Clinical

Why Binocular Vision Matters in Myopia Management

By Daniel Tilia, BOptom (Hons), MOptom, GradCertOcTher, FBCLA, FAA

Optometry plays an important role in both diagnosing and managing binocular vision disorders. Binocular vision disorders have been associated with increased near-work symptoms1 and reduced academic achievement,2 while successful treatment of a binocular vision disorder has been associated with reduced adverse academic behaviors and reduced parental concern regarding academic achievement.3 A binocular vision assessment is, therefore, an important component of a routine optometric consultation.

In addition to the above considerations, practitioners offering myopia management need to know the effect a patient’s binocular vision status has on their management strategies. Even though it is debatable, several binocular vision functions have been associated with myopia progression. The various myopia-management strategies may also affect binocular vision, which may or may not be beneficial depending on the patient’s binocular vision status. For example, center-distance multifocal soft contact lenses increase near exophoria and provide near plus.4 This may be beneficial for eso-related or accommodative insufficiency-related disorders, but it is less beneficial for exo-related or accommodative excess-related disorders. It is, therefore, incumbent on the practitioner performing myopia management to be aware of a patient’s binocular vision status and manage a patient’s binocular vision disorder. Management of a binocular vision disorder may involve choosing myopia management strategies that are beneficial to a patient’s binocular vision status, performing vision therapy, or referring to another practitioner specializing in vision therapy.

The International Myopia Institute5 (IMI) recommends the following tests be performed at a baseline examination and at follow-up visits to monitor changes with myopia management strategies:

  • Accommodative accuracy/response (lag or lead)
  • Amplitude of accommodation
  • Distance and near accommodative facility
  • Distance and near heterophorias
  • Near fixation disparity
  • Accommodative convergence / accommodation (AC/A) ratio

The IMI also lists various clinical methods that can be used to measure these outcomes.5

In addition to these tests, the practitioner may also consider tests at baseline that aid in the differential diagnosis of a binocular vision disorder. These include monocular accommodative facility, near point of convergence, negative and positive fusional reserves at distance and near and negative and positive relative accommodation (B+ and B-, respectively) at near.6

Much of the interest in binocular vision and myopia management stems from differences in myopes compared to non-myopes for various aspects of binocular function, particularly accommodative function. These differences appear to be associated with a need for myopes to increase accommodative effort at near, characterised by a higher lag of accommodation7 and lower amplitude of accommodation.8 This has a direct effect on other aspects of accommodative function, including reduced B-9, 10 and accommodative facility,8, 11 and an indirect effect on vergence function, including increased esophoria10 and higher AC/A ratio.8, 12

Even though several studies have found an association between lag of accommodation,8, 13, 14 AC/A ratio14, 15 and accommodative facility8 with myopia progression, other studies have not found an association for any of these binocular vision functions.11, 12, 14, 16, 17 The Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study found an association between lag of accommodation and AC/A ratio with myopia progression in younger children but not older children in the univariate analysis, but significance was lost in the multivariate analysis.18 Another study found a significant correlation between AC/A ratio and myopia progression in a single-factor analysis, but not in a multifactorial model.8

Esophoria has not been associated with myopia progression in spectacle lens studies employing progressive addition19 or executive bifocal20 lenses when all subjects used the same near add power. One study reported good myopia management efficacy with ACUVUE® Bifocal (Johnson & Johnson, USA) contact lenses.21 Near add power was increased until the associated near esophoria was neutralized, but the exact mechanism for efficacy is unknown.21

In terms of myopia management, these findings are of little consequence as the primary objective is to minimize myopia progression. However, strategies used in myopia management can affect binocular vision function. The most obvious is the muscarinic agonist atropine.22 Atropine causes a dose-dependent reduction of the amplitude of accommodation,23-25 leading to reduced accommodative function and tendency towards esophoria.

The effect of spectacle lenses used for myopia management is also well-known. Near plus reduces near accommodative response resulting in an exophoric shift dependent on the near add power and the AC/A ratio. Near plus also reduces near hyperopic blur caused by a high lag of accommodation. Bifocal lenses are expected to have a greater effect at similar add power compared to progressive addition lenses, as the maximum near power is more easily accessible. Executive bifocal lenses with base-in prism reduce the near exophoria induced by near plus power, which may be beneficial in children with a low lag of accommodation.20

The effect on binocular vision function of contact lenses used in myopia management depends on lens design. Center-distance multifocals act similarly to spectacle near plus in that they reduce near accommodative response26, 27 and increase near exophoria.4, 26 Center-distance contact lenses do not appear to affect amplitude of accommodation,4 while the effect on accommodative facility is debateable.4,28

There are no published results for binocular vision status while wearing MiSight® (CooperVision, USA) contact lenses. One study assessed differences in binocular vision function while wearing best-corrected subjective refraction in a trial frame between two groups habitually wearing either MiSight or single vision contact lenses.29 There were no differences between groups for distance and near phorias, calculated AC/A ratio, amplitude of accommodation or accommodative response.29

There are also no published results for binocular vision status while wearing MYLO® (mark’ennovy, Spain) contact lenses. One study assessed within-group differences in binocular vision function between a lens of similar design to MYLO (i.e., extended depth of focus [EDOF] designed via deliberate manipulation of multiple modes of spherical aberration terms) and a single vision contact lens.30 There were no significant differences between lens designs for distance and near phoria and accommodative facility, while EDOF lenses provided less central hyperopic defocus.30

Orthokeratology induces more exophoria and less lag of accommodation compared to soft, single vision contact lenses.31

In summary, treating a binocular vision disorder has benefits that may not extend to myopia management. Practitioners performing myopia management should be aware of their patient’s binocular vision status before commencing treatment. Practitioners should also be willing to manage binocular vision disorders, especially when myopia management strategies exacerbate a pre-existing binocular vision disorder.

