Convergence Insufficiency

From EyeWiki
Article initiated by:
Gregory I. Ostrow, MD FAAO FAAP, Laura Kirkeby, CO
All authors and contributors:
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
Assigned editor:
Angeline Nguyen, MD
Review:
Assigned status Update Pending
 by Allison Umfress, MD on July 14, 2022.


Convergence Insufficiency
ICD-10
H51.1


Convergence Insufficiency (CI) is 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 when reading, closing 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

The etiology of isolated CI, not related to trauma or neurological disease, has not been completely determined. Primary CI is thought to be caused by an imbalance of vergence eye movements that is either an inborn deficiency or an acquired etiology.[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 vergences 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 may include fatigue, drugs (parasympatholytic), uveitis, Adie tonic pupil, glasses inducing a base-out prism effect, postexanthematous 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.[10]

Clinical Diagnosis 

The most common signs of CI include a increased near point of convergence (NPC), decreased convergence amplitudes and an exodeviation at near.[2]  An NPC value that is less than 10 cm (4 inches) from the bridge of the nose is considered to be within normal limits and most normal young patients can maintain fusion when converging all the way to the tip of the nose. If a patient’s NPC is farther than 10 cm from their nose then an evaluation to rule out CI should be performed. 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] 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.[12] In general, fusional convergence amplitudes of less than 15 to 20 prism diopters at near are a sign of convergence insufficiency.[11][13] 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.

History

The treatment of CI was first medically documented by von Graefe in 1855[3]. Since then, orthoptic exercises have been the leading treatment option for this condition.

Signs

A diagnosis can be determined with a standard binocular vision examination. Patients with convergence insufficiency will have:

·        A remote near point of convergence (NCP) of 6cm for prepresbyopes and 10cm presbyopes [14]

·        Decreased convergence amplitudes or likely both.[15]

·        Low accommodative convergence/accommodation (AC/A) ratio <2:1[16]

·        Large exophoria (XP) or intermittent exotropia, greater (≥4∆) at near than distance

·        Reduced positive fusional vergence (PFV) <15∆

·        High CI symptom Survey (CISS) score ≥16 [17][18]

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. These symptoms are exacerbated when doing prolonged near work, such as reading and computer or any other electronic device usage. [2][11][19]

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) is a reliable instrument to use as an outcome measure for children aged 9 to 18.[18][10]

Differential Diagnosis

·          Uncorrected refractive Error: Hyperopia or over-minused myopia [20][4]

·        Accommodative Insufficiency (AI): Reduced accommodative amplitude. 21Often in pre-presbyopia age range from 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

Start by correcting any refractive error. Slightly undercorrect hyperopia, and fully correct myopia. Encourage good lightning and relaxation time between periods of close work. Orthoptic therapy is the primary treatment modality used by most eye care professionals for the treatment of CI. They are tailored to improve the tonic and proximal vergences components through procedural therapies, as they are adaptable with exercises. The plasticity of the fusional convergence reflex system allows patients to improve their convergence amplitudes with simple exercises[21]. There are numerous different types of eye exercises; however, 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.[19]

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.

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 converge 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

Eye care professionals will some times 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. . It incorporates purposeful, controlled manipulation of target blur, disparity, and proximity with the aim of normalizing the accommodative and vergence systems. Clinical trials on the effectiveness demonstrated a 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 America Academy of Pediatrics.[22]

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[23]. However, additional studies have suggested that base-in prism glasses are effective at reducing CI symptoms in presbyopic patients.[19]

Randomized Clinical Trial Treatment

In 2011 Sheiman, Gwiazda, and Li, in association with the Cochrane Collaboration, published a study detailing non-surgical interventions for convergence insufficiency. They did a system wide database analysis to review all abstracts related to non-surgical treatment methods for CI. The objective of the study was to review all randomized controlled trials (RCT) and analyze their methodology, risk of bias and outcome data. Out of 529 abstracts reviewed, only 6 studies met their criteria for RCTs. Four of the six studies were judged to below risk for bias, while the other two studies were deemed high risk for bias. All four studies determined to be low risk for bias were performed by the Convergence Insufficiency Treatment Trial (CITT) study group.[19]

In 2005, the CITT study group published 3 studies related to non-surgical treatment for convergence insufficiency[23]. In one study 72 children with symptomatic CI were randomly assigned to wear either base-in prism reading glasses or placebo reading glasses for all near tasks. The authors found no significant improvement in symptoms or convergence ability after 6 weeks of using base-in prism glasses as compared to the placebo group.[23] The 3 remaining studies outlined in the Cochrane review focused on the effectiveness of home-based, office-based and computer convergence exercises[19][24]. The most recent study in 2008 randomly assigned 221 children to receive either home-based pencil push-ups, home based computer therapy with additional pencil push ups, office-based therapy with home reinforcement or office based placebo treatment[13][19]. The authors report that children randomized to the office-based treatment group had the most significant improvement in convergence amplitudes, NPC and a lower symptom survey score. Several eye care professionals have reported flaws in the methodology of this study. Reported flaws in the study 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 with additional 60 minutes of treatment time per week. Another controversial limitation of the study was the use of “pencil pushups” for home-based convergence exercises. Many practitioners feel this is a misrepresentation of conventional orthoptic therapy. Most eye care professionals that prescribe home-based exercises include a variety of exercises and use accommodative targets.[25] Symptom severity is one of the primary criteria used to diagnose and monitor patients with CI. It is important to include a placebo group when investigating the efficacy of a treatment modality, especially when symptom surveys are used as a success criterion. Excellent results have been obtained with all three types of CI exercises; however spontaneous resolution of symptoms has also been reported. Moreover, clinical studies with placebo groups have also shown that patients in the placebo group tend to show an improvement in symptoms, although to a much less degree.

