Key points

Convergence insufficiency (CI) is a common binocular disorder in which the eyes do not work well at near fixation. The incidence of CI in the general population has been estimated to be 2.5% to 13%. The near point of convergence (NPC) is reduced, and the eyes drift out as a fixation target is moved closer. The NPC is the closest distance in which the eyes can maintain clear and equal focus on a near accommodative target. In general, it should be less than 6 to 7 cm in healthy children (children with refractive errors should be tested with their glasses on).

What are the symptoms of CI?

These symptoms may occur in children with CI while performing near tasks (reading, working on a computer, using a cell phone, playing hand-held video games, making crafts, and so on)

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  Headaches

  
  
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  Eyestrain

  
  
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  Double vision

  
  
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  Blurred vision

  
  
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  Loss of place while reading

  
  
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  Excessive tiredness when reading

  
  
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  Covering one eye

  
  
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  Complaints of the words moving on the page

  
  
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  Short attention span for reading

  
  
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  Constantly adjusting the distance of the book, phone, and other objects, to see better

These symptoms can be aggravated by illness, tiredness, anxiety, and stress.

All of these symptoms can be caused by other ocular and nonocular problems.

Any child with these symptoms deserves a complete eye examination to rule out other eye diseases that could cause some of these symptoms, such as dry eyes, strabismus, refractive errors, optic neuritis, iritis, and other diseases. Children deserve therapy for symptomatic CI.

Double vision may not be present even with an obvious eye misalignment because a child can ignore a misaligned image if the deviation starts at a young enough age (approximately less than 6 years old) when the visual system is still maturing. Suppression is the term used to describe the ability to ignore a second image. It is an acquired neurologic rewiring of the visual cortex. There may be a moment when the eye deviates outward in a child with CI and some children will complain of blurry vision instead of double vision.

What are the symptoms of CI?

These symptoms may occur in children with CI while performing near tasks (reading, working on a computer, using a cell phone, playing hand-held video games, making crafts, and so on)

• •
  

  Headaches

  
  
• •
  

  Eyestrain

  
  
• •
  

  Double vision

  
  
• •
  

  Blurred vision

  
  
• •
  

  Loss of place while reading

  
  
• •
  

  Excessive tiredness when reading

  
  
• •
  

  Covering one eye

  
  
• •
  

  Complaints of the words moving on the page

  
  
• •
  

  Short attention span for reading

  
  
• •
  

  Constantly adjusting the distance of the book, phone, and other objects, to see better

These symptoms can be aggravated by illness, tiredness, anxiety, and stress.

All of these symptoms can be caused by other ocular and nonocular problems.

Any child with these symptoms deserves a complete eye examination to rule out other eye diseases that could cause some of these symptoms, such as dry eyes, strabismus, refractive errors, optic neuritis, iritis, and other diseases. Children deserve therapy for symptomatic CI.

Double vision may not be present even with an obvious eye misalignment because a child can ignore a misaligned image if the deviation starts at a young enough age (approximately less than 6 years old) when the visual system is still maturing. Suppression is the term used to describe the ability to ignore a second image. It is an acquired neurologic rewiring of the visual cortex. There may be a moment when the eye deviates outward in a child with CI and some children will complain of blurry vision instead of double vision.

How to test convergence and diagnose CI

The pediatrician can easily perform a simple check for NPC.

This simple check should be done when a child is getting ready to start kindergarten, or sooner if a parent notices any sign or symptom that might indicate a problem such as winking an eye or a drifting eye. The test requires an accommodative target (small letters or a detailed small picture attached to the end of a tongue depressor; Fig. 1 ). The target should be positioned an arms’ length away at eye level and brought toward the child’s face. Ideally the child should read the letters as the stick is coming closer. The tester should be observing the position of the eyes as they focus on the target. Accommodation is linked to convergence, and as the child focuses (accommodates), the eyes converge to stay focused on the same object. At some point the child will no longer be able to continue to converge and focus on the target. This point is referred to the near point of convergence ( Fig. 2 ).

Example of an accommodative target.

A patient is fixated on the letters as the stick gradually moves toward the nose.

A pediatric ophthalmologist will perform 3 tests as part of the complete eye examination, before diagnosing CI. They include the following:

• 1.
  

  Cover test: This test is done to check for any misalignment of the eyes in the distance or at near. Other forms of strabismus can cause or aggravate convergence problems. If a child has an exotropia (manifest drifting out) in the distance, this can certainly affect the NPC. If the distance exotropia is poorly controlled or decompensates, surgery is often necessary. Once the distance deviation is taken care of, the near alignment can be evaluated. Often the near alignment is fine and no further treatment is needed. Some children have a CI type of exotropia whereby the near deviation is greater than the distance deviation. In these children, they often need surgery for the distance deviation and convergence therapy for the near deviation. In patients with CI, there is a near exophoria (latent deviation) of 4 or more prism diopters greater than the distance phoria.

  
  
• 2.
  

  Near point of convergence: This test should be performed several times as described above, looking for signs of fatigue. In patients with CI, NPC should measure greater than 6.

  
  
• 3.
  

  Convergence amplitudes: In this test a horizontal prism bar is held in front of one eye while the child tries to keep one of the target letters clear and single. The prism bar is slowly moved to increase the prism that the convergence effort must overcome. Eventually, the child cannot keep the image single and clear. This point determines the convergence amplitude (a measurement of the strength of convergence that often indicates the ability to maintain convergence without fatigue; Fig. 3 ).

  
  

  
  

  
  

  
  

  
  

  Test to determine convergence amplitude.

  
  

Secondary causes of convergence insufficiency

• 1.
  

  Pseudotumor cerebri

  
  
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  Fourth nerve palsy

  
  
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  Duane syndrome

  
  
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  Traumatic brain injury/concussion

  
  
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  Behavioral medications

  
  
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  Distance exotropia

After addressing the primary problem, these patients often need convergence therapy. With the new concussion guidelines recommending prolonged “brain rest” until symptoms resolve, it is important to consider that a prolonged headache associated with near work might be a symptom of CI and not unresolved brain trauma.