Abv 1 - Lecture 5 - Accommodation And Vergence

Front 1

Which of the following two statements are true regarding PFV testing?

A)ranges are expected to be low in a patient with high esophoria
B)Accommodation is stimulated after the blur point
C)Accommodation is relaxed after the blur point
D)It indirectly measures a patient’s ability to relax accommodation before the blur point
E)It indirectly measures a patient’s ability to stimulate accommodation before the blur point

Back 1

Not sure

Front 2

What four pieces of information do you need to calculate the AC/A ratio?

Back 2

1) Patient's PD (cm)
2) Target Distance (m)
3) Far CT finding
4) Near CT finding

Front 3

What is the equation for Calculated AC/A ratio?

Back 3

AC/A = IPD(cm) + NFD(m)(Hn-Hf)

EXO = (-)
ESO = (+)

Front 4

HIGH AC/A ration will be more ____ at near.

LOW AC/A ratio will be more ____ at near.

Convergence (excess or insufficiency) implies that the patient is going to have issues at ___________.

DIvergence (excess or insufficiency) implies that the patient is going to have issues at ___________.

Back 4

HIGH AC/A = more ESO at near


LOW AC/A = more EXO at near

Convergence - Near Point (Low AC/A ratio - If we have NP problems, we would expect more EXO at near)

Divergence - Far Point

Front 5

How is the Gradient AC/A measured?

Back 5

The NEAR phoria is repeated with - 1.00 and + 1.00 lenses.

The difference in phoria measurement with and without the lenses give the AC/A ratio.

Front 6

How do MINUS lenses effect the vergence posture?

How do PLUS lenses effect the vergence posture?

Back 6

PLUS increase the EXO posture (relaXes accommodation which stimulates DIVERGENCE)

MINUS increase the ESO posture (stimulates accommodation which stimulates CONVERGENCE)

***This holds true only if the change in the lens power affects the accommodative system***

Front 7

For an uncorrected hyperope, when we correct with lenses, how do we change accommodation?

Back 7

Without glasses they are relatively ESO but when we put a (+) lens in front of their eye, the posture moves more toward EXO

Front 8

A + 2.50 uncorrected myope's FP is at 40 cm. How much are they accommodating?

What about when they wear their correction?

Back 8

None.

Accommodating +2.50 D with correction on.

Front 9

What is the Golden Rule of Binocular Vision?

What kind of vision does this produce?

Back 9

Accommodation affects Vergence effects Accommodation effect Vergence...

The two systems are linked.

Accommodation stimulates convergence (AC/A) which stimulate Accommodation (CA/C)

Clear, Comfortable and Single binocular vision

Front 10

Define the AC/A ratio in words.

Back 10

The amount of accommodative vergence (in prism diopters) associated with a diopter of accommodation is known as the AC/A ratio, and is typically about 4:1.

It can range from about 1:1 to 7:1.

Analysis of the AC/A ratio is important to diagnosis and management of binocular vision anomalies.

Similarly, the ratio of the accommodation (diopters) stimulated per prism diopter of reflex vergence is the CA/C ratio, and is typically about 1:10 for a young adult.

Front 11

Define the CA/C ratio in words.

Back 11

The ratio of the accommodation (diopters) stimulated per prism diopter of reflex vergence is the CA/C ratio, and is typically about 1:10 for a young adult.

Front 12

What is the difference between a Response AC/A and a Stimulus AC/A?

Back 12

The Response AC/A is usually larger by about 10%. This is because individuals do not typically accommodate the full 2.5 D for an object at 40 cm. (This would be a LAG of accommodation and is common by about +0.50 D.)

Front 13

By ______________ the accommodative system via MINUS lenses, there will be an increase in ______________ by the amount of the ______________.

What test can this be seen on?

Back 13

Stimulating

ESOphoria

AC/A Ratio

VG Phoria Measurement - by dissociating the patient we open the convergence feedback loop and are able to see the influences accommodation has on vergence - this is known as an "open - loop" condition.

Front 14

A - 1.00 lens is placed in front of a fully corrected individual viewing a target at 40 cm. If the patient showed a 3XP without the lens and has and AC/A ratio of 4/1, what would the phoria through the -1.00 lens be?

