Convergence insufficiency (CI) is a syndrome in which the ability to turn both eyes inward (converge) when focusing on a near target is reduced, making it impossible to maintain binocular fusion. It is a condition in which accommodative convergence (convergence that occurs with the activation of accommodative effort) and fusional convergence (convergence that occurs to align the images from the retinas of both eyes) are insufficient, resulting in inadequate convergence movement. It is characterized by a receded near point of convergence (NPC), reduced convergence amplitude, and exophoria at near (typically greater than 10 prism diopters [∆]).
Convergence disorders are classified into the following three types.
| Type | Definition | Features |
|---|---|---|
| Functional convergence insufficiency | A syndrome characterized by receded near point of convergence, decreased convergence amplitude, and near exophoria | Most common. May be accompanied by accommodative dysfunction. |
| Convergence paralysis | An organic disease with acute onset where convergence becomes completely impossible | Caused by midbrain dorsal syndrome such as pineal tumor. Head MRI is essential. |
| Convergence spasm | Convergence abnormality with excessive adduction and miosis of both eyes. Often psychogenic. | Differentiation from pseudo-sixth nerve palsy is important. |
It occurs in almost all age groups but is most common in young adults. Prevalence varies widely between studies from 1.7% to 33%, and the incidence in the general population is estimated at 0.1–0.2%. CI is found in 11–19% of children with exophoria. There is no gender difference. CI accounts for about 15.7% of adult-onset strabismus. It also tends to occur in VDT workers, those engaged in near work, and schoolchildren/students.
In general, CI does not improve naturally. However, the severity of symptoms varies with the amount of near work. CI after concussion may improve over time.
The annual incidence of CI is estimated at 8.4 per 100,000 people. CI is found in 11–19% of children with exophoria, and symptoms often become apparent after starting school when near work increases (ages 7–10). In modern society where VDT work is common, adult CI is also increasing 5).
It is most common in young adults, but occurs across a wide age range from children to the elderly. CI is seen in 11–19% of children with exophoria, and accounts for about 15.7% of new-onset strabismus in adults. It is common among VDT workers and those engaged in near work, and also occurs in school-age children and students.
Subjective symptoms of CI worsen with near work. They become noticeable with prolonged use of reading, computers, smartphones, etc.
In functional convergence insufficiency, patients complain of severe eye strain during near work. Because accommodation and convergence ability are reduced, prolonged near work leads to exotropia at near, crossed diplopia, sensory abnormalities, and eye strain.
The CISS (Convergence Insufficiency Symptom Survey) developed by the CITT group consists of 15 questions answered on a Likert scale, quantifying symptom severity with a score from 0 (best) to 60 (worst). A score of 16 or higher is considered significant. Reliability has been validated in children aged 9–18 and adults.
Unlike functional convergence insufficiency, convergence paralysis presents with acute onset of inability to converge, resulting in exotropia only at near and diplopia. Adduction is possible and there is no restriction of eye movement, but convergence is impossible. Therefore, exotropia and crossed diplopia occur at near. An important distinguishing feature is that diplopia occurs only at near and not at distance.
The CISS, developed by the CITT group, is a standard patient-reported outcome measure that quantifies the severity of convergence insufficiency symptoms. It consists of 15 questions answered on a Likert scale (0–4 points), with a total score ranging from 0 to 60 1).
Representative question items:
A CISS score of 16 or higher is considered the threshold for significant symptoms. The reliability of repeated measurements in the same patient (ICC 0.87) and sensitivity to changes before and after treatment intervention have been confirmed, and it is used in both clinical trials and daily practice 2). Using the amount of score improvement (treatment effect indicator: a decrease of 6 points or more) when explaining to patients helps in sharing treatment goals.
