December 1, 2022
By Eric Chow, OD, FAAO
Addressing binocular vision problems promotes the holistic care of your patients, which might be the missing piece in the myopia management puzzle.
Two of the most common conditions I see as a pediatric optometrist, especially since the COVID-19 pandemic began, are myopia development/progression and binocular vision disorders. This should come as no surprise to optometrists, as many studies have shown an increase in the usage of digital devices during the pandemic compared to the pre-pandemic period.1
Of particular interest is a case series that reported four patients who developed acquired concomitant esotropia from excessive near device usage during the COVID-19 lockdown, all with normal neurological exams and imaging.2 Two of the four cases were myopes, who were reported to intensively use the computer for more than eight hours per day. This raises the question: Does progressive myopia have anything to do with the development of binocular vision conditions, or is the presence of binocular vision disorders a harbinger of progressive myopia?
It is important to look into lifestyle and environmental factors related to myopia development and progression. The top three recommendations I discuss with all my patients who are developing or progressing in myopia are:
- Spend at least two hours a day outdoors.
- Take breaks when reading — every 20 minutes, spend five minutes looking away from near work.
- Hold reading material at Harmon’s distance — approximately the distance between your knuckle and elbow when you make a fist and hold it against your chin in front of you.3
Why Are These Recommendations Essential?
While research shows that spending approximately two hours a day outdoors may prevent or delay myopia onset, it is less clear whether outdoor time is effective in slowing myopia progression in eyes that are already myopic.4 When outside, children typically look a lot farther away than they do when inside, and pupil miosis is greater due to higher illumination levels, which leads to a greater depth of focus and less accommodative demand.5 An outdoor environment is, on average, 100 times brighter than indoors. In the presence of bright light, dopamine is released in the outer retina. This starts a cascade of signaling dopamine, a strong stop signal for axial elongation.6
A prospective population study conducted in Taiwan showed that discontinuing near work every 30 minutes and spending more time outdoors are protective behaviors against the onset and progression of myopia.7 Also, when a child works at a distance closer than 40 centimeters, it increases the demands on both accommodation and vergence, potentially exacerbating binocular vision symptoms.8 Asymmetric head posture while sitting at a desk can lead to differences in accommodative demands between the two eyes, which can affect vergence postures, further disrupting binocularity.9 The bottom line is to reduce accommodative and vergence demands, given that intensive near work has harmful effects on one’s binocular vision.
Accommodation, Binocular Function, and Myopia
Interesting research has examined the relationship between accommodation and binocular function regarding myopia development and progression. Most commonly studied are the roles of accommodative amplitude, accuracy (lag of accommodation), eye alignment measures (phoria), and accommodative convergence to accommodation ratios (AC/A).
A lag of accommodation occurs when an eye is focused farther than the stimulus. Several studies have attempted to look into the relationship between lag of accommodation and the onset or progression of myopia. A large longitudinal study done by Mutti and colleagues published in 2006 found that lag of accommodation was greater in children who developed myopia compared with persistent emmetropes four years before myopic onset. They also found that accommodative lag was not significantly elevated during the first year of the onset of myopia.10 However, other studies show that myopes had a higher lag of accommodation than emmetropes.11 Research has found that hyperopic defocus in the peripheral retina leads to the development and/or progression of myopia. Animal studies have shown that form deprivation by diffuse blur, mimicking a high lag of accommodation can also cause hyperopic defocus. It is postulated that relative hyperopic blur alongside an increased lag of accommodation can be a stimulus for myopia development.
An AC/A ratio is the relationship between the amount of convergence caused by accommodation and the amount of accommodation that produces that convergence. It has been shown that children with higher AC/A ratios have an increased risk of myopia development. Higher AC/A ratios have been documented in myopic children compared to emmetropic children, and it can be an important risk factor for rapid onset.12 Mutti and colleagues found that a higher AC/A ratio is correlated with a greater lag of accommodation, but they did not find an association with a faster rate of myopia progression.13
Drobe and deSaint-Andre in 1995 reported that pre-myopes tended to show esophoria when compared to emmetropes. Gross and Jackson in 1996 studied a group of 87 children over three years. They noted that when the near phoria lies outside the range of 1 esophoria to 3 exophoria, this is a risk factor for the development of myopia. They also found that near phorias are more convergent in the “became-myopic” group than in the “remained emmetropic” group.14 Although these major studies are almost 30 years old, the concept has held up that an atypical near phoria is a predictor of the onset and progression of myopia. Clinically, when I see a near phoria that is not the expected 2-6 diopters of exophoria and the child presents with symptoms of a binocular vision disorder, a more in-depth binocular vision evaluation is indicated.
How Do Myopia Treatment Options Affect Binocularity?
The four myopia management strategies currently in use are topical low-dose atropine, orthokeratology, dual focus soft contact lenses/center-distance multifocal contact lenses, and in some cases, bifocal or multifocal glasses.
