Astigmatism is a type of refractive error, a general term used to describe the mismatch between the focusing power of the eye and the length of the eyeball. Clear vision is dependent on light entering the eye to focus at a sharp point on the sensory retina lining the inside of the eyeball. If light focuses too early this results in myopia, or short-sightedness (the eyeball is too long for the focusing strength of the eye); if light comes to a point too late, we consider this to be hyperopia, or long-sightedness (the eyeball is too short).
Astigmatism is slightly different from both myopia and hyperopia in that it causes light to focus not only at the wrong point within the eye, but in fact causes light to focus at multiple different points. Astigmatism can be present in conjunction with both myopia and hyperopia.
Astigmatism typically arises from an uneven curvature of the cornea, the transparent dome of light-transmitting tissue at the front of the eye. A smaller proportion of astigmatism cases may be due to the lens inside the eye refracting light unevenly; this is known as lenticular astigmatism but tends to be found less commonly than corneal astigmatism.
Astigmatism is often explained with the analogy of a ball. In the case of a soccer ball, the lines of curvature are the same no matter which way you run them across the ball – this would be considered an eye without astigmatism. An astigmatic eye is represented by an AFL football, where the lengthways axis of the football is a flatter curve than the axis running from side to side. In the situation of an actual cornea, light entering the steeper meridian of the eye would be refracted more sharply than light entering along the flatter curve, resulting in two different focal points within the eye. Understanding the type of astigmatism of an individual eye can play a part in guiding your eye care practitioner to decide on the best astigmatism treatment.
Studies have found that astigmatism is an inheritable trait amongst many families, though is not guaranteed that it will be passed on to later generations. Infants are found to have a higher prevalence of astigmatism but this becomes less common in early school years as the eye develops and changes, however, the development of astigmatism in adulthood is not uncommon.
Symptoms of astigmatism include:
- Blurry, distorted vision
- Increased difficulty with vision at night-time
- Headaches and eyestrain
- Glare sensitivity, especially from oncoming headlights or street lamps at night
Can Astigmatism Get Worse?
It is possible for all types of refractive error to worsen with time, including astigmatism. The exact cause of astigmatism progression is not fully understood, but research indicates that the most influential factor is the concurrent presence of myopia. There is some suggestion that ethnicity, age, gender, and the axis of astigmatism may also play a role in the likelihood of astigmatic progression but this is not yet well-established in the scientific literature.
Certain eye conditions are associated with astigmatism, the most common of these being a corneal thinning disease known as keratoconus. As keratoconus progresses, it can cause the astigmatism to get worse, often inducing very high degrees.
Options for Astigmatism Treatment
Many people will have some degree of astigmatism without even realising, as low amounts don’t tend to significantly affect vision and can go uncorrected. For patients noticing blur or headaches from their astigmatism, treatment is often first suggested in the form of glasses or contact lenses. Very high degrees of astigmatism can be addressed with optical correction, though options in soft contact lenses become very limited past -2.75 dioptres of astigmatism; prescriptions past this, often will need to consider custom-made soft lenses or hard (rigid gas permeable) contacts.
Despite the availability of optical correction, glasses and contact lenses do not suit all lifestyles and activities. Fortunately, we now have access to multiple surgical options for astigmatism treatment for patients who find spectacles inconvenient or are unable to wear contact lenses.
- LASIK and PRK laser eye surgery techniques can correct degrees of astigmatism up to about -5D, though this will depend on the anatomy of each individual eye, such as the thickness of corneal tissue available for reshaping with the laser.
- SMILE® eye surgery is a minimally invasive technique that sculpts the inner layers of the corneal tissue through a keyhole incision. SMILE® offers shorter recovery times, reduced risk of complication, and can correct astigmatism up to around -3D.
- Refractive lens exchange is similar to a cataract surgery procedure and is typically recommended for older patients for whom presbyopia (the natural age-related decline of near focus) has developed. The eye’s natural lens is removed and a synthetic intraocular lens (IOL) is inserted in its place, calculated to correct for the eye’s prescription. The amount of astigmatism corrected depends on the parameters of the IOL design.
- An intraocular contact lens (ICL) procedure involves inserting a thin synthetic lens between the coloured iris and the eye’s natural lens. An ICL can correct astigmatism of up to around -4D depending on the manufacturer’s parameters.
For astigmatism treatment options past ordinary glasses and contact lenses, contact Eye Laser Specialists for your complimentary consultation to discuss how eye surgery can help you: 1300 297 583