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Vision Correction Through Surgery



Vision Correction Through Surgery

Over the past twenty five years, more than a million Americans have turned to eye surgery to correct their vision. If your glasses or contact lenses give you good vision and you are happy with the correction, you should not consider surgery. But, if you can't wear contacts and don't want to wear glasses as much - or if your job demands good vision without glasses - surgery is something you should consider.

Correcting one's vision through surgery is a subject that has received much attention in the media in recent years. The technology is changing rapidly and the options for patients considering vision correction continue to increase. This discussion will describe the nature of vision correction and present the current options available to patients.

Normal Vision

Normal Eye
Normal Eye

As with most organs, we don't really appreciate them until something goes wrong. Our eyes are no different. The human eye is the organ which gives us the sense of sight, allowing us to learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, playing sports, watching television, writing a letter, driving a car, and in countless other ways. Probably most people would agree that sight is the most precious of the five senses, and many people fear blindness more than any other disability. The eyeball, which measures approximately one inch in diameter, is set in a protective cone-shaped cavity in the skull called the "orbit" or "socket." The orbit is surrounded by layers of soft, fatty tissue which protect the eye and enable it to turn easily. Six muscles regulate the motion of each eye. The eye's job is to change visible light rays into electrical signals which are sent to the brain over the optic nerve. In the brain, we interpret these electrical signals as visual images made up of colors and shapes.

The front of the eyeball bulges forward as the cornea ,the transparent dome which serves as the window of the eye. The transparency of the cornea is due to the fact that it contains hardly any cells and no blood vessels. The cornea is the primary element the focuses light waves onto the back of the eyeball. Beneath the cornea is the lens which also helps focus light on to the back of the eyeball, the retina. The iris is The colored part of the eye; regulates the amount of light entering the eye. The pupil is the opening at the center of the iris. The iris adjusts the size of the pupil and controls the amount of light that can enter the eye. With this system, our eyes can adjust for varying amounts of light and focus from a few inches to a few miles away. The center of the eye is filled with a clear vitreous fluid and the entire organ is encased in a tough fibrous shell called the sclera.

Much like a camera, the eye must adjust its shutter and lens to focus light on its "film" - in this case the retina. With normal vision, light rays enter the eye and focus precisely on the inner most eyeball layer, the retina. The retina contains nerve endings, which convert optical images into nerve impulses. The curved surface of the eye, its cornea, bends the light rays precisely onto the retina. We call this bending, refraction.

Myopia (nearsighted)

More than seventy million Americans are nearsighted. This condition occurs when an eye is too long for the cornea's curvature.

Myopia (nearsighted)
Myopia (nearsighted)
Light rays entering the eye can't come into sharp focus on the retina at the back of the eye. Instead, they focus forward producing a blurred image. Nearsighted people can see "near" objects clearly without glasses or contacts but objects farther in the distance are blurry.

Hyperopia (farsighted)

With farsightedness, or hyperopia, light entering the eye is focused at a point behind the retina. Farsightedness can be caused by an excessively flatcornea or an eye, which is abnormally short.

Hyperopia (farsighted)
Hyperopia (farsighted)
The result is that objects close to the viewer are very blurred while objects in the distance may be seen in sharp focus.

Astigmatism

Both nearsighted and farsighted people may have some degree of astigmatism, or ovalness to their corneas. Astigmatism is the most common eye condition and occurs to some extent in most eyes.

Astigmatism
Astigmatism
Astigmatism occurs when the cornea is shaped more like an over inflated football than a basketball. As a result, people with astigmatism experience distorted or tilting of images. This happens because the light rays bend un-equally as they enter the eye. People with high degrees of astigmatism have blurred vision, not only for distance objects, but for near objects as well.


Presbyopia

Presbyopia is the process by which people who normally see well at a distance begin to have difficulty focusing on objects at near. They develop "short arms" and may require glasses to improve near vision or bifocals added to their present glasses. Presbyopia usually occurs to patients who are in their late thirties to mid forties. Presently there is no surgical vision correction for presbyopia. The time honored treat-ment is the wearing of bifocals or reading glasses. Some people wearing contact lenses select mono vision, where one eye is focused for distance and the other is focused for near. Not all patients can accept this image disparity.