Low-dose atropine is a muscarinic receptor antagonist which has been shown to be effective at slowing myopia progression in 0.01%, 0.025%, and 0.05% dosing. The LAMP study published in 2019 reported that 0.05% was the most effective at controlling spherical equivalent progression and axial length elongation over a period of two years.15 Even at low concentrations, low-dose atropine negatively affects accommodation and increases the tendency of a patient to display esophoria. Most recently, a case report was published of children who developed convergence excess esotropia (CEET) following 0.01% atropine eye drops.16
I have seen this in my practice. I have a patient in active vision therapy because of acquired esotropia, which is believed to be triggered by atropine (he was given 1% even though 0.01% was prescribed for myopia management). The patient received a neuro-ophthalmic examination and had imaging, and no neurological cause was found for the sudden-onset esotropia. All neurological and imaging studies came back normal. It is believed that the use of atropine caused a breakdown in binocularity, resulting in a large angle constant esotropia. The atropine significantly knocked out the child’s ability to accommodate, and consequently, there was excessive accommodative convergence (due to the child’s innervational drive to accommodate against the effects of the atropine drops), effectively resulting in an extremely high AC/A ratio in action. Once this happened, atropine was discontinued, and vision therapy commenced to improve his accommodative and vergence control. At the onset, he needed 45 prism diopter Fresnel to have binocular fusion, and after 30 sessions of vision therapy, he now uses 12 prism diopters of Fresnel to fuse.
Given this case report, low-dose atropine should be used cautiously in children with esophoria. It is reported that there are minimal accommodative or photophobic effects, but I recommend progressive addition lenses (PALs) and photochromic lenses for all children prescribed low-dose atropine for myopia progression control.
It has also been noted that intermittent exotropia (IXT) has been associated with a higher prevalence of myopia. Half of children with IXT are myopic by age 10, and 90% are myopic by age 20.17 Although it has not yet been studied, the use of low-dose atropine in patients with IXT poses an interesting clinical question, given how atropine can stimulate accommodative convergence.
Orthokeratology is another effective way to manage myopia progression. The theory behind treatment with OrthoK is its effect on inducing peripheral myopic defocus. Interestingly, a study has shown that children with lower baseline amplitudes of accommodation showed a 56% better myopia control response to OrthoK than myopes with normal accommodation in a two-year study.18 OrthoK has also been shown to increase exophoria in young adult myopes.19 A patient with low amplitudes of accommodation and esophoria may be a good candidate for OrthoK. I recommend evaluating the near base out vergence ranges at the first contact lens follow-up to ensure that Sheard’s criterion is met. While the potential increase in exophoria may be good for a child with esophoria, those with intermittent exotropia or high exophoria may not be the best candidates for this management option.
Center distance multifocal and dual-focus soft lenses have been shown to be effective at reducing peripheral hyperopic defocus. One prospective study showed that children wearing multifocal contact lenses showed reduced accommodative responses and more exophoria compared to those in single vision contact lenses.20 However, in other studies, no difference in binocular or accommodative function can be detected in children wearing dual-focus contact lenses or extended depth of focus lenses, compared to single vision contact lenses.20,21 In an abstract presented at the International Myopia Conference, subjects wearing extended depth of focus lenses had more regressive saccades during reading than dual focus or single vision contact lenses.22
When a near addition lens is prescribed over a patient’s distance manifest refraction, it reduces the accommodative response and results in an exophoric shift. The idea behind using a near add is to improve accommodative accuracy and minimize retinal blur. Multiple studies show that myopic children with near esophoria placed in single-vision spectacle lenses progress more quickly than children in PALs. In addition, children with a higher lag of accommodation in the PALs group showed greater treatment effect.24,25 Whenever possible, I recommend executive bifocals (ensuring the bifocal line bisects the pupil) because it permits more plus lens power to affect a larger retinal surface area. However, the challenge is that PALs are more cosmetically acceptable. So, whenever I prescribe PALs for myopia management, I make a note in the patient’s prescription to set the seg height 1 mm above the pupil center, so there is wider access to near plus power to minimize retinal blur and stabilize accommodative response.
Additional Tests Before Commencing Myopia Management
In addition to a binocularly balanced refraction, I check the cover test at distance and near, accommodative amplitudes, retinoscopy done at the near point, near point of convergence, and then I may check accommodative facility and subjective distance/near phorias depending on if anything else was found.
It is important to understand that there is a relationship between accommodation and vergence with myopia development and myopia control. While individual test results are important, it is equally, if not more important, to ask about any visual symptoms a patient may be experiencing. Is the child at my practice for a myopia management consult also reporting focusing problems, double vision, skipping lines when reading, and suffering from headaches or eye fatigue? To streamline the exam, I use the COVD Quality of Life Questionnaire to screen if there are any binocular vision concerns. Sometimes, a patient needs a referral to a vision therapy optometrist before discussing myopia management strategies. Vision therapy is the first-line treatment for accommodative and vergence abnormalities. It improves the awareness and efficiency of one’s accommodative control in addition to binocularity, depth perception, and ocular motor movements.
In conclusion, as optometrists seeing children and adolescents with myopia, let’s not focus our efforts on just their myopia. Often these patients have multiple problems affecting their visual development. Addressing binocular vision problems promotes the holistic care of your patients, which might be the missing piece in the myopia management puzzle.
