When I was at optometry school there was mention that some practitioners would under correct people with myopia in order to stop or slow down its progression. Nothing further was said about whether this was a successful technique.
In my experience, some practitioners remain of the opinion that under correcting myopia, prescribing glasses with less minus necessary to give a sharp focus on the fovea, will slow myopic progression. Under-correction of myopia has been considered as a reasonable approach to slow the progression of a child’s or a young adult’s myopic progression for many years.
The idea is that prescription of spectacle lenses with under-correction of modest magnitude (e.g., 0.50D) would reduce the near accommodative stimulus, and in-turn partially reduced the blur-driven accommodative response required for clarity of near vision without much sacrifice to distance visual acuity.
In addition, it reduced the potentially retinal defocus at near, as it also effectively functioned as a low plus lens add for near to reduce the blur-driven component of the overall accommodative stimulus.
Reasonable research has shown that this approach is likely to increase myopic progression and not slow it.
Recent research has shown that cells in the retina are sensitive to defocus and can even tell if the focal point of the miss focus is in front of or behind the eye. Myopic miss focus at the fovea is shown to be a driver of eye elongation and therefore of myopic progression. Hyperopic defocus in the retinal periphery is known to be a driver for ocular elongation and myopic progression. Hyperopic defocus at the fovea has not shown to be a driver for ocular elongation and myopic progression.
In summary, under-correction of myopes by a modest magnitude will not slow myopic progression but increase it.