By The Eye PracticePublished On: 3 November 20173.1 min read

Astigmatism is one of those conditions that usually sounds worse than it is. But having an eyeball that is not perfectly spherical is actually the norm, so why do people get upset about this condition?

Let’s be clear – astigmatism is nothing to worry about in most cases.

Low astigmatism

Did you know that it is more normal to have a little astigmatism than none at all? That’s because the eye is a flexible structure, and as it sits in a tight little socket, it gets a little squashed. This is so subtle that it is not noticeable until you have about 0.75 dioptres of astigmatism or more. Even then, it’s mainly noticeable at night, especially around lights. Low levels of this condition require no treatment – not even glasses – unless you are suffering from eyestrain, in which case a 0.75 correction may help your eyes work more effectively with less effort.

Mid-range astigmatism

Once you have more than 1 dioptre difference between the two curves of your eye, you’re in this range and glasses usually make a noticeable difference to your vision. Astigmatism usually comes in combination with myopia (short-sightedness) or long-sightedness, but not always. Your optometrist will prescribe glasses (if you need them) to correct the blur. Contact lenses are also an option and come in a variety of modalities, including disposables.

High astigmatism

You’ve reached this territory once you have over 4 dioptres of difference between the two curves of your eye. You’ll need specially-made spectacle lenses and contact lenses are harder to fit. Even slight movement of the lens on your eye will cause blur. A rigid gas permeable – or RGP – contact lens may be a better option, but these are tricky to fit successfully and need an experienced contact lens practitioner. If you have laser eye surgery, it may not yield a perfect result.

Keratoconus

This is a progressive disease that causes thinning and steeping of your cornea. It often presents as worsening astigmatism that is not fully corrected with glasses – also called irregular astigmatism. The surface of the eye usually behaves in a mathematically predictably, making it possible to correct your error with a spectacle lens.

But with irregular astigmatism, the amount of curvature varies across the cornea and cannot be corrected fully with a glasses lens. Specialised RGP contact lenses are the mainstay of keratoconus management and, once successfully fitted by an expert, you can enjoy relatively good vision and continue to drive, play sports, have a career etc.

This disease rarely leads to permanent vision loss or the need for a corneal transplant if it is managed properly from the start.

What about laser eye surgery?

It is an urban myth that you can’t have laser eye surgery if you have astigmatism. As long as you are within the range catered to by LASIK and SMILE, of course you can. Even higher degrees of astigmatism won’t stop you from having LASIK, but it may mean you get a less than perfect result.

The only exception is if you have keratoconus, which will make you unsuited to any laser surgery to your cornea (the front surface of your eye). You may have a sub-clinical form of keratoconus that only shows up during the in-depth testing performed during a consultation for laser eye surgery.

Sometimes, even having a sibling with keratoconus is enough to prevent you from being a suitable candidate for surgery.

Bear in mind that keratoconus is a rare disease, affecting only 1 in 2, 000 people, and it is much more likely that you have the common or garden form of astigmatism.