Back 14

1EP

Front 15

A + 1.00 lens is placed in front of a fully corrected individual viewing a target at 40 cm. If the patient showed a 3XP without the lens and has and AC/A ratio of 4/1, what would the phoria through the + 1.00 lens be?

Back 15

7XP

Front 16

By ______________ the accommodative system via PLUS lenses, there will be an increase in ______________ by the amount of the ______________.

Back 16

Relaxing

EXOphoria

AC/A ratio

Front 17

What is the equation for calculating Convergence Demand?

What equation does it implement?

Back 17

Convergence Demand = Fd

F = (1/target distance in meters)
d = IPD in cm

End result is in prism diopters.

Implements Prentices Rule

Front 18

If you were to measure the Target Distance, where would you measure?

If you wanted to calculate the Center of Rotation, what would you add?

Back 18

From the Target to the Spectacle Plane

+ 2.7 cm

Front 19

What does a high AC/A ratio mean in layman's terms?

Back 19

When I change the accommodative system, I am going to get a ton of change in the vergence system.

I am going from the far point to the target at near so accommodation is stimulated and thus convergence is stimulated (in the ESO direction).

If we dissociate this patient and have them accommodate by +2.50 then they are going to OVER - Converge because they are over doing it for accommodation.

Front 20

How do you calculate Accommodative Demand?

Back 20

AD = (1/distance of target)

Front 21

Why do we use dim lighting with the BCC?

Back 21

We do not want to effect DEPTH OF FIELD.

Front 22

What test can the CA/C be measured through?

How is this done?

What is the norm?

How else can the CA/C be determined?

Back 22

BCC

The BCC is repeated through 6 prism diopter.

Norm = 0.50 D / 6 prism diopters

Through MEM on a patient looking through a 6 prism diopter at a DOG Card (this is not an accommodative target).

Front 23

What is the ability to RELAX accommodation under the influence of the vergence system?

Back 23

Negative Relative Accommodation (NRA)

This is done at near while maintaining fusion.

Front 24

What is the role of vergence during the NRA/PRA?

Back 24

Keeping the target single

Front 25

During the NRA, where does the plane of accommodation move in reference to the target?

What lenses are added during the NRA?

Back 25

Plane of accommodation moves back as plus lenses are added - relaxing accommodation.

Plus lenses

Front 26

During the NRA, what must be stimulated in order to keep the target single and therefore avoid diplopia?

Explain.

Back 26

Positive Relative Vergence (PRV)

With accommodation RELAXED, the vergence system is stimulated to move in the direction of the new plan of accommodation (this would be a DIVERGENCE movement) by way of the AC/A ratio.

In order to remain aligned on the target and avoid diplopia, Positive Relative Vergence (PRV) is stimulated and therefore counteracts the urge to DIVERGE.

Front 27

As a patient becomes more presbyopic, NRA finding change or remain unchanged?

Back 27

Remain unchanged

Aging affects the ability of accommodation to stimulate, not relax.

Front 28

What does NRA measure:

Directly?

Indirectly?

Back 28

Directly measure the ability of accommodation to RELAX while vergence is maintained constant.

Indirectly measures the patient's CONVERGENCE ability or PRV.

Front 29

What are the two possible endpoints (BLUR) for the PRV?

Back 29

1) Accommodation cannot relax anymore

2) PRV cannot be stimulated any further independent of accommodation

Front 30

During NRA/PRA, how would we test which system (accommodative or vergence) is having difficulty?

Back 30

Cover one eye

If the target CLEARS - PRV problem

Front 31

If the endpoint of the NRA is diplopia, what could be going on?

Back 31

Patient is a HIGH EXO with a LOW PRV (The patients eyes already tend to rest out, when you had plus lenses in front of the eye, accommodation relaxes and wants vergence to DIVERGE (EXO posture) and they eyes rest so far out is almost impossible for the PRV (CONVERGENCE) to bring them in enough to keep the target single. Essentially the PRV has start the race farther back.)

