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How the eye works

• Light rays enter the eye through the clear cornea, pupil and lens.

• These light rays are focused directly onto the retina, the light-sensitive tissue lining the back of the eye.

• The retina converts light rays into impulses, sent through the optic nerve to your brain, where they are recognized as images.

• 70% of the eye's focusing power comes from the cornea and 30% from the lens.

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Refractive errors

• Inability to see clearly is often caused by refractive error.

• Four types of refractive error: Myopia (nearsightedness) Hyperopia (farsightedness) Astigmatism Presbyopia

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Refractive errors: myopia

• In myopia (nearsightedness), there is too much optical power in the eye The distance between the

cornea and the retina may be too long or the power of the cornea and the lens may be too strong.

• Light rays focus in front of the retina instead of on it.

• Close objects will look clear, but distant objects will appear blurred.

Myopia, or nearsightedness

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Refractive errors: hyperopia

• In hyperopia (farsightedness), there is too little optical power.

• The distance between the cornea and the retina may be too short.

• Light rays are focused behind the retina instead of on it.

• In adults (but not children), distant objects will look clear, but close objects will appear blurred.

Hyperopia, or farsightedness

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Refractive errors: astigmatism

• In astigmatism, the cornea is curved unevenly—shaped more like a football than a basketball.

• Light passing through the uneven cornea is focused in two or more locations.

• Distant and close objects may appear blurry.

Astigmatism occurs when light passes through football-shaped cornea and/or lens

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Refractive errors: presbyopia

• Presbyopia is an age-related condition in which your eyes gradually lose the ability to see things up close, because the lens of the aging eye can no longer change shape.

• When we are young, the lens in our eyes is flexible and is able to change focus easily between near and far objects, like an autofocus on a camera.

• At around age 40, this flexibility begins to gradually decrease, making it more difficult to see objects up close, unless the eye has nearsightedness.

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What is refractive surgery?

• A group of outpatient surgical procedures used to alter how your eye focuses light rays on the retina, thereby improving vision and reducing dependence on glasses and contact lenses.

• In most cases, refractive surgery affects the shape of your cornea to redirect how light is focused onto the retina. Popular procedures include LASIK, LASEK, PRK and CK.

Refractive surgery procedure on the cornea

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What is refractive surgery?

• Most refractive surgery is performed on the cornea and affects only the front of your eye, while the rest of your eye will change naturally as you age.

• In some cases, refractive surgery procedures don’t reshape the cornea; instead, the eye’s natural lens is either replaced or enhanced by an implantable lens that helps correct vision.

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What is Astigmatic Keratotomy (AK)?

• A refractive surgery procedure used to treat astigmatism.

In a normal eye, the cornea is shaped like a basketball

The astigmatic cornea is shaped like a football

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How is AK performed?

• A pre-operative eye exam includes measurements to give the surgeon the necessary information to perform the procedure: Refractive error measurement. Tonometry: measurement of your

eye’s intraocular pressure (fluid pressure inside your eye).

Corneal topography: mapping the surface details of the cornea.

Keratometry: measurement of the form and curvature of the cornea.

Pachymetry: measurement of corneal thickness.

A phoropter is used to measure refractive errors

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How is AK performed?

• The AK procedure flattens the steep parts of your cornea that are causing astigmatism.

• Your ophthalmologist (Eye M.D.) makes a series of microscopic incisions along the steeper part of the cornea.

• This causes the steeper sides to relax so that the cornea becomes more round.

With AK, your ophthalmologist makes microscopic incisions along

the steeper part of the cornea

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How is AK performed?

• After the procedure, the reshaped cornea focuses light more accurately on the retina, improving vision.

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Considerations for AK surgery

• Low to moderate degree of astigmatism.

• Effect of surgery is age-dependent.

• Less invasive procedure than intraocular surgery, thus reducing quality-of-vision complaints.

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Considerations against AK surgery

• High degrees of astigmatism that are beyond the scope of the procedure.

• Eye disease that would contraindicate the procedure.

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Risks and possible side effects of AK surgery

• Over-correction or under-correction (with a possible need for a re-treatment).

• Vision fluctuation.

• Discomfort after surgery.

• Corneal infection.

• Perforation.

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To be a candidate for AK, you should…

• Be free from eye disease.

• Have a stable eyeglass prescription for at least a year within a correctable range.

• Understand and accept risks, limitations and side effects of the procedure as explained by your ophthalmologist.

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What is Radial Keratotomy (RK)?

• Outpatient refractive surgery used to treat low degrees of nearsightedness (myopia).

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How is RK performed?

• As with other procedures, pre-operative measurements are taken of your eye.

• Radial incisions are made in the cornea of the eye with a highly precise diamond blade, set to a particular depth. The number, length and location of the

incisions are determined by the degree of nearsightedness.

• Due to pressure inside the eye, these incisions allow the sides of the cornea to bulge outward, thereby flattening the central portion of the cornea.

With RK, radial incisions are made in the cornea of

the eye

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How is RK performed?

• Once the cornea begins to flatten, the focal point of the eye moves closer to the retina and improves one's distance vision.

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Considerations for RK surgery

• May be recommended for patients with low degrees of myopia.

• Effect of surgery is age-dependent.

• Less invasive procedure than intraocular surgery, thus reducing quality-of-vision complaints.

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Considerations against RK surgery

• May not be recommended for patients with high degrees of myopia, hyperopia or astigmatism.

• More invasive technique.

• Effect may regress.

• In some patients there is a progression to hyperopia which may limit both distance and near vision.

• Fluctuating vision.

• RK is infrequently used, as it has been replaced by other, newer refractive procedures.

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Risks and possible side effects of RK surgery

• Glare.

• Starburst patterns around lights at night.

• Potential for healing to take a long time, up to a few weeks.

• Weakened cornea.

• Perforation.

• Infection.

• Fluctuating vision during first few months.

• Over-correction or under-correction (with a possible need for a re-treatment).

• Late (years) regression.

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To be a candidate for RK, you should…

• Be free from eye disease.

• Have a stable eyeglass or contact lens prescription within a correctable range.

• Understand and accept risks, limitations and side effects of the procedure as explained by your ophthalmologist.

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Is refractive surgery right for you?

• Advanced surgical procedures, including incisional procedures, are creating more opportunities for people who want to be less dependent on glasses or contacts.

• Surgery may not entirely eliminate your need for corrective lenses. Glasses/contacts may still be needed for activities such as fine or detailed work, reading and perhaps night driving.

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Is refractive surgery right for you?

• A large part of the success of any refractive surgery depends on your understanding of the procedure and your expectations.

• Since refractive surgery is an elective procedure, you have the opportunity and responsibility to become fully informed about its risks and benefits.

• Your ophthalmologist will explain the specific technique, its benefits, as well as possible risks and side effects associated with your case.

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Discuss options and questions with your ophthalmologist

• With the help of your ophthalmologist, it’s ultimately your responsibility to weigh the risks and side effects of a procedure with the benefits it has to offer.

• If you decide refractive surgery is right for you, you may join millions of people who have reduced their dependence on glasses or contacts.