Contact Lenses For Astigmatism
Toric Contact Lenses - For Astigmatism
Astigmatism is a type of focusing error that is usually caused by the cornea being non-spherical. Rather than the surface being completely round like a football, it is a bit ‘pointy’ more like a rugby ball.
If the astigmatism is over a certain amount it will need to be corrected to give good vision. Small degrees of astigmatism usually don’t cause any problems, and often people will not bother having it corrected.
Astigmatism can be corrected by either soft or gas permeable lenses.
Soft Toric Lenses
Such a lens has two different powers eg. one power running along one meridian and then a different one along another one.
The lens must sit on the cornea with these powers running along specific directions. To ensure that the lenses stay in the required positions and don’t rotate, the lenses incorporate some form of stabilisation. Lenses by different manufacturers have different stabilisation designs and some brands work better in some eyes than others. It is sometimes necessary to try a few different makes to find a good fit.
Soft toric lenses can be in disposable or non-disposable form:
- Toric Disposables are now available to correct a wide range of astigmatism strengths. There are daily, two weekly and monthly disposable options. The monthly’s have the highest range of power choices and are thus the mostly prescribed option.
- Toric Non Disposable these are usually only required when disposable lenses are out of the required power or fitting range.
Gas Permeable Contact Lenses For Astigmatism
These lenses work by artificially making the corneal surface spherical again and thus ‘eliminating’ the astigmatism. The lenses themselves are spherical and they float on the surface of the cornea, trapping a tear layer beneath it. The tear layer acts like a liquid lens, and the combination of lens and tears provides the required correction.
Gas Permeable Toric Contact Lenses
In very high degrees of astigmatism the corneal surface is very pointy. In such cases a lens with a spherical curvature will not sit stably but will rock back and forth against the surface. This will give poor vision and will be uncomfortable.
In these eyes, a lens that is moulded so that it matches the shape of the cornea is required. This type of lens is known as a Toric Gas Permeable