Difference between revisions of "Convergence Ability"

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Test should be performed more than one time to be sure that patient understood and concentrate to test. For patients with convergence insufficiency repeated tests will give more far near point of convergence.
 
Test should be performed more than one time to be sure that patient understood and concentrate to test. For patients with convergence insufficiency repeated tests will give more far near point of convergence.
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[http://eyewiki.org/File%3ANear_point_of_convergence.jpg]
  
 
=== Results  ===
 
=== Results  ===

Revision as of 17:45, May 31, 2017

Assigned editor:
Review:
Assigned status Update Pending
 by Liene Muceniece, MD on May 31, 2017.


Convergence ability can be tested with 2 different methods: 1. Near point of convergence (NPC) - is the point where the visual axes intersect under the maximum effort of convergence. It is a measure of pursuit convergence. 2. Jump convergence - convergence level increased by rapid jump to closer point. A qualitative assessment of the quality of convergences fixation jumps from distant to mid-distant target at near point.

Convergence ability should be a part of routine examination. Patients with a poor convergence can be suffering from headache and diplopia while they read. As well people can complain of blurry words after some time of reading. Child can be shy and not complain about this symptoms. Still, need to be reminded that patients with convergence weakness can be asymptomatic. If a child is noticed by convergence weakness it should be re-tested and obtaining a history of patients complains. Asymptomatic convergence weakness don't need any specific treatment. It is not appropriate to test convergence ability for heterotropia patients

Near point of convergence

This is a standard test for convergence ability. It is easy to make and does not require special equipment. Equipment: fixation target and ruler. As a fixation target can be used a pencil or pen. To get child attention it is better to use some small toy with common character. It should be with small details that are clearly to see. It is available to use some specific ruler for convergence and accommodation ability testing. If there is a high level myopia or hypermetropia test should be done with needed correction.

Test performing

1. Patient should sit straight and look directly to fixation object what is placed at nose level approximately 50 cm from it. 2. Room should be illuminate well so there could be option to see any changes at eye movements 3. Slowly and smoothly move fixation object closer to patient, speed should be proximately 10s to move it from 40 cm till nose. 4. Ask for the patient to say when there is 2 objects. It should be explained for patient that object can become blurry, but still need to fixate to it. 5. While performing test should examine patients eyes because some patients are not feeling diplopia. When one of eyes is not fixating to object anymore then is found near point of convergence. 6. Move fixation object more far from patient till both eyes start to fixate on subject - there is a recovery near point of convergence.

Test should be performed more than one time to be sure that patient understood and concentrate to test. For patients with convergence insufficiency repeated tests will give more far near point of convergence.

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Results

Normal near point of convergence is about 6-10 cm. but convergence renewing point till 15 cm. If NPC is more than 10 cm it is a sign of poor convergence. Meanwhile recovery near point of convergence that is more than 15 cm can be a cause of astenopic complains if there is an intense reading.

Result of test should be noted for example, NPC 7cm, CRP 12 cm

Jump convergence

Test is more realistic to typical near viewing situation. Test can be used additionally for patients that are showing some signs of convergence insufficiency. Equipment: dot card or Brock string. Length of card can be variating but not smaller than 20 cm. At the middle of card is well seen points that are placed 1-2 cm from each other If patients is high myopic or hypermetropic then test should be performed with needed correction.

Test performing

1. Patient should sit straight. At the end of nose add a dot card. 2. Room should be well illuminated, so it would be easily to notice any changes at eye movements. 3. Patient is asked to fixate at forest point on the card and should ask:

- how many lines are there
- are they crossing at this fixation point

4. If patient can fixate to this point then move to closer point till patient see 2 parallel lines or just one eye (other eye is suppressed) 5. Last point where patient can see 2 lines that are crossed at the fixation point is near point of convergence.

Test should be performed more than one time to be sure that patient understood and concentrate to test. For patients with convergence insufficiency repeated tests will give more far near point of convergence.

Results

Test results should be written down for example convergence 8 cm (Brock string) Person with a good convergence ability both test should show similar results.

Most commune errors

1. Relying upon subjective NPC measures. Objective observation should be done to notice converge 2. Carrying test only once. 3. Moving the target too rapidly that can over estimate convergence ability. Moving target too slowly so child is loosing interest of it. 4. Not encouraging patient enough to keep the NPC target - use different targets for children each time. 5. Not testing at slight downward gaze


References

1. David B. Elliott PhD, Clinical procedures in Primary eye care Fourth edition. Elsevier limited, 2014 2. Brad Bowling Kanski's Clinical ophthalmology Eight edition. Elsevier limited, 2016 3. Frank Eperjesi PhD, Hannah Bartlett PhD, Mark Dunne PhD Ophthalmic Clinical Procedures Elsevier limited, 2007 4. Darcy A.Umphred PhD, Gordon U.Burton PhD, Rolando T. Lazaro PhD, Margaret L. Roller Umphred's neurological rehabilitation Six edition. Mosby, 2013.