Dr. Eric Chow is a co-owner of Miami Vision Therapy (established in 2021) where his team offers vision therapy and myopia management services. He graduated from the SUNY College of Optometry in 2016 and completed a residency in pediatrics and binocular vision from NOVA Southeastern College of Optometry in 2017. Dr. Chow is a Fellow of the American Academy of Optometry and is currently working toward completing his fellowship with the College of Vision Development.
- Serra, Gregorio, et al. “Smartphone Use and Addiction During the Coronavirus Disease 2019 (COVID-19) Pandemic: Cohort Study on 184 Italian Children and Adolescents – Italian Journal of Pediatrics.” BioMed Central, 2 July 2021.
- Vagge, A, et al. “Acute Acquired Concomitant Esotropia From Excessive Application of Near Vision During the COVID-19 Lockdown – PubMed.” PubMed, 20 Oct. 2020.
- Cobbs, Sarah. Harmon Revisited. 1990, www.fusd1.org/cms/lib03/AZ01001113/Centricity/Domain/52/Sarah%20Cobb%20Harmon%20Revisited.pdf.
- Xiong, S, et al. “Time Spent in Outdoor Activities in Relation to Myopia Prevention and Control: A Meta-analysis and Systematic Review – PubMed.” PubMed, 1 Sept. 2017.
- Logan, Nicola S., et al. “IMI Accommodation and Binocular Vision in Myopia Development and Progression.” ARVO Journals, 1 Apr. 2021.
- Zhou, X, et al. “Dopamine Signaling and Myopia Development: What Are the Key Challenges – PubMed.” PubMed, 1 Nov. 2017.
- Huang, P, et al. “Protective Behaviours of Near Work and Time Outdoors in Myopia Prevalence and Progression in Myopic Children: A 2-year Prospective Population Study – PubMed.” PubMed, 1 July 2020.
- Bababekova, Y, et al. “Font Size and Viewing Distance of Handheld Smart Phones – PubMed.” PubMed, 8 July 2011.
- Wang, Y, et al. “Reading Behavior of Emmetropic Schoolchildren in China – PubMed.” PubMed, 28 June 2013.
- Mutti, Donald O., et al. “Accommodative Lag Before and After the Onset of Myopia.” Investigative Ophthalmology and Visual Science. 1 Mar. 2006.
- Kaphle, D, et al. “Accommodation Lags Are Higher in Myopia Than in Emmetropia: Measurement Methods and Metrics Matter – PubMed.” PubMed, 1 Sept. 2022.
- Mutti, D, et al. “AC/A Ratio, Age, and Refractive Error in Children – PubMed.” PubMed, 1 Aug. 2000.
- Mutti, D, et al. “The Response AC/A Ratio Before and After the Onset of Myopia – PubMed.” PubMed, 1 March 2017.
- Goss, D and Jackson, T. “Clinical Findings Before the Onset of Myopia in Youth: 3. Heterophoria – PubMed.” PubMed, 1 Apr. 1996,
- Yam, J, et al. “Two-Year Clinical Trial of the Low-Concentration Atropine for Myopia Progression (LAMP) Study: Phase 2 Report – PubMed.” PubMed, 1 July 2020.
- Kothari, M, et al. “Convergence Excess Consecutive Esotropia Associated With 0.01% Atropine Eye Drops Usage in Patients Operated for Intermittent Exotropia – PubMed.” PubMed, 1 Apr. 2020.
- Ekdawi, N, et al. “The Development of Myopia Among Children With Intermittent Exotropia – PubMed.” PubMed, 1 Mar. 2010.
- Zhu, M, et al. “The Impact of Amplitude of Accommodation on Controlling the Development of Myopia in Orthokeratology – PubMed.” PubMed, 1 Jan. 2014.
- Gifford, K, et al. “Zone of Clear Single Binocular Vision in Myopic Orthokeratology – PubMed.” PubMed, 4 Mar. 2020.
- Gong, C, et al. “Accommodation and Phoria in Children Wearing Multifocal Contact Lenses – PubMed.” PubMed, 1 Mar. 2017.
- Tilia, D, et al. “Vision Performance and Accommodative/Binocular Function in Children Wearing Prototype Extended Depth-of-Focus Contact Lenses – PubMed.” PubMed, 1 July 2019.
- Mojarrad, Ghorbani. Eye Movements and Accommodative Microfluctuations in Daily Disposable Myopia Management Contact Lenses. International Myopia Conference, 2022. Accessed 16 Nov. 2022.
- Ruiz-Pomeda, A, et al. “Binocular and Accommodative Function in the Controlled Randomized Clinical Trial MiSight Assessment Study Spain (MASS) – PubMed.” PubMed, 1 Jan. 2019.
- Yang, Z, et al. “The Effectiveness of Progressive Addition Lenses on the Progression of Myopia in Chinese Children – PubMed.” PubMed, 1 Jan. 2009.
- Gwiazda, J, et al. “A Randomized Clinical Trial of Progressive Addition Lenses Versus Single Vision Lenses on the Progression of Myopia in Children – PubMed.” PubMed, 1 Apr. 2003.