SURGICAL OPTIONS

What are the surgical options for vision correction? The options are continually increasing. They include Radial Keratotomy (RK), Astigmatic Keratotomy (AK), Photo Refractive Keratectomy (PRK), Laser In Situ Keratomileusis (LASIK), Laser Thermo Keratoplasty (LTK), and the corneal ring. All of the above treatments use some type of laser for correction, except for RK, AK, and the surgically implanted corneal ring.

RK

RK corrects nearsightedness by altering the shape of the cornea. The surgeon does this by placing very fine cuts along the outer portion of the cornea. This surgery is performed with a hand held, diamond tipped blade that fashions the incision with the aid of an operating microscope. The surgery flattens the curvature of the cornea allowing light rays to enter the eye and focus properly on the retina. The cuts are usually placed in a radial fashion, hence the name radial keratotomy.

AK

AK, a variation of RK, corrects astigmatism by placing incisions in a circumferential pattern. Most people experience little or no discomfort with AK or RK surgery. They are conscious, but often sedated and the surgeon uses anesthetic eye drops to numb the eye. The surgeon works on only one eye at a time. The procedure typically takes twenty to thirty minutes. Over a million people world wide have reduced their dependency on glasses with RK surgery, however, the availability of lasers has largely replaced RK surgery with one of the laser procedures.

PRK

Photo Refractive Keratectomy (PRK) was the first popular procedure that incorporated the use of the Excimer Laser. Excimer Lasers were initially invented to etch micro chips more than two decades ago. It was then discovered that the lasers can be used to precisely resculpt human tissue, particularly the corneal surface, with high precision. Excimer Lasers use an Argon/Fluoride gas that can remove 39 millionths of an inch of tissue in as little as 12 billionths of a second. The Excimer works by breaking molecular bonds and can remove single cells without damaging the adjacent cells.

PRK is a painless, outpatient procedure that usually takes about twenty minutes to perform. Your corneas new curvature is shaped to duplicate the power of your contact lens or glasses prescription. This allows patients to reduce or eliminate the dependency on glasses or contacts. The laser does its work in less than 60 seconds. At the completion of the procedure a bandage contact lens is worn for three to five days. During this time patients use antibiotic and anti inflammatory eye drops with numbing drops to improve comfort.

LASIK

LASIK (Laser Assisted in-Situ Keratomileusis) is a painless outpatient procedure, much like PRK.LASIK was first performed in 1989 by an ophthalmologist in Greece and was introduced to American surgeons in 1990. The same Excimer Laser is used for both LASIK and PRK. With LASIK, however, the surgeon first creates a protective corneal flap exposing the inner corneal tissue. The flap is temporarily folded out of the way and the Excimer Laser is applied to the inner layer of the cornea, the flap is then re-positioned. No protective contact lens is needed after the procedure as the corneal surface is largely unaffected. There is slightly greater risk to the procedure, as complications can be associated with fashioning the corneal flap. Benefits include less pain, clearer vision faster after surgery and fewer infections.

Both LASIK and PRK are both effective laser procedures utilizing the Excimer Laser. Originally this treatment was available only for patients with nearsightedness and astigmatism. Recently the FDA has approved the procedure for treatment of farsightedness, with or without astigmatism. In the long run, both LASIK and PRK are probably equally effective. Some patients and doctors prefer LASIK feeling that it results in slightly faster visual recovery, less risk of discomfort after surgery, and less risk of associated corneal haze and scarring. These advantages need to be weighed against the increased risk of creating a corneal flap.

Laser Thermo Keratoplasty

LTK involves the use of a laser to apply discrete burns to the corneal surface that will correct low to moderate degrees of hyperopia (farsightedness). This procedure has not yet received FDA approval and is not widely available. With FDA approval, LTK will offer an alternative to patients with hyperopia, however, presently these patients only have the option of hyperopic PRK.

