Here are 4 key points about astigmatism:
- An imperfect shape of the front of the eye
- Causes blurry vision at higher degrees
- A common finding in vision examinations
- Rapid changes associated with other conditions
- Corrected with prescription spectacles or contact lenses
What is astigmatism?
A refractive error occurs when the cornea (the front surface of the eye) is flattened in one direction, rather than being perfectly spherical. It is often likened to the shape of a rugby ball, rather than a perfectly spherical soccer ball. Consequently, it causes blurry, distorted vision.
The cornea bends light entering the eye. Only part of the image is focused onto the retina with astigmatism. This causes the image to be clear along one axis and blurry in the other. The flattening of the cornea may be horizontal, vertical or oblique which determines the axis of astigmatism.
Causes of astigmatism
Astigmatism occurs as the eye grows from birth to adulthood. The cornea’s structure changes over time. Sometimes, a pterygium (UV-related growth on the front of the eye), an injury or surgery that causes scar formation can also distort the cornea.
If the astigmatism is changing rapidly it may be due to a condition called keratoconus where the cornea thins and bulges outwards over time. It is important to diagnose keratoconus quickly. Early intervention can drastically improve the outcome.
Symptoms can vary with severity. However, the most common symptoms include:
- eyestrain and headaches after prolonged visual tasks,
- reduced concentration,
- difficulty reading and focusing,
- difficulty seeing at night,
- distorted and blurry vision, up close and far away,
- image becoming stretched in one direction.
The cornea’s exact shape is measured by the optometrist. So, the optometrist can quantify the amount of astigmatism. Furthermore, corneal topography provides a detailed topographical map of the front of the eye. Additionally, the optometrist will check the best corrected visual acuity on an eye chart and use diagnostic spectacle lenses to obtain the clearest vision.
Prescription spectacles or contact lenses are often enough to treat the symptoms of astigmatism. Sometimes, if astigmatism is changing rapidly due to keratoconus, corneal cross-linking can be performed. Laser surgery can also correct the shape of the eye.
Reducing your risk
Astigmatism is not preventable. Regular visits to the optometrist will catch it early, so you can reduce your risk of developing symptoms. Regular screen checks are also important to detect important conditions such as keratoconus early. So this is important to avoid more serious vision problems from developing.