What is astigmatism?

What is astigmatism?

Questions and Answers on Astigmatism

What is it?

It is one of the most common vision problems that results from the cornea not being totally spherical, which causes refractive errors.

What causes astigmatism?

When the eyeball is shaped like a perfectly round ball, the cornea is completely spherical, the light rays enter the eye and are focused evenly to provide a clear image. However, if the eye has a curvature imperfection (or more oval shape, like a rugby ball), the light rays are focused differently. The image is focused on one axis and blurred on the other, i.e. not fully focused. 

This curvature and the non-ideal refraction of light make objects appear blurred.

What are the symptoms?

• Blurred vision;
• Willingness to squeeze the eyes, which helps focus the image;
• Headaches;
• Poor night vision;
• Asthenopia, feeling of discomfort in the eye;
• Double vision - very strong astigmatism

Where does it come from?

• It can be present from birth and is a genetically transmissible trait;
• It can develop during life due to an injury that alters the curvature of the cornea or due to surgical intervention;
• Disorders such as keratoconus deform the cornea and generate an irregular astigmatism;

What are the various types of astigmatism?

• Regular - associated or not with other refractive errors, it is normally corrected with glasses.
• Mixed Regular - in which one meridian is negative, i.e. myopic, and the other positive, i.e. hyperopic.
• Irregular - like keratoconus, not correctable with spectacles and will require surgery or special contact lenses.

How is astigmatism diagnosed?

In a visual check-up, astigmatism can be diagnosed using a refractometer or by the doctor in an ophthalmology consultation when he/she does a refraction.

O topographer is a device which allows characterising and measuring any type of astigmatism. It is a computer that builds a colour map of the cornea from the data collected from the patient. It uses concentric light rings that are projected onto the cornea to detect any change in curvature, whether regular or irregular.

A corneal topography is a very important examination because it allows diagnosing subclinical keratoconus and also in cases of advanced keratoconus to make the appropriate study for surgery.

The ophthalmologist, based on the information gathered by the examinations, will choose the most appropriate way to correct the pathology, by means of surgery, glasses or contact lenses.

Does it affect night vision?

Astigmatism affects vision during all hours of the day, but can have a particular effect on night vision. Lights may appear fuzzy or surrounded by a halo, glare or appear duplicated. 

For people with this condition it is particularly important that they wear corrective lenses when driving at night.

What are the possible treatments for astigmatism?

It can be corrected with glasses, contact lenses or surgery. When the degree is high, correction with spectacles is more difficult, as is correction with contact lenses. In this case, it is advisable to resort to definitive correction by laser surgery (LASIK or PRK), which reshapes the cornea so that it takes on a spherical shape, correcting the defect.

Are corrective lenses different from normal lenses?

Yes, spectacle lenses are toric, i.e. cylindrical with an axis in the direction of the astigmatism in order to correct blurriness resulting from the shape of the cornea. 

Contact lenses are also an option, but you will need to wear toric lenses: 

• All contact lenses rotate when we blink. The soft lenses used for this condition, called toric lenses, are designed to return to the same place every time.
• Rigid (hard) gas permeable contact lenses are a better choice if astigmatism is high.

Do toric lenses require any special habituation?

Initially, wearing glasses with these types of lenses can cause a feeling of tilting on flat surfaces, for example when looking at the floor or a table. 

When these lenses are first prescribed, the ophthalmologist may advise you to go below the correct grade to give the patient time to adapt. This effect should disappear as they get used to it. It is important to wear the glasses first thing in the morning for a few hours at a time and to adjust them slowly. If your vision does not improve, you should see your ophthalmologist to check your prescription.

Can children have astigmatism?

Yes, in children it is common for children to have regular ones which evolve with growth and consequently with the size of the eye. It is important that they are observed before school age so that they can be corrected for a problem that most of the time they are not aware of. 

The best practice is to start regular eye examinations before the age of 4.

Signs of visual problems in children:

• Squeeze your eyes shut or cover one eye;
• Tilts head when doing close activities (more than 50 cm from the eyes);
• Avoids looking at books and puzzles, prefers toys they can manipulate;
• Holding books too close to the face or keeping the face too close to the table surface.

Are there cases of blindness due to the pathology?

There are no known cases of blindness for astigmatism.

What is the Ophthalmology Private Practice perspective?

Children should always have a first visit before the age of 4 or earlier if there are complaints or parents find vision problems.

As for correction in adults, the cases of regular astigmatism with little repercussion on vision, we advise the use of corrective glasses. 

In cases above 2 dioptres associated or not with myopia or astigmatism, the use of glasses may be sufficient. 

The use of contact lenses does not usually allow an adequate correction because the movement of the lens causes frequent blurring. In these cases, laser refractive surgery(LASIK) may be indicated.

In cases of irregular astigmatism, especially in cases of keratoconus, only semi-rigid contact lenses or contact lenses especially suitable for these cases achieve an acceptable quality of vision.

In more difficult cases and above all in situations of evolutive keratoconus, we advise surgery with corneal rings associated with crosslinking, This improves visual acuity and above all stabilises the keratoconus.

In rare cases, only corneal transplant can help to solve the problem.

How to read a prescription for astigmatism?

The prescription contains several letters and numbers. 

Definition of the letters:

• OD stands for oculus dexter or right eye;
• THE stands for oculus sinister or left eye;
• OR means oculus uterque, or both eyes.

The numbers are the measurements called dioptres.

• The first number indicates the spherical correction. If it has a minus sign, there is myopia. If there is a plus sign, there is hyperopia;
• The second figures are the cylindrical correction;
• The third is the axis of astigmatism, which corresponds to the direction of blurring or the location of the astigmatism on the cornea.

For example, a prescription of "OD -1.00 x -2.00 x 155" means that the right eye has 1 diopter of myopia and 2 diopters of astigmatism at 155 degrees on the cornea.