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Astigmatism is usually caused by the presence of a non-uniform shape to the cornea, with the cornea being more or less steeply curved in particular areas (meridians). Book a consultation today & discover your treatment options.
If your spectacle prescription contains two numbers with a multiplication sign between them e.g. -1.00 / +2.00 x 150 you are astigmatic.
Astigmatism is a little more optically complex than near or far-sightedness alone so you can be myopic or hyperopic and astigmatic or the two focal points can straddle the retina, this is called mixed astigmatism so people often say that they are both long and short-sighted. Astigmatism causes blurry or distorted vision at all distances.
Astigmatism is an optical term (not a disease or eye condition) that describes light focussed to different points within the eye depending on the curvature of the cornea (and less so, the lens). If the cornea is round, it will focus light to the same point whichever meridian light enters but most human corneas are asymmetric vertically and flatter horizontally i.e. like a rugby ball laying on it’s side, so they have a higher focal power vertically than horizontally. If you think of the cornea like a clock face, the vertical meridian is between 12 and 6 o’clock and the horizontal meridian between 3 and 9 o’clock and these are the meridian most likely to have different curvatures in astigmatism. Most people have some degree of astigmatism but as the difference increases all images become blurred whether they are near or distant unless they are corrected by spectacles, contact lenses or surgery.
When the meridians of astigmatism are at 90 degrees to each other it is described as regular. If the steeper curvature is at the 90 degree meridian this is known as ‘with the rule’ astigmatism because it is the most frequently occurring. If the steeper meridian is at 180 degrees this is known as ‘against the rule’ astigmatism because it occurs less commonly. An axis between the two is known as oblique astigmatism. These are types of regular astigmatism and can be corrected with lenses, either in spectacles, contact lenses, ICL’s or intra-ocular lenses (IOL’s).
Irregular astigmatism is usually the result of an injury or infection or a condition like Keratoconus where the pattern of curvature is irregular and asymmetric. This type of astigmatism may be corrected using a rigid contact lens or therapeutic treatment like topography-guided laser vision correction.
Spectacles and contact lenses can have toricity (different curved surfaces) manufactured onto the lens to correct for regular astigmatism. Oblique astigmatism can be difficult to correct in contact lenses because of the movement of the lens with blinking. High levels of astigmatism may result in spectacles being difficult to tolerate or a change in astigmatic power resulting in vision seeming to swim so spectacles may deliberately under correct astigmatism balancing comfort against visual performance.
LASIK, ReLEx SMILE® and ASA are all methods employed to correct astigmatism accurately and safely and this correction can be combined with any other refractive error. LASIK is the most widely performed procedure with an estimated 40,000,000 procedures performed to date whilst ReLEx SMILE® is the fastest growing refractive procedure, think ‘Keyhole LASIK’. ASA or LASEK is similar to PRK and was the first excimer procedure to be performed to correct vision, visual outcomes are the same as the others but surface treatment have a slightly slower and less comfortable recovery.
Both the EVO and EVO+ Visian ICL® are available in toric forms employing a thin, biocompatible Collamer® lens to sit behind the iris (so that it is not visible) and in front of the natural crystalline lens (so that accommodation is preserved) and can correct astigmatic errors up to 6.0D. It is an effective alternative if the cornea is unable to support laser vision correction.
Precise measurements are made of the eye when cataract or lens replacement surgery is planned. Correction of astigmatism will be factored into the calculation of intra-ocular lens power, whichever type of lens is selected. A toric correction can be combined with monofocal, extended depth of focus or multifocal IOL’s.
People with astigmatism will usually experience blurred or distorted vision at all distances. Looking at a letter like a ‘T’ they may be aware that either the long vertical or short horizontal bar looks sharper, hour markings on a clock face may be clearer vertically or horizontally. In addition, astigmatism will often contribute to symptoms of eyestrain or cause people to squint (partially close their eyes) to see more clearly.
Most people have some degree of astigmatism but as the value increases, particularly over 1.00D vision becomes more noticeably blurry if uncorrected.
Yes, astigmatism is associated with other refractive errors like myopia or hyperopia and can usually be corrected at the same time.
It is not possible to fully eliminate a refractive error because the eye is constantly changing focus and the pupil constantly changes size. In addition, it may be advantageous in certain circumstances to retain some degree of astigmatism. We will usually aim to reduce astigmatism to as small a degree as possible or to alter the meridian of astigmatism to one more optically desirable for your eye.
Astigmatism will be detected and measured by your optician on routine sight testing. At a medical consultation we will also employ specialist scans called corneal topography scans to accurately and objectively measure corneal astigmatism prior to surgery.
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