Astigmatism Explained PDF

# Astigmatism ## What is it? Astigmatism means that the cornea of the eye has an irregular shape, causing vision problems. The cornea is the clear covering over the lens and the iris. It protects these structures and helps to transmit light through the eye. The cornea is normally spherical, altho...

# Astigmatism ## What is it? Astigmatism means that the cornea of the eye has an irregular shape, causing vision problems. The cornea is the clear covering over the lens and the iris. It protects these structures and helps to transmit light through the eye. The cornea is normally spherical, although in people with astigmatism, it may be shaped like a football or oval. This causes light to scatter instead of focus on a single point as it passes through the cornea, resulting in blurred vision. ## What causes astigmatism? Astigmatism is usually hereditary, which means it’s a condition biological parents pass down to their children. It can also be caused by your eyelids putting too much pressure on your cornea. Astigmatism usually isn't caused by health conditions. Some conditions and issues that can cause astigmatism include: - Genetics: Astigmatism can be inherited, as well as other related eye conditions, such as **keratoconus**. - Environment: Temporary or seasonal astigmatism may result from working for long hours with one’s head at an angle. This can often be corrected naturally. - Corneal conditions: In less common cases, astigmatism can be due to corneal conditions, such as **keratoconus**. Scarring or thinning of the cornea creates a risk for astigmatism. - IVR injection: Intravitreal injection of **ranibizumab** for wet AMD may cause astigmatism. - Intraocular lens implant: Astigmatism may become more severe after cataract surgery when a standard monofocal IOL is implanted. - Pterygium: Corneal tissue growth may cause astigmatism; it may eventually cover the cornea. ## Types of Astigmatism Astigmatisms are described relative to the shape of the cornea. - **Regular:** The midlines (meridians) are perpendicular. - **With-the-rule:** The vertical meridian is the steepest, like a football on its side. - **Against-the-rule:** The horizontal meridian is the steepest. - **Oblique:** The steepest curve is between 120 and 150 degrees and 30 and 60 degrees. - **Irregular:** The principal meridians are not perpendicular. ## Astigmatisms are also described in terms of where the focus falls on the retina: - **Simple astigmatism** can cause hyperopic vision (farsighted) or myopic vision (nearsighted) with one focus point on the retina, and the other either behind or in front of the retina, respectively. - **Compound astigmatism.** Both focus points are either behind (hyperopic) or in front of (myopic) the retina. - **Mixed astigmatism.** One focus point is in front of the retina, and the other is behind it. ## Management and Treatment ### How is astigmatism treated? Most people with astigmatism need corrective lenses. Your [eye care specialist](https://www.allaboutvision.com/eyecare/eye-doctor.htm) will recommend **eyeglasses** or **contact lenses** to help you see clearly. ## Symptoms - Blurred vision or distorted vision at near, distant, or both. - Eyestrain, such as headaches, blurred vision, eye redness, eye fatigue, and/or twitching. - Distorted line perception, such as when straight lines appear crooked, or lines appear clearer in one direction than the other. - Monocular double vision is double vision when only one eye is open. - Migraine headaches may be experienced. ## Spheric Eye vs. Astigmatism The image shows how light focuses on the retina differently in a **spheric eye** versus an eye with **astigmatism**: - **Spheric eye**: The cornea is a smooth, spherical dome shape and light focuses on one focal point on the retina. - **Astigmatism**: The cornea, instead of being a perfect sphere, is more oval-shaped. This causes light to focus at multiple focal points rather than one, causing blurred vision. The diagram also includes a representation of how the different shapes of the cornea affect the way light is focused. Astigmatism is a common type of refractive error. It means that some part of your eye (either the cornea or lens) is more curved than it should be. This altered eye shape makes your vision blurry. Most cases of astigmatism can be treated with corrective lenses like eyeglasses or contact lenses.