Original Articles

Authors: Dr Grant Hannaford & Thao Hannaford

1. General Principles of Myopia Control Spectacle Designs

Current myopia control spectacle designs (e.g., DIMS/HALT lenses like Hoya MiYOSMART, Essilor Stellest; Defocus Incorporated Multiple Segments; Highly Aspherical Lenslets; Rodenstock MyCon; Zeiss MyoCare) rely on introducing controlled peripheral or simultaneous myopic defocus while maintaining clear central vision.

• They assume stable binocular vision so the wearer can process simultaneous foci without inducing suppression or asthenopia.
• Patients with compromised binocular vision (BV) may not respond as expected, or may experience symptoms such as diplopia, blur, or discomfort.

2. Binocular Vision Conditions That Reduce Efficacy

A. Significant Phorias and Tropias

• Constant strabismus (eso/exotropia):
  • The myopic defocus signal will be poorly integrated due to suppression of one eye.
  • Studies suggest reduced effectiveness in non-fusing patients.
• Large latent phorias:
  • Exophoria at near can decompensate due to peripheral blur, increasing symptoms.
  • High esophoria may interact negatively with plus power zones (particularly in designs with lenslets creating near-defocus patterns).

B. Reduced Fusional Vergence Reserves

• Children with limited vergence adaptation may struggle to tolerate simultaneous blur/clear signals.
• Reduced convergence reserves at near can lead to fatigue and poor compliance.

C. Accommodative Dysfunction

• Accommodative insufficiency or infacility:
  • The additional blur from defocus segments may exacerbate symptoms.
  • Compliance and wear time often drop in these cases.
• High accommodative lag:
  • These patients benefit more from near addition or progressive lenses; defocus spectacle designs may not fully compensate.

D. Suppression and Stereopsis Deficits

• Suppression scotomas in intermittent strabismus or amblyopia mean the retina is not sampling the intended peripheral defocus.
• Reduced stereoacuity correlates with weaker treatment effects, as binocular integration is part of the underlying emmetropisation feedback loop.

3. Clinical Preclusions and Cautions

• Unstable binocular vision status (decompensating phoria, recent strabismus surgery).
• Amblyopia (especially with poor fixation in one eye).
• Poor compliance risk due to discomfort from blur zones (needs careful adaptation trials).
• Near work symptoms exacerbated by induced defocus (important in high academic load children).

4. Suitable Candidates

• Children with stable binocular alignment, normal accommodative function, and good stereoacuity.
• Mild phorias that are well-compensated with good vergence reserves.
• Motivated families who understand the need for full-time wear to achieve efficacy.

5. Clinical Recommendations

• Always perform a full BV assessment (cover test, vergence ranges, near point of convergence, accommodative function, stereoacuity) before prescribing.
• If issues are detected, consider:
  • Vision therapy or orthoptic exercises before/alongside lens prescription.
  • Alternative myopia control modalities (orthokeratology, soft myopia control contact lenses, low-dose atropine) when BV limitations are significant.
• Review compliance and symptoms at 1–3 months after dispensing to ensure tolerance.

✅ In summary:

Myopia control spectacle lenses are most effective in children with stable binocular vision and good accommodative function. Significant strabismus, suppression, poor stereoacuity, large uncompensated phorias, or accommodative dysfunction may preclude their use or reduce efficacy, necessitating alternative approaches.

Conditions and Preclusions for Prescribing Myopia Control Spectacle Lenses

1. Lenslet-Based Designs (DIMS, HALT, MyoCare, MyCon, etc.)

These lenses employ multiple defocus segments or aspherical lenslets to provide simultaneous myopic defocus.

• Require: stable binocular vision, balanced accommodation, intact stereoacuity.
• Precluded by:
  • Constant tropia (due to suppression).
  • Large, uncompensated heterophorias (eso >6Δ, exo >10Δ at near).
  • Significant suppression or abnormal retinal correspondence.
  • Accommodative dysfunctions (lag, insufficiency, infacility).

2. Progressive Addition Lenses (PALs)

PALs have been investigated (e.g., COMET study). They offer modest efficacy (~15–20% slowing of myopia).

• Useful in: high accommodative lag and near esophoria, where plus at near reduces strain.
• Limitations: limited peripheral defocus signal; less potent effect compared with lenslets.
• Precluded by:
  • Poor adaptation to progressive optics.
  • Symptomatic exophoria (may worsen).

3. Executive Bifocals and Prism-Control Bifocals

These lenses are a distinct category with both optical and binocular vision effects.

• Mechanism:
  • The segment add provides constant near plus, reducing accommodative lag.
  • When combined with base-in prism, they directly relieve convergence demand in children with near esophoria or accommodative lag.
  • Some randomised controlled trials (e.g., Cheng et al., 2010 with 3 base-in prism in the near segment) show ~50% reduction in progression, particularly effective in children with esophoria at near.

• Indications:
  • Near esophoria with high accommodative lag.
  • Symptomatic children with poor adaptation to lenslets.
  • Cases where binocular vision anomalies are the suspected driver of progression.

• Advantages:
  • Targeted therapy for a specific subgroup of myopes (eso + lag).
  • Stronger efficacy in this subgroup compared with standard PALs or lenslet lenses.

• Limitations:
  • Cosmesis (executive bifocal line).
  • Risk of adaptation issues in children without esophoria.
  • Less effective in exophoria or well-compensated phorias.

• Precluded by:
  • Exophoria at near (base-in prism reduces convergence demand, which worsens exo).
  • Tropia or suppression (no benefit from vergence demand management).
  • Poor compliance due to cosmesis (especially in older children/teens).

4. Clinical Decision Framework

• Stable BV, normal accommodation → Lenslet lenses (MiYOSMART, Stellest, MyoCare, etc.).
• High accommodative lag, near esophoria → Consider PALs or bifocals.
• Near esophoria + accommodative lag not corrected by PALs → Prism-control executive bifocals.
• Strabismus, amblyopia, suppression → Poor candidates for optical myopia control → consider atropine or contact lens modalities instead.
• High exophoria → Caution: avoid bifocals with base-in prism; lenslets may be trialled if well compensated.

✅ Summary

• Lenslet myopia control designs require intact binocular integration and are precluded in strabismus, suppression, or severe phorias.
• PALs are modestly effective, mainly useful in accommodative lag with eso tendencies.
• Prism-control bifocals are uniquely valuable in near esophoria + accommodative lag, where they outperform both PALs and lenslet lenses.
• A BV assessment is non-negotiable in deciding which category of lens to prescribe.