Astigmatism is a very common eye disease, usually caused by corneal curvature. Astigmatism is mostly formed congenitally, and in some cases, astigmatism may occur if a long-term chalazion compresses the eyeball for a long time. Astigmatism, like myopia, is irreversible. Generally, astigmatism above 300 degrees is called high astigmatism.
There are many problems associated with high astigmatism glasses, especially for children and teenagers. In actual work, our opticians often encounter people with high astigmatism. It is very important to choose appropriate lenses and frames.
The imaging difference between astigmatism and myopia
The shape of the cornea is irregular, not spherical but ellipsoidal. The refractive power in the vertical direction and the horizontal direction are different. As a result, after the external light is refracted by the cornea, it cannot form a focus when it enters the interior of the eye. Instead, it forms a focal line, causing the retina to The projection is blurred, causing vision loss. Problems with astigmatism, especially mild astigmatism, may not have a big impact on vision, but high levels of astigmatism will definitely have an impact on vision.
Myopia occurs when external parallel light enters the eyeball and is refracted by the eye's refractive system. The focus of the image cannot fall on the retina, causing the problem of blurred vision in the distance. There are essential differences in the imaging of myopia and astigmatism, and they are also very different in the actual visual process. Many people have insufficient understanding of this, causing confusion.
There are a small number of patients with simple astigmatism, and most of them have near astigmatism or far astigmatism. In the process of optometry, it is particularly important to provide prescription corrections based on the imaging distinction between astigmatism and myopia.
The definition and manifestation of high astigmatism
The severity of astigmatism is divided according to the degree. Astigmatism below 150 degrees is mild astigmatism, astigmatism between 150 and 300 degrees is moderate astigmatism, and astigmatism above 300 degrees is high astigmatism. High astigmatism can cause many harms to our eyes:
1. Cause headaches, sore eyes, etc.: High astigmatism without correction is more likely to cause headaches, sore eyes, etc. It can also easily lead to bad postures such as head tilt. Therefore, those with severe astigmatism must be corrected.
2. Visual fatigue: Due to the different refractive power of each meridian, astigmatism cannot form a focus when refracting parallel light, but two focal lines, so the brain is prone to selective interpretation of objects. In order to see the scenery relatively clearly, astigmatism should be adjusted as much as possible to reduce the size of the circle of diffusion to improve image quality. High astigmatism, if not corrected properly or without glasses, can easily cause headaches, visual fatigue and other symptoms, making it easier to develop visual fatigue. .
3. Blurred vision of near and far objects: People with severe astigmatism experience blurry vision of both distant and near objects. Patients often have the habit of half-closing their eyelids and squinting into gaps to see objects clearly. clearer.
4. Vision loss: In astigmatic eyes, the visual target in the direction away from the focal line of the retina will become lighter in color, the edges will be blurred, and it will be difficult to identify. The vision will decrease, and in severe cases, double vision will occur. In addition to physiological astigmatism, all kinds of astigmatism can easily cause vision loss.
5. Pressure on the eyeball: Astigmatism is generally corrected with ordinary glasses or contact lenses. If trauma and chalazions on the eyelids are not treated in time, they will oppress the eyeball for a long time and cause astigmatism. In some cases, astigmatism can also be combined with pseudomyopia. Note that the pseudomyopia part needs to be removed, and the astigmatism can be corrected with glasses.
6. Amblyopia: The disease is more common in high astigmatism, especially hyperopic astigmatism. Because it is difficult to see far and near clearly, and the vision cannot be exercised, amblyopia is prone to occur, and then strabismus tends to occur.
Highly astigmatic glasses
Highly astigmatic lenses are difficult to make due to their deep power. Therefore, high astigmatism can generally be equipped with high-refractive index resin lenses and aspherical designs, so that they will not appear too thick. It should be noted that lenses with high astigmatism are generally customized series of lenses. The higher the astigmatism, the more difficult it is to customize, and the more complex parameters need to be designed. For extremely high astigmatism, frame parameters also need to be provided to help with lens design.
When choosing frames, you also need to consider the special characteristics of ultra-high astigmatism. Since the edge thickness of astigmatism lenses varies greatly, you should be particularly careful when choosing frames. Choose pure titanium or titanium alloy frames with relatively small transverse diameters and strong material toughness. You can also choose acetate fiber or plate frames with good shrinkage. wait.
