Can laser eye surgery really cure my astigmatism?
Laser eye surgery is one of the most effective treatments for astigmatism, with LASIK, ASLA and SMILE laser all having the ability to comfortably correct several dioptres of astigmatism. So why do so many patients think they’re not suitable for laser eye surgery just because their eyeballs are not perfectly round?
Astigmatism….that sounds bad, right?
Wrong! Astigmatism is one of the least understood of the standard range of eyeball shapes. While many people understand the general principles of short-sightedness and long-sightedness, most do not quite ‘get’ astigmatism. Yet all it is, is a little asymmetry in the curve of your cornea – the front of your eyeball. Just as you may have one foot a little larger than the other, or one eyebrow a little higher, so too do most people have a small difference in the curvature of their cornea. It is popular to imagine the cornea as being a little like an egg or a rugby ball rather than a perfect sphere, but astigmatism really is very subtle and cannot be seen with the naked eye.
How is astigmatism corrected?
A small amount of astigmatism up to about 0.75 dioptres is normal in most eyes and doesn’t require any correction. Eyes are flexible structures, a bit like rubber balls, and are contained by muscles in a bony socket. All of this can squeeze the eye a little, creating a small degree of astigmatism. If glasses are worn for other reasons – to correct distance or near vision, then the correction for astigmatism is usually incorporated into the glasses prescription. Glasses can correct large amounts of astigmatism, as long as the cornea is regular, and doesn’t suffer from an eye disease like keratoconus. (Keratoconus is an eye disease that causes the cornea to progressively become thin and bulge forward). But spectacles to correct high degrees of astigmatism can cause distortion when looking through them and
require some getting used to.
Correcting astigmatism with contact lenses is not as straightforward as glasses as there are two different curves to the cornea to correct and, unlike glasses lenses, there is no frame to hold the contact lenses in the correct orientation. The options are to either use a hard lens, which creates a spherical surface on the eye’s surface, or, to use a specially shaped soft ‘toric’ lens, which is weighted to correct the two curves. Success with these lenses depends on a number of factors including the experience of the optometrist fitting the lenses as well as the shape of your eye and the fit of the lens.
How can laser eye surgery cure astigmatism?
A laser eye surgery procedure such as LASIK, ASLA or SMILE, can easily correct several dioptres of astigmatism as part of a surgical plan to eliminate or reduce dependence on glasses. The laser simply removes more tissue from one contour of your cornea than the other, resulting in a spherical shape. Almost all eyes undergoing laser eye surgery have some degree of astigmatism. Remember! It’s more common to have a little astigmatism than none at all. It is also worth noting that many eyes have a very small degree of astigmatism (typically 0.25 to 0.50 dioptres) after their laser vision correction procedure, and this does not stop them from clearly reading the 20-20 line of the chart (or better).
How much astigmatism can the laser correct?
There are no hard and fast rules with this. A lot depends on the shape and thickness of your cornea. Astigmatism up to about 4 dioptres is commonly corrected, and there are many patients with even higher amounts who have had very successful results. Your surgeon will be able to advise you on realistic expectations for your particular prescription.