The following four items are used as diagnostic criteria for CI.
| Test Finding | Abnormality Threshold |
|---|---|
| Receded Near Point of Convergence (NPC) | ≥6 cm (pre-presbyopic) / ≥10 cm (presbyopic) |
| Exophoria at near | >10∆ |
| Decreased Positive Fusional Vergence (PFV) | Near <15~20∆ |
| CISS score | ≥16 points (subjective symptoms) |
The Convergence Insufficiency Symptom Survey (CISS) is a 15-item Likert scale questionnaire that quantifies the severity of CI symptoms from 0 to 60 points. A score of 16 or higher is considered the threshold for suspecting CI, and it is also used to evaluate treatment effectiveness. Its reliability has been validated in children aged 9 to 18 years and in adults.
Primary CI
Congenital imbalance of convergence and divergence: Due to differences in innervation, the ability to converge for near vision is limited.
Insufficient fusional convergence: CI mainly results from incomplete fusional convergence (the convergence that occurs to align the retinal images of both eyes).
Acquired CI
Convergence insufficiency with accommodative dysfunction: Excessive near work and VDT (visual display terminal) work reduce accommodative function, leading to insufficient accommodative convergence and fusional convergence.
Fatigue and excessive near work: It tends to occur in people who engage in prolonged VDT work (technostress eye strain) or near work.
Medications and systemic diseases: Anticholinergic drugs, uveitis, post-concussion, and CNS diseases such as Parkinson’s disease can be causes.
Trauma and others: Head trauma, glasses that induce a base-out prism effect, and encephalitis can also be causes.
Convergence is composed of four components (Maddox classification).
| Type of convergence | Description |
|---|---|
| Accommodative convergence | Convergence induced by accommodative effort. Expressed as the AC/A ratio. |
| Fusional convergence | Voluntary convergence to align retinal images from both eyes. |
| Proximal convergence | Convergence due to perceived proximity of the target (other than disparity). |
| Tonic convergence | Convergence for maintaining sustained eye position at rest. |
In CI, fusional convergence is primarily insufficient, but may also be accompanied by decreased accommodative convergence (CI with accommodative dysfunction). The relationship between convergence and accommodation is not proportional but exists within a certain range. Prolonged near work in inappropriate environments can disrupt this relationship, leading to persistent impairment of accommodation and convergence.
Convergence paralysis is caused by organic lesions. The dorsal midbrain syndrome, mainly due to tumors near the cerebral aqueduct (especially pineal tumors), demyelination, inflammation, and vascular lesions, is known. Unlike functional convergence insufficiency, it is an acute-onset emergency requiring neuroimaging.
A direct causal relationship has not been established, but prolonged VDT work can impair convergence and accommodation functions, worsening CI symptoms. It is recognized as technostress eye strain, and it is recommended to limit continuous VDT work to one hour, followed by a 10-15 minute break.
The diagnosis of CI is based on subjective symptoms and the following clinical examination findings. A comprehensive sensorimotor examination, assessment of refractive status, and dilated fundus examination are recommended.
The main examination methods are shown below.
| Examination | Method Overview | Abnormal Value Threshold |
|---|---|---|
| Near Point of Convergence (NPC) | Move fixation target from 40-50 cm toward the nose | ≥6 cm (pre-presbyopic) / ≥10 cm (presbyopic) |
| Positive Fusional Vergence (PFV) | Measured with base-out prisms | Near <15-20∆ |
| AC/A Ratio | Heterophoria method or gradient method | <2:1 |
A target such as a finger or toy is moved slowly from a position 40–50 cm in front of the face, slightly below the horizontal, toward the bridge of the nose. The distance from the bridge of the nose to the point where the target appears double or one eye deviates outward (break point) is measured. Normal value is approximately 6–8 cm. Repeated measurement of accommodative and convergence functions is useful for diagnosis; a gradual increase in the near point with repeated testing also suggests convergence insufficiency.
It is important to perform this test under full refractive correction. In the heterophoria method, the AC/A ratio is calculated from the difference in strabismus angle between distance (5 m) and near (33 cm). Normal value is approximately 4 ± 2, and it is low in convergence insufficiency.
