Convergence Insufficiency

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Article initiated by:
Gregory I. Ostrow, MD FAAO FAAP, Laura Kirkeby, CO
All contributors:
Michelle Lin, Monica Sujeiry Morales, MD, Gregory I. Ostrow, MD FAAO FAAP, Mustafa R. Al-Hashimi, MD, Monte A Del Monte, MD, S. Grace Prakalapakorn, MD, MPH, Allison Umfress, MD, Angeline Nguyen, MD
Assigned editor:
Angeline Nguyen, MD
Review:
Assigned status Up to Date
 by Angeline Nguyen, MD on October 19, 2024.


Convergence Insufficiency
ICD-10
H51.1


Convergence Insufficiency (CI) is a syndrome characterized by a decreased ability to converge the eyes and maintain binocular fusion while focusing on a near target. CI is usually accompanied by a reduced near point of convergence (NPC), decreased convergence amplitudes or an exodeviation (usually > 10 prism diopters) at near. Patients often complain of eye strain, needing to close one eye when reading, or blurred vision after short periods of near work. The diagnosis of primary CI is based on the patient’s presenting symptoms and the aforementioned clinical signs.[1] [2] [3]

Etiology

Primary CI is thought to be caused by an inborn imbalance of vergence eye movements.[2][3] It is presumed to be an innervational difference that results in the limited capacity to converge with near demands. The Maddox components of vergence include tonic, proximal, fusional, and accommodative vergences. Tonic vergence describes the angle of vergence in the absence of a stimulus. Proximal refers to vergence stimulated by a perceived distance or depth. Fusional or disparity vergence utilizes feedback from retinal image disparity to maintain ocular alignment. Lastly, accommodative convergence describes the coupling relationship between stimulated convergence and the response to ensure clarity by accommodation.

Acquired etiologies of CI may include fatigue, drugs (parasympatholytic), uveitis, Adie tonic pupil, glasses inducing a base-out prism effect, encephalitis, or traumatic injury. [4]

Pathophysiology

Although the exact disease mechanism that causes CI is unknown, scientists have been able to discover the neurological centers that control convergence eye movements. The midbrain reticular formation is involved with controlling the velocity and amplitude during fusional and accommodative convergence movements. The nucleus raphe interpositus is associated with fast vergence movements, whereas the nucleus reticularis tegmenti pontis is activated during slow vergence movements.[5]

Prevalence 

Although CI can present at almost any age, it is most common in the young adult population. Prevalence range varies among studies, ranging from 1.7% to 33%. [6][7] The incidence of CI in the general population is estimated to be 0.1 to 0.2%.[2] While exodeviations are only present in 1% of the general population[8], CI is present in 11-19% of children with an exodeviation[9]. There does not appear to be a correlation between gender and CI.[10]

Clinical Diagnosis 

The most common signs of CI include the following:

  • Increased (or “remote”) near point of convergence (NPC):  The NPC is tested by having the patient focus on a near target while slowly moving the target towards their nose. An exotropia will occur when the patient can no longer maintain fusion. This is referred to as the break point.[11]  A near point of convergence greater than 6 cm from the bridge of the nose (for pre-presbyopes) or 10 cm from the bridge of the nose (for presbyopes) is considered increased and abnormal.[12]
  • Decreased convergence amplitudes: convergence amplitudes are measured with base out prisms while the patient focuses on a target at near. [11] Normal convergence amplitudes are 38 prism diopters at near and 14 prism diopters at distance.[13] In general, fusional convergence amplitudes of less than 15 to 20 prism diopters at near are a sign of convergence insufficiency. [11][14] It is important to measure the exodeviation in all positions of gaze to rule out any eye muscle imbalance that could make the exodeviation greater in downgaze. Measurements at near should be done in both primary position and reading position. Superior oblique over action can cause an exodeviation greater in downgaze and can be mistaken for CI.
  • Exodeviation at near:  patients will typically exhibit a large exophoria or intermittent exotropia, greater (≥4∆) at near than distance.


