BASICS

DESCRIPTION

The inability to converge the eyes smoothly and effectively from distance to near and/or the inability of maintain the convergent near point.

EPIDEMIOLOGY

Prevalence

Reports vary from 1–25% of the population.

RISK FACTORS

Like many strabismic conditions, symptoms are aggravated by stress, illness, or lack of sleep.

Genetics

No specific gene or locus known, although there are complex genetic influences on fusional amplitudes, version amplitudes, and AC/A ratio.

GENERAL PREVENTION

Avoidance of near tasks prevents symptoms but there is no prevention for the disorder.

PATHOPHYSIOLOGY

• Ineffective muscular action on attempted convergence results in an inability to maintain proper binocular alignment on visual objects as they approach from distance to near. This causes an exophoria or intermittent exotropia at near.

• The increased convergence effort and/or the increased accommodative effort facilitated in the attempt to maintain ocular alignment causes a variety of symptoms ranging from mild to severe.

• Particularly distressing is when the divergent strabismus causes binocular diplopia at near.

• Symptoms result from sustained effort to increase fusional convergence.

ETIOLOGY

• Our current understanding suggests an innervational etiology because of the dramatic response to treatment both in the patient’s subjective improvement and the objective measurements of near point of convergence and fusional convergence amplitudes.

• The symptoms of convergence insufficiency are directly related with reading or other near vision tasks.

COMMONLY ASSOCIATED CONDITIONS

Closed head trauma and lesions in the pretectal area or the dorsal midbrain have been associated with acquired convergence insufficiency.

DIAGNOSIS

HISTORY

• Headaches – occurring during reading or after long periods of reading but may not be associated with reading at all. Frequently located in the frontal or periocular area. Can potentiate other underlying headaches such as migraines.

• Asthenopia – can manifest as tired, strained eyes or eyes that hurt or feel sore with near work. Some patients describe a pulling or pressure sensation around the eyes.

• Difficulty with reading/near tasks – patients describe intermittent blurriness of the words, print moving on the page, frequently losing their place, lack of concentration, or difficulty with comprehension. Increased time at the near task usually increases symptoms. Some patients will not describe symptoms at near because of their strong avoidance of near tasks.

• Diplopia – can present as 2 distinct images or an overlap of images. Many patients will have difficulty deciphering the double images and will complain of blur. Some patients will close one eye to read to relieve the diplopia.

PHYSICAL EXAM

• Complete eye examination including cycloplegic refraction to rule out other causes of symptoms (e.g., papilledema due to increased intracranial pressure causing headaches, high hyperopia causing convergence spasm)

• Measure near point of convergence. Have the patient fixate on a near target as the target is slowly moved toward the patient’s eyes. The eyes will converge until a point is reached when the eyes will deviate from a convergent position to a divergent position. The point prior to the divergent deviation is the near point of convergence. In a normal child this point should be 4 cm or closer to their nose.

• Assess the ability to converge. Look for increased effort with convergence manifesting as a slow and/or jerking movement rather than a smooth consistent movement seen in normal convergence.

• Look for inability to maintain near fixation.

• Measure fusional amplitudes. Look for low fusional convergence amplitudes. Have the patient fixate on a line of Snellen letters and add base-out prism in a slow, gradual manner. Diplopia will occur when fusion is no longer possible. The amount of prism added is the measurement of fusional convergence.

• Assess for strabismus at near by alternate cover test. Most commonly, exodeviations at near including exophoria, intermittent exotropia, or a constant exotropia.

– Lack of a strabismus at near or even a mild esophoria has been observed.

– Some patients will have a reduced stereoacuity.

DIAGNOSTIC TESTS & INTERPRETATION

Imaging

Initial approach

No initial imaging necessary if accommodation and pupillary reflexes are intact.

Follow-up & special considerations

Consider neuroimaging if symptoms and clinical measurements fail to improve with orthoptic therapy or if other neurologic indicators present or severe recalcitrant headaches especially if vomiting or waking from sleep or other constitutional symptoms (e.g., weight loss).

DIFFERENTIAL DIAGNOSIS

• Patients with high-uncorrected hyperopia will make little or no effort to accommodate as the demand outweighs their accommodative ability

• Some myopic patients have little need to accommodate to maintain clear vision at near.

• First-time bifocal wearers will get relief of their sustained accommodative convergence by the bifocal segment which can initiate an exophoria and other symptoms of convergence insufficiency.

• Accommodative insufficiency can be associated with convergence insufficiency. These patients usually have more severe symptoms and can be less responsive to treatment. Causes include febrile illness, viral encephalopathy, closed head trauma, and anticholinergic drugs.

• Convergence paralysis is a distinct clinical entity. The patient is unable to converge but maintains normal adduction and manifests diplopia at near. Normal accommodation and pupillary reflexes are present on attempted convergence. Results most commonly from head trauma but can be seen with encephalitis, midbrain lesion, and other intracranial pathology.

• Headaches can be from a wide variety of causes including brain tumor, migraine, and convergence spasm.

TREATMENT

MEDICATION

First Line

• Orthoptic therapy/computer orthoptics – There is recent strong and persuasive evidence to support its use for treatment for convergence insufficiency. (1)[A] The patient performs vergence/ accommodative therapy with a series of exercises using lenses, prisms, and stereograms. Recently, computerized orthoptics programs are used to perform similar exercises.

• Pencil push-ups/accommodative target – have been used as a mainstay of treatment. Despite their widespread use, very limited studies have evaluated their effectiveness. (2) [B] In this exercise, the patient is instructed to maintain single vision as a target (commonly the letters on a pencil are used for fixation) is moved toward their eyes. The patient then sustains the closest fixation possible before diplopia occurs.

Second Line

Base-in prism reading glasses – have been shown to decrease symptoms of convergence insufficiency in the presbyopic population. (3)[A]

ADDITIONAL TREATMENT

Additional Therapies

• Bifocal glasses (plus lenses) can be used to reduce symptoms as they magnify the print and lessen the need for accommodation and its related convergence. This therapy may worsen the convergence insufficiency in some patients due to lack of accommodative demand.

• Over-minus glasses (glasses with excessive myopic correction for the patient) can be used to stimulate accommodation and its related convergence. This may intensify the symptoms in some patients.

SURGERY/OTHER PROCEDURES

Eye muscle surgery (typically unilateral or bilateral medial rectus resection) should be reserved for only the most protracted cases. The decision to proceed with surgery should be made only after all nonsurgical treatment efforts have failed.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Nonsurgical therapy will need to be continued until symptoms are controlled and convergence is well maintained at the near point.

Patient Monitoring

• Improvement in symptoms at near tasks, especially reading

• Reduction of headaches with near tasks

• Resolution of diplopia at near

PATIENT EDUCATION

• Inform the patient that the symptoms will reoccur with time and therapy may need to be restarted periodically.

• During the presbyopic years it may be difficult to differentiate if the symptoms at near are secondary to the normal loss of accommodation or the recurrence of the convergence insufficiency.

PROGNOSIS

Excellent prognosis with reduction or elimination of symptoms with treatment.

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