It is not advisable to choose frameless or half-frame frames. It is better to choose full-frame frames. When processing and manufacturing, pay special attention to the problem of lens deviation that changes the astigmatism axis of the lens due to poor fitting technology and fixed equipment.
How to choose highly astigmatic frames:
A. Give priority to lightweight materials
The weight of the frame material is one of the factors that affects the weight of the glasses. For people with high myopia, when choosing frames, you can pay more attention to materials such as pure titanium, tungsten carbon, thin sheets, and TR90. Frames made of these materials are generally lighter and easier to wear. Highly comfortable, durable and not easily deformed.
B.Full frame>Half frame>Frameless frame
High astigmatism generally has thicker lenses, and rimless and semi-rimless frames will expose the lenses, which not only affects the appearance, but also makes the frames easy to deform, causing changes in the center distance of the glasses and the astigmatism axis of the lenses, affecting the correction effect. People with high astigmatism are better off choosing full-frame frames.
C. Large frame is not a good choice
People who wear large-framed glasses for a long time may experience decreased vision and narrowed field of vision. Wearing them for a long time may cause dizziness and dizziness. Large-frame glasses are generally heavy and are not suitable for people with high myopia. Wearing them for a long time will put heavy pressure on the nose, which may easily lead to deformation of the bridge of the nose over time.
There are many important parameters for optometry and glasses, such as diopter and interpupillary distance. When wearing large-frame glasses, you must pay special attention to whether the distance point corresponding to the center of the two lenses corresponds to the distance position of the pupil of your eye. If there is a deviation, even if the prescription of the glasses is correct, you will feel discomfort after wearing the glasses. Try to choose a frame with a smaller mirror width, and try to keep the upper and lower heights smaller, so that the comfort will not be reduced due to peripheral deformation.
D. Choose a frame with a relatively close distance between the eyeglasses.
The eye-eye distance refers to the distance between the rear vertex of the lens and the front vertex of the cornea. Astigmatism correction lenses are cylindrical lenses. If the eye-eye distance increases, the effective refractive power will decrease (the higher the degree, the greater the reduction), and the corrected vision will also decrease. decline. The distance between the eyeglasses of highly astigmatic glasses should be as small as possible. In terms of frame style selection and frame adjustment, you should try to choose nose pads or lenses with a relatively close distance between the eyeglasses.
E. Don’t choose frames with temples that are too thin
If the temples are too thin, the force on the front and back of the frame will be uneven, making it easy for the frame to be top-heavy and put most of the weight on the bridge of the nose, causing the glasses to slide down easily and affecting the wearing comfort. If you have astigmatism (especially those with moderate to high astigmatism), when choosing glasses, you must choose frames that are suitable for the interpupillary distance.
The influence of astigmatism axis position on glasses
The astigmatism axis range is 1-180 degrees. I will focus on the selection of frames for the 180 and 90 astigmatism axes.
First we need to know that the astigmatism axis is at 180°, then the thickness is at 90° (vertical direction). Therefore, the frame height of the frame we choose must not be high. If we choose a frame with a low frame, the thickness in the vertical direction will be worn away, and the resulting lenses will naturally be lighter and thinner. (If the frame is high, it will naturally be round; if the frame is low, it will naturally be square.)
On the contrary, if the axis position is 90, the thickness will be 180 (horizontal direction). Often our thickest part is on the outside, and the thickness of astigmatism is added on the outside, so the thickness is exaggerated. Therefore, the frame needs to be smaller and thinner, that is, the closer the sum of lens width + center beam width is to your interpupillary distance, the thinner it will be. It is necessary to choose a higher index lens to make the thickness less noticeable.
In the fitting of glasses, "comfort" and "clearness" are often contradictory and difficult to reconcile. This contradiction is even more obvious on glasses with astigmatism. Clarity requires adaptation, but comfort does not necessarily mean clarity. For example, not wearing glasses is the most comfortable, but it is definitely not clear.
Glasses with high astigmatism are more sensitive and require more precise consideration in optometry and prescription. When encountering high astigmatism, you must pay attention to the matching of the frame/lens with the astigmatism degree and axis position to avoid customer complaints and discomfort due to product problems.
Post time: Nov-17-2023