Before we can ask "How do toric lens work", we really need to understand what they do, and what they were created for. Toric contact lenses can be soft, meaning they are made from soft plastic that can alter its shape to fit the shape of the eye. This is as opposed to hard (gas permeable - GP) lenses which are rigid in construction. A toric lens is special, in that it was designed to help correct astigmatism. What Is Astigmatism? Astigmatism can take two forms, but it is usually understood to mean an optical malfunction caused by a misshaping of either the cornea or the optic lens. A normal cornea is one with is round in shape, just like a ball. In an astigmatic, the shape is different, and the ends of the cornea have extended ends. More rugby ball or american football shaped. What happens then is that the light hits the cornea in two places rather than one. This is because the shape of the astigmatic eye has a steeper and flatter curve due to the shape of the cornea. This is called corneal astigmatism. Sometimes, astigmatism is the result of an irregularly shaped optic lens, which is located behind the cornea. This is called lenticular astigmatism. The effect to the sufferer is much the same though. Astigmatism manifests itself as slightly blurred vision, but can also cause headaches and eye aches. How Is a Toric Lens Different To Other Contact Lenses? When you place a contact lens in your eye, the lens sits on top of a film of water. If it didn't, your eye would be dry, and it would cause you discomfort. Because the lens is on a liquid platform, it can rotate, but in non astigmatics, this is not really a problem. However, in an astigmatic, the lens needs to stay put in order to correct the astigmatism. In a toric lens, this is achieved by weighting the lens so that the bottom is heavier than the top. This of course means that the bottom of the lens will always point downwards, ensuring that the prescription of the lens acts correctly. There is one other difference of a toric lens over a normal one, in that the lens has two prescriptions in one. One will correct the astigmatism, and the other will correct the shortsightedness or long sightedness (depending on what you have). Because of the more complex nature of the toric lens, they are often more expensive than conventional lenses. |
