Why your arms got shorter after forty

Somewhere between the late thirties and the mid forties, almost everyone notices the same thing: the menu has to be held further away, the phone is harder in dim light, and threading a needle has become someone else's job.

This is presbyopia. It is universal, it is not a disease, and it is not caused by reading too much, using screens, or having worn spectacles.

What is actually happening

Inside the eye, behind the iris, sits a transparent lens. To focus on something close, a ring of muscle contracts and the lens becomes more curved. That change of shape is called accommodation, and it depends on the lens being flexible.

The lens grows throughout life, adding layers, and stiffens as it does. From childhood onward the amount of accommodation available declines steadily. It simply happens that the decline crosses the threshold needed for comfortable reading at around the age of forty-five — earlier if you are long-sighted, later if you are short-sighted.

The process is entirely normal. Nothing you did brought it on and nothing will stop it. It continues until around sixty-five, by which point accommodation is essentially gone, and then it is over.

Why short-sighted people are smug about it

If you are short-sighted, your eye focuses at a near point without any effort at all. Take your distance spectacles off and you can read comfortably. You have not escaped presbyopia — you have a built-in workaround. Whether that remains convenient depends on the strength of your prescription and how much of your day involves switching between distance and near.

The options

Reading spectacles. Simple, effective, cheap. Suitable if your distance vision is good and you need help only at near. The drawback is having to take them off to see across the room.

Ready-made readers. A reasonable stopgap. They correct both eyes identically, do not correct astigmatism, and are not centred for your pupils, so they suit people whose two eyes happen to need the same thing and who use them only briefly. They are not a substitute for an examination — which is the real cost of relying on them, because the examination is what would find glaucoma.

Bifocals. Distance above, reading below, with a visible line. Effective and inexpensive; the abrupt jump at the line takes some getting used to, and there is no intermediate zone, which is awkward for computer work.

Varifocals (progressives). A continuous gradient from distance through intermediate to near, with no line. The most versatile option, and what most people settle on. There is an adaptation period of a week or two, the clear corridor narrows as it descends, and the peripheral parts of the lens are distorted — which is why the fit and the frame matter and why these are worth buying from someone who measures properly.

Occupational lenses. If your day is a desk, a lens optimised for screen-and-paper distance is more comfortable than a general-purpose varifocal, as a second pair.

Contact lenses. Multifocal lenses exist and work well for many people. Monovision — one eye corrected for distance, the other for near — suits some and not others; it can be trialled before committing.

Two things worth knowing

The prescription will change for a while. Expect updates every couple of years until the process completes. This is not the spectacles "making your eyes worse" — a persistent belief, and a false one. The lens inside your eye is stiffening on its own schedule.

Forty-five is when other things start too. Glaucoma risk rises, as does the risk of diabetic and hypertensive retinal change. The appointment you make because reading has become difficult is a good opportunity to check for the conditions that give no warning at all. Ask for a comprehensive examination rather than a reading test.

When it is not presbyopia

See someone promptly rather than buying readers if near vision has changed suddenly, if one eye is much worse than the other, if straight lines look bent or wavy, if there is a patch missing in the centre of your vision, or if reading difficulty comes with headaches, double vision or eye pain.