Astigmatism is a common visual distortion caused by an irregular shape of the cornea.
Light rays passing through an irregularly shaped cornea produce two different focal points. As a result, vision is blurred at various distances. Astigmatism is usually hereditary, although other factors such as poor light levels or fatigue may contribute. Symptoms include squinting, occasional headaches and eye strain. In most cases, astigmatism is accompanied by nearsightedness and farsightedness.
A myopic eye is able to see objects clearly within a certain distance, while distance vision is always blurry.
In most cases, myopia occurs when the eyeball is too long for the focusing power of the crystalline lens and the cornea and makes the eye too powerful, causing images to be focused in front of the retina. To solve this problem, a “negative” lens is needed to “weaken” the eye so as to allow clear vision from a distance.
Hypermetropia occurs when an eyeball is too short for the focusing power of the lens and cornea.
This causes light to be focused behind the retina. The eye then sees distant objects more clearly, while near objects appear blurry. In this situation, the eye has a reduced ability to see. In order to correct this problem, a “positive” lens is needed that allows for clear vision of nearby objects. The hypermetropic can see objects to infinity only using the mechanism of accommodation and, for this reason, his ciliary muscle is never fully relaxed. The main symptoms are headaches, burning, tearing and occur especially in near vision, as a result of excessive use of accommodation, such as too much study. Only in a more advanced stage there is a decline in visual acuity that manifests itself first in near vision then also in distance vision, when accommodation is no longer able to compensate for hyperopia.
Presbyopia, the ancient used the word for “aging eye,” is caused by the natural aging and stiffening of the eye’s lens.
In people after age 40, the lens thickens and begins to lose elasticity. Gradually, control of the eye muscle decreases and people experience increasing difficulty in focusing on nearby objects. In addition to blurry vision, symptoms include: eye strain and a tendency to pull reading material away from the eyes. A curiosity about presbyopia: according to several studies, it is lower for people living in low latitudes.
Solutions for presbyopia
The approach to far or near vision changes from person to person, according to daily needs, and deeply influences expectations and perception of comfort.
Progressive lenses allows to shape the original design of a progressive lens through the continuous variation of some key parameters
- far/close amplitude ratio;
- length and inset of the progression channel;
- far/close balance adjustment based on lifestyle, reading distance and type of use.