Astigmatism is a condition in which your eye, especially your cornea or the clear front part of the eyeball, isn’t completely round.
Ideally, an eyeball is shaped like a perfectly round ball. Light comes into it and bends evenly, which gives you a clear view. But if your cornea is shaped more like a football, light gets bent more in one direction than another. That means only part of an object is in focus. Things at a distance may look blurry and wavy.
It’s common to have astigmatism along with nearsightedness (myopia) or farsightedness (hyperopia). These three conditions are called refractive errors because they involve how your eyes bend (refract) light.
If you have astigmatism, you may have:
• Eye strain.
• Blurred vision (at all distances).
• Squinting to see clearly.
These symptoms are also symptoms of several other conditions. An eye specialist can help diagnose the problem.
Different types of astigmatism include:
• Corneal astigmatism: This is the most common type of astigmatism.
• Lenticular astigmatism: This type of astigmatism occurs due to changes in the eye’s lens.
• Irregular astigmatism: In this type, the curvature of the cornea is uneven.
Astigmatism can also occur with myopia, hyperopia, or both:
• Myopic astigmatism: Myopic astigmatism happens when astigmatism combines with myopia, and the two curves in the cornea or the lens — the curves from top to bottom and side to side — are focused in front of the retina.
• Hyperopic astigmatism: This occurs when hyperopia combines with astigmatism, and the two curves are focused behind the retina.
• Mixed astigmatism: This is when one curve produces symptoms of hyperopia and the other produces symptoms of myopia.
It can also be regular or irregular:
• Regular astigmatism
If astigmatism is regular, the two curves are at a 90-degree angle to each other, and the curvature of each is uniform.
• Irregular astigmatism
In irregular astigmatism, the two curves are not at 90-degree angles to each other, and the curvature of each is not uniform or even. Irregular astigmatism can often result from trauma, surgery, or keratoconus, which is the thinning of the cornea.
The eye has two structures with curved surfaces that bend (refract) light onto the retina, which makes the images:
• The cornea, the clear front surface of the eye along with the tear film
• The lens, a clear structure inside the eye that changes shape to help the eye focus on near objects
In a perfectly shaped eye, each of these elements has a round curvature, like the surface of a smooth ball. A cornea or lens with such curvature bends (refracts) all incoming light equally to make a sharply focused image directly on the retina at the back of the eye.
A refractive error
If either the cornea or the lens is egg-shaped with two mismatched curves, light rays aren’t bent the same, which means that two different images form. These two images overlap or combine and result in blurred vision. Astigmatism is a type of refractive error.
It’s not known what causes astigmatism, but genetics is a big factor. It’s often present at birth, but it may develop later in life. It may also occur as a result of an injury to the eye or after eye surgery. Astigmatism often occurs with nearsightedness or farsightedness.
Sometimes, though, a rare condition called keratoconus causes astigmatism. This eye disease affects the cornea, causing the clear tissue on the cornea to thin and bulge out. This leads to cloudy or blurry vision, and sensitivity to bright lights. The cause of keratoconus is also unknown, but it’s believed to be hereditary, too.
It may occur in combination with other refractive errors, which include:
• Nearsightedness (myopia).
This occurs when the cornea is curved too much or the eye is longer than usual. Instead of being focused precisely on the retina, light is focused in front of the retina, making distant objects seem blurry.
• Farsightedness (hyperopia).
This occurs when the cornea is curved too little or the eye is shorter than usual. The effect is the opposite of nearsightedness. When the eye is in a relaxed state, light never comes to a focus at the back of the eye, making nearby objects seem blurry.
Risk Factors –
Astigmatism can occur in children and adults. Your risk of developing it may be higher if you have any of the following:
• a family history of astigmatism or other eye disorders, such as keratoconus (degeneration of the cornea)
• scarring or thinning of your cornea
• excessive nearsightedness, which creates blurry vision at a distance
• excessive farsightedness, which creates blurry close-up vision
• a history of certain types of eye surgery, such as cataract surgery (surgical removal of a clouded lens)
If left untreated, astigmatism can cause complications. For example, a lazy eye (amblyopia) can occur when a person has astigmatism in only one eye, or the astigmatism in one eye is worse than the other, and the condition isn’t corrected. Additionally, astigmatism can sometimes cause eye strain and headaches.
Surgery to treat astigmatism also has risks. Side effects of surgery are often temporary and improve within a few weeks. These include dry eyes, sensitivity to light, and night vision problems.
But other (and more permanent) complications can occur, too, such as vision loss or vision reverting to pre-surgery state.
The early detection and treatment of astigmatism are important.
An eye specialist may use the following techniques when examining the eyes:
• Visual acuity test:
A visual acuity test checks how well a person can read letters or characters at a distance. It typically involves reading lines of letters on a chart. The letters become progressively smaller on each line.
A keratometer is a device that measures the reflected light from the surface of the cornea. This provides an eye doctor with information about the shape and curvature of the cornea.
• Corneal topography:
Corneal topography is a type of imaging technology that provides measurements of the cornea alongside images. This offers a much more detailed assessment than keratometry.
Refraction assesses how the eyes focus light, and it involves placing a series of lenses in front of the eyes. An eye doctor will ask which lenses make a person’s vision better.
The goal of treating is to improve vision clarity and eye comfort. Treatments are corrective lenses or refractive surgery.
▪︎ Corrective lenses
Wearing corrective lenses treats astigmatism by counteracting uneven curvatures of your cornea or lens.
Types of corrective lenses include:
Eyeglasses are made with lenses that help compensate for the uneven shape of the eye. The lenses make the light bend into the eye properly. Eyeglasses can also correct for other refractive errors, such as nearsightedness or farsightedness.
• Contact lenses.
Like eyeglasses, contact lenses can correct most astigmatism. They are available in a variety of types and styles.
Contact lenses are also used in a procedure called orthokeratology. In orthokeratology, rigid contact lenses are worn during the night while sleeping until the curvature of the eye evens out. Then the lenses are worn less frequently to maintain the new shape. If treatment is discontinued, the eye returns to its former shape and refractive error.
▪︎ Refractive surgery
Refractive surgery improves vision and reduces the need for eyeglasses or contact lenses. An eye surgeon uses a laser beam to reshape the curves of the cornea, which corrects the refractive error. Before surgery, doctors will evaluate you and determine if you’re a candidate for refractive surgery.
Types of refractive surgery for astigmatism include:
• Laser-assisted in-situ keratomileusis (LASIK).
• Laser-assisted subepithelial keratectomy (LASEK).
• Photorefractive keratectomy (PRK).
• Small-incision lenticule extraction (SMILE).
Other types of refractive surgeries include clear lens extraction and implantable contact lenses. There is no one best method for refractive surgery, and you should make a decision only after a complete evaluation and thorough discussion with your surgeon.
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