Other signs of CI include:

·      Low accommodative convergence/accommodation (AC/A) ratio <2:1[15]

·      Reduced positive fusional vergence (PFV) <15∆

·      High CI symptom Survey (CISS) score ≥16[16][17]

Symptoms

Symptoms of convergence insufficiency include eye strain, double vision (diplopia), headaches, blurred vision at near, eye fatigue (asthenopia), tension in and around the eyes, print moving on page, and frequent loss of place when reading. Younger children may exhibit behaviors such as eyelid rubbing, head shaking, palpebral narrowing, and closing of one eye [31]. These symptoms are exacerbated when doing prolonged near work, such as reading and computer or any other electronic device usage. [2][11][18]

The CITT group (Convergence Insufficiency Treatment Trial Investigator Group) developed a questionnaire to quantify the symptoms reported by the patients, the CISS (Convergence Insufficiency Symptom survey). This allows classification of the visual condition from suspected to definite. The overall score is obtained by a Likert type scale with responses from 15 items with symptom severity ranging from 0 (best) to 60 (worst). The CISS has been shown to be  a reliable instrument to use as an outcome measure for adults and children aged 9 to 18.[17][19]

Differential Diagnosis

·          Uncorrected refractive error: hyperopia or over-minused myopia. [20][4]

·        Accommodative Insufficiency (AI): reduced accommodative amplitude causing the inability to sustain focus at near. This condition can occur in the pre-presbyopia age range or in non-presbyopes with uncorrected low hyperopia or over-minused myopia. While reading, a 4-diopter base-in prism blurs the print in AI but improves clarity in CI. Rarely, adolescents may develop transient paresis of accommodation, requiring reading glasses or bifocals. This idiopathic condition resolves in several years. [4]

·        Convergence paralysis: acute onset of exotropia and diplopia on near fixation only; normal adduction and accommodation. Usually results from a lesion in the corpora quadrigemina or the third cranial nerve nucleus and may be associated with Parinaud Syndrome. Prompt neuroimaging to rule out an intracranial lesion should be done. [4]

General Treatment

Overall, treatment for CI can involve refractive error correction, convergence exercises, prisms, and/or strabismus surgery, based upon severity of the condition.

Symptomatic CI should be treated first with correcting any refractive error, including slightly undercorrecting hyperopia and fully correct myopia. Good lighting and relaxation time between periods of close work should be encouraged.

If further treatment is needed, orthoptic therapy (or “eye exercises”) can be used to improve tonic and proximal vergences.[21] There are numerous different types of eye exercises. The primary treatment modalities for CI include home-based exercise, in-office exercises, computer vergence exercises or a combination of these. Some studies have suggested that performing both the home-based exercises and the computer program is more effective than either modality performed on its own. [18] 

Conventional convergence exercises (home-based convergence therapy)

There are two mechanisms used in conventional CI exercises to improve convergence amplitudes. CI 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. In disparity vergence, patients are presented with a visual target from a position not aligned with the fovea in each eye. This causes a reflexive convergent or divergent movement of the eyes to align the image which is recorded by an eye tracker.[22][23]

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 (BSV) and then slowly move the target toward their nose while maintaining BSV. 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 CI 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 a superimposed, combined image of the two pictures.[21]

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.[2]

Base out prism exercises

Base out prisms can also be used to stimulate the convergence reflex. The base out prism induces crossed diplopia and the patient must converge to overcome the prism strength and obtain BSV. 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 CI has emerged. A computer based orthoptic program known as Computer Vergence System (CVS) 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

Optometrists sometimes prescribe both in-office and home-based CI 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.. In-office treatment incorporates purposeful, controlled manipulation of target blur, disparity, and proximity with the aim of normalizing the accommodative and vergence systems. Clinical trials demonstrated success in approximately 75% of patients compared to placebo.[10] 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 American Academy of Pediatrics.[24]

Base–in prism glasses

Base-In prism glasses are sometimes prescribed if conventional CI exercises are unsuccessful. The practitioner will usually prescribe the least amount of prism necessary to achieve comfortable BSV at near. Interestingly, a study by the CITT group found that base-in prism glasses were no more effective than plano placebo reading glasses in children.[25] However, additional studies have suggested that base-in prism glasses are effective at reducing CI symptoms in presbyopic patients.[18]

