PC - Clinical Assessment of Accommodative-Vergence Interactions - Week 3

Question 1

Describe the accommodation-vergence cross-link.

Answer 1

Retinal bur drives accommodation and alters vergence through the cross-link.
Retinal disparity drives convergence and alters accommodation through the cross-link.

Question 2

Name 2 objective means of measuring binocularity, and what they do.

Answer 2

Cover test - evaluates alignment in all 9 directions of gaze

Hirschberg - evaluates alignment and estimates magnitude of any deviation

Question 3

Name 2 subjective means of measuring binocularity, and what they do.

Answer 3

Stereopsis - Fly, lang, and randot tests

Suppression - Worth 4 dot D and N, diplopia awareness, prism doubling, polarised tests

Question 4

Describe the Hirschberg test.

Answer 4

Light is shined into the patient’s eye, and the corneal reflex is observed. Normally, it is reflected slightly nasally, in the centre of the pupil.
Abnormally, the eye will be shifted to one side, and the reflex will fall elsewhere.

Question 5

Describe the Krimsky test, and when it would be used.

Answer 5

Measures the magnitude of strabismus when an alternate cover test isnt possible/appropriate.
The patient fixates on a pentorch at near, and prisms are added over the fixating eye (with the normal corneal reflex) until the corneal reflex of the deviated eye is centred.
The prism required is a measure of magnitude.

Question 6

Describe the Worth 4 dot test.

Answer 6

Can be done at distance or near.
A series of 4 LEDs are shown in a diamond formation.
The patient wears red/green goggles, red over right, green over left.
The red LED is always the top, the two sides are green, and the bottom LED is white.
If they see all four dots, they have no suppression.
If they see three green dots, then they have right eye suppression.
If they see two red dots, they have left eye suppression.

Question 7

Describe 3 tests that check for suppression.

Answer 7

Worth 4 dot test
Diplopia awareness
Polarised images

Question 8

Define and describe NPC, the normal values for adults and children, and what is considered clinically abnormal.

Answer 8

Near point convergence, measuring the break and recovery of a fixation target in cm.
Normal values are typically 5cm/8cm.
Anything over 10cm is abnormal.
In children, >5cm is abnormal.

Question 9

What happens to the mean NPC with age?

Answer 9

It increases

Question 10

Define and describe NRA and PRA, and what they measure.

Answer 10

Negative and positive relative accommodation.
They measure the amount of accommodation a patient can exert or relax to maintain clarity.
An N8 target is viewed at 40cm through the phoropter, set to converging.
+ and - lenses are added until a sustained blur is reported.

Question 11

Describe which of PRA and NRA use + or - lenses.

Answer 11

NRA uses + lenses, and PRA uses - lenses.

Question 12

What are the normal values for PRA and NRA in non-presbyopic adults?

Answer 12

NRA around +2.50D
PRA around -2.50D
St. dev. ~±0.75D

Question 13

Describe whether NRA/PRA is undertaken binocularly, and how this impacts whether or not it is purely a measure of accommodation or vergence.

Answer 13

Taken binocularly, and so isnt purely accommodative.

It therefore additionally tells how accommodation behaves when vergence is active to maintain single, clear vision.

Question 14

Define and describe the AC/A test.

Answer 14

Accommodative convergence/Accommodation
A prentice card is used at near, with a 6^BD prism, the phoria is measured.
It is repeated for ±1.00D, and ±2.00D using flippers.

Question 15

What is the expected value for AC/A, what happens to it with age, and why is this the case?

Answer 15

4^/1D, standard deviation of ±2.00D.
This increases with age, likely due to accommodation reducing with age, thus convergence response must increase to compensate.

Question 16

Does the amount of accommodative vergence created from accommodating increase or decrease with increased accommodative effort?
Describe 3 scenarios that apply to this.

Answer 16

It increases.
Applies to:
Increased near workload
Increased demand due to presbyopia
Any accommodative dysfunction

Question 17

Differentiate between fiation disparity and strabismus.

Answer 17

Fixation disparity is a small misalignment of the eye, but still within panums fusional area, resulting in fixation being a single entity.
Strabismus is similar, but much larger, and prevents binocular vision.

Question 18

Describe 4 means of quantifying fixation disparity.

Answer 18

Mallett card
Bernell lantern slide
Wesson card
Sheedy disparometer
Associated phoria is the prism needed to bring fixation disparity to 0.

Question 19

Consider the 4 means of quantifying fixation disparity. Name 2 advantages.

Answer 19

• Tests are taken binocularly

- Some studies show they are effective in determining the amount of prism needed to prescribe

Question 20

Consider the 4 means of quantifying fixation disparity. Name 2 disadvantages.

Answer 20

• Testing doesnt provide direct information about accommodation and vergence
• Clinically time consuming

Question 21

Describe the 3 characteristic signs of accommodative insufficiency.

Answer 21

High lag
Low amplitude
Poor facility

Question 22

Describe the 3 characteristic signs of accommodative excess.

Answer 22

Variable VA
No lag or lead
Fails + facility

Question 23

Describe the 2 characteristic signs of accommodative spasm.

Answer 23

Reduced VA

Fails + facility

Question 24

Describe the 2 characteristic signs of ill-sustained accommodation.

Answer 24

High variable lag

Slow facility

Question 25

Describe the characteristic sign of accommodative infacility.

Answer 25

Slow ± facility (both)

Question 26

Describe the 3 characteristic signs of convergence insufficiency.

Answer 26

Near exophoria greater than distance
Reduced PRC
Reduced BO facility

Question 27

Describe the 3 characteristic signs of convergence excess.

Answer 27

Near esophoria greater than distance
Reduced NRC
Reduced BI facility

Question 28

Describe the 3 characteristic signs of divergence insufficiency.

Answer 28

Distance esophoria greater than near
Reduced NRC at distance
Distance blur/diplopia

Question 29

Describe the 2 characteristic signs of divergence excess.

Answer 29

Distance exophoria greater than near

Reduced PRC at distance

Question 30

Describe the characteristic sign of basic esophoria.

Answer 30

D = N esophoria

Question 31

Describe the characteristic sign of basic exophoria.

Answer 31

D = N exophoria

Question 32

Describe the characteristic sign of vergence infacility.

Answer 32

Reduced BI/BO facility