CITT-trained and certified optometrists or ophthalmologists using a previously described standardized protocol performed all testing (baseline and masked). An unmasked examiner performed eligibility testing, which included the following: best-corrected visual acuity at distance and near; cover testing at distance and near with objective prism neutralization; near point of convergence; positive and negative fusional vergence at near (fusional convergence and divergence amplitudes); near stereoacuity; monocular accommodative amplitude; and monocular accommodative facility (the ability to quickly achieve clear vision while alternately viewing 20/30 equivalent print through +2 D and −2 D lenses); cycloplegic refraction with 1% cyclopentolate; and an ocular health evaluation. All near testing with at 40cm. A masked examiner administered the CISS.
Major eligibility criteria for the study included best-corrected visual acuity at distance and near of 20/25 or better, no strabismus, heterophoria at near between 2Δ esophoria and 8Δ exophoria, near point of convergence closer than 6.0 cm break, negative fusional vergence at near greater than 7Δ BI-break and 5Δ BI-recovery, positive fusional vergence at near greater than 10Δ BO-break and 7Δ BO-recovery, monocular amplitude of accommodation in diopters greater than 15 minus 25% of the child’s age, and at least 500 seconds of arc of random dot stereopsis on the Randot® Stereotest (Stereo Optical Co, Chicago, IL). A refractive correction was required when the magnitude of uncorrected refractive error or change in refractive error (based on a cycloplegic refraction performed within 2 months) in either eye differed from the current prescription by 0.50 D or more in spherical equivalent of myopia, 1.50D or greater in spherical equivalent of hyperopia, or 0.75 D or greater of astigmatism. Table 1 has the complete listing of eligibility and exclusion criteria.