Evidence for Convergence Exercises

In 2020, the Cochrane Collaboration published an updated systematic review and meta-analysis on the effectiveness of non-surgical interventions for  CI.[26] The study included twelve randomized controlled trials, six in children and six in adults. In children, high-certainty evidence supports better convergence ability in office-based therapy with home reinforcement compared to home-based computer therapy and pencil push-ups alone. Moderate-certainty evidence suggests improved symptoms of CI with the aforementioned treatment comparison, and no significant improvement in both symptoms and  convergence ability in children treated with base-in prism reading glasses.[26] Among adults, base-in prism glasses improved symptoms, but not convergence ability, and the effectiveness of other treatment modalities remain uncertain.

Several eye care professionals have reported limitations in the methodology of the 2005 CITT included in this Cochrane analysis[26]. These include unequal treatment dosing and a misrepresentation of home-based exercises. Patients in the office-based treatment group were prescribed significantly more treatment time than any other randomized group. Additionally, many practitioners feel that the use of “pencil pushups” is a misrepresentation of conventional orthoptic therapy, which includes a variety of exercises with accommodative targets. Finally, it is important to include a placebo group when investigating treatment efficacy, as spontaneous resolution of symptoms have been reported in patients with CI.

In 2019, the Convergence Insufficiency Treatment Trial - Attention and Reading Trial (CITT-ART) coordinated a randomized, multicenter clinical trial to assess whether treatment of symptomatic CI improved reading comprehension in children aged 9 to 14.[27] Participants were randomized to either office-based vergence/accommodative therapy or office-based placebo therapy. After 16 weeks, it was found that CISS scores did not significantly differ between the two groups. Therefore, office-based vergence/accommodative therapy was not more effective than office-based placebo therapy in improving reading comprehension for children with symptomatic CI.[28]

Surgery

Surgery may be indicated for cases of intractable convergence insufficiency. Research suggests the importance of surgical intervention once symptoms begin to worsen, else waiting too long may limit the effectiveness of the surgical outcome.[29] Additionally, surgical management is the definitive treatment of convergence insufficiency  in intermittent exotropia, especially in later stages of the condition.[29]

Indications for surgery[29]:

  • Exotropia that occurs more than half of the time
  • Worsening of exotropia control, reduced stereoacuity, increase in exodeviation size, and worsening asthenopia
  • Rapid loss of control of exotropia occurring in younger patients (under four years old)
  • Persistent diplopia


Surgical options include bilateral lateral rectus (LR) recession, bilateral medial rectus (MR) resection, unilateral MR resection, conventional unilateral LR recession with MR resection, and slanting procedures.[30] More recently, botulinum toxin has been demonstrated as a potential therapy for patients who experience little benefit from prior non-surgical or surgical treatment techniques.[31]

Prognosis

Published success rates for convergence insufficiency treated with convergence exercises  vary between 70 to 80% depending on the patient population and study size.[14][18][32][33] Most patients remain symptom-free following one year after discontinuing treatment.[10] Depending on the type of surgery, success rates for patients with convergence insufficiency pattern exotropia ranges from 18 to 92%.

Associated Disorders

Convergence insufficiency can be associated with several neurological disorders. Neuro-degenerative diseases affecting the basal ganglia, such as Parkinsons Disease, progressive supranuclear palsy (PSP) and Huntington’s Chorea have a higher incidence of convergence insufficiency.[3][34] [35] Lesions in the pretectum and posterior commissure can cause dorsal midbrain Parinaud’s syndrome, which is also known to have a higher incidence of CI. Finally, CI can be associated with head trauma, myasthenia gravis, thyroid ophthalmopathy, chemical or pharmacological agents, oculomotor nerve palsy, dorsal midbrain syndrome, and internuclear ophthalmoplegia.[2][3][34][36][10]

