Astigmatism: Causes, Symptoms and Treatment

What is astigmatism?

Astigmatism is a visual defect in which images become distorted, double or blurred. It becomes difficult to distinguish details of objects both near and far away. Astigmatism, in simple words, is a distortion of vision. The defect is due to improper refraction of light. Normally, rays pass through the cornea and lens and are accurately focused on the retina. From it, the optic nerve delivers a clear image to the brain. In astigmatism, the light rays are focused at different points near and on the retina, causing the picture to be distorted and double. Light is not focused accurately because the cornea or lens has an uneven surface. They are never perfectly smooth, which is why everyone has a slight distortion of vision. However, sometimes the surface of the cornea or lens is so uneven that images become too blurred.

Small astigmatism is present in almost everyone. It does not always require correction. But sometimes without it, the details of objects and the picture of the world are too distorted, which prevents you from performing everyday tasks. Specialist help is needed to restore comfortable vision.

Causes and types of astigmatism

The development of astigmatism can be natural or influenced by external factors, i.e. it can be congenital and acquired. Congenital astigmatism is related to genetics. It is inherited from parents or other relatives. Congenital astigmatism occurs in most children and is not a pathology in itself. As a rule, its value does not exceed 0.5 diopters and even without correction does not affect visual acuity. However, in a child under a year old, astigmatism above 1 diopter can be detected. It can be caused by complications during pregnancy that affected the state of the cornea or lens, or genetic predisposition. In most cases, the congenital defect affects both eyes.

Acquired astigmatism can be caused by many things, including:

• traumatic injuries that have resulted in scarring of the cornea;
• consequences of eye surgeries, such as cataract removal;
• inflammatory processes on the cornea of the eye - these include diseases such as keratitis and keratoconjunctivitis;
• corneal dystrophy.

In some cases, it is impossible to determine the specific cause of the occurrence and development of astigmatism.

An acquired defect may affect not both eyes, but only one of them.

Also, this visual impairment can be combined with myopia (myopia) and hyperopia (hypermetropia). Accordingly, experts distinguish several varieties of astigmatism:

• simple hyperopic or myopic astigmatism - in this case, there is normal refraction in one meridian of the eyeball and myopia or hyperopia in the other;
• complex hypermetropic or myopic astigmatism - both main meridians of the eye show signs of hyperopia or myopia of different degrees;
• mixed astigmatism - myopia is diagnosed in one meridian of the eye and hyperopia in the other.

Astigmatism is also subdivided into forward, inverse, and oblique axis astigmatism. These terms are used to describe the orientation of the major meridians:

• in forward astigmatism, the “steepest” meridian (axis) is along the vertical line. Images along the vertical line will be sharper than those along the horizontal line.
• with inverse astigmatism, the greatest curvature is along the horizontal line. In this case, images along horizontal lines will be sharper than along vertical lines.
• in oblique astigmatism, the main meridians are inclined. So images along both horizontal and vertical lines will be distorted.

A detailed understanding of astigmatism can better help in selecting the best method of astigmatism correction.

Degrees of astigmatism

Like other refractive disorders, the degree of astigmatism is measured in diopters. In this case, due to the violation of the normal sphericity of the eye, the refractive power will be different in different meridians of the corneal surface, that is, in the conventional lines connecting the poles of the eyeball. The closer the shape of the eye surface is not to a sphere, but to an oval, the more vividly it is expressed.

It is accepted to distinguish three degrees of this defect:

• Weak - up to 3 diopters, and if the indicator is not more than 1 diopter, the symptoms are often almost imperceptible, and only in the ophthalmologist's office, during the examination, a person can learn that he has astigmatism;
• Medium - up to 6 diopters: the consequences of the irregular shape of the cornea or lens are strongly felt, the person feels the visual impairment acutely, and astigmatism over 3 diopters is often combined with corneal pathologies;
• High - more than 6 diopters: occurs mainly with corneal pathologies. In addition to problems with the perception of the surrounding world, a person experiences tearing in the eyes and headaches, often feels dizziness, and the distortion of objects is so great that it is impossible to do without correction. However, it can be difficult to find an effective correction for high degree of astigmatism.

Timely referral to a specialist will help to control astigmatism.

Symptoms of Astigmatism

The main symptom of astigmatism is the perception of objects of the surrounding world blurred: the contours can double, distorted, and, unlike nearsightedness or farsightedness, there is no difference in the distance from you these objects are located. A person with astigmatism perceives blurred both what is close to him or her and what is quite far away.

Symptoms may be the same as in other visual disorders. They are usually:

• Visual impairment;
• rapid fatigue, especially when using a computer, laptop or mobile devices;
• tearing, burning in the eye;
• redness;
• headache as a result of increased visual strain;
• having to squint to get a clearer view of an object;
• Perceptual errors - for example, confusing similar letters and numbers;
• double vision;
• inability to focus on an object.

If you have similar symptoms of this disease, it is recommended to make an appointment with an ophthalmologist and we recommend you to do our eye exercises. Timely diagnosis of the disease will prevent negative consequences for your health.

How is astigmatism detected?

Modern vision diagnosis begins with autorefractometry. Using the device, the specialist determines the refraction of each eye - the refractive power or optical power. The autorefractometer clearly records how the eye refracts light and can detect various refractive disorders (optical power) of the eye, including astigmatism.

The patient is then asked to undergo a visual acuity test. It is conducted according to Sivtsev's table: you need to clearly name the symbols in each row. If something you do not see or confuse similar letters, which is typical for astigmatism, the specialist records the result and indicates your visual acuity (visus).

Next, a test for astigmatism is performed, usually the “Radiant Figure” or “Siemens Star” tests. As well as further refinement with cross-cylinder tests. The specialist, having determined the parameters of visual distortion, selects the appropriate lenses that return clarity to the images.

Keratometry may be required for a more objective assessment of astigmatism. The method determines the curvature of the cornea, which is necessary for fitting contact lenses.

The doctor may also perform biomicroscopy - a study of the anterior segment of the eye. The examination allows to exclude inflammation or damage to the cornea, which can cause astigmatism.

Optical coherence tomography is used less frequently. The examination is necessary to exclude damage to the deep structures of the eye, which may lead to astigmatism or other diseases accompanied by blurred and unclear images.

Astigmatism correction

Different methods can help to improve vision in astigmatism. Depending on the complexity of this defect, specialists may recommend:

• corrective glasses with cylindrical lenses;
• toric (astigmatic) contact lenses;
• scleral lenses;
• laser vision correction.

Corrective glasses to correct astigmatism

This is the easiest and fastest way to improve vision in astigmatism. Corrective glasses are made with cylindrical lenses. They have different curvature or degree of curvature on the lens surface. This design allows you to set the correct refraction of light and improve vision.

For example, if straight astigmatism is diagnosed, where horizontal lines are distorted, a cylindrical lens will alter the path of these rays so that they focus correctly on the retina.

In addition to the cylindrical design, the lens can have a standard spherical or flat aspherical surface shape. The former is suitable for correcting mild degrees of astigmatism. But for high diopters, you should give preference to aspherical lenses, as they have less distortion at the edge. In addition, they are lighter and thinner, which will add to the aesthetics of glasses.