Introduction

Photo of a man reading something on a tablet device (PantherMedia / Fabrice Michaudeau)

It happens to all of us eventually: You have to start holding newspapers or books further away in order to be able to read them and clearly recognize letters without straining your eyes.

Seeing nearby objects less clearly is a normal part of aging. Known as presbyopia, this typically becomes noticeable in your mid-forties.

Although there are no effective treatments for the causes of presbyopia, the effects can be corrected. The best and easiest way to do so is using reading glasses.

Symptoms

Early signs of presbyopia usually become apparent when reading – especially when you're tired or reading in dim light. It gets harder to read for longer periods of time because the letters start blurring. You have to strain your eyes to see clearly and they might start burning. You may also get a headache after a while.

Causes

In order for you to see clearly, the lenses of your eyes have to be able to change shape. The job of the lens is to focus light onto the retina to produce sharp images. You can only see both nearby and faraway objects clearly if your eyes are able to adjust to various distances. To do so, the lenses of your eyes change their refractive power (focusing power) by changing their shape: When looking at nearby objects the lenses become curved and thicker, and when looking at faraway objects they become flatter and thinner. The medical term for these adjustments is accommodation.

The movements that cause the lens to change shape are controlled by a circular muscle known as the ciliary muscle, which surrounds the lens and is attached to it by fine fibers. In order for you to see nearby objects, the ciliary muscle contracts, making the lens curve and thicken. But the lenses of your eyes become harder and less flexible with age, so they start losing their ability to change shape. The ciliary muscle becomes weaker over time too.

Presbyopia could be described as age-related farsightedness. But normal farsightedness (hyperopia), which often already becomes noticeable in childhood, is caused by something else: People with hyperopia are usually born with eyeballs that are too short. When they look at nearby objects, the refractive power of the eye lens isn't high enough to focus light onto the retina. As a result, the eye can only see objects clearly if they are further away, and nearby objects appear to be blurred.

 

 Illustration: Adjusting to nearby and distant objects – as described in the articleAdjusting to nearby and distant objects

Risk factors

While some people already start having trouble reading in their early forties, this may only happen much later in others. It's not clear why that is. What is known, though, is that people who have medical conditions like diabetes, cardiovascular disease or multiple sclerosis may develop presbyopia at a younger age.

Women often start wearing reading glasses at a younger age than men do. This is mainly because they tend to do something about the problem sooner, though. There is no difference between men and women in terms of when presbyopia starts.

Outlook

Toddlers can often see objects clearly even if they are right in front of their eyes. This ability is lost as people grow older. A reading distance of about 35 cm is considered to be normal in adults. This distance gradually increases in your early forties, and most of us will need reading glasses by the age of 45. People tend to become increasingly farsighted until around the age of 60, when presbyopia generally stabilizes.

In shortsighted people, who have problems seeing distant objects clearly, the effects of presbyopia are usually milder and occur later. They can counterbalance these effects by not wearing their glasses.

In contrast, the hardening of the eye lenses is more of a problem for people who are already farsighted because it then becomes even harder for their eyes to adjust to see nearby objects.

Diagnosis

Presbyopia can be diagnosed by an ophthalmologist (an eye doctor) or at an optician's. This involves using a small instrument (a phoropter) to measure the refractive power of your eyes, followed by an eye test to determine the prescription strength needed for corrective lenses. In the eye test you are asked to look at eye charts or projected letters, numbers or at broken rings of decreasing size. Because your eyesight is usually different in each eye, your eyes are tested separately by first covering one eye and then covering the other. The results of the test determine what kind of corrective lenses are needed to improve your sight.

Like the refractive power of your natural eye lenses, the refractive power of glasses or contact lenses are measured in diopters (D).

 

 Illustration: Correcting presbyopia – as described in the articleCorrecting presbyopia

Prevention

Special eye exercises are sometimes recommended for the prevention of presbyopia. These exercises usually focus on training the eye muscles. Even if there are a lot of descriptions of how to do such eye exercises on the internet or in books, doing them won't prevent presbyopia. Training the ciliary muscles in your eyes won't stop your eye lenses from becoming harder and less flexible as you grow older.

Treatment

Although there are no effective treatments to fight the cause of presbyopia, the effects of presbyopia are easily corrected. The easiest way to solve the problem of not being able to see nearby objects is wearing ready-made reading glasses available in shops. But these readily available reading glasses don't account for possible differences in vision between your eyes or other features, such as astigmatism (an irregularly shaped cornea). Individually adjusted prescription reading glasses are only available from an optician's, where glasses with the required lens power are made especially based on the results of an eye test. The distance between the pupils of your eyes and other factors are also taken into account. Reading glasses are often narrow enough for you to be able to look over them if you want to see things that are further away.

If you already wore prescription glasses before presbyopia started becoming an issue, multifocals are an option. Bifocal glasses (bifocals) are one type of multifocal glasses. They have two zones divided in the middle by a visible horizontal line. The lower half of the glasses is for looking at nearby objects, and the upper half is for looking at objects that are further away. Trifocals have a visibly separate third zone for seeing objects at intermediate distances too. In varifocals (also known as progressive lenses), the lines dividing the different zones have been smoothly polished so you can’t see them. They are the most common kind of glasses.

 

Illustration: Varifocals (progressive lenses) with gradual change in strength

As an alternative to glasses, contact lenses can be used to correct the effects of presbyopia too. But because people who have presbyopia don’t usually need corrective lenses at all times in order to see clearly, contact lenses make more sense for people who already needed glasses or contact lenses before. You can get the right kind of contact lenses for you from an eye doctor (ophthalmologist) or an optician’s. People with presbyopia can use bifocal or multifocal contact lenses. A third kind of contact lenses, known as “monovision” contact lenses, are also available. Here you wear a contact lens to see nearby objects in one eye (the “reading eye”), and a contact lens to see objects that are further away in the other eye. It can take a while to get used to monovision contact lenses. What’s more, people who use monovision contact lenses need to wear distance glasses when driving, so the “reading eye” can see objects that are further away clearly and to enable spatial vision.

Laser treatment is often advertised in magazines and on the internet, and sometimes recommended by doctors too. But this treatment approach isn’t suitable for people who only have presbyopia and no other problems affecting their vision. Although people who have laser treatment may not need reading glasses, or may only need to start wearing them later, this purely cosmetic outcome has possible disadvantages such as problems with spatial vision or trouble seeing things in the distance. Laser treatment is also associated with risks, including a general worsening of vision and potential complications of the procedure.

The same is true for other surgical procedures like the implantation of synthetic lenses and corneal inlays. The advantages of not having to wear reading glasses have to be weighed against the possible risks and consequences associated with eye surgery.

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