Astigmatism:
Astigmatism is a common vision condition that causes blurred or distorted vision. It occurs when the cornea (the front surface of the eye) or the lens (inside the eye) has an irregular curvature. This irregular curvature causes light to focus unevenly on the retina, resulting in blurred or distorted images.

Cause of Astigmatism:
The cause of astigmatism is an irregular curvature in both horizontal and vertical lines.

Varying Curvature in Both Horizontal and Vertical Lines:
Astigmatism occurs when the cornea or lens has differing curvatures in different meridians. The cornea is normally smooth and evenly curved, like a basketball. However, in astigmatism, the cornea may be shaped more like a football, with one meridian being steeper or flatter than the other.

The varying curvature in both horizontal and vertical lines causes light rays entering the eye to be focused at different points on the retina. This results in blurred or distorted vision at all distances.

Effects on Vision:
Astigmatism can cause a variety of vision problems, including:

1. Blurred vision: Objects may appear blurry or out of focus at any distance.
2. Distorted vision: Straight lines may appear wavy or distorted.
3. Eye strain: The effort required to focus on objects can cause eye fatigue and discomfort.
4. Headaches: Eye strain can lead to headaches, especially after prolonged periods of close-up work.
5. Difficulty with night vision: Astigmatism can make it harder to see clearly in low light conditions.

Diagnosis and Treatment:
Astigmatism can be diagnosed through a comprehensive eye exam, which includes a series of tests to measure the curvature of the cornea and the shape of the lens.

Treatment options for astigmatism include:

1. Eyeglasses: Prescription glasses with cylindrical lenses can correct the irregular curvature and provide clear vision.
2. Contact lenses: Special toric contact lenses can be used to correct the astigmatism and provide clear vision.
3. Refractive surgery: Procedures like LASIK or PRK can reshape the cornea to correct the irregular curvature and eliminate the need for glasses or contact lenses.

It is important to visit an eye care professional for a proper diagnosis and treatment plan for astigmatism. Regular eye exams can help ensure optimal vision and overall eye health.