Surgery

As a last option, some surgeons will perform a small medial rectus resection of one or both medial rectus muscles muscles or a lateral rectus slanting recession. In patients with ocular dominance a recession-resection surgery can be performed on the non-dominant eye or the more exotropic eye[26]. This is somewhat controversial and some authors have shown poor results with this surgery.[11] 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 consecutive esotropia, diplopia at distance, and/or the development of A and V patterns after surgery.

Medical Follow up

The follow-up schedule for CI exercises is dependent on the treatment prescribed and is determined by the eye care professional. The follow up schedule is usually based on the severity of the patient’s signs and symptoms. Some patients may require a follow assessment once a month, while other patients may require follow-up every two weeks. In general, home-based and computer exercises have a longer duration between follow up appointments and tend to be significantly less expensive than in-office exercises.

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[13][19][25][27]. Most patient remain symptom-free following one year after discontinuing treatment[10]

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 (PSP) and Huntington’s Chorea have a higher incidence of convergence insufficiency[3][28] [29]. 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. CI can also be associated with head trauma, myasthenia gravis, thyroid ophthalmopathy, chemical or pharmacological agents, oculomotor nerve palsy, dorsal midbrain syndrome, internuclear ophthalmoplegia, or ischemia.[2][3][28][30][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 2.6 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 3.4 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 10.4 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 11.4 Wright KW, Spiegel PH. Pediatric Ophthalmology and Strabismus, second edition. New York: Springer, 2003.
  12. ↑ Nelson LB, Olitsky S. Harley’s Pediatric Ophthalmology. Fifth edition. Philadelphia: Lippincott Williams & Wilkins, 2005. pp 88.
  13. ↑ 13.0 13.1 13.2 The Convergence Insufficiency Treatment Trial Study Group. Randomized Clinical Trial of Treatments for Convergence Insufficiency in Children. Arch Ophthalmol. 2008;126(10):1336-1349.
  14. ↑ 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
  15. ↑ Wright KW, Spiegel PH. Pediatric Ophthalmology and Strabismus, second edition. New York: Springer, 2003.
  16. ↑ Scheiman M, Mitchell L, et al. A Randomized Clinical Trial of Treatments for Convergence Insufficiency in Children. 2005; 123: 14-24.
  17. ↑ Trieu LH, Lavrich JB. Current concepts in convergence insufficiency. Current opinion in ophthalmology. 2018;29(5):401-406. doi:10.1097/ICU.0000000000000502
  18. ↑ 18.0 18.1 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
  19. ↑ 19.0 19.1 19.2 19.3 19.4 19.5 19.6 Scheiman M, Gwiazda J, Li T. Non-surgical Intervention for Convergence Insufficiency. Cochrane Database of Systematic Reviews. 2011; 3: No CD006768.
  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. ↑ Handler SM, Fierson WM et al. Learning Disabilities, Dyslexia, and Vision. Pediatrics 2011;127:818-856.
  23. ↑ 23.0 23.1 23.2 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.
  24. ↑ Scheiman M, Mitchell L, et al. A Randomized Clinical Trial of Treatments for Convergence Insufficiency in Children. 2005; 123: 14-24.
  25. ↑ 25.0 25.1 Kushner B. The treatment of Convergence Insufficiency. Arch Ophthalmol 2005; 123: 100-101.
  26. ↑ Farid MF, Abdelbaset EA. Surgical outcomes of three different surgical techniques for treatment of convergence insufficiency intermittent exotropia. Eye (Lond). 2018;32(4):693-700. doi:10.1038/eye.2017.259
  27. ↑ Grisham DJ, Visual therapy results for convergence insufficiency: A literature review. Am J Optom Physiol Optics 1988;65:448-454.
  28. ↑ 28.0 28.1 Cohen M, Groswasser Z, Barchadski R, Appel A. Convergence Insufficiency in Brain Injured Patients. Brian Inj 1989: 3: 187-191.
  29. ↑ Biousse V, Skibell BC, et al. Ophthalmologic features of Parkinson’s Disease. Neurology 2004; 62: 177-180.
  30. ↑ Bruke JP, Shipman TC, Watts MT. Convergence Insufficiency in Thyroid Eye Disease. J Pediatr Ophthalmol Strabismus. 1993;30: 127-129.
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