The Corneal Ring

Surgical implantation of a corneal ring can alter the shape of the cornea and correct certain degrees of nearsightedness. This procedure has appeal to some individuals as it is potentially reversible (the ring can simply be removed) and it does not involve surgery of the central cornea or visual axis. This eliminates the risk of developing corneal haze and related symptoms. Corneal ring implantation has not yet achieved wide acceptance and does not have the general appeal to the public as procedures that involve the use of a laser.


SURGICAL CANDIDACY

While more than 200,000 people in the USA have had laser eye surgery, millions more could benefit. More than 63 million people in the USA are nearsighted, the condition laser surgery helps the most. The technique has also been used to help those with other vision problems, including astigmatism, distortion from a misshapen eye, and farsightedness.

So, who is a candidate for surgery? Patients should be at least 21 years of age before considering refractive surgery. Furthermore, the glasses prescription should be stable, having demonstrated no change for at least one year prior to the surgery. Patients cannot have a history of connective tissue disease (such as lupus). There must be no history of past corneal disease (such as herpes keratitis) or other inflammations of the cornea.

Why are expectations important? Without realistic expectations going in, the chances are greater for patient dissatisfaction. If patients expect their uncorrected vision to be virtually equal to their best corrected preoperative vision - and nothing less will be acceptable - surgery should not be considered. Uncorrected acuity of 20/20 vision is not obtained in all cases. A high percentage of patients (at least 85%) are likely to see 20/40 or better without correction post-operatively with just about all of the procedures described here. Patients who have high degrees of nearsightedness or farsightedness preoperatively, may require more than one laser treatment to achieve the full effect. Repeat treatment, sometimes called enhancements, are usually not done for at least six months following the original surgery.


SURGICAL RISKS

Under correction and over correction

The more severe your initial prescription, the more treatment your eye will require, the more healing will be required, and the greater the likelihood that your eye may not be fully corrected with just one procedure. It is estimated that roughly 10% of patients will require a second procedure or enhancement. These operations are done one to four months after LASIK procedures and a minimum of four to six months after PRK. In FDA trials, less than l% of PRK patients experienced significant over correction or under correction.

Infection

Infection rarely occurs. Using the proper postoperative drops reduces the likelihood of this to less than 1% of patients.

Corneal haze and glare

Almost everyone experiences a mild degree of corneal haze and subsequent glare, however, this usually resolves over the first several months after surgery and is rarely disabling. Less than 1% of PRK patients experiences haze in the long run.

Loss of best corrected vision

A small number of patients will experience a slight loss of visual acuity following laser correction. You may not be able to read the very bottom lines of the eye chart, either with or without glasses, when you were able to read these lines prior to surgery. Loss of best corrected acuity can improve for at least 6-12 months after surgery. Fewer than 1% of patients experience a permanent loss of best corrected vision.

Corneal flap risks

While LASIK offers a faster recovery, there is increased risk due to the presence of a corneal flap. Irregularities in the flap can result in a loss of best corrected vision. Rarely, corneal epithelial cells can grow beneath the corneal flap requiring a procedure to remove the ingrowing cells.


CONSIDERING SURGERY

Patients who meet the visual and medical criteria, and are eligible for surgery, must undergo a careful preoperative examination by their eye doctor. Both soft and hard contact lenses must be removed for a period of time prior to this examination. Typically, soft lenses must be removed one week before the exam and hard lenses a minimum of three weeks prior to the examination. This is never convenient but is truly necessary for a good surgical outcome. During the preoperative examination your eye doctor can help you decide which is the best procedure for you, in what order, and at what interval the two eyes should receive surgery, and should mono vision be considered (for presbyopia). Your doctor will answer questions regarding any restrictions that may be imposed on your activity post-operatively. You can also find out what your postoperative care schedule will entail.

Copyright:

Daniel J. Nadler, M.D.

Daniel J. Nadler & Associates
Eye Physicians and Surgeons

Sewickley Office
409 Broad Street - Suite 270
Sewickley, PA 15143
Phone 412 741-5577
Beaver Office
1200 Sharon Road - Suite 202
Beaver, PA 15009
Phone 724 774-5920


Text & Images Courtesy of Three Rivers Endoscopy Center
© Dr. Robert Fusco, Three Rivers Endoscopy Center, All Rights Reserved





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