Relationship between near phoria, fusional amplitudes and personalized addition values for myopia control

Abstract

Purpose : Personalized addition values for myopia control were determined based on the highest addition that satisfied Sheard’s criterion without inducing any lead of accommodation. This study examines the relationship between near phoria, fusional amplitudes and personalized addition values in a sample of myopic children.

Methods : Two hundred and eleven Chinese myopic children (7 to 12 years old) with myopia between -0.75 and -4.00D (cycloplegic autorefraction) were enrolled in PACT (Personalized Addition value Clinical Trial). Near phoria was measured at 33 cm using the modified Thorington test and either base-in (near esophoria) or base-out fusional amplitudes (FA) (near exophoria & orthophoria) were measured with a phoropter with the children wearing their far vision prescription. Three measurements of each parameter were averaged for analysis. Personalized addition value was determined for each child by a non-linear regression using a FA/Phoria = abs(a/(b × Addition + c)) rational function, where “a” represents a form factor and “–c/b” the addition value for which the phoria is null.

Results : When measured without any addition, personalized addition (pADD) values increased significantly when near esophoria increased or exophoria decreased (r² = 0.19, P < 0.001). There was no correlation between personalized addition values and FA (r² = 0.002, P = 0.523). A multivariate linear regression, performed to quantify the variation of pADD with near phoria and FA when measured without any addition value, explained only a limited amount of variance (r² = 0.263, pADD = 1.411+ 0.078×Phoria + 0.027×FA).

Conclusions : Only near phoria values or fusional amplitudes measured without any addition are not enough to obtain a good estimation of personalized addition values based on Sheard’s criterion. According to our previous study (Yu et al., OVS, 2015), near addition lens values should be calculated for each addition and fitted using a rational function to satisfy Sheard’s criterion (FA/Phoria ≥ 2).

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.