What is Astigmatism: Definition, Symptoms, Diagnosis, and Treatment
What is Astigmatism and how is it defined?
Astigmatism is an aspherical refractive defect where the eye exhibits different refraction in two sections. Astigmatism may be regular (most frequent) or irregular.
- Regular astigmatism – looks more like a rugby ball (curvature of meridians is uniform)
- Irregular astigmatism – associated with trauma, disease or degeneration, odd shape, scars (none of the curvature of any one meridian is uniform)
Astigmatism may not only involve the cornea but may be lenticular or retinal.
- Astigmatismus of the cornea (the most common)
- Astigmatismus of the eye lens
- Astigmatismus of the retina
Astigmatism is a type of refractive error in which the eye does not focus light evenly on the retina. The elongated cornea lets the light-reflected objects, which focus on two points on the pupil of the eye instead of just one, which is why the image is blurred. This refractive error requires a different eye correction, like special contact lenses with cylinder and axis.
In our previous blog you can read more about the different types of parameters, including those for toric contact lenses.
Astigmatism operates on a different principle, although is often accompanied by short-sightedness or farsightedness. Therefore it can't be corrected by normal lenses or glasses which have only the plus or minus power. Toric contact lenses are usually prescribed for eye care patients with astigmatism. These contact lenses for astigmatism have a thicker zone at the bottom to keep them from rotating while in the eye. This helps orient the lenses consistently and predictably for better visual acuity.
Which contact lenses are best for astigmatism?
- 1-DAY Acuvue Moist for Astigmatism
- DAILIES AquaComfort Plus Toric
- Biofinity Toric CooperVision (6 lenses)
- PureVision Toric (6 lenses)
- Air Optix for Astigmatism (6 lenses)
The 3 most common types of Astigmatism
There are three primary types of astigmatism:
- Myopic Astigmatism. One or both principal meridians of the eye are nearsighted. (If both meridians are nearsighted, they are myopic in differing degree.)
- Hyperopic Astigmatism. One or both principal meridians are farsighted. (If both are farsighted, they are hyperopic in differing degree.)
- Mixed astigmatism. One principal meridian is nearsighted, and the other is farsighted.
Diagnosis of Astigmatism
Astigmatism is detected during a routine eye exam with the same instruments and techniques used for the detection of short-sightedness and far-sightedness.
Your eye doctor can estimate the amount of astigmatism you have by shining a light into your eye while manually introducing a series of lenses between the light and your eye. This test is called retinoscopy.
Symptoms of Astigmatism
The symptoms may differ in each person and it's also possible that no symptoms at all can be experienced. Some of the most common symptoms are the unclear image and the blurry vision. They can vary together with the astigmatism degree. If it's too small, no vision problems will be noticed. If the astigmatism degree is higher, it causes fatigue in the eyes mainly when reading and using a computer due to the efforts of the eye to adjust.
In fact, most people probably are born with some degree of astigmatism or very often it is inherited. If you notice the symptoms of astigmatism, have a look at your family tree. There is big chance that someone from your relatives has it too. When astigmatism has been diagnosed in early childhood, there is a possibility for it to increase or decrease with the ageing. Astigmatism can be caused by an injury or eye surgery too.
How is the astigmatism treated?
There are several astigmatism correction options:
• Toric contact lenses (or corrective eyeglasses). Patients with astigmatism are usually prescribed toric lenses for correction of vision. Toric lenses have a larger angle of reflection in a certain direction.
After your doctor has conducted the visual acuity assessment test to your eyes, he will determine which lenses are the most appropriate for your form and degree of astigmatism.
• Refractive surgery This is another method of correcting astigmatism. It consists of a change in the shape of the eye cornea, which is performed by refractive or laser surgery of the eyes. In order to undergo such type of intervention, your eyes need to be healthy. This means you have no problems with the retina, wounds and scars on the cornea and other eye diseases.