What Is the Difference Between Myopia and Astigmatism?

Astigmatism is an abnormal refraction of the eye that is related to the curvature of the cornea. After the parallel rays enter the eye, because the eyeballs have different refractive powers on different meridians, they cannot be gathered at one point (focus), and a clear object image cannot be formed. This situation is called astigmatism. Astigmatism can not form a clear image by adjusting the effect or the distance between the moving target and the eye. Only by wearing a suitable cylindrical lens can a clear image be formed on the retina. According to the form of expression, astigmatism can be divided into regular astigmatism and irregular astigmatism, the former can be corrected with lenses, the latter can not be corrected with lenses.

Basic Information

English name: astigmatism
Visiting department: Ophthalmology
Common causes: Congenital factors or corneal diseases

Common symptoms: Vision loss, amblyopia, visual fatigue, eye pain, tearing, headache, etc.
Contagious: no

Causes of astigmatism

1. Different curvature

That is, the curvature of the surface of the eye's refractive body is inconsistent, which mostly occurs in the cornea, and can also occur in the lens. Mild astigmatism is considered to be physiological. The most common is that the corneal vertical curvature is greater than that of the horizontal, generally about 0.2D. It is caused by the frequent compression of the upper and lower eyelids. With the increase of age, this physiological defect tends to grow slightly.

Most of the astigmatism is congenital, and it is often caused by corneal disease. Such as keratoconus, peripheral corneal degenerative lesions or scars left after corneal inflammation, mostly cause irregular astigmatism. In addition, irregular astigmatism can be caused by cataract surgery or eyelid masses compressing the eyeballs.

2. Optical center deviation

Mostly caused by disease or trauma, the lens is dislocated or the position is obviously deflected, and the astigmatism caused is very obvious.

3.Different refractive index

It is caused by the difference in the refractive rate of different areas of the lens, such as the change of refractive media caused by cataracts, which can lead to various astigmatisms, resulting in deformed vision and polypsy.

Clinical manifestations of astigmatism

Vision loss

Vision loss is closely related to the degree and type of astigmatism. People with mild astigmatism usually have normal vision, and middle and high astigmatism have far and near vision. The vision of pure astigmatism is slightly reduced, and the vision of renatured astigmatism and mixed astigmatism is obviously reduced. If the correction is poor, amblyopia can be formed.

Visual fatigue

As for blurred images on the retina, fine adjustments need to be made continuously, and the vision is distorted. Therefore, astigmatic eyes, especially those with hyperopia astigmatism, are prone to vision fatigue. It is manifested as eye pain, tears, and headache, especially on the forehead, double vision, and short-term work can not last.

3. Compensation for head position and squinting vision

People with highly asymmetric astigmatism in their eyes, in order to see more clearly, often take a tilted head position to cause strabismus, astigmatism can be restored after correction. In order to obtain a larger retinal image, patients often take objects close to them like patients with myopia. People with high astigmatism often squint when looking at distant or near targets, achieving pinholes and fissures to improve vision. Looking through a pinhole or crack can reduce the effect of astigmatism on vision.

Astigmatism

1. Anterior segment routine examination

Routine examination of eyelid, conjunctiva, cornea, lens. Determine whether there is drooping of the upper eyelid, whether the eye conjunctiva has any mass compression, whether the cornea has ulcers, whether there is pterygium, the shape, location, and degree of opacity of the lens.

Vision test

Astigmatism can be found by far and near vision tests. Patients with severe astigmatism have poor distance vision and near vision.

3. Astigmatism observation

The subjective examination of the astigmatism eye can be observed with an astigmatism table to get a preliminary understanding of the shape of the blurred image on the meridian retina of the examined eye.

4. Retinoscopy

When any of the following 5 cases is encountered, it indicates that there is astigmatism: the refractive power of a pair of meridians is different; the reflection bandwidth is narrow; clipping; the fundus reflection is irregular; Direction of movement is not consistent.

5. Check the diopter

(1) Objective refraction Astigmatism is measured by the cylindrical lens method and the spherical lens method. Can determine the axis of astigmatism and astigmatism. According to the degree can be divided into mild (2.00D), moderate (2.25 ~ 4.00D), severe (> 4.00D) astigmatism. Below 1.00D is a physiological astigmatism.

(2) Subjective trial optometry is generally performed after objective trial optometry.

6. Corneal astigmatism

Includes keratometer or corneal topography or quantitative corneal astigmatism.

7. Fundus examination

Visual nipples are often oval and highly astigmatism, the vertical edge of the nipple can be clearly seen, but the horizontal edge is not clear, or vice versa. According to the shape of the nipple, the axial direction of astigmatism can be roughly understood.

Astigmatism diagnosis

Based on the patient's medical history, symptoms, distance vision, and eye examination results, a clear diagnosis of astigmatism can be made. Key points for inspection and diagnosis: those with low astigmatism have normal far and near vision; those with high astigmatism have poor far and near vision, blurred vision, and are prone to fatigue; examinations with the Plastidox disc and corneal curvature meter can find various Astigmatism; Trying on various types of astigmatism lenses can improve vision.

Astigmatism treatment

Including optical correction and surgical treatment. Wearing a cylindrical lens for optical correction is the main treatment for astigmatism.

Regular astigmatism

It can be corrected by different cylindrical lenses according to the type of astigmatism and the power of astigmatism. Convex cylindrical lens for hyperopia astigmatism, concave cylinder lens for myopic astigmatism.

Mild astigmatism, no correction is needed if there are no clinical symptoms, and those with vision loss or visual fatigue and visual disturbance should also wear corrective glasses.

Children, especially preschool children, must fully correct astigmatism to prevent the formation of amblyopia.

Optometry should be performed before wearing, and mydriatic optometry should be used for adolescents and children. Combining the measurement of corneal curvature meter to understand the nature and extent of astigmatism, combined with subjective trials, the prescription of optics can be determined.

High astigmatism can not be adapted to the frame glasses can choose contact lens correction.

2.Irregular astigmatism

It is not easy to correct with lenses, you can use contact lens correction.

3. Surgery

It is suitable for congenital or acquired high astigmatism caused by ocular surgery such as cataract or corneal transplantation, such as excimer laser refractive corneal surgery, laser corneal thermoplasty, and keratotomy.

Astigmatism prevention

1. It is best to do the first full eye examination at the age of 3 to 4 years old, and then perform regular eye examinations once or twice a year. Instruct young children to develop good hygienic habits, and not to contact the eyes with their hands or their articles, to avoid infection of eye diseases. When reading a book, the light should be sufficient, and the light should preferably come from the left rear; the reading posture should be correct, and maintain a distance between 30 cm and 40 cm.

2. The font should be clear and not too small when selecting reading materials.

3. TV must be 5 to 7 times from the diagonal of the TV screen. Reading continuously for no more than an hour. Those who need glasses should be checked by a doctor.