The current theory of accommodation is the one proposed by Helmholtz which says that the ciliary muscles contracts which relaxes the lens zonules, allowing the lens to bulge more, thus increasing its power.
As we age, the composition of the lens changes and causes it to harden.
because the lens is stiffer, it cannot change shape per the Helmholtz theory.
The time when the lens stiff enough to not allow for accommodation is sometime during the 40s in most people.
There are not exercises or medicines that will prevent the lens changes from occurring.
The lens hardening can happen faster in people who have general poor health, increase UV sun exposure, poor diet.
So, being healthy with proper nutrition is the best way to delay the loss of accommodation, however, it is something that everyone will have to deal with.
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