High/Irregular Astigmatism

Your cornea is a clear, round dome that covers the iris and pupil of your eye. A normal, healthy cornea is smooth and curves equally in all directions, allowing light to focus properly onto the retina at the back of your eye. This is what allows you to see clearly. If your cornea has an uneven curvature, this irregularity leads to improper refraction of light, resulting in blurred vision.

Astigmatism can also occur in the lens of your eye, which sits just behind your cornea. If you’re diagnosed with lenticular astigmatism, it means you have a misshapen lens.No matter what type of astigmatism you have — corneal or lenticular — objects both near and far may appear blurry and distorted.

Moderate or severe astigmatism may also cause eye strain, squinting, chronic headaches, and poor night vision.  Because astigmatism is often inherited, most people who have the problem were born with it.  It can also occur following an eye injury, eye disease, or ocular surgery.

The level of significance of astigmatism is measured in diopters. Diopters are a measurement of the reciprocal of the focal length of the eye. A perfect eye with no astigmatism has a measurement of 0 diopters.

Most people do not have perfectly round eyes – they may have up to .75 diopters of astigmatism, and this is considered normal and will likely not require correction. Between .75 and 2 diopters is considered mild astigmatism. Between 2 and 4 diopters is moderate astigmatism, and 4 or more diopters is considered significant or “bad” astigmatism. Generally, eyes with 1.5 diopters of astigmatism or more require correction.

Small amounts of astigmatism are fairly easy to correct with either glasses or contacts.  For small amounts of astigmatism, many people opt for eyeglasses, which are made with a special cylindrical lens prescription that offsets the astigmatism.

However, moderate to high levels of astigmatism are difficult to fully correct with conventional contact lenses due to the uniqueness of each patient’s cornea. Astigmatism can cause convention contact lenses to rotate, causing discomfort and blurred vision, even with the optimal prescription.  In patients with moderate or high levels of astigmatism, specialty contact lenses tend to be the best option.

Astigmatism affects your vision during all times of day, but can have a particular effect on night vision. Specifically, lights may appear fuzzy or surrounded by a halo, glare, or streaks. For those with astigmatism, it is particularly important that they wear corrective lenses for night time driving.