The Ultimate Guide to Convergence Insufficiency

Convergence insufficiency (CI) is one of the most common binocular vision disorders that is encountered in optometry. It is a condition that was first described by Von Graefe in 1855 and has been the focus of many studies since then. Jeffery Cooper, O.D, M.S., and Nadine Jamal, O.D. have recently published a paper that compiles all of the research thus far.

I assembled a brief overview of the most important concepts concerning convergence insufficiency:

 

Definition:

A convergence insufficiency is a sensory and neuromuscular disorder that inhibits a person’s ability to accurately view a near target. The criterion to diagnose a CI is not clear-cut because there is no ‘gold standard’ to the classification; that is, all of the studies classify a CI differently. However, combinations of these following three signs are the most commonly used:

1)   Exophoria greater at near than at distance

2)   Reduced NPC

3)   Decreased PFC (BO) ranges at near- especially the recovery

 

Prevalence:

This is difficult to discern as there is a large variability depending on the study; however, average prevalence is believe to be about five percent^1-6.

*It should be noted that the CITT studies have shown that there is a higher prevalence of CI in school-aged children than previously expected. Like I’ve said in previous posts- ask the right questions and do the basic binocular tests on all children to increase the chances for early detection⁷.

 

CI Etiology:

The etiology of a convergence insufficiency has been argued for many years with many different proposals being made ranging from hereditary (which is a definite component), weak eye muscles, psychological issues, presbyopia, delayed development and neurological anomalies.⁵ It should be noted that there are multiple mechanism for this condition, but recent studies have shown a consistent etiology in symptomatic CIs to be linked to the slow adaptive vergence system; namely there is “a breakdown of accommodative convergence cross-links fusional convergence or voluntary convergence interactions’²⁰…it is not fast vergence, as previously assumed, but slow adaptive vergence^{.”  21-23}

There are also three main factors that have been identified as the possible cause for ocular fatigue associated with convergence insufficiency: The first is the fact that there has to be a constant balance of accommodation and convergence to perform near tasks. Secondly this balance must remain stable and unfaltering throughout the task. Lastly the reduced stereo at near may make it more difficult for the eyes to maintain fusion.¹⁹  Whether it is one of these issue or all of them combined, it is essential that you figure out where your patient’s weaknesses lie.  Once you do that, you can rehabilitate them to have the ability to maintain fusion and perform near tasks for an extended period of time comfortably.

 

Symptoms:

Like any condition, CI can manifest differently for each person. These are just some of the most common symptoms (often which occur at the end of the day and following extensive near work).  ^5,8-11

1. Diplopia ^5,8,12-17

2. Eye strain¹⁴

3. Blurred vision ^5,8,15,16

4. Headaches ^{8, 14}

5. Loss of place while reading/ needing to re-read ¹⁸

5. Eye fatigue/general fatigue

To help quantify symptoms, CITT developed the Convergence Insufficiency Symptom Survey (CISS): A questionnaire designed to quantify symptoms associated with reading and near work. The score ranges from 0 to 60, with 60 representing the most symptomatic case. The CITT group determined that a score of >16 for children under 18 and a score of >21 for adults 19-30 indicates a symptomatic CI. 24-26 Although this a good tool to start and understand your patient, it should be used in conjunction with the patient’s level of discomfort and your clinical judgment for treatment purposes.

 

A Deeper look into the signs of CI:

Each of the three signs used to diagnose CI have been extensively studied and with that has come norms to gauge patient’s performances.

For many it is automatic and ingrained to think that a person with a CI has a greater exo deviation at near than far, but it is actually not necessary to make the diagnosis of a CI. With that being said, CITT study found over half (53%) of the patient had an exophoria at near with the mean exodeviation to be 9.4 PD.²⁷ It is helpful to know the near posture of your patient, but it is important realize that it is not the only sign of this condition.

According to Duane, a reduced NPC is actually considered the “most consistent clinical sign found in persons with CI²⁸.” The proper target for NPC is varied depending on which study you look at: some use an accommodative target where others use penlights, and a red lens with a penlight (the former has been proposed to help pick up more subtle CIs²⁹). The normal value for NPC, which was found using an accommodative target, was determined as

Adults: <5cm/ 7cm²⁹and Children: <6 cm.³⁰

As stated in the review, “The majority of patients with a CI have reduced PFC ranges.” ^6,31,32 It was determined that a PFC of <15 PD is abnormal for both a patient with a CI as well as the normal population. According to Cooper & Duckman, the recovery on PFC ranges is probably the more important finding as the “recovery is a better indication of fusional potential over time as it represents the patient’s ability to voluntarily regain fusion on the basis of sensory information.” Regardless of what you decide gives you the most information, all sources point to the fact that the “fusional vergence amplitude must be larger than the magnitude of the phoria to avoid ocular fatigue.”³¹

 

CI & accommodation:

Psuedo-CI is an important differential to make when diagnosing a convergence insufficiency. One must probe the accommodative system to see if the lack of convergence is related to the inability to accommodate (as you know the accommodative and vergence systems are intimately intertwined). Up to 58% (!) of children with a CI have a compounding accommodative issue.³³This deficiency should be address concomitantly with the convergence insufficiency during treatment.

 

CI & related conditions:

Throughout the literature you will find studies that try to find a connection between a common condition and a CI. There is no link to any sort of refractive error, but there is a correlation between children with learning/attention issues. It is difficult to discern what the exact link is, but it is known that kids with ADHD are 3x as likely to have a CI. ³⁴

The hot topic right now is traumatic brain injury (TBI) and how it affects the functioning of the visual system. What we know so far is that there is a high prevalence of these mild TBI patients suffering from “ reading difficulties, CIs and accommodative dysfunctions. ^35-37 This is a subject to keep your eye on as much research is being done.

As for systemic conditions that might be the underlying cause of a CI, the main culprits are Grave’s, Myasthenia Gravis and Parkingson’s disease.^38-40

 

Treatment options:

Now that you have a good understanding of CI signs and symptoms, you’re probably asking “What is the best way to treat it?”  The core of the CITT studies was to determine the most effective and efficient way to treat CI. They compared performing office-based therapy with at home supplemental therapy, placebo office-based therapy, home-based computerized home therapy with pencil push ups and just pencil push-ups.

The most effective treatment? In office therapy with home supplemental therapy that utilized tradition methods as well as computed based training.

 The second best? Home-based computerized therapy with pencil push-ups.  This treatment was monitored closely with frequent follow-ups.

Both of these showed the long-term effects at the 6 and 12-month mark. ^41-43 More studies are being done to provide further support of the effects of office therapy.

 

Final words:

With this condition being so prevalent I encourage all of you to know CI and know it well. Test for it, recognize it, and treat it (or refer to someone who can!).

Here is the link to the full article:

http://coopereyecare.com/studies/CI%20Major%20Review%20copy.pdf

 

References

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