Front 32

If the endpoint of the NRA is abnormally LOW, what could be going on?

Back 32

1) Patient has difficulty RELAXING accommodation

2) Patient has HIGH NEAR EXO (low PFV reserves)

Front 33

If the endpoint of the NRA is abnormally HIGH, what could be going on?

Back 33

1) Latent hyperopia

2) Significant LAG of accommodation ( + lenses would push the image on to the retina)

3) OVER - MINUS or UNDER - PLUS the manifest

Front 34

What is the ability to STIMULATE accommodation under the influence of the vergence system?

Back 34

Positive Relative Accommodation (PRA)

Front 35

Where does the plane of accommodation move during the PRA when MINUS lenses are added?

Back 35

Accommodation is being stimulated so the plane of accommodation moves CLOSER.

Front 36

How is diplopia avoided during the PRA?

Explain.

Back 36

Negative Relative Vergence (NRV) must be stimulated to avoid diplopia.

When (-) lenses put in front of the eye, they stimulate accommodation which then stimulates CONVERGENCE. To keep the target single, NRV must counteract the urge to CONVERGE and the NRV must DIVERGE

Front 37

During NRA/PRA if vergence is allowed to move with accommodation, what occurs?

Back 37

Diplopia

Front 38

During the PRA, we are measuring what

Directly?

Indirectly?

Back 38

Directly measuring the ability of accommodation to STIMULATE while vergence is maintained constant.

Indirectly measuring NRV

Front 39

When does the endpoint (BLUR) occur for the PRA?

Back 39

1) When accommodation cannot be stimulated any further

2) NRV cannot be stimulated any further "independent" of accommodation

Front 40

To test which system (accommodation or convergence) is having difficulty, cover one eye.

What happens if it clears?

Back 40

If it clears, it NOT a problem with accommodation, it is a problem with NRV (stimulating divergence independent of accommodation)

Front 41

For PRA, if the endpoint is diplopia, what is going on?

Back 41

HIGH ESO at near with LOW PRV

(+) lenses in front of the stimulates accommodation which then causes vergence to converge. To keep the target single, NRV must DIVERGE to counteract the convergence signal from accommodation. If the patient is a HIGH ESO meaning their posture is IN then they will have to work really hard to try and converge.

Front 42

What does a HIGH PRA mean?

Back 42

Patient could be suppressing an eye which in that case you are performing a MINUS LENS TO BLUR AMPLITUDE inadvertently.

Front 43

What does a LOW PRA mean?

Back 43

1) Difficulty stimulating accommodation

2) High EXO at near compared to the distance

Front 44

What does the actual limit of the PRA depend on?

Back 44

- Amplitude of Accommodation

- AC/A ration

- BI Vergence measurement at Near (How well the patient can DIVERGE at near or their NRV essentially)

Front 45

An individual with a LOW AC/A ratio coupled with a HIGH BI to blur finding will yield a higher or lower PRA finding compared to an individual with a HIGH AC/A ration and LOW BI to blur findings?

Back 45

LOW AC/A means that when accommodation is stimulated, it is not asking vergence to do alot

HIGH BI finding mean the patient is good at DIVERGING/NRV so they will be able to keep the target single for longer on the PRA

So ... HIGHER

HIGH AC/A means whenever accommodation is stimulated it asks vergence to work overtime

LOW BI finding means the patient does not DIVERGE very well and will have a LOW NRV and thus will blur quicker = LOW PRA

Front 46

What is the typical stopping point for PRA?

Back 46

- 2.50

Front 47

What is the Relative Point Value?

Back 47

Remember that the NRA and PRA are always relative to some starting point.

This relative point is the lens that the nearpoint data is being tested through (BCC or Manifest).

If it is through the MANIFEST = 0

If it is through the BCC = BCC Value

Front 48

What two methods can you use for balancing NRA/PRA?

Back 48

1) Equation

(NRA + PRA)/2 + Relative Point Value

This would be the new BCC that balances NRA and PRA

2) Number Line

Front 49

What is the GOAL for balancing NRA/PRA?