Acknowledgements

Contributing Author: Laura Kirkeby CO

References

  1. ↑ American Academy of Ophthalmology. Basic and clinical science course. Pediatric Ophthalmology and Strabismus. Section 6. San Francisco: American Academy of Ophthalmology, 2006.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Arnoldi K, Reynolds J. A review of Convergence Insufficiency: What Are We Really Accomplishing with Exercises? AOJ 2007; 57: 123-130.
  3. ↑ 3.0 3.1 3.2 3.3 von Noorden GK, Campos E. Binocular Vision and Ocular Motility. Theory and Management of Strabismus, Sixth Edition. St. Louis: Mosby, 2002
  4. ↑ 4.0 4.1 4.2 4.3 Bagheri N, Wajda B, Calvo C, Durrani A. The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease. 7th ed. Wolters Kluwer; 2016
  5. ↑ Mays LE, Porter JD, et al. Neural Control of vergence eye movements: Convergence and divergence neurons in the midbrain. J Neurophysiol 1984; 54: 1091-1108.
  6. ↑ Gantz L, Stiebel-Kalish H. Convergence insufficiency: Review of clinical diagnostic signs. Journal of optometry. Published online 2021. doi:10.1016/j.optom.2021.11.00
  7. ↑ Nunes, A.F., Monteiro, P.M.L., Ferreira, F.B.P. et al. Convergence insufficiency and accommodative insufficiency in children. BMC Ophthalmol 19, 58 (2019). https://doi.org/10.1186/s12886-019-1061-x
  8. ↑ Rutstein RP, Corliss DA. The Clinical Course of Intermittent Exotropia. Optom Vis Sci 2003; 80: 644-649.
  9. ↑ Govindan M, et al. Incidence and Types of Childhood Exotropia. Ophthalmology 2005; 112: 104-108.
  10. ↑ 10.0 10.1 10.2 10.3 Goering M, Drennan KB, Moshirfar M. Convergence Insufficiency. [Updated 2022 May 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554390/
  11. ↑ 11.0 11.1 11.2 11.3 Wright KW, Spiegel PH. Pediatric Ophthalmology and Strabismus, second edition. New York: Springer, 2003.
  12. ↑ Gantz L, Stiebel-Kalish H. Convergence insufficiency: Review of clinical diagnostic signs. Journal of optometry. Published online 2021. doi:10.1016/j.optom.2021.11.00
  13. ↑ Nelson LB, Olitsky S. Harley’s Pediatric Ophthalmology. Fifth edition. Philadelphia: Lippincott Williams & Wilkins, 2005. pp 88.
  14. ↑ 14.0 14.1 The Convergence Insufficiency Treatment Trial Study Group. Randomized Clinical Trial of Treatments for Convergence Insufficiency in Children. Arch Ophthalmol. 2008;126(10):1336-1349.
  15. ↑ Scheiman M, Mitchell L, et al. A Randomized Clinical Trial of Treatments for Convergence Insufficiency in Children. 2005; 123: 14-24.
  16. ↑ Trieu LH, Lavrich JB. Current concepts in convergence insufficiency. Current opinion in ophthalmology. 2018;29(5):401-406. doi:10.1097/ICU.0000000000000502
  17. ↑ 17.0 17.1 Borsting EJ, Rouse MW, Mitchell GL, et al. Validity and reliability of the revised convergence insufficiency symptom survey in children aged 9 to 18 years. Optom Vis Sci. 2003;80(12):832-838. doi:10.1097/00006324-200312000-00014
  18. ↑ 18.0 18.1 18.2 18.3 Scheiman M, Gwiazda J, Li T. Non-surgical Intervention for Convergence Insufficiency. Cochrane Database of Systematic Reviews. 2011; 3: No CD006768.
  19. ↑ Rouse MW, Borsting EJ, Mitchell GL, Scheiman M, Cotter SA, Cooper J, Kulp MT, London R, Wensveen J; Convergence Insufficiency Treatment Trial Group. Validity and reliability of the revised convergence insufficiency symptom survey in adults. Ophthalmic Physiol Opt. 2004;24(5):384-90. doi: 10.1111/j.1475-1313.2004.00202.x. PMID: 15315652.