Using a major amblyoscope, rotary prism, Bagolini striated lens, etc., the range of convergence that maintains binocular single vision while keeping accommodation constant is measured. In fusional range measurement with a major amblyoscope or base-out prism, even if initial fusional convergence is sufficient, the near point of convergence may be extended.
In convergence paralysis, adduction is possible during eye movements, but convergence movement is completely absent. When measuring the fusional range with a major amblyoscope or base-out prism, the fusional range in the convergence direction is almost unmeasurable, which is an important distinguishing point from functional convergence insufficiency.
Since the pupillary light reflex is normal, light-near dissociation (normal light reflex but absent near response [miosis, accommodation, convergence]) is observed. Acute-onset convergence paralysis requires prompt neuroimaging (e.g., head MRI) to rule out intracranial lesions.
| Disease | Key points to differentiate from CI |
|---|---|
| Convergence paralysis | Acute onset, fusional range almost unmeasurable, light-near dissociation, head MRI required |
| Convergence spasm | Extreme bilateral adduction, miosis, limitation disappears with monocular occlusion, associated accommodative spasm |
| Divergence paralysis | Increased esotropia at distance; near deviation within normal range |
| Abducens nerve palsy | Monocular abduction limitation (CI involves bilateral convergence insufficiency) |
| Dry eye / accommodative dysfunction | Near symptoms and asthenopia are similar, but NPC and fusional vergence are normal |
Treatment of CI is performed stepwise according to severity and type. First, confirm the type and evaluate the presence of accommodative dysfunction, then determine the treatment plan.
If accommodative dysfunction is present, convergence training may worsen asthenopia. Therefore, it is important not to perform convergence training. Prioritize environmental improvement: limit continuous VDT work to 1 hour, followed by a 10–15 minute break.
Refractive correction is performed in all cases. After cycloplegic refraction (e.g., using Mydrin P ophthalmic solution), prescribe near-vision glasses tailored to the actual VDT working distance. Intermediate-near progressive lenses are acceptable, but distance-near bifocals or progressive lenses are not recommended because the near segment is too small. If dry eye is present, use artificial tears or hyaluronic acid eye drops.
In functional convergence insufficiency without accommodative dysfunction, combine convergence training, prism glasses, and surgery based on refractive correction.
In CI without accommodative dysfunction, convergence training improves fusional convergence. It is important to perform it daily, even for a short time. Home convergence training (e.g., pencil push-ups, convergence cards) tends to be less effective than in-office therapy, but in symptomatic children with CI, home training alone has been shown to provide improvement 6).
Home Training
Pencil push-ups: Focus on a small target and slowly bring it toward the nose while maintaining single binocular vision.
Convergence card: Hold the card at the bridge of the nose and shift gaze from the farthest point gradually to nearer targets.
Stereograms: Cross-view two horizontally separated images to produce a third fused image in the center.
In-office training
In-office vision therapy: Intentionally and controllably manipulate target blur, disparity, and proximity to eliminate suppression and normalize convergence and accommodation.
Computer vergence training (CVS): A program using random-dot stereograms that gradually increases the required convergence amount, allowing progress monitoring.
A Cochrane systematic review by Scheiman et al. (2020) of 12 RCTs (1289 participants) showed “high-certainty evidence” that in-office therapy with home reinforcement produces better convergence ability in children than pencil push-ups alone or computer therapy 2). Children treated with base-in prism reading glasses showed no significant improvement 2). In adults, base-in prism glasses improved symptoms but not convergence ability 2). In young adults aged 19–30, in-office training was more effective than home training for improving positive fusional vergence (PFV), but no significant differences were found in NPC or patient symptoms 1).
Success rates and long-term outcomes of convergence training
Reported success rates for in-office convergence training are 70–80%, and many patients remain asymptomatic one year after discontinuing treatment 1). However, recurrence rates have also been reported, and regular follow-up is recommended, especially in cases of high CI, post-concussion CI, and CI with accommodative dysfunction.
In the CITT study (2005), 73% of children who received in-office convergence training (1 session/week plus 12–24 hours/week of home training) achieved a CISS score ≤15 (normalization), compared to only 43% with pencil push-ups alone 4). This result provides evidence that supervised in-office convergence training is superior to home training alone.
