The "zoom" function of the eye is performed by the crystalline lens. When the lens is young, it is transparent and elastic, and able to change its shape to focus on distant and nearby objects. This movement is achieved through a precise and complex combination of functions carried out by different eye structures (ciliary muscle, zonule of Zinn, pressure of the vitreous body, etc.). The transparency of the crystalline lens ensures that images are focused sharply on the retina, which, using the analogy with the camera, would be the "photographic film". From the age of 40, the crystalline lens ages and gradually loses its properties: elasticity, transparency and ability to focus. Depending on the condition of the eye, presbyopia can have different consequences.
Presbyopia in myopic patients
Myopic patients have difficulty focusing on distant objects. After the age of 40, the condition usually stabilises, but presbyopia increases. These patients require glasses with a lower optical power for near vision than for distance vision.
Presbyopia in hyperopic patients
Hyperopia particularly affects near vision. It is similar to presbyopia, although hyperopia is stable and presbyopia is progressive. As a result, hyperopia is often mistakenly called "old eyes". These patients gradually lose vision at all distances and, in general, rapidly. They require glasses for near and distance vision.
Presbyopia in patients who have never worn glasses
These patients, who are usually between the ages of 40 and 45, only need glasses for near vision tasks. The optical power is usually low at first, but increases later.