MAY 30, 2012
This prospective study in the January issue of Ophthalmology examined the effectiveness of optical correction alone in the form of spectacles at improving visual acuity in children with strabismic and combined strabismic-anisometropic (combined-mechanism) amblyopia. The results indicate that optical treatment alone of strabismic and combined-mechanism amblyopia resulted in clinically meaningful improvement in amblyopic eye visual acuity for most children between the ages of 3 and 6, with the condition resolving in at least 25 percent of them without additional treatment. The authors recommend consideration of prescribing refractive correction as the sole initial treatment for children with strabismic or combined-mechanism amblyopia before initiating other therapies.
The study included 146 children between ages 3 and 6 with previously untreated strabismic amblyopia (n = 52) or combined-mechanism amblyopia (n = 94). Optical treatment was provided as spectacles (prescription based on a cycloplegic refraction) that were worn for the first time at the baseline visit. Visual acuity with spectacles was measured using the Amblyopia Treatment Study HOTV visual acuity protocol at baseline and every nine weeks thereafter until there was no further improvement in visual acuity.
At 18 weeks, amblyopic eye visual acuity had improved by a mean of 2.6 lines (95% confidence interval [CI], 2.3 - 3.0), with 75 percent of children improving by at least two lines and 54 percent improving by at least three lines. Resolution of amblyopia occurred in 32 percent (95% CI, 24% - 41%) of the children. The treatment effect was greater for strabismic amblyopia than combined-mechanism amblyopia (3.2 vs. 2.3 lines; adjusted P = 0.003). Visual acuity improved regardless of whether eye alignment improved.
The authors say that the gains in amblyopic eye visual acuity were similar for all children regardless of angle of deviation. They found no association between visual acuity improvement and ocular alignment at baseline or subsequent visits.
The time course of maximum improvement in amblyopic eye visual acuity varied, with approximately 50 percent of the children achieving their best acuity by nine weeks, 90 percent by 18 weeks and all of them by 45 weeks. Given this variability and that nearly one third experienced resolution with spectacles alone, the authors say it is reasonable to monitor visual acuity in spectacles until no further improvement has occurred before instituting additional amblyopia treatment.
They note that improvement in amblyopic eye visual acuity with spectacles alone in patients with pure anisometropic amblyopia is understandable because the refractive correction provides equally clear retinal images. However, they say that the mechanism by which visual acuity improves in strabismic amblyopia, with or without anisometropia, is not apparent unless the optical correction eliminates the patient's strabismus at one position of gaze, thereby allowing binocular vision.