The Cochrane review noted that evidence for treatment of CI in adults is limited compared to children, and further research is needed 2). For post-concussion CI, no standardized protocol has been established, and individual balancing of active training and rest is necessary 1).
Prescribed when convergence training is ineffective or in cases of convergence paralysis. Use the minimum prism amount necessary to achieve comfortable binocular single vision at near. Incorporate 2–4∆ base-in prisms in each eye (total 4–8∆ correction) into the near vision refractive correction glasses and perform a wearing test to determine the optimal prism power 7). Long-term wear may be necessary regardless of the underlying disease. In adults with presbyopia, base-in prisms may be effective 7).
In convergence paralysis, improvement can be expected if the underlying disease is treated effectively. Meanwhile, prescribe base-in prism glasses for near vision to symptomatically reduce diplopia. For underlying diseases such as pineal tumors, demyelinating diseases, and vascular lesions, treatment in collaboration with neurology and neurosurgery is necessary.
Detailed Protocol for Convergence Training
The standard protocol for convergence training for functional CI without accommodative dysfunction is shown below 2).
| Training Type | Method | Target Frequency |
|---|---|---|
| Pencil Push-up | While fixating on a pencil with both eyes, bring it toward the bridge of the nose. Stop just before double vision appears, hold for 5 seconds, and return. 10 repetitions per set. | 3–5 sets per day |
| Convergence Card (Brock String) | Attach three beads at equal intervals on a 70 cm string, and train convergence stepwise by gazing at each bead sequentially from the nearest. | 2 times per day, 5 minutes each |
| In-office Vision Training | Gradual loading of convergence and accommodation. Use vectograph, convergence card, and Brewster stereoscope. | 1–2 times per week (total 12–16 weeks) |
| Computer training (HTS) | Gradually increase convergence using a binocular vision program on screen. Progress is confirmed by automatic recording. | 15–20 minutes per day |
It is important to perform convergence training daily; even short sessions continued consistently are key to long-term success. The treatment goal is to improve the CISS score to 16 or less, NPC to 5 cm or less, and PFV to 20∆ or more 1).
CI with accommodative dysfunction should be treated as a separate condition 1).
Additional diagnostic check items:
In the treatment of CI with accommodative dysfunction, environmental improvements and spectacle prescription take priority before convergence training. Near-vision glasses (addition of +0.75 to +1.25 D) may reduce accommodative load and contribute to symptom improvement.
Surgery is indicated for refractory CI or CI with intermittent exotropia.
Indications for surgery: manifest deviation at distance, consistent symptoms, and failure of prism glasses.
Main surgical procedures include bilateral lateral rectus recession (based on distance deviation angle), bilateral medial rectus resection (based on near deviation angle), and unilateral lateral rectus recession with medial rectus resection 8). Botulinum toxin injection is also an option for refractory cases.
The reported success rate of convergence training is 70–80%, and most patients remain asymptomatic even one year after discontinuing treatment. However, convergence training is contraindicated in convergence insufficiency with accommodative dysfunction; environmental improvements and spectacle prescription should be prioritized. Even when training is performed, the maintenance of effects varies among individuals, so regular follow-up is recommended.
The exact disease mechanism of CI is not fully understood, but the neural centers controlling convergence movements have been identified.
This condition is based on accommodative dysfunction, where both accommodative convergence and fusional convergence become insufficient, resulting in inadequate convergence movement. The relationship between convergence and accommodation is not proportional but exists within a certain range. Prolonged near work in inappropriate environments gradually leads to persistent decline in accommodative and convergence functions. Technostress eye strain due to VDT work is a typical example.
Improvement of the VDT work environment, wearing appropriate glasses, and instillation of artificial tears are effective.
Convergence paralysis is primarily an organic disorder due to dorsal midbrain syndrome. Lesions near the cerebral aqueduct damage the convergence center. The pupillary light reflex is preserved, but the near response (miosis, accommodation, convergence) is impaired, resulting in light-near dissociation. Unlike functional convergence insufficiency, the fusional range in the convergence direction is almost unmeasurable, which is characteristic.
Divergence insufficiency is characterized by increased esotropia at distance, contrasting with the near exophoria of CI. The adult strabismus PPP clearly outlines the differential diagnosis flow between divergence insufficiency and convergence paralysis, and both conditions require exclusion of organic lesions (elevated intracranial pressure, central nervous system disorders) 1).
In divergence insufficiency, the main complaint is horizontal diplopia at distance, which is reduced or disappears at near. This contrasts with the near diplopia of CI, and history taking is the first step in differentiation. In differentiation from abducens nerve palsy, the presence or absence of monocular abduction limitation is important; note that both CI and divergence insufficiency are disorders of binocular convergence and divergence movements 1).
CI occurs in association with several neurological disorders.
Convergence eye movements are integratively controlled by multiple nuclei in the midbrain and pons. The main neural structures involved in convergence are as follows:
In convergence paralysis, dorsal midbrain syndrome (Parinaud’s syndrome) may be accompanied by upward gaze palsy, convergence-retraction nystagmus, and light-near dissociation. Pineal tumors, demyelination, hemorrhage, and trauma are the main causes; in acute-onset convergence paralysis, detailed evaluation with head MRI is essential1).
In functional convergence insufficiency, no organic lesion is found, but accommodative muscle fatigue due to prolonged near work and functional overload of the convergence center are considered central to the pathology. In the modern era of rapidly increasing digital device use, the rise in CI in the context of technostress eye strain (VDT syndrome) has become a concern.
The Convergence Insufficiency Treatment Trial – Attention and Reading Trial (CITT-ART) was a randomized multicenter clinical trial that examined whether treatment for symptomatic CI improves reading ability in children aged 9 to 14 years.
Participants were randomly assigned to office-based vergence/accommodative therapy or office-based placebo therapy. After 16 weeks, CISS scores showed no significant difference between the two groups, and office-based vergence/accommodative therapy was not more effective than placebo therapy in improving reading ability in children with symptomatic CI 3).
This result suggests that even if CI treatment improves convergence ability and symptoms, it may not directly lead to improved reading ability.
Several ophthalmology experts have pointed out methodological limitations of the 2005 CITT 4). The office-based treatment group was prescribed significantly longer treatment time than the other groups (inequality of treatment dose). Additionally, there is criticism that “pencil push-ups” do not accurately represent traditional vision therapy, which includes a variety of exercises using accommodative targets 4).
Spontaneous remission of symptoms has been reported in CI patients. Therefore, it is considered important to include a placebo group when evaluating treatment effects 5). CI is found in 11–19% of children with exophoria, and the annual incidence of CI is estimated at 8.4 per 100,000 people 5).
Although the CITT-ART (2019) showed that vergence/accommodative therapy did not improve reading ability 3), this does not mean that CI treatment is not useful. Improvements in CISS scores and near point of convergence were observed; only the impact on the composite outcome of reading ability was limited. Office-based vergence training significantly improved CISS scores (treatment group: 16.0→9.0, placebo group: 16.0→12.5), and this improvement directly contributes to patient quality of life 3).
Setting improvement in children’s reading ability as the primary endpoint was a unique strength of CITT-ART, but there is also criticism that reading ability is influenced by multiple factors such as learning environment, cognitive function, and attention, making it inherently difficult to capture improvement from vergence training alone 1).
CI after sports-related concussion (SRC) is increasingly recognized as a special subtype of symptomatic CI. The characteristics of post-concussion CI are as follows 1):
It is important to incorporate CI assessment and management into the return-to-sports protocol, and collaboration between ophthalmology and sports medicine is beneficial1).
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Scheiman M, Mitchell GL, Cotter S, et al. A randomized clinical trial of treatments for convergence insufficiency in children. Arch Ophthalmol. 2005;123:14-24.
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