 

 

 

Daniel Tilia, BOptom (Hons), MOptom, GradCertOcTher, FBCLA, FAAO is a PhD candidate at the Brien Holden Vision Institute.

 

References

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  2. Shin HS, Park SC, Park CM. Relationship between accommodative and vergence dysfunctions and academic achievement for primary school children. Ophthalmic Physiol Opt 2009;29:615-624.
  3. Borsting E, Mitchell GL, Kulp MT, et al. Improvement in academic behaviors following successful treatment of convergence insufficiency. Optom Vis Sci 2012;89:12.
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  9. Drobe B, de Saint-Andre R. The pre-myopic syndrome. Ophthalmic Physiol Opt 1995;15:375-378.
  10. Goss DA. Clinical accommodation and heterophoria findings preceding juvenile onset of myopia. Optom Vis Sci 1991;68:110-116.
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  12. Mutti DO, Mitchell GL, Jones-Jordan LA, et al. The Response AC/A Ratio Before and After the Onset of Myopia. Invest Ophthalmol Vis Sci 2017;58:1594-1602.
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  15. Gwiazda J, Thorn F, Held R. Accommodation, accommodative convergence, and response AC/A ratios before and at the onset of myopia in children. Optom Vis Sci 2005;82:273-278.
  16. Berntsen DA, Sinnott LT, Mutti DO, et al. Accommodative lag and juvenile-onset myopia progression in children wearing refractive correction. Vision Res 2011;51:1039-1046.
  17. Weizhong L, Zhikuan Y, Wen L, et al. A longitudinal study on the relationship between myopia development and near accommodation lag in myopic children. Ophthalmic Physiol Opt 2008;28:57-61.
  18. Zadnik K, Sinnott LT, Cotter SA, et al. Prediction of Juvenile-Onset Myopia. JAMA Ophthalmol 2015;133:683-689.
  19. Progressive-addition lenses versus single-vision lenses for slowing progression of myopia in children with high accommodative lag and near esophoria. Invest Ophthalmol Vis Sci 2011;52:2749-2757.
  20. Cheng D, Woo GC, Drobe B, et al. Effect of bifocal and prismatic bifocal spectacles on myopia progression in children: three-year results of a randomized clinical trial. JAMA Ophthalmol 2014;132:258-264.
  21. Aller TA, Liu M, Wildsoet CF. Myopia Control with Bifocal Contact Lenses: A Randomized Clinical Trial. Optom Vis Sci 2016;93:344-352.
  22. Troilo D, Smith EL, 3rd, Nickla DL, et al. IMI – Report on Experimental Models of Emmetropization and Myopia. Invest Ophthalmol Vis Sci 2019;60:M31-m88.
  23. Chia A, Chua WH, Cheung YB, et al. Atropine for the treatment of childhood myopia: safety and efficacy of 0.5%, 0.1%, and 0.01% doses (Atropine for the Treatment of Myopia 2). Ophthalmology 2012;119:347-354.
  24. Chua WH, Balakrishnan V, Chan YH, et al. Atropine for the treatment of childhood myopia. Ophthalmology 2006;113:2285-2291.
  25. Yam JC, Jiang Y, Tang SM, et al. Low-Concentration Atropine for Myopia Progression (LAMP) Study: A Randomized, Double-Blinded, Placebo-Controlled Trial of 0.05%, 0.025%, and 0.01% Atropine Eye Drops in Myopia Control. Ophthalmology 2019;126:113-124.
  26. Kang P, Wildsoet CF. Acute and short-term changes in visual function with multifocal soft contact lens wear in young adults. Cont Lens Anterior Eye 2016;39:133-140.
  27. Theagarayan B, Radhakrishnan H, Allen PM, et al. The effect of altering spherical aberration on the static accommodative response. Ophthalmic Physiol Opt 2009;29:65-71.
  28. Ozkan J, Fedtke C, Chung J, et al. Short-Term Adaptation of Accommodative Responses in Myopes Fitted With Multifocal Contact Lenses. Eye Contact Lens 2018;44 Suppl 1:S30-s37.
  29. Ruiz-Pomeda A, Perez-Sanchez B, Canadas P, et al. Binocular and accommodative function in the controlled randomized clinical trial MiSight(R) Assessment Study Spain (MASS). Graefes Arch Clin Exp Ophthalmol 2018.
  30. Tilia D, Sha J, Thomas V, et al. Vision Performance and Accommodative/Binocular Function in Children Wearing Prototype Extended Depth-of-Focus Contact Lenses. Eye Contact Lens 2018;[Epub ahead of print].
  31. Gifford K, Gifford P, Hendicott PL, et al. Near binocular visual function in young adult orthokeratology versus soft contact lens wearers. Cont Lens Anterior Eye 2017;40:184-189.

 

 

 

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