We all will experience around the age of 40 a decrease in focusing power at near. Depending on the current state of your vision, that will determine if you would need reading glasses, bifocals or progressives. For those whose distance is 20/20 or close to it possibly just a pair of over the counter readers or customized reading glasses would be enough to help with the changes in vision. Though most patients like the convince of having their distance vision and near vision all in one lens. If you already wear glasses for distance then bifocals or progressive would be a better option.
Both bifocals and progressive are lens designs that one has to take the time with adapting. This means that a patient may need to gradually wear the glasses. Starting with a few hours a day in a safe and familiar environment then increase a few hours at a time until the patient can wear the glasses for a full day.