REFRACTIVE
SURGERY:
A LOW-RISK ALTERNATIVE TO GLASSES
Abstract
The purpose of this research paper is to examine the viability of refractive surgery as an alternative to wearing glasses. The research for this paper included a recently published book, several Internet sources, as well as a personal interview conducted with an experienced LASIK surgeon to clarify the current procedures and the more common complications experienced by patients as a result of the surgery. The research indicates that, although a small percentage of patients experience minor complications, PRK and LASIK are safe, effective, and permanent cures for certain vision problems.
REFRACTIVE
SURGERY:
A LOW RISK ALTERNATIVE TO GLASSES
Background
Refractive surgery, changing the curvature of the cornea to correct impaired vision, was introduced in Canada in the early 1980s. At that time, radial keratotomy (RK) was the method used. RK used spoke-like incisions in the cornea to flatten it, which changed the way light was refracted (Armstrong 221). RK was painless and permanent with rapid results. However, RK had its limits and was most successful at treating those with very mild nearsightedness or to correct residual astigmatism.
Photorefractive keratectomy (PRK) was introduced in Canada in the late 1980s. Unlike RK, PRK did not involve manual incisions but rather a removal of the top surface of the cornea and a computer-assisted laser to resculpt the curvature of the eye. The results achieved with PRK were consistently predictable, safe, and permanent.
Following quickly on the heels of PRK
was laser in-situ keratomileusis, or LASIK.
LASIK differs from PRK in that a surgical instrument called a
microkeratome creates a flap on the cornea rather than complete removal. A laser beam then reshapes the cornea and the flap is
repositioned. After seven years
of clinical trials at a dozen U.S. medical centers, the U.S. Food and Drug
Administration approved LASIK for use in the United States in November 1998.
Since LASIK’s approval, RK and PRK are on the decline, while LASIK is
on the rise in total volume of procedures (Duffey).
Dr. Bob Woods, a six-year surgeon with the Lexington Eye Institute of Surrey, British Columbia, reports that more than 250,000 Canadians have had either PRK or LASIK refractive surgery and in the United States the numbers are growing at a rapid rate. In 1999, $2.1 billion was spent in the US alone for laser eye surgery. Advertisements on radio and television and in newspapers and magazines are touting the wonders of these procedures, but of course these advertisements lack a comparative examination of the strengths and weaknesses between and within each procedure.
The purpose of the following paper then is to
examine the two most commonly used procedures and their risks and
complications so that one might make an informed
decision about possibly going without glasses.
It begins with an explanation of the refractive errors of the eye, a
description of the surgical procedures, photorefractive keratectomy and laser
in-situ keratomileusis, and then describes the FDA approval process.
Next, the paper examines qualifications to be eligible for the surgical
procedure, followed by complications and risks involved.
Lastly, the paper draws a conclusion regarding the viability of
undergoing the procedure as an alternative to a lifetime of wearing glasses.
Understanding Refractive Errors
To see clearly, the cornea and the lens must bend, or refract, light rays so they focus on the retina, a layer of light-sensing cells that line the back of the eye. The retina converts the light rays into electrical impulses that are sent to the brain, where they are recognized as images. What is seen is a direct result of how focused the light is when it reaches the retina. If the light rays don’t focus on the retina, the image seen is blurry (Armstrong 47). This is refractive error. There are three basic types of refractive errors.
Myopia--Nearsightedness. In most cases of nearsightedness, the eyeball is longer
than normal, and light comