Around the age of 40, the eye will slowly lose accommodation capacity because the lens of the eye becomes less flexible and cannot become convex enough to see nearby objects sharply. This is called presbyopia (old-sightedness). The bottom line is that the proximity point (see schematic image) will be further away. It is a normal condition, which is age-related and will therefore affect everyone. The ideal reading glasses depict an object that is approximately 30 cm away in the proximity point. The reading glasses thus compensate for the shortage of accommodation, so that close vision can be seen again.
If someone is also nearsighted or farsighted, the correction required for presbyopia is added to the pre-existing myopia or hyperopia correction. The extra strength for presbyopia correction is called reading addition or simply addition. It is therefore possible that reading glasses are negative. This will be the case when the myopia correction is stronger than the reading addition. The reading glasses are then always less negative than the myopia correction. Many of these people, in their early presbyopia, when they had no reading glasses or reading area, had the habit of taking off their (normal) glasses when reading: at short distances, the presbyopia was more or less compensated by the myopia.
The reading addition can also be integrated into ordinary glasses. This then results in a bifocal (possibly even a trifocal) or a multifocal lens.
Some spectacle wearers find that separate screen glasses – with or without a reading area – are more comfortable with long-term screen use than multifocal glasses with a relatively small area for screen use.