Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BVA > 8. Vergence > Flashcards

8. Vergence Flashcards

1
Q

How can people learn to dissociate accommodation and convergence?

A
  1. Positive relative convergence/negative relative accommodation
  2. Negative relative convergence/positive relative accommodation.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Explain Positive relative convergence/negative relative accommodation

A

When convergence is produced in excess of accommodation.
How much convergence can be induced before image blurs (due to over accommodation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What can positive relative convergence/negative relative accommodation be used to treat?

A

Useful to treat exo deviations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe method for positive relative convergence/negative relative accommodation using sphere lenses.

A
  1. Plus lenses (decreases accommodation)
  2. View 6/9 near letter
  3. Increase positive lenses in 0.25DS steps.
  4. Patient reports when blurred
  5. Lenses relax accommodation, so vergence must be increased to keep eyes aligned. Blur point reached when accommodation is unable to relax further.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe method for positive relative convergence/negative relative accommodation using prisms

A
  1. Use base OUT prism
  2. Base OUT prisms induce convergence, so accommodation is relaxed
  3. Blur point in prism fusion reserves (PFR) indicates maximum relative convergence (too much accommodation)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe method for positive relative convergence/negative relative accommodation using stereograms

A
  1. A card with image is held by Px.
  2. Images can be : Cats, Buckets, Circles.
  3. Px looks at a pencil that is front of the card.
  4. So eyes converge on the pencil, but also accommodate to see the image on card.
  5. Aim to achieve 3 clear cats/buckets/circles.

Pen proximal = Positive relative convergence (exo)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain Negative relative convergence/Positive relative accommodation

A

Convergence is relaxed in relation to accommodation.
How much convergence can be relaxed before image blurs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What can negative relative convergence/positive relative accommodation be used to treat?

A

Useful to treat eso deviations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe method for negative relative convergence/positive relative accommodation using sphere lenses.

A
  1. Minus lenses (Stimulates accommodation)
  2. View 6/9 near letter
  3. Increase minus lenses in 0.25DS steps.
  4. Patient reports when blurred
  5. Lenses stimulate accommodation, so vergence must be relaxed to keep eyes aligned. Blur point reached when accommodation is unable to increase further.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe method for negative relative convergence/positive relative accommodation using prisms

A
  1. Use base IN prism
  2. Base IN prisms reduce convergence, so accommodation is increased
  3. Blur point in prism fusion reserves (PFR) indicates maximum relative convergence (Accommodation can’t be increased further)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe method for negative relative convergence/positive relative accommodation using stereograms.

A
  1. A card with image is held by Px.
  2. Images can be : Cats, Buckets, Circles.
  3. Px looks at a pencil that is behind the card.
  4. So eyes converge less on the pencil, but also accommodate to see the image on card.
  5. Aim to achieve 3 clear cats/buckets/circles.

Pen distal = negative relative convergence (eso)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is fusional vergence?

A

It’s a type of vergence used to correct any small misalignments between the eyes, ensuring the brain can “fuse” the images seen by each eye into a single, clear image.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the importance of fusional vergence?

A

Important to maintain BV in presence of phoria.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

If fusional vergence is weak what symptoms can this lead to?

A

Eye strain
Headaches
Diplopia
Blurred vision
Lack of stereopsis
If fusion reserves are low, this can lead to decompensation of a phoria.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How is fusional vergence measured?

A

Using the prism fusion range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the method for the prism fusion range

A
  1. Px needs to have BSV (so can’t perfom on those with strabismus or who can’t fuse)
  2. Px wears their refractive correction
  3. Px fixates on accommodative target (6/6 letter) and prism introduced in front of one eye
  4. Prism is increased until diplopia experience (break point)
  5. Decrease the prism until BSV is regained (recovery point)
  6. Fusion taken as the prism value before break point
  7. repeat for both near and distance
  8. repeat for Base OUT (Positive) and Base IN (Negative).
17
Q

What are the results to record for the prism fusion range? And explain them.

A

Blur, break and recovery points.

Blur point is the limit of positive/negative relative convergence. When can no longer accommodate

Break point is the limit of motor fusion. Loss of bifoveal fixation resulting in diplopia

Recovery point is where motor fusion can restore bifoveal fixation.

18
Q

What is the normal results for Positive prism fusion range? (Base OUT)

A

Near: 35/40
Distance: 14

19
Q

What is the normal results for Negative prism fusion range? (Base IN)

A

Near: 14
Distance: 4/6

20
Q

What is the normal results for verticle prism fusion range? (Base UP/DOWN)

A

Near: 3
Distance: 3

21
Q

What is tonus?

A

Continuous, low level contraction of muscles at rest.

22
Q

How can tonus affect prism fusion range?

A

If you do Base OUT first, fusional vergence movements would make small inward movements everytime prism increased. The medial recti muscle becomes a bit tighter.
So if Base IN is done next, which is already the weakest range, it is going to be harder to make the movements as we have tonus of medial recti muscles. Resulting in a further weaker range for Base IN

23
Q

What should be done to avoid the effects of Tonus?

A

Measure prism fusion range for the most likely weakest first.

24
Q

How to interpret results to check reserves?

A
  1. Compare positive and negative reserves= If positive low then possible exo deviation.
  2. Compare the amplitudes with normal
  3. Sheards criterion = Fusional reserve in opposite direction to phoria should be twice the size of phoria
  4. Compare break and recovery points =
    Normal difference 4-6. If difference is large, this indicates that Px finds it difficult to restore fusion once it is broken down - poorly developed fusion reflex.
25
Q

What factors influence the measurement of PFR?

A
  1. Fixation target = If target is small then convergence may elicit earlier blur point.
  2. Instructions = Prompt the Px to try and get fuse the image together once seen as double.
    If Px is not used to seeing double they may miss the double image and the break point.
  3. Risley prism preferred over prism bar. As it has smooth change of prism power.
  4. Rate of change of prism. Make sure to not go too fast as it would make it harder for Px to maintain fusion.
26
Q

What is proximal vergence?

A

Stimuli that give the impression of being nearer/further provoke vergence.

E.g. increasing the size of an object can cause vergence.

It occurs in absence of disparity or accommodation cues.

27
Q

Decompensation can be caused by problems with….?

A
  1. Accommodation
  2. AC/A
  3. Fusion reserves
28
Q

What are the optical causes of decompensation?

A
  1. Uncorrected/undercorrected spherical refractive errors =
    -Esophoria decompensated by hypermetropia
    -Exophoria decompensated by myopia
    -Anisometropia (unfocused image of one eye; this is where there is a significant difference in the refractive power between the two eyes)
    - Early presbyopia
  2. Wrongly corrected refractive errors
  3. Ill fitting spectacles causing prismatic effect
  4. Aniseikonia (Where there is a difference in the percieved size or shape of images between the two eyes; The unequal image sizes prevent sensory fusion. This can result from a miscalculated intraocular lens following cataract surgery)
29
Q

What are the medical causes of decompensation?

A
  1. Poor general health causing disruption of fusion or accommodation
  2. Head trauma causing loss of sensory and motor fusion
  3. Medication which disrupts accommodation
  4. Alcohol
30
Q

What are the other causes of decompensation?

A
  1. Close work- if they have convergence weakness exophoria and do a lot of close work this could lead to decompensation.
  2. Distance work i.e driving- if they have divergence weakness esophoria and do distance work this could lead to decompensation.
  3. Demand on vision during monocular viewing. E.g. Jewellers glass, microscopes, have acquired visual loss in one eye meaning the other eye is being used in demand.
31
Q

What is convergence insufficiency (CI)?

A

When the eyes struggle to work together while focusing on nearby objects. Present if near point of convergence is less than 10cm.

Primary CI present if other causes have been exculded.

32
Q

What are the symptoms caused by convergence insufficiency (CI)?

A

Causes symptoms such as double vision, eyestrain, headaches, and difficulty maintaining focus on close objects.

33
Q

What are the signs caused by convergence insufficiency (CI)?

A
  1. Cover test results in exophoria for near with poor recovery time.
  2. Convergence will be less than 10cm. (Can measure using RAF rule)
  3. Measure accommodation uniocularly and binocularly. If uniocular is better, this suggests CI.
  4. Prism fusion reserves test results in + range being low.
34
Q

What’s the significance of symptoms?

A

Some patients have very small phorias that produce severe symptoms.

Significance of symptoms can be made sure of by:
-Diagnostic prims: Correct phoria with prism and see if symptoms are relieved over a 2-3 week period.
- Diagnositic occlusion: e.g a patch- worn as much as possible over 2-3 week period. Symptoms should disappear during occlusion

BVA (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions