What is convergence insufficiency

Convergence insufficiency is the inability to keep the two eyes working together, to converge the eyes and maintain binocular fusion while focusing on a near target. In convergence insufficiency, eye misalignment occurs when focusing at near target. Typically, one eye will turn outward (intermittent exotropia) when focusing on a word or object at near. Patients often complain of eye strain when reading, closing one eye when reading, or blurred vision after short periods of near work. Convergence insufficiency has a reported prevalence among children and adults in the United States of 2.5 to 13% ¹.

Occasionally, a well controlled intermittent exotropia (outward eye turning) will be present at near and distance in a patient with convergence weakness; however, in convergence insufficiency the deviation is symptomatic and occurs spontaneously only when focusing on near objects.

Symptoms of convergence insufficiency include diplopia (double vision) and headaches when reading. Many patients will complain that they have difficulty concentrating on near work (computer, reading, etc.) and that the written words will move around and become blurry after prolonged periods of reading. Patients may be noted to squint or close one eye when reading. Symptoms can vary with convergence insufficiency and not all symptoms are present in every patient.

Convergence insufficiency is diagnosed by an ophthalmologist, optometrist or orthoptist after obtaining a history of the patient’s symptoms and measuring convergence ability. The examination includes determining the distance from the eyes that the patient can hold the eyes together without double vision (near point of convergence) and the amount of prism that can be placed in front of the eyes at a particular distance before double vision is seen (fusional vergence amplitude). Presence of any refractive errors, eye muscle dysfunction, or weaknesses in accommodation (near focusing) should also be evaluated.

During a routine eye examination, convergence weakness may be diagnosed even without the above-mentioned symptoms. Some patients test in the office as having poor convergence; however, they are asymptomatic. This may be the result of true convergence weakness, but is often found when the patient is distracted, shy, overly excited or does not understand the directions given. These patients should either be retested at another time or simply watched for symptoms of diplopia or headaches with near work. A patient who is not having difficulty with near tasks but tests positive for convergence insufficiency in the office does not require any treatment but should be followed.

Conversely, a child with adequate convergence in the doctor’s office may occasionally have symptoms at home or school consistent with convergence insufficiency. In these cases, a course of treatment for convergence weakness can be instituted and the child followed for improvement in symptoms.

If convergence insufficiency isn’t causing symptoms, you generally don’t need treatment. But for people with symptoms, treatment with eye-focusing exercises can increase the eyes’ convergence ability.

Patients with convergence insufficiency are often permanently cured by practicing convergence through eye exercises to strengthen their convergence. These exercises may be prescribed by an orthoptist (a medical technician who is specifically trained in ocular muscle function and binocular vision) or by an ophthalmologist. There is also a computer program available which may be used on a home computer to increase convergence ability. The results of the computer program are often followed by your eye care professional with print outs that can be brought in to the office visit. Continued near work following convergence therapy tends to help maintain adequate convergence once treatment is discontinued. At times, convergence insufficiency symptoms will resurface after illness, lack of sleep or increased near work demands. If treatment had been successful previously, an additional course of treatment tends be successful at resolving recurrent symptoms.

Are there associated problems with vision in patients with convergence insufficiency?

Patients with convergence insufficiency usually have a normal range of refractive errors and good visual function. Testing for accommodative amplitude (the ability to focus each eye individually at near) is always performed by the specialist evaluating convergence insufficiency. Rarely, this is also found to be weak. If both accommodation and convergence are weak, reading glasses, sometimes with prism added, may be a great option for these patients. It is very difficult to improve accommodation with exercises.

Convergence insufficiency prognosis

Idiopathic convergence insufficiency responds very well to convergence exercises and has a very high reported success rate. Published success rates vary between 70 to 80% depending on the patient population and study size ².

Convergence insufficiency complications

Difficulties with reading and concentrating can affect a child’s learning. Convergence insufficiency does not cause learning disabilities, but it makes using your eyes difficult and tiring.

Convergence insufficiency causes

The cause of convergence insufficiency isn’t known, but it involves a misalignment of the eyes when focusing on nearby objects. The misalignment involves the muscles that move the eye. Typically, one eye drifts outward when you’re focusing on a word or object at close range.

Associated Disorders

Convergence insufficiency is also associated with several neurological disorders. Neuro-degenerative diseases affecting the basal ganglia, such as Parkinsons Disease, Progressive supranuclear palsy and Huntington’s Chorea have a higher incidence of convergence insufficiency ³. Lesions in the pretectum and posterior commissure can cause dorsal midbrain (Parinaud’s syndrome) which is also known to have a higher incidence of convergence insufficiency. Convergence insufficiency can also be associated with head trauma, myasthenia gravis, thyroid ophthalmopathy, chemical or pharmacological agents, or ischemia ⁴.

Convergence insufficiency symptoms

Not everyone with convergence insufficiency has signs and symptoms. Signs and symptoms occur while you’re reading or doing other close work and might include:

• Tired, sore or uncomfortable eyes (eyestrain)
• Headaches
• Difficulty reading — print moving on page, and frequent loss of place when reading ⁴ – words seem to float on the page, you lose your place or you read slowly, which might cause you to avoid reading or not complete schoolwork
• Double vision (diplopia)
• Difficulty concentrating
• Squinting, rubbing or closing one eye
• Blurred vision at near
• Eye fatigue, tension in and around the eyes

It is not unusual for a person with convergence insufficiency to cover or close one eye while reading to relieve the blurring or double vision. Symptoms will be worsened by illness, lack of sleep, anxiety, and/or prolonged close work.

Convergence insufficiency typically isn’t detected in routine eye exams or school-based vision screenings. Reading difficulties of children with the condition might lead to an evaluation for learning disabilities, but it’s important to rule out this eye disorder.

Convergence insufficiency diagnosis

People with convergence insufficiency might have otherwise normal vision, so it’s important to mention reading or learning concerns to your eye care provider. To diagnose convergence insufficiency, your eye doctor might:

• Take a medical history. This might include questions about problems you have with focusing, blurred or double vision, headaches, and symptoms.
• Measure the near point of convergence. This test measures the distance from your eyes to where both eyes can focus without double vision. The examiner holds a small target, such as a printed card or penlight, in front of you and slowly moves it closer to you until either you have double vision or the examiner sees an eye drift outward.
• Assess positive fusional vergence. During this test, you’re asked to read letters on an eye chart while looking through prism lenses. The examiner will note when you begin to have double vision.
• Perform a routine eye exam. If you have any other vision problems, such as nearsightedness, your eye doctor might conduct tests to assess the degree of the problem.

Convergence insufficiency treatment

Convergence insufficiency can often be treated by practicing convergence through exercises. These exercises may be prescribed by an orthoptist (a medical technician who is specifically trained in ocular muscle function and binocular vision) or by an ophthalmologist. There is also a computer program available which may be used on a home computer to increase convergence ability. The results of the computer program are often followed by your eye care professional with print outs that can be brought in to the office visit.

Which method of treatment will be used for an individual patient depends on the age of the patient requiring treatment, the proximity to an orthoptist or vision therapist and the preference of the patient. Important aspects to consider in choosing a treatment regimen are the convenience and expense of treatment as any method chosen tends to be successful if the prescribed regimen in followed. Most studies show that a short course of treatment is usually successful. Prolonged therapy does not show significant advantages and is usually unnecessary.

Occasionally, a patient will not respond to therapy. In these cases, prism glasses may be used for reading in order to artificially align the eyes and allow for more comfortable binocular vision. In rare cases, surgical intervention may be suggested.

One method of therapy to resolve convergence insufficiency is the use of base-out prisms which force the system to work harder to converge. They are used only during short periods of time while performing therapy as they are very tiring to the eyes.

Base-in prisms can be used to artificially align the eyes for reading; however, their use will make it unlikely that the patient will develop stronger convergence on their own.

