Convergence refers to the ability of the eyes to converge or to direct their independent gaze on a single object. Depending on how close the subject is from the two eyes, each eye must be able to turn inward for both to look directly at the same point. For example, if a finger is held up a few inches in front of the nose, both eyes need to be able to turn sharply inward in order to see the finger.
There are no obvious visual signs that someone has convergence insufficiency; both eyes appear correctly aligned. But because in-school vision exams test only far vision, a child with 20/20 vision insufficiency is not identified. For that reason, teachers have sometimes thought that such instances where a child has trouble reading are the result of dyslexia or learning- or reading disabilities. Estimates of prevalence vary greatly, from 2.25% to 13%, and there is little information about contributing factors such as age, race, gender, or ethnicity.
What is Convergence Insufficiency?
If the eyes can't maintain this inward gaze toward a finger, then convergence insufficiency (CI) is experienced. When the eyes either cannot focus on a near point, or they have difficulty holding their point of convergence when doing close work, their eyes tend to drift outwards. The result is blurred or double vision for near vision.
At near point viewing, people with convergence insufficiency experience continued or intermittent exophoria, in which the eyes tend to diverge away from the centerline of vision. The point at which the two eyes can focus on a near object is further away than the norm. People with convergence insufficiency may also have difficulty changing or maintaining focus (accommodative insuffiency), or difficulty changing focus rapidly (accommodative infacility). They may also experience fusional-vergence dysfunction, in which they are unable to efficiently utilize the information that their eyes take in.
A number of symptoms are common in both children and adults.
- Asthenopia, vision eyestrain (often accompanies CI in both adults and children)
- Blurred near vision
- Difficulty with reading and close-up work
- Headache while/after reading or doing close work
The cause is unknown but manifests as a misalignment of the muscles controlling eye movement while focusing on something nearby. But scientists have identified causes of the resulting eye fatigue:
- The need for continual balance between convergence and accommodation (a reflex of convergence) for near work
- Keeping that balance stable
- Converting the viewed two images into one clear image with increasing difficulty
Most doctors use a number of treatments. Researchers investigated which were the most commonly prescribed. Optometrists and ophthalmologists who responded to a survey, recommended pencil push-up therapy (38–50%), home-based vision therapy (22–21%), and office-based vision therapy (16%); none recommended base-in prism.1
A 2008 study funded by the National Eye Institute found that 75% of patients who received therapy in an office setting by a trained therapist, in addition to treatment at home, had the best results. They compared pencil push-up therapy, plus computer vision therapy, and in-office therapy combined with "at home" work. These three therapies, including the placebo therapy, resulted in only 33% to 35% improvement. Interestingly, the placebo therapy was better than pencil push-ups.2 A 2012 follow-up study confirmed these results.3
Surgery is rarely recommended, and then, only for instances where the inability to converge is severe, or where additional refractive problems make vision therapy ineffective.4
There are several options in vision therapy:5
Prism reading glasses. There are various types of prism reading glasses used at home, but they have been found to be no more effective than regular reading glasses.
- Base-in glasses are made with the part of the lens toward the nose thicker, to assist with vision as the eyes converge.
- Base-in glasses plus a progressive-addition lens-design feature, a gradient of increasing lens power, was found to be better than plain base-in glasses.
Home-based exercises. The most common exercise prescribed for at-home use is pencil push-ups.
Home-based therapies. There are therapies that can be performed at home that are more effective than pencil push-ups, including prism glasses, stereoscopes, and computer software programs.
Outpatient vision therapy includes activities prescribed and monitored by a professional vision therapist. With children, outpatient vision therapy/orthoptics is more effective than exercise (usually pencil push-ups) and/or computer vision therapy at home.6 With adults, the differences between various therapies are less consistent than with children.7
Lifestyle factors and diet to support overall vision health are important baseline practices for people with convergence issues. General nutrient support is also helpful.
- Key self help tips Maintain good vision with eye disease prevention pointers
- If you are a computer user, please review our section on computer vision syndrome
1. Scheiman, Mitchell, Gwiazda, J., Li, T. (2014). Non-surgical interventions for convergence insufficiency. Cochrane Database Syst Rev, Mar 16;(3):CD006768.
2. National Eye Institute. (2008). More Effective Treatment Identified for Common Childhood Vision Disorder. Retrieved May 22 2018 from https://nei.nih.gov/news/pressreleases/101308.
3. Westman, M., Liinamaa, M.J. (2012). Relief of asthenopic symptoms with orthoptic exercises in convergence insufficiency is achieved in both adults and children. J Optom, Apr-Jun;5(2):62-67.
4. Wang, B., Wang, L., Wang, Q., Ren, M. (2014). Comparison of different surgery procedures for convergence insufficiency-type intermittent exotropia in children. Br J Ophthalmol, Oct;98(10:1409-13.
5. Ibid. Scheiman. (2014).
6. Scheiman, M., Mitchell, G.L., Cotter, S., Cooper, J., Kulp, M., et al. (2005). A randomized clinical trial of treatments for convergence insufficiency in children. Arch Ophthalmol, Jan;123(1):14-24.
7. Ibid. Scheiman. (2014).