Astigmatism is a refractive irregularity of the eye that is related to the curvature of the cornea. In some eyes, the cornea is more curved in one angular region and flatter in other angular regions. The cause of astigmatism is that the refractive index of each meridian of the cornea is not uniform due to the uneven thickness or curvature of the cornea, so that the light passing through these meridians cannot gather at the same focus and the light cannot be accurately focused on the retina to form a clear image, a condition called astigmatism.
Etiology
Most cases of regular astigmatism are due to congenital anomalous changes in the cornea, and there may also be lens astigmatism. There are also some acquired astigmatism, such as eyelids with needle eyes or cornea, long-term poor eye posture (such as squinting, rubbing eyes, lying down to read, etc.), so that the eyelid pressure on the cornea will also change the corneal curvature, resulting in astigmatism and an increase in astigmatism, and some eye surgery such as cataract and corneal surgery may also change the degree and axis of astigmatism.
Irregular astigmatism is mainly due to unevenness of the refractive surface of the cornea, such as corneal ulcers, scarring, cone corneas, pterygium, etc.
Clinical manifestations
1.Blurring
Blurred vision is closely related to the degree and mode of astigmatism. People with mild astigmatism usually have normal vision, but may experience headaches, eyestrain, and blurred vision when looking at objects at a certain distance. People with severe astigmatism have blurred and distorted vision. Seeing far and near is not very clear, and working at close range for a long time means that the eyes are swollen and headache reading scurry or have double vision.
2.Vision fatigue
For the blurred image on the retina requires constant fine adjustment, coupled with the distortion of visual objects, so astigmatism, especially hyperopic astigmatism patients, is prone to visual fatigue. Young people with compound hyperopic astigmatism can often compensate with accommodation, which can form pseudo simple hyperopic astigmatism, pseudo simple myopic astigmatism or pseudo compound myopic astigmatism depending on the degree of accommodation.
3. Normal head and eye position
People with high asymmetric astigmatism in both eyes tend to adopt a tilted head position in order to see more clearly, resulting in strabismus, which can be restored after astigmatism correction. People with high astigmatism often squint when looking at distant targets to achieve pinhole and slit effects to improve vision. Seeing through pinholes or slits can reduce the effect of astigmatism on vision.
Examination
1.Subjective examination
(1) Astigmatism table observation The subjective examination of astigmatism can be observed by astigmatism table to get a preliminary understanding of the shape of the object image masked on the astigmatic meridian retina of the examined eye.
(2) Subjective trial optometry subjective trial optometry is generally performed after objective optometry. Jackson crossed cylindrical lens correction astigmatism axial and astigmatism has an important role, to achieve both the best visual acuity and the most comfortable visual effect; second, binocular visual balance test, including binocular vision test for ordinary vision standard, red-green vision standard, stereo vision standard, etc..
To achieve relatively good binocular vision. Especially in the case of both eyes needing astigmatism correction, objective optometry astigmatic axis is not in the vertical or horizontal position, good results in the monocular test, but binocular vision test, there is a possibility of object distortion and tilt, visual optics called spatial distortion, must be adjusted column mirror axis position, to eliminate this phenomenon. It is believed that for small angle astigmatic axes in both eyes, the column mirror axes are better adjusted to the adjacent horizontal or vertical position.
2.Objective examination
(1) Corneal astigmatism examination
(2) ocular astigmatism examination objective measurement of ocular astigmatism is also known as the measurement of refractive error, that is, the so-called objective optometry, the most commonly used objective optometry in clinical practice is computerized optometry optometry and inspection mirror inspection optometry.
Diagnosis
Astigmatism diagnosis, low astigmatism with normal distance and near vision; high astigmatism with poor distance and near vision, blurred vision and easy visual fatigue; various kinds of astigmatism can be found by using Predacido’s disc and corneal curvature meter; vision can be improved by trying on various types of astigmatic lenses.
Treatment
1.Regular astigmatism
It can be corrected by different cylindrical lenses according to the type of astigmatism and the degree of astigmatism.
2.Irregular astigmatism
Can be corrected with corneal contact lenses.
3.Surgery
High astigmatism in adults over 18 years old can be considered for corneal refractive surgery.
Prevention
1, it is best to do the first full eye examination at the age of 3 to 4 years old, and after that, 1 to 2 times of frightening in O tile business consultation. Instruct young children to develop good hygiene habits and not to casually touch their eyes with their hands or their chemical substances to avoid infectious eye diseases. When reading a book to have enough light, light is best from the left rear; reading posture should be correct, and keep the distance between 30 cm to 40 cm.
2, the choice of reading materials, the font should be clear, not too small.
3, watching TV shall be 5 to 7 times the diagonal from the TV screen. Do not read continuously for more than one hour. For those who need glasses, they should be examined by a physician before prescription.