Astigmatism is not a disease, but a description of eye-shape where it is oval like a rugby ball rather than round like a soccer ball.
Symptoms can include blurring at distance and near as some parts of an image are more out of focus than others. For example, with a letter ‘T’ the vertical bar may be clear while the horizontal bar is not. The eyes tire as they try to find the best compromise in focusing. This can result in tired eyes and headaches, especially when concentrating for long periods on close or distance tasks.
The correction of astigmatism usually includes the use of spectacles (or sometimes contact lenses) which may be worn all the time or only for certain tasks. Both clarity and comfort are improved which results in better visual efficiency.