By Alastair Lockwood, Eye Health Advisor, Ophthalmologist and Eye Surgeon, an associate of Feel Good Contacts
Among the most common vision problems, astigmatism may sometimes go unnoticed for many years. When it’s a mild prescription, you can get by for a while, but that rarely holds up forever. Unfortunately, astigmatism does not simply disappear. However, it can change as your eyes continue developing.
Our eyes are changing all of the time, throughout our lives. So, sticking to opticians’ recommendations and obtaining a new eye exam result at least every two years is very important.
What causes astigmatism?
In particular, the curvature of the cornea, ‘the window of the eye’. If spherical, light waves in all planes will focus on the same point at the retina. If oval or “rugby ball” in shape, light waves entering the eye in one plane will focus at a different point to those in another plane.
Astigmatism is categorised as either regular or irregular, and direct or indirect. With regular astigmatism, the cornea is more curved in one direction compared to the other. Whereas with irregular astigmatism, the curvature is not even across the eye’s surface and can have multiple directions.
Direct astigmatism occurs when the vertical meridian is steeper, making vertical lines appear blurry. With indirect astigmatism, the horizontal meridian is affected instead. As a result, your eyes won’t be able to focus on horizontal lines.
When should I be concerned about an astigmatism?
Astigmatism causes vision to be blurry and may be simply corrected with glasses or contact lenses.
Aside from blurred vision, astigmatism can also cause additional symptoms that may be inconvenient, uncomfortable or even painful. These include:
- Eye strain
- Fatigue
- Headaches
There are three other main types of visual complications that astigmatism can create, too:
- Myopic astigmatism – one or both of the principal meridians in the eye cause short-sight
- Hyperopic astigmatism – one or both of the principal meridians in the eye cause long sight
- Mixed astigmatism – one or both of the principal meridians in the eye cause short-sight, while the other sees better at long distances
How do I know if I have an astigmatism?
If you are experiencing vision problems, the first thing you should do is arrange an eye test with your optician. An optician will test your eyes for visual acuity, focusing power and the curvature of the eye to determine the cause of the issue.
Visual acuity is measured using a letter chart, and aims to determine the clarity of your vision. Based on the assumptions of your acuity test, opticians use a series of lenses to test and measure your focusing power. The lenses that correct vision most accurately will be noted as your “prescription”.
To measure the eye’s curvature, a keratometer or similar tool may be used.
How does an optician correct astigmatism?
The mainstay treatment is to wear glasses. Glasses for astigmatism refract (bend) light in different meridians before it enters your eye. This correction can be added to myopia, hyperopia or presbyopia prescriptions in the same pair of glasses.
Another option is a toric contact lens. These work out more expensive than glasses if you opt for daily, two weekly or monthly contact lenses, but they offer more convenience in terms of visual freedom. Toric contact lenses are a different shape from regular contact lenses. Instead of being spherical, they are a torus shape which can be compared to a slice of a ring doughnut shape. This design bends the light so that a clear image can be received by the retina. In order for this to work, toric contacts rotate into a position that aligns with the meridians of power as needed.
If you want to learn more about astigmatism and you have to wait a few days before you can consult your optician, there some basic online tests available to use as a starting point.
