How does axial length increase in myopia? Do regular glasses cause an increase in axial length & myopia? Also, how do contacts like MiSight aim to control myopia? Thanks!
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In order to see clearly, our eyes need to focus incoming light onto our retina. Light from different sources needs to be bent differently in order to focus. Light from nearby objects needs to be bent more than light from distant objects.
We can control how much we bend the light by stretching or relaxing a structure in the eye called the lens. However, we can only stretch or relax it so much, leading to a range of distances that we can focus on.
The longer the axial length, the less the light needs to be bent in order to come into focus. This decreased bending requirement means that it is easier to focus on nearby objects, but harder to focus on far away objects, hence myopia
Glasses and contacts primarily act to prebend the light. The glasses bend the incoming light out so that the eye needs to bend that light inward more, allowing people with myopia to focus things that are far away. Glasses for people with hyperopia bend light the other way, letting them focus things that are nearby.
OPTOMETRIST here….
How does axial length increase in myopia? It’s a complex process that we don’t completely understand. However, we are fairly sure that blur around the area of focus stimulates growth hormone to increase axial length and Corneal curvature. In many cases, corneal curvature is responsible for a lot of low to moderate myopia, along with small-ish increases in axial length. In higher amounts of myopia, axial length seems to take a larger role.
Do regular glasses cause an increase in axial length & myopia? Probably not directly; maybe somewhat indirectly. We do know that sustained near work (reading and writing at normal reading distances) plays a role in stimulating increased myopia. Correcting a person who is myopic with glasses or contacts simulates moving objects closer. But it’s also true that people who are becoming more nearsighted seem to continue to get more nearsighted even when they don’t wear correction.
Also, how do contacts like MiSight aim to control myopia? MiSight lenses use an aspheric design that is supposed to decrease blur on the retina outside of the fovea (the fovea is the part of the retina where the ‘center of vision’ focuses). This should, if the theory is correct about what causes myopia in the first place, decrease the amount of myopic progression.
Alcon, creators of MiSight lenses tout studies with some very strong claims about myopia control. I think the jury is out on how well this actually works, but it does look somewhat promising. I don’t want to bash Alcon too much on this, but I have not found them to be 100% trustworthy on some of their claims in the past, so pardon me if I don’t back their claims as strongly as their website suggests.
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