eMedicine Specialties > Ophthalmology > Extraocular Muscles

Convergence Insufficiency

Michael J Bartiss, OD, MD, Medical Director, Ophthalmology, Family Eye Care of the Carolinas
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Updated: Jun 29, 2007

Introduction

Background

Convergence insufficiency is a common condition that is characterized by a person's inability to maintain proper binocular eye alignment on objects as they approach from distance to near. There is typically an exophoria or intermittent exotropia at near, a receded near point of convergence, reduced positive fusional convergence amplitudes, and a low accommodation convergence/accommodation (AC/A) ratio. The symptoms associated with convergence insufficiency vary from mild to severe, but they are often extremely troublesome for patients with this condition, especially when associated with a small angle exotropia at the near working distance.

Pathophysiology

The underlying etiology for convergence insufficiency is probably innervational. The dramatic reduction of symptoms demonstrated by patients after undergoing appropriate therapy, which is accompanied by objective clinical findings of improved near point of convergence and fusional convergence amplitudes, strongly supports this hypothesis.

Some cases of convergence insufficiency also appear to have an etiologic connection to accommodative dysfunction.

Convergence insufficiency is associated most commonly with an exophoria binocular posture at near, but patients with this disorder may demonstrate orthophoria or even mild esophoria at the time of their examination. The reasons for this variability are described within this article.

In the past, many ophthalmologists considered convergence insufficiency and its associated symptoms to be a neurotic manifestation of nonrelated psychological problems best dealt with by a psychiatrist. However, it is now clear that convergence insufficiency is a legitimate, problematic binocular dysfunction. The clinician must consider whether the behavioral manifestations displayed by patients really result from the frustration caused by their inability to perform desired near visual tasks.

Frequency

United States

The prevalence of convergence insufficiency has been reported to be approximately 3-5% of the population. Incidence increases with additional near work demand. The disorder is rare in children younger than 10 years; however, the increased visual demands of schoolwork and prolonged periods of reading exacerbate symptoms in older children. Indeed, many patients with this disorder have vocational and/or avocational visual demands that require prolonged close work. The most common presentation encountered by a clinician is that of a high school or college student who develops symptoms when excessive demands are placed on the visual system during extended periods of studying. Lack of sleep, illness, and anxiety are known to aggravate the problem.

International

The prevalence of this condition is the same as in all industrial societies.

Mortality/Morbidity

The morbidity of convergence insufficiency relates to the near point visual demands of the patient's activities. Headaches, fatigue, frequent loss of place when reading, as well as frank binocular diplopia associated with near point tasks are among the symptoms associated with this condition.

Race

No racial predilection exists for convergence insufficiency.

Sex

No sexual predilection exists.

Age

The frequency of symptoms may increase with age as patients' ability to compensate for their relative divergent binocular alignment decreases with time.

Clinical

History

Patients typically present as teenagers or in early adulthood, complaining of gradually worsening eyestrain, periocular headache, blurred vision after brief periods of reading, and, sometimes, crossed diplopia with near work. It is not unusual for the patient to squint one eye while reading to relieve blurring or diplopia. Few, if any, symptoms are present at distance fixation. Symptoms are aggravated by illness, lack of sleep, anxiety, and prolonged near work. Untreated, the exophoria at near may break down to a poorly controlled intermittent exotropia. Fortunately, in most cases, convergence insufficiency is very amenable to orthoptics and vision therapy.

• The symptoms of convergence insufficiency are directly associated with reading or other close work visual demands. Many patients with objectively measured convergence insufficiency may not complain of symptoms. This usually occurs because of suppression of the nonfixating eye or avoidance of near vision tasks. The clinician should inquire about any such avoidance behavior in patients who are not experiencing any symptoms but who have clinical objective findings consistent with convergence insufficiency. The most common symptoms associated with convergence insufficiency include asthenopia (eyestrain) and headache, diplopia, blurred vision, and perceived moving of print when reading.
• Asthenopia (eyestrain) and headache
  
  
  • These symptoms were described clearly by von Graefe as early as 1855. Classically, such symptoms occur after short periods of reading or other close work. This most commonly occurs due to the sustained increased effort required to increase fusional convergence.
  • Accommodative insufficiency is often associated with convergence insufficiency and symptoms of asthenopia and headache. This occurs as the patient tries to eliminate near vision diplopia by increasing accommodative effort. The increased accommodative effort results in increased convergence, which may be more than what is required for the near vision task, thereby resulting in an esophoria (as mentioned above). This also explains why the frequent accompaniment of blurry vision and diplopia with asthenopia and headache symptoms occurs.
• Diplopia
  
  
  • The diplopia that manifests in some patients with convergence insufficiency may present as 2 distinct images or just on overlap of 2 images. This distinction may be difficult for the patient to decipher, and it may be reported only as blurry vision. Proper testing can distinguish the 2 entities; test for blurry vision monocularly.
  • Patients with uncorrected hyperopia in excess of 5.00 diopters (D) may produce little or no accommodative effort at near. Patients with mild-to-moderate myopia do not need to stimulate accommodation to see clearly at the near working distance. This lack of accommodative effort results in decreased accommodative convergence.
  • Patients with early treated presbyopia often demonstrate convergence insufficiency. The relief provided by plus lenses at near is thought to translate to an inappropriate abandonment of appropriate accommodative effort. This results in decreased accommodative convergence and the manifestation of an exophoria that previously was partially compensated by using accommodative convergence.
  • Some patients with convergence insufficiency do not have symptoms of diplopia despite an obvious exodeviation at near. This probably occurs because of suppression of the nonfixating eye.
• Blurred vision
  
  
  • Patients with uncorrected hyperopia in excess of 5.00 D may produce little or no accommodative effort at near. This lack of accommodative effort results in blurry near images.
  • Efforts to primarily increase convergence through stimulation of accommodative convergence to eliminate diplopia can cause blurry vision by simultaneously producing blurred near vision via over-accommodation.
• Moving of print: This occurs because of fluctuating binocular alignment relative to the reading material. This usually occurs when the patient tries to bring in enough fusional convergence to maintain binocular vision.

Physical

The diagnosis of convergence insufficiency is based on the findings of a reduced convergence near-point along with decreased positive fusional convergence amplitudes at near.

• Remote near point of convergence: Patients should be able to maintain fixation on a fusional target as it is brought up to at least 5 inches from the tip of the nose.
• Significant exophoria or intermittent exotropia at near: Rarely, patients are orthophoric or even exhibit a small degree of esophoria at near, but all have a remote near point of convergence.
• Patients may demonstrate small-to-nonexistent exophoria at distance.
• Patients may demonstrate reduced stereoacuity at near.
• Normal near point of accommodation may be present in many patients.

Causes

The causes of convergence insufficiency are not completely clear. A connection has been made between accommodative insufficiency and convergence insufficiency. A significant exophoria at near with inadequate fusional convergence appears to be the primary underlying problem. Von Graefe, who first described the condition in 1855, believed that this condition was myogenic in etiology, but subsequent electromyographic work has failed to demonstrate support for this theory. Closed head trauma and lesions in the pretectal area of the brain have been associated with acquired convergence insufficiency. Lesions in the midbrain dorsal to the third cranial nerve nuclei may cause convergence insufficiency with normal third nerve function.

References

• Diplopia
• Exotropia, Acquired
• Myasthenia Gravis
• Oculomotor Nerve Palsy