Astigmatism is an eye disorder that leads to blurred or distorted vision. It is the result of a change in the curvature of the eye lens or shape of the cornea and statistics say that it affects millions of people.
Types of Astigmatism
There are three types of astigmatism:
- Myopic. One of the main meridians of the eyes is nearsighted. (If both of them nearsighted, they the meridians are myopic and may have different degrees.)
- Hyperopic. One of the main meridians of the eyes is farsighted. (In case both of them are farsighted, the meridians are both hyperopic and may have differing degrees.)
- Mixed astigmatism. A combination of the above – one main meridian is farsighted and the other is nearsighted.
Astigmatism can also be regular or irregular.
- Regular astigmatism means that the two meridians are perpendicular on each other (they form a ninety degrees angle)
- Irregular astigmatism is any astigmatism that is not regular, i.e. the meridians form an angle that is not of 90 degrees.
Contact Lenses for Astigmatism Correction
Contacts are one of the three ways of correcting astigmatism, next to eyeglasses and refractive surgery.
Gas permeable (GP) lenses are semi-hard and usually smaller than soft contacts. They correct the cornea irregularities by making the surface of the eye spherical. GP’s are the most popular way used to correct irregular astigmatism, which could be the result of a disease or a cornea transplant. The outer side of the lens is spoon-shaped – therefore perfectly spherical – and the eye’s tears can fill the irregularities between the cornea and the lens. This creates an artificially smooth optical surface and leads to crisper vision.
Toric lenses are also used to correct astigmatism. They are made of a hydrophilic and flexible material, which comes with various resistance powers in various meridians. In order to work properly, certain weights and forces have to line up with certain zones and eye vectors. Several designs are commonly used – and each of them boils down to high school Physics. A common setup is that of prism-like ballast, where the lens comes with a thicker area that will naturally rest on the bottom to keep the lens in a steady position. Without either that or some other way of stabilizing the lens, the lens could move any time the patient blinks and therefore the vision would vary.