It's caused when the front surface of your eye, called the cornea, is not perfectly round. So, instead of having equal curvatues like a basketball, it has several different curvatures like a football. As a result, light is focused differently in your eye, which leads to blurred vision. Astigmatism can be corrected with toric contact lenses. However, traditional toric lenses are expensive and require weekly enzyme cleaning.
Many people find weekly enzyme cleaning to be inconvenient and costly.
Unfortunately, with traditional lenses, weekly enzyme cleaning is necessary to remove protien deposits that build up and cloud lenses over time. Focus lenses are different. Focus lenses are designed to be replaced once a month, so your lenses always feel clean and fresh. Frequent replacement reduces the problems caused by deposit build up because you throw your lenses away before excessive build up occurs. This may eliminate the need for weekly enzyme cleaning.