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Ashraf Armia Eye Clinic

Cataract Surgery

Astigmatism Symptoms

Astigmatism usually causes vision to be blurred or distorted to some degree at all distances.
Symptoms of uncorrected astigmatism are eye strain and headaches, especially after reading or other prolonged visual tasks.
Squinting also is a very common symptom.

What Causes Astigmatism?

Astigmatism usually is caused by an irregularly shaped cornea. Instead of the cornea having a symmetrically round shape (like a baseball), it is shaped more like a football, with one meridian being significantly more curved than the meridian perpendicular to it.

(To understand what meridians are, think of the front of the eye like the face of a clock. A line connecting the 12 and 6 is one meridian; a line connecting the 3 and 9 is another.)

The steepest and flattest meridians of an eye with astigmatism are called the principal meridians.

In some cases, astigmatism is caused by the shape of the lens inside the eye. This is called lenticular astigmatism, to differentiate it from the more common corneal astigmatism.

Types of Astigmatism

There are three primary types of astigmatism:

Myopic astigmatism. One or both principal meridians of the eye are nearsighted. (If both meridians are nearsighted, they are myopic in differing degree.)
Hyperopic astigmatism. One or both principal meridians are farsighted. (If both are farsighted, they are hyperopic in differing degree.)
Mixed astigmatism. One prinicipal meridian is nearsighted, and the other is farsighted.
Astigmatism also is classified as regular or irregular. In regular astigmatism, the principal meridians are 90 degrees apart (perpendicular to each other). In irregular astigmatism, the principal meridians are not perpendicular. Most astigmatism is regular corneal astigmatism, which gives the front surface of the eye a football shape.

Irregular astigmatism can result from an eye injury that has caused scarring on the cornea, from certain types of eye surgery or from keratoconus, a disease that causes a gradual thinning of the cornea.

How Common Is Astigmatism?

Astigmatism often occurs early in life, so it is important to schedule an eye exam for your child to avoid vision problems in school from uncorrected astigmatism.

In a recent study of 2,523 American children ages 5 to 17 years, more than 28 percent had astigmatism of 1.0 diopter (D) or greater.

Also, there were significant differences in astigmatism prevalence based on ethnicity. Asian and Hispanic children had the highest prevalences (33.6 and 36.9 percent, respectively), followed by whites (26.4 percent) and African-Americans (20.0 percent).

In another study of more than 11,000 eyeglass wearers in the UK (both children and adults), 47.4 percent had astigmatism of 0.75 D or greater in at least one eye, and 24.1 percent had this amount of astigmatism in both eyes. The prevalence of myopic astigmatism (31.7 percent) was approximately double that of hyperopic astigmatism (15.7 percent).

 

Astigmatism Test

Astigmatism is detected during a routine eye exam with the same instruments and techniques used for the detection of nearsightedness and farsightedness.

Your eye doctor can estimate the amount of astigmatism you have by shining a light into your eye while manually introducing a series of lenses between the light and your eye. This test is called retinoscopy.

Though many eye doctors continue to perform retinoscopy, this manual procedure has been replaced or supplemented in many eye care practices with automated instruments that provide a faster preliminary test for astigmatism and other refractive errors.

Whether your eye exam includes retinoscopy, an automated refraction, or both, your optometrist or ophthalmologist will perform another test called a manual refraction to refine the results of these preliminary astigmatism tests.

In a manual refraction (also called a manifest refraction or subjective refraction), your eye doctor places an instrument called a phoropter in front of your eyes. The phoropter contains many lenses that can be introduced in front of your eyes one at a time so you can compare them.

As you look through the phoropter at an eye chart at the end of the exam room, your eye doctor will show you different lenses and ask you questions along the lines of, "Which of these two lenses makes the letters on the chart look clearer, lens A or lens B?" Your answers to these questions help determine your eyeglasses prescription.

Astigmatism Correction Options

Astigmatism, like nearsightedness and farsightedness, usually can be corrected with eyeglasses, contact lenses or refractive surgery.

In addition to the spherical lens power used to correct nearsightedness or farsightedness, astigmatism requires an additional "cylinder" lens power to correct the difference between the powers of the two principal meridians of the eye.

So an eyeglasses prescription for the correction of myopic astigmatism, for example, could look like this: -2.50 -1.00 x 90.

  • The first number (-2.50) is the sphere power (in diopters) for the correction of myopia in the flatter (less nearsighted) principal meridian of the eye.
  • The second number (-1.00) is the cylinder power for the additional myopia correction required for the more curved principal meridian. In this case, the total correction required for this meridian is -3.50 D (-2.50 + -1.00 = -3.50 D).
  • The third number (90) is called the axis of astigmatism. This is the location (in degrees) of the flatter principal meridian, on a 180-degree rotary scale where 90 degrees designates the vertical meridian of the eye, and 180 degrees designates the horizontal meridian.


If you wear soft toric contact lenses for astigmatism correction, your contact lens prescription will likewise include a sphere power, cylinder power and axis designation.

Gas permeable contact lenses are also an option. Because these lenses are rigid and optically replace the cornea as the refracting surface of the eye, a cylinder power and axis may or may not be needed, depending on the type and severity of astigmatism correction required. The same is true for hybrid contact lenses.

 

This type of lens will allow you to see near and far – similar to varifocal glasses. The lenses work by using several different optical powers at varying points across the lens, and it works by relying on your eye muscles to move when needed in order to bring the correct distance into focus. These work best if they are implanted into both eyes.
 

  • A large proportion of people, approximately 85 per cent, find that they no longer need to wear glasses for their daily activities once they have made the choice to have these lenses implanted.
  • Multifocal lenses can often offer excellent distance and near vision, meaning that if you work at a computer all day it could be the perfect choice for you.
  • Somewhere between five and ten per cent of patients who opt for this lens suffer some kind of halo or glare when looking at lights at night. However, often, patients claim that this is something that they are able to get used to after a short period of time.
  • This type of lens can sometimes be associated with a struggle with contrast, which may have a negative impact if you are trying to read something in dim light. Of course, it is bad for your eyes if you read in dim light anyway – so this should be avoided whether you have had lens replacement surgery or not.
  • This type of lens is not able to correct astigmatism, which may be an issue for patients who suffer with it. This may not be an issue for much longer, however, as there has been some research into multifocal toric lenses – but how soon these will be available to patients is very much unknown.

With this type of lens, your vision will be in focus at just one distance – either near, far, or intermediate distance. You also have the option of having different lenses in each eye so that you can see at two different distances. This is called monovision, which is useful, but can take some getting used to.
 

  •  If you suffer from astigmatism, you may be able to have this fixed by a monofocal lens called a toric lens, which could improve your vision more than having a standard monofocal lens fitted.
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  •  If you still require glasses after you have had your surgery, you may find that you have better vision in low light than you would have had if you had chosen multifocal lenses, as multifocals can have an impact on your ability to cope with contrasts in low light.
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  •  If you take the option to improve your distance vision, you will still need to use glasses when reading. This also works in reverse – if you have chosen to improve your short sightedness, you may need to wear glasses for distance - for example when you are driving.
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  •  If you have astigmatism and choose to go for the standard monofocal lens, you could find that your vision is still blurred, and you may still suffer from short sightedness or long sightedness.

Your Lens Replacement Options

Once your cataract is removed, a new lens implant is inserted to replace it. Your lens implant choice will determine your vision after cataract surgery. There are many different types of intraocular lens implants (IOLs) to choose from. In addition, many people with clear lenses are opting for lens exchange to improve near and distance vision. Lens replacement is the most frequently performed surgery in the U.S. and one of the safest. You have three categories of lens implant to choose from.

Correcting Distance Vision with a Monofocal IOL
A monofocal IOL is designed to provide clear distance vision. This means, after cataract surgery, you will be able to see objects far away. However, you will need glasses for reading and any type of close detailed work. Monofocal IOLs have been the standard implant used for decades to help patients see after a cataract is removed. Millions of monofocal IOLs have been successfully implanted providing cataract patients with clear distance vision.

 

Correcting Distance Vision and Astigmatism with a Toric IOL


Astigmatism Management is a vital new area of cataract surgery. Astigmatism is a common condition where your eye is out-of-round, shaped more like a football than a basketball. Your vision is potentially affected by two types of astigmatism — corneal and lenticular — and we can correct both with new astigmatism management tools. Today’s cataract patient demands excellent vision after surgery, and wants their astigmatism and refractive error corrected at the same time. There are two ways we correct pre-existing astigmatism during cataract surgery. The most advanced method uses a new type of lens implant, called a Toric lens, which incorporates unique optics to compensate for specific deficiencies in your vision. Toric lenses greatly reduce the likelihood of needing a second procedure to correct residual astigmatism. For those patients who suffer from astigmatism so pronounced that they are outside the power range of the Toric lens, we recommend a combination treatment of lens replacement and relaxing incisions that delivers both improved vision and astigmatism correction. Once we fully understand your level of astigmatism, and desire for improved distance vision and/or near vision, we will recommend the appropriate lens implant option for you.

 

Correcting Distance and Near Vision with Multifocal or Accommodating IOLs


Previous lens replacement technologies provided only one focal point – distance – leaving people dependent upon reading glasses or bifocals after cataract surgery. Recent advances in accommodative and multifocal technology now make it possible for you to read the words on prescription bottles, magazines, newspapers and computer screens, without magnifying glasses or bifocals, while still clearly seeing objects at a distance. These lenses have the ability to consistently offer improved vision at all ranges — near through distance. With the introduction of three advanced technology lenses — ReSTOR, Crystalens and Tecnis – the vision we can help you maintain as you age is better than ever before in the history of ophthalmology.

 

 

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