Patching is not an option to strengthen convergence because wearing a patch will disrupt any ability to exercise binocular function (use the two eyes together). Occasionally, patients will patch one eye temporarily in order to relieve double vision during times when a large amount of near work is required.

Convergence insufficiency exercises

Conventional convergence exercises

There are two mechanisms used in conventional convergence insufficiency exercises to improve convergence amplitudes. Convergence insufficiency exercises can either utilize voluntary convergence or disparate retinal images to evoke fusional convergence. Voluntary convergence exercises include gradual exercises (pencil push-ups), jump convergence exercises and stereograms.

Gradual Convergence Exercises

Gradual exercises are performed by having the patient focus on a small target (usually an accommodative target) at a remote distance to acquire binocular single vision and then slowly move the target toward their nose while maintaining binocular single vision. This exercise requires the patient to be able to recognize physiologic diplopia. If a patient suppresses an image from one of their eyes, then a red filter can be used over one eye as an anti-suppression technique. Caution always needs to be taken when performing anti-suppression exercises to ensure intractable diplopia does not occur.

Convergence Cards

There are several different types of convergence cards that are used for convergence insufficiency and usually consist of dots or circles. The patient holds the card toward the bridge of their nose while focusing on the most remote dot or circle and progressively moves their eyes to a closer target. For example, ‘dots on a line’ creates an “X” crossing through the fixation dot. If a patient is suppressing then they will only see one line.

Stereograms

A stereogram is a card that consists of two similar images that are separated on the horizontal axis. The patient then converges their eyes to an area in front of the card in order to elicit physiological diplopia. If the patient is successful then a third image will appear in the middle of the two pictures on the card. The middle image is actually a superimposed, combined image of the two pictures ⁵.

Vergence facility exercises

Vergence facility is another type of exercise that has the patient look from a target at near to a target at distance with rapid fixation switches ⁴.

Base out prism exercises

Base out prisms can also be used to stimulate the converge reflex. The base out prism induces crossed diplopia and the patient must converge to overcome the prism strength and obtain binocular single vision. Some practitioners give a patient a single prism and have them do gradual exercises or near tasks, while other practitioners have the patient use a prism bar and to overcome increasing prism strengths while focusing on a near target.

Computer based convergence exercises

In recent years a new treatment method for convergence insufficiency has emerged. A computer based orthoptic program known as Computer Vergence System is used by many eye care professionals. The program uses random dot stereograms to form pictures that require bi-foveal fixation to stimulate the vergence system. The program gradually increases the amount of vergence required to appreciate the stereogram picture and can monitor progression online.

In-Office vision therapy

Eye care professionals will some times prescribe both in-office and home-based convergence insufficiency exercises. Occasionally patients will require additional treatment strategies such as anti-suppression or extra time and assistance with the exercises and will require in-office treatment. It is important to note that some of the treatment strategies used by behavioral optometrists are known as vision therapy and are not medically proven and are not supported by the American Academy of Ophthalmology, American Academy of Pediatric Ophthalmology and Strabismus or the America Academy of Pediatrics ⁶.

Base – In prism Glasses

Base-In prism glasses are sometimes prescribed if conventional convergence insufficiency exercises are unsuccessful. The practitioner will usually prescribe the least amount of prism necessary to achieve comfortable binocular single vision at near. Interestingly, a study by the Convergence Insufficiency Treatment Trial found that base-in prism glasses were no more effective than plano placebo reading glasses in children ⁷. However, additional studies have suggested that base-in prism glasses are effective at reducing convergence insufficiency symptoms in presbyopic patients ⁸.

Convergence insufficiency surgery

As a last option, some surgeons will perform a small medial rectus resection of one or both medial rectus muscles. This is somewhat controversial and some authors have shown poor results with this surgery ⁹. Prior to surgery it is important to determine divergence amplitudes at distance and test for post operative diplopia at distance. Patients should be fully advised of the risks of diplopia at distance after surgery.

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