The good eye is covered to activate visual development in the eye with poorer vision. The duration of the covering is adjusted individually, depending on the age of the child and the severity of the visual impairment. Regular checks are carried out to see whether the visual acuity of the worse eye improves. The aim is to achieve equal visual acuity for near and far. This is usually only achieved after months to years. Subsequently, a reduced period of coverage may be necessary to maintain visual acuity until around the age of 10. After that, the risk of the eye becoming weak-sighted again decreases.
An existing strabismus or defective vision is not corrected by the masking treatment. Conspicuous strabismus can be improved after masking treatment with eye muscle surgery, but a high degree of defective vision usually remains.