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Presbyopia
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Presbyopia is the change in eyesight that comes with age: little by little, the eye loses its ability to focus on things up close. It is common, and it happens to nearly all adults after age 40.
To understand it, you need to know about the lens, the natural focusing lens inside the eye. In a young person it is flexible, and when the ciliary muscle, a muscle inside the eye, contracts, the lens changes shape. That change is what lets us focus up close, and it is called accommodation. Over the years, the proteins in the lens gradually bond to one another, or cross-link, and the lens becomes stiffer and stiffer. Think of a new eraser that bends easily, and an old one that has hardened and barely gives.
When accommodation declines, the image of nearby things comes into focus behind the retina, the layer at the back of the eye that receives the image, instead of right on it. That is why, at first, small print becomes hard to read, especially in dim light, like a restaurant menu in a dark room.
In brief
Presbyopia, common with aging, gradually reduces the eye's ability to focus up close in nearly all adults over 40.
The young lens is flexible and changes shape when the ciliary muscle contracts; with age, its proteins cross-link and it becomes stiffer.
A soft lens that hardens over the years and changes shape less.
Accommodation declines and near images come into focus behind the retina; at first, small print becomes hard to read, especially in dim light.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPresbyopia, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated