JUN 09, 2014
This prospective study found that bifocal lenses can slow high myopia progression in children even during the third year of treatment, and that prismatic bifocals are more effective for myopic children with low lags of accommodation.
Investigators compared the effect of single-vision lenses, regular bifocals and prismatic bifocals in controlling high myopia progression in children. Subjects included 128 Chinese-Canadian children aged 8 to 13 years (mean age, 10.29 years) with mean myopia of −3.08 D and myopia progression of at least 0.50 D in the preceding year randomly assigned to single-vision lenses, +1.50 D executive bifocals, or +1.50 D executive bifocals with 3-Δ base-in prism in the near segment of each lens.
Over the three-year treatment period, both bifocals and prismatic bifocals significantly inhibited myopia progression compared with single-vision lenses, and the magnitude of myopia inhibition was similar. The observed treatment effect of both bifocals and prismatic bifocals accumulated over time but was greatest in the first year and then decreased and was sustained in the second and third years. The results also suggested that bifocals were as effective as prismatic bifocals for myopic children with high lags of accommodation, whereas for children with low lags, prismatic bifocals produced a greater treatment effect. The treatment effect of both bifocals and prismatic bifocals was independent of the near phoria status.
They write that the lack of an effect of phoria status may be related to the fact that a large portion of esophoric children will have significant lens-induced exophoria with the bifocals in place because of the high response accommodation convergence to accommodation ratio usually found in this group of children. They speculate that in prescribing bifocals for myopia control, it is the state of lens-induced near phoria instead of baseline near phoria that plays a role in determining success because it is this uncontrolled phoria that disrupts the oculomotor equilibrium.