PC - Clinical Assessment of Accommodative-Vergence Interactions - Week 3 Flashcards
Describe the accommodation-vergence cross-link.
Retinal bur drives accommodation and alters vergence through the cross-link.
Retinal disparity drives convergence and alters accommodation through the cross-link.
Name 2 objective means of measuring binocularity, and what they do.
Cover test - evaluates alignment in all 9 directions of gaze
Hirschberg - evaluates alignment and estimates magnitude of any deviation
Name 2 subjective means of measuring binocularity, and what they do.
Stereopsis - Fly, lang, and randot tests
Suppression - Worth 4 dot D and N, diplopia awareness, prism doubling, polarised tests
Describe the Hirschberg test.
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.
Describe the Krimsky test, and when it would be used.
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.
Describe the Worth 4 dot test.
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.
Describe 3 tests that check for suppression.
Worth 4 dot test
Diplopia awareness
Polarised images
Define and describe NPC, the normal values for adults and children, and what is considered clinically abnormal.
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.
What happens to the mean NPC with age?
It increases
Define and describe NRA and PRA, and what they measure.
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.
Describe which of PRA and NRA use + or - lenses.
NRA uses + lenses, and PRA uses - lenses.
What are the normal values for PRA and NRA in non-presbyopic adults?
NRA around +2.50D
PRA around -2.50D
St. dev. ~±0.75D
Describe whether NRA/PRA is undertaken binocularly, and how this impacts whether or not it is purely a measure of accommodation or vergence.
Taken binocularly, and so isnt purely accommodative.
It therefore additionally tells how accommodation behaves when vergence is active to maintain single, clear vision.
Define and describe the AC/A test.
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.
What is the expected value for AC/A, what happens to it with age, and why is this the case?
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.
Does the amount of accommodative vergence created from accommodating increase or decrease with increased accommodative effort?
Describe 3 scenarios that apply to this.
It increases. Applies to: Increased near workload Increased demand due to presbyopia Any accommodative dysfunction
Differentiate between fiation disparity and strabismus.
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.
Describe 4 means of quantifying fixation disparity.
Mallett card Bernell lantern slide Wesson card Sheedy disparometer Associated phoria is the prism needed to bring fixation disparity to 0.
Consider the 4 means of quantifying fixation disparity. Name 2 advantages.
- Tests are taken binocularly
- Some studies show they are effective in determining the amount of prism needed to prescribe
Consider the 4 means of quantifying fixation disparity. Name 2 disadvantages.
- Testing doesnt provide direct information about accommodation and vergence
- Clinically time consuming
Describe the 3 characteristic signs of accommodative insufficiency.
High lag
Low amplitude
Poor facility
Describe the 3 characteristic signs of accommodative excess.
Variable VA
No lag or lead
Fails + facility
Describe the 2 characteristic signs of accommodative spasm.
Reduced VA
Fails + facility
Describe the 2 characteristic signs of ill-sustained accommodation.
High variable lag
Slow facility
Describe the characteristic sign of accommodative infacility.
Slow ± facility (both)
Describe the 3 characteristic signs of convergence insufficiency.
Near exophoria greater than distance
Reduced PRC
Reduced BO facility
Describe the 3 characteristic signs of convergence excess.
Near esophoria greater than distance
Reduced NRC
Reduced BI facility
Describe the 3 characteristic signs of divergence insufficiency.
Distance esophoria greater than near
Reduced NRC at distance
Distance blur/diplopia
Describe the 2 characteristic signs of divergence excess.
Distance exophoria greater than near
Reduced PRC at distance
Describe the characteristic sign of basic esophoria.
D = N esophoria
Describe the characteristic sign of basic exophoria.
D = N exophoria
Describe the characteristic sign of vergence infacility.
Reduced BI/BO facility