Back 49

The goal is to determine a nearpoint lens that places the patient's posture of accommodation in the middle of the NRA and PRA for maximum comfort.

Front 50

For vergence testing, which tests should always be performed first?

Back 50

BI/NFV to RELAX accommodation before BO/PFV

Front 51

By introducing BI prism in front of the eyes, light is bent toward the base of the prism and lands on _______________ in both eyes.

What about BO prism, where does the image fall?

What does the eye do when this happens?

What type of movement accomplishes this?

Back 51

BI - Nasal Retina - DIVERGENCE

BO - Temporal Retina - CONVERGENCE

To correct this initial retinal disparity, the eyes move to place these images back on the fovea.

Front 52

Because of the CA/C link,

CONVERGENCE does what to accommodation?

DIVERGENCE does what to accommodation?

Back 52

Convergence = Stimulates accommodation

Divergence = Relaxes accommodation

Front 53

During the NRV testing, what must be stimulated in order to keep the target clear?

Back 53

Positive Relative Accommodation (PRA)

During the BI/NRV the eyes are DIVERGING and therefore are STIMULATING accommodation.

Front 54

During the NRV/BI testing, what are we measuring UP UNTIL THE BLUR POINT?

What are we measuring FROM THE BLUR POINT ON?

What are measuring from the START of the test to DIPLOPIA?

Back 54

Negative Relative Vergence (NRV) or Negative Fusional Reserve Vergence (NFRV)

Negative Accommodative Vergence (NAV)

A decrease in accommodation will support the divergence movement.

Total Negative Vergence (TNV)

Front 55

What does the blur point represent?

Back 55

The blur point represent the point where the patient can no longer compensate for the prism - induced retinal disparity while maintaining stable accommodation

Front 56

During the NRV/BI testing, blur will occur for what reasons?

Back 56

1) Low DIVERGENCE reserves like in ESO

2) Accommodation NOT being stimulated

Front 57

During the PRV/BO testing, what are we measuring UP UNTIL THE BLUR POINT?

What are we measuring FROM THE BLUR POINT ON?

What are measuring from the START of the test to DIPLOPIA?

Back 57

Positive Relative Vergence (PRV) or Positive Fusional Reserve Vergence (PFRV)

Positive Accommodative Vergence (PAV)

A increase in accommodation will support the convergence movement.

Total Positive Vergence (TPV)

Front 58

What does a LOW NRV/BI finding mean?

Back 58

1) Near ESO (eyes rest in and therefore they have hard time DIVERGING out)

2) Difficulty STIMULATING accommodation

Front 59

What does a HIGH NRV/BI finding mean?

Back 59

1) Near EXO (eyes rest out and therefore have less to go when they DIVERGING out)

2) Difficulty RELAXING accommodation

Front 60

Because of the CA/C link, during PRV/BO testing accommodation is initially ___________ but in order to maintain clarity _______________ is stimulated.

Back 60

BO = Convergence = Stimulation of accommodation

NRA = Relaxes accommodation

Front 61

During PRV/BO testing, what are some reasons blur occurs?

Back 61

1) Low CONVERGENCE ability like in HIGH EXO at Near

2) Difficulty RELAXING accommodation (NRA)

Front 62

When does the blur occur?

What happens after the blur occurs?

When does diplopia occur?

Back 62

When accommodation can no longer act independently from the vergence system.

Accommodation then supports convergence to keep the target single.

Diplopia occurs when PRV (causes they eyes to converge) and PAV can no longer keep up with the increasing amounts of convergence.

Front 63

LOW PRV/BO finding mean what?

Back 63

1) Near EXO

2) Difficulty RELAXING accommodation

Front 64

HIGH PRV/BO finding mean what?

Back 64

1) Near ESO

2) Difficulty STIMULATING accommodation

Front 65

What is the vergence movement used to resolve retinal disparity of an image?

Back 65

Fusional Vergence

Front 66

What term will be reserved for describing the vergence movements free from accommodation during fusional vergence testing (before the blur point)?

Back 66

Relative Vergence

Front 67

What encompasses both relative vergence and accommodative vergence?

Back 67

Total Vergence
(Positive or Negative)