What is astigmatism?

What is Astigmatism?

The refractive power of the eyeball on each meridian is uneven. After the parallel light enters the inside of the eyeball, due to the different refractive power of the eyeball on each meridian, it cannot gather at a point (focus) on the retina but forms some scattered focal points.

What Causes Astigmatism?

Astigmatism is a refractive error that occurs when the cornea (clear outer layer) of the eye is irregularly shaped, causing light to focus unevenly on the retina. Kids are more likely to have astigmatism if one or both parents have it. Poor eye habits, such as reading in poor lighting or squinting, can also cause astigmatism.

Through optometry, the visual effects of astigmatism in patients are identified. From an optical standpoint, astigmatism occurs when the eye's cornea or lens has an irregular shape, preventing light rays from focusing properly on the retina. Instead of forming a single clear image, the irregular curvature causes light to scatter and create multiple focal points, leading to blurred or distorted vision. This condition can affect vision at all distances and is often accompanied by other refractive errors such as myopia (nearsightedness) or hyperopia (farsightedness).

Astigmatism vs Normal Vision

Astigmatism cannot form a clear image with the help of accommodation or moving the distance between the target and the eye, so the lines look blurry. The difference in vision between people with astigmatism vs. with normal vision can be significant, especially when driving at night.

What is A Prescription for Astigmatism?

An optometrist or ophthalmologist usually determines whether you have astigmatism after a refraction test. An astigmatism prescription specifies the type and power of lenses needed to compensate for the irregular curvature of the cornea or lens, and the key pieces of information are as follows:

Sphere (SPH): This indicates nearsightedness (myopia) or farsightedness (hyperopia) in diopters. Negative values ​​indicate nearsightedness and positive values ​​indicate farsightedness.

Cylinder (CYL): This measures the amount of astigmatism in diopters. It shows how much correction is needed to compensate for the irregular curvature of the cornea or lens.

Axis: This indicates the direction of the astigmatism in degrees, ranging from 0 to 180. It specifies the direction in which the cylinder correction should be applied to counteract the astigmatism.

A complete vision prescription will also contain other information, such as OD, OS PD, etc. Learning how to read a vision prescription will help you better understand your vision status.

Astigmatism Can Be Roughly Divided Into:

1. Regular astigmatism, irregular astigmatism;

2. Astigmatism along the rule, against the rule astigmatism, oblique axis astigmatism;

3. Simple myopia astigmatism, simple hyperopia astigmatism, compound myopia astigmatism, compound hyperopia astigmatism, mixed astigmatism;

4. Corneal astigmatism, crystal astigmatism, etc.

What are The Dangers of Astigmatism?

Astigmatism can cause headaches and blurred vision. Due to the refractive error of the astigmatic eyeball, parallel light rays cannot form a focus on the retina, which can lead to blurred vision or even double vision. People with astigmatic vision often have the habit of squinting in order to see objects clearly, which leads to fatigue and decreased vision.  When your eyes have to work harder to focus, the muscles around the eyes are highly tense, and astigmatism can cause headaches over time.

What Causes Astigmatism to Worsen?

Although astigmatism usually develops in childhood and can remain relatively stable throughout life, several factors may cause it to worsen:

Eye damage: Even minor eye damage can change the shape of the cornea, potentially increasing the severity of astigmatism.

Keratoconus: This disease causes the cornea to gradually thin and bulge, and astigmatism can worsen significantly over time.

Certain eye surgeries: While eye surgeries like LASIK usually correct astigmatism, they can sometimes cause the cornea to change shape, making the astigmatism worse.

Age: Although uncommon, some people may experience worsening astigmatism as they age due to changes in eye shape.

Eye diseases: Some eye diseases, such as cataracts or dry eye, can cause astigmatism to worsen.

Medications: Certain medications, such as antihistamines and decongestants, can cause dry eye syndrome, which indirectly affects astigmatism.

Wearing Contact Lenses: Improperly fitted or incorrectly fitted contact lenses can cause changes in the shape of the cornea, which may worsen astigmatism.

Excessive eye rubbing: Long-term eye rubbing can fatigue the cornea and lead to increased astigmatism.

Protect Your Eyes, Experts Recommend:

1. It is best to have regular eye examinations, 1 to 2 times a year. Develop good hygiene habits and do not touch your eyes with your hands or other objects to avoid spreading eye diseases.

2. The reading posture should be correct, keep a distance of 30cm~40cm, and the fonts should be clear and not too small when choosing reading materials.

3. Do not rub your eyes. Protect your eyes and avoid eye trauma. This is the way to prevent pathological astigmatism.

4. For patients with astigmatism, wearing prescription glasses promptly is important. The appropriate prescription will reduce the symptoms of astigmatism and prevent eye fatigue when working and studying.