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Kate Gifford, Katrina L Schmid, Peter L Hendicott; The interaction of vergence and tonic accommodation in pediatric myopic contact lens wear. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2959. doi: https://doi.org/.
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Numerous models link myopia to accommodative inaccuracy. While accommodation has been shown to respond to open-looped vergence cues and its interaction with closed-loop vergence measures has been modelled, it has not been experimentally demonstrated. We compared measures in single vision soft contact lens (SCL) and orthokeratology (OK) wear in myopic children to determine if changes in binocular vergence provided a directional cue for changes in tonic accommodation.
Sixteen children (8-16 years) were recruited to compare baseline measures in single vision soft contact lenses (SCL) to 12 months of OK wear. Monocular tonic accommodation measures using a free-space autorefractor (Shin-Nippon SRW-5000, Japan) were dark induced tonic accommodation (TA) and nearwork induced transient myopia (NITM: measured after 4D demand for 7 min). Binocular vergence outcome measures were distance phoria, near phoria, base-in (BIFR) and base-out fusional reserves (BOFR: blur, break and recovery measures).
Twelve children (13.2±2.1yrs, R-2.55±1.32D L-2.61±1.28D) completed the study. TA gain was -0.16±0.35D (p=0.048) and NITM reduction was 0.59±0.41D (p=0.046). Distance phoria did not change (p=0.11); near phoria became more exophoric (-1.1±0.9Δ, p=0.006); BOFR blur (p=0.47) and break (p=0.33) did not change while BOFR recovery reduced (5.2±5.8Δ, p=0.042). BIFR increased in blur (3.2±3.5Δ, p=0.036), break (3.1±2.9Δ, p=0.033) and recovery (3.1±4.1Δ, p=0.022) measures. Lower baseline TA was correlated with lower BIFR (blur, break and recovery) in SCL wear (blur: r=-0.54, p=0.047), with this relationship affirmed in OK wear (blur: r=-0.58, p=0.030). NITM improved more with reduced BOFR (recovery: r=-0.78, p=0.001). There were no correlations between level of myopia and any of the experimental measures.
OK improved TA, NITM and BIFR in pediatric myopes, with loss in one BOFR measure. Cross-linked higher convergence/lower accommodation relationships were shown whereby improvements in TA and reduction in NITM occurred with improvements in divergence, indicating a monocular residual of binocular proximal convergent accommodation. This is the first experimental demonstration to confirm modelled relationships, and indicates a beneficial effect of OK on visual function in the young myope, with responses shifting towards improved accuracy as in emmetropia.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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