  20. ↑ Wajuihian SO. Is there an association between convergence insufficiency and refractive errors? African vision and eye health. 2017;76(1):1-7. doi:10.4102/aveh.v76i1.363
  21. ↑ 21.0 21.1 Petrunak JL, The treatment of Convergence Insufficiency. AOJ 1999; 49: 12-16.
  22. ↑ Talasan H, Scheiman M, Li X, Alvarez TL. Disparity vergence responses before versus after repetitive vergence therapy in binocularly normal controls. J Vis. 2016;16(1):7. doi: 10.1167/16.1.7. PMID: 26762276; PMCID: PMC4743712.
  23. ↑ Erkelens IM, Bobier WR. Reflexive Fusional Vergence and Its Plasticity Are Impaired in Convergence Insufficiency. Invest Ophthalmol Vis Sci. 2020;61(10):21. doi: 10.1167/iovs.61.10.21. PMID: 32780865; PMCID: PMC7441356.
  24. ↑ Handler SM, Fierson WM et al. Learning Disabilities, Dyslexia, and Vision. Pediatrics 2011;127:818-856.
  25. ↑ Scheiman M, Cotter S, et al. A randomized clinical trial of the effectiveness of base-in prism reading glasses verses placebo reading glasses for symptomatic convergence insufficiency in children. Br J ophthalmol 2005;89(10): 1318-1323.
  26. ↑ 26.0 26.1 26.2 Scheiman M, Kulp MT, Cotter SA, Lawrenson JG, Wang L, Li T. Interventions for convergence insufficiency: a network meta-analysis. Cochrane Database Syst Rev. 2020;12(12):CD006768. doi: 10.1002/14651858.CD006768.pub3. PMID: 33263359; PMCID: PMC8092638.
  27. ↑ CITT-ART Investigator Group. Effect of Vergence/Accommodative Therapy on Reading in Children with Convergence Insufficiency: A Randomized Clinical Trial. Optom Vis Sci. 2019;96(11):836-849. doi: 10.1097/OPX.0000000000001442. PMID: 31651592; PMCID: PMC6855328.
  28. ↑ Chang MY, Morrison DG, Binenbaum G, Heidary G, Trivedi RH, Galvin JA, et al. Home- and office-based vergence and accommodative therapies for treatment of convergence insufficiency in children and young adults: a report by the American Academy of Ophthalmology. Ophthalmology. 2021; 128: 1756– 65.
  29. ↑ 29.0 29.1 29.2 Rosenbaum EA, Santiago AP. Clinical Strabismus Management: Principles and Surgical Techniques. Philadelphia, PA: WB Saunders; 1999.
  30. ↑ Farid M, Abdelbaset E. Surgical outcomes of three different surgical techniques for treatment of convergence insufficiency intermittent exotropia. Eye. 2018;693–700.
  31. ↑ Hofsli M, Torp-Pederson TE, Lonkvist CS, Saunte JP. Botulinum Toxin A Injection for Convergence Insufficiency. Journal of Pediatric Ophthalmology and Strabismus, 2023;60(2):108-113. doi: 10.3928/01913913-20220324-02
  32. ↑ Kushner B. The treatment of Convergence Insufficiency. Arch Ophthalmol 2005; 123: 100-101.
  33. ↑ Grisham DJ, Visual therapy results for convergence insufficiency: A literature review. Am J Optom Physiol Optics 1988;65:448-454.
  34. ↑ 34.0 34.1 Cohen M, Groswasser Z, Barchadski R, Appel A. Convergence Insufficiency in Brain Injured Patients. Brian Inj 1989: 3: 187-191.
  35. ↑ Biousse V, Skibell BC, et al. Ophthalmologic features of Parkinson’s Disease. Neurology 2004; 62: 177-180.
  36. ↑ Bruke JP, Shipman TC, Watts MT. Convergence Insufficiency in Thyroid Eye Disease. J Pediatr Ophthalmol Strabismus. 1993;30: 127-129.
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