Astigmatism is a refractive irregularity of the eye that is related to the curvature of the cornea. The human eye is not perfect, and some eyes have a curved cornea in one angular region and a flatter cornea in other angular regions. The reason for astigmatism is that these uneven thicknesses or curvatures of the cornea make the refractive index of the corneal meridians inconsistent, so that the light passing through these meridians cannot gather at the same focal point. In this way, the light can not be accurately focused on the retina to form a clear image, and this condition is called astigmatism.
I. Etiology
Most regular astigmatism is due to congenital anomalous changes in the cornea, and there may also be lens astigmatism. In addition, some eye surgeries (such as cataract and cornea surgery) may also change the degree and axis of astigmatism.
Irregular astigmatism is mainly due to the unevenness of the refractive surface of the cornea, such as corneal ulcer, scar, cone cornea, pterygium, etc.
Second, 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 headache, 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.
III. 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 usually performed after the objective optometry. The purpose is twofold: first, the subjective determination of the accuracy of monocular corrective lenses, Jackson crossed cylindrical lens correction astigmatism axial and astigmatism has an important role to play, to achieve both the best visual acuity and the most comfortable visual effect; second, binocular visual balance test, including binocular vision test of ordinary visual standards, red and green visual standards, stereo visual standards, etc.. To achieve relatively good binocular vision. Especially in the case of both eyes needing astigmatism correction, the objective optometry astigmatic axis is not in the vertical or horizontal position, the effect is good in the monocular test, but in the binocular vision test, there is a possibility of object distortion and tilt, known as spatial distortion in visual optics, the axis of the column mirror must be adjusted 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 the measurement of refractive error, that is, the so-called objective optometry, the most commonly used objective optometry in clinical practice is computerized optometry and shadowing 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 with Predacido’s disc and corneal curvature meter; try to wear various types of astigmatic lenses to improve vision.
V. 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 later on, 1 to 2 times of frightening in O tile business consultation. Instruct young children to recognize which are dangerous games and toys to reduce eye trauma. Instruct children to develop good hygiene habits and not to touch their eyes with their hands or other chemical substances to avoid eye infections, and to minimize going out if they have eye infections. Read books with sufficient light, preferably from the left rear; read books in the correct posture and keep the distance between 30 cm and 40 cm. Do not read in a rocking car, and do not lie down to read a book.
2, select reading material in a clear font, not too small.
3, the TV is placed a little below the height of the eye parallel, there must be watching TV from the diagonal of the TV screen 5 to 7 times. Continuous reading no more than one hour, 30 minutes rest 5 minutes. Nutrition should be balanced. Go to the countryside more often and look at the green wilderness in the distance. If you need glasses, you should be examined by a physician and get glasses. Take the initiative to get in touch with the school and cooperate actively.