then find recovery. Must watch eyes carefully as often patients have tropia if they need this test.

Question 8

1) Assess fusional reserves how?
Purpose:
Equipment:
Patient requirements:
Target:

2) PFV and NFV are?

Answer 8

1) Purpose: Assess limits of vergence. How they maintain bifoveal fixation when stressed. Fusional reserves are used to compensate for phorias.
Equipment: Prisms, target
Patient requirements: BSV, corrected for full distance (and if add needed, can use)
Target: Single letters or line of letters (vertical if measure horizontal and vice versa).

2) Positive/negative fusional vergence.
+ve = convergence
-ve = divergence

Question 9

1) To measure horizontal fusional reserves, we… (method?)
2) What about vertical reserves?
3) What happens to the different systems during the test?

Answer 9

1)
- Confirm target is single and clear.
- Increase prism until sustained blur or diplopia. If blur, continue until break.
- After break, reduce prism until recovery.
- Record as blur/break/recovery.
Always do divergence first. Always encourage patient to try harder.

2) Same thing. Expect usually no blur point.

3)
- As base increases, reflex fusional reserves maintain BSV
- When reflex runs out, voluntary vergence mantains BSV but accom will increase which blurs image. 50% can skip blur.
- All fusional systems eventually run out causing break
- As base decreases, voluntary vergence picks up to give BSV.

Question 10

What’s Percival’s critereon?

Answer 10

“Greater reserve must not be more than twice the lesser opposing reserve” or “Zero prism must fall within the middle third of their reserve range”
Ranges uses first sign of blur (or break if no blur).

Question 11

What’s Sheard’s criterion?

Answer 11

At a given viewing distance, “The compensating reserve should be twice the phoria”. Requires phoria measurement and opposite fusional reserve.

Question 12

Graphic analysis?
- What information is required?

Answer 12

Analyses zone of single clear vision.
- Distance + near phoria
- Distance + near NFV + PFV
- Accommodation amplitude binocular
- BPA and BMA at near if possible.