do you know how myopia management contacts work? my understanding is that they're multifocal and this slows down myopia progression somehow????
Ooh an optics and physiology question. I'm going to need diagrams.
The main reasons for myopia in the first place is a long Axial length (eye too long) or the front curvature of the eye is too steep. Soft contact lens myopia control goes with the Axial length problem.
Traditional myopia glasses can focus light correctly at the fovea (central reading vision) but miss the retina in the periphery. They actually overshoot the retina and cause hyperopic defocus, so the image is behind the eye. This gives a young eye stimulus to grow longer to reach that defocused image. Myopia control is for kids/teens due to their rapid growth rate which responds to this stimulus.
I'll link the paper this diagram comes from at the end. The left image shows the hyperopic defocus. The right image shows a theoretical glasses lens that causes myopic defocus, no stimulus for axial elongation.
You can cause myopic defocus by undercorrecting the glasses or contact lenses with less Rx than the child needs, but that causes blurred vision. We can't have kids walking around blurry while also trying to teach them how to read. Bifocals were the first attempt, but only having 1 hemisphere undercorrected wasn't enough. Multifocal contact lenses used in myopia control have a reading add (plus power) in concentric rings.
The center distance design gives clear distance vision in the middle and reading power on the outer edges 360. Myopic defocus, no stimulus for growth, less axial elongation. I say less because this slows the rate of growth but does not halt it completely; kids' bodies are still growing and that includes their eyes.
Last myopia control article I read had three different glasses lens companies coming out with myopia control glasses with a myopic defocus on the periphery. I haven't seen the clinical results yet since they are so new.
Other options for myopia control are Ortho-keratology and atropine 0.05% drops.
Myopia is the most common refractive error in the world, and its’ prevalence continually increases. The potential pathological and visual co
