Patient Education / Refractive Surgery

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Refractive Errors

Refractive errors occur when light does not focus properly on the retina because of the shape of the eye. The resulting image is blurred. Common refractive errors are myopia (nearsightedness), hyperopia (farsightedness), astigmatism (distorted vision), and presbyopia (aging eyes).


A myopic eye is longer than a normal eye or has a cornea that is too steep, causing light rays to focus in front of the retina instead of on it. With myopia, close objects appear clear, but distant ones appear blurred.


A hyperopic eye is shorter than normal or has a cornea that is too flat. The light rays focus beyond the retina instead of on it. Distant objects appear clear, but close ones appear blurred.


The cornea of an astigmatic eye is curved unevenly. Images focus in front of and beyond the retina, causing both close and distant objects to appear blurry.


Presbyopia refers to the hardening of the lens that occurs with age. After the age of 40, the lens becomes more rigid and cannot change shape as easily to accommodate near objects. This makes reading and other tasks performed at close range difficult. Presbyopia can occur in combination with any of the other three refractive errors.

Refractive errors are usually corrected with eyeglasses or contact lenses. Sometimes surgery is needed or desirable. Some common surgical procedures include the following:


This popular procedure uses an instrument called a microkeratome to create a flap in the cornea so that the underlying corneal tissue can be reshaped with a laser.


This procedure is similar to LASIK in that it also uses a laser to reshape the cornea, but it uses a different device to create the corneal flap.

Photorefractive Keratectomy

Photorefractive keratectomy (PRK) sculpts the surface of the cornea using a laser. A “bandage” contact lens is then applied for about three days to allow it to heal.

Intrastromal Corneal Rings

Intrastromal corneal rings are crescent-shaped plastic segments implanted in the cornea to flatten the cornea and correct mild nearsightedness.

If you are considering any of these surgical procedures, it is important to discuss them with your ophthalmologist (Eye M.D.) so as to make an informed decision about whether refractive surgery is right for you. Sometimes the best option is to choose eyeglasses or contact lenses instead of surgery to correct a refractive error.

Side effects of any of these refractive surgery techniques include blurring, glare, poor night vision, corneal scarring, or permanent vision loss. No one method is known to be better than another. The most appropriate method depends on the specific condition and lifestyle of the patient.

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Refractive Lens Exchange

Today, many people choose to correct their refractive errors with techniques other than wearing eyeglasses or contact lenses. Surgeries like laser-assisted in situ keratomileusis, or LASIK, improve vision by permanently changing the shape of the cornea to redirect how light is focused on the retina. However, in certain cases, LASIK or other refractive surgeries to reshape the cornea may not be a patient’s best option. In these cases, instead of reshaping the cornea, the eye’s natural lens can be removed and replaced with an intraocular lens (IOL) with a procedure called refractive lens exchange (RLE).

IOLs are artificial lenses surgically implanted in the eye. These lenses help your eye regain its focusing and refractive ability. RLE can be used to correct moderate to high degrees of myopia (nearsightedness) and hyperopia (farsightedness). In many cases, it is especially useful in treating presbyopia, the inability to focus at near distances with age.

The most common type of implantable lens is the monofocal or fixed-focus lens. It helps you attain clearer vision at one distance. Note that eyeglasses or contact lenses are still required to see clearly at all ranges of distance.

Another type of IOL is the multifocal IOL. The multifocal IOL has several rings of different powers built into the lens. The part of the ring you look through will determine if you can see clearly at far, near, or intermediate distances.

A third type of IOL is the accommodative IOL. This IOL has a hinge designed to work with your eye muscles, allowing the lens to move forward as the eye focuses on near objects and backward as the eye focuses on distant objects. Other styles of accommodative IOLs are currently being developed.

Implanting an IOL takes about 20 minutes in an outpatient procedure much like cataract surgery. In addition to a preoperative eye exam, the eye surgeon takes certain measurements of the eye. Your eyes are then numbed with topical or local anesthesia. A few small incisions are made at the edge of the cornea. Then a small ultrasound instrument is inserted into the eye to break up the center of the eye’s natural lens. The lens is vacuumed out through one of the incisions. The IOL is usually folded and then inserted through the same incision. These incisions are usually self-sealing, requiring no stitches.

Once implanted, multifocal and accommodative IOLs allow you to focus on near or distant objects. You will probably have to take an antibiotic and steroid eyedrop for several days after the procedure, and you will need to wear an eye shield at night for one week to protect the eye.

Some advantages of refractive lens exchange are that unlike other forms of refractive surgery, RLE can be used to treat people with dry eye, thin corneas, or high refractive error. In addition, if you have RLE, you will never develop cataracts, as the natural lens is removed.

Risks associated with implanting IOLs include overcorrection or undercorrection, infection, increased “floaters” or retinal detachment, dislocation of the implant, halos and glare, dry eye, decreased contrast sensitivity, clouding of a membrane behind the IOL (this requires a quick laser procedure to remove it), and loss of vision.

You should consult with your ophthalmologist to determine if refractive lens exchange is the best treatment for your specific condition and vision needs. If you are considering RLE, you should discuss which IOL might be best suited for you.

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Wavefront-Guided Laser Surgery

Laser-assisted in situ keratomileusis,or LASIK, is an outpatient surgical procedure that uses an excimer laser to reshape the eye’s cornea (the clear window in the front of the eye) to correct refractive errors. Refractive errors are problems with the way the eye focuses light, which cause nearsightedness (myopia), farsightedness (hyperopia), or astigmatism. LASIK is used to surgically correct refractive errors, rather than using eyeglasses or contact lenses.

Wavefront-guided LASIK is an enhanced version of LASIK. It uses a special device to precisely measure the eye’s unique irregularities and variations as well as your need for corrective lenses. This procedure has been compared to taking a fingerprint of the eye. You may benefit from this customized approach.

Wavefront measuring devices, called “analyzers” or “aberrometers,” create a precise map of the eye. It is very detailed and records subtle distortions in your eye’s visual system. Using this map, the excimer laser can be programmed to correct for these measured distortions, giving you clearer vision than was possible before with conventional treatments.

With your chin resting on the aberrometer, you will be asked to stare past what is called a target light. A targeted beam of light will be sent through your eyes and will focus on the retina. A sensor will measure the irregularities in the wavefront pattern of the light as it emerges from your eye. Using wavefront technology before performing LASIK can help your ophthalmologist (Eye M.D.) enhance the outcome of your surgery by correcting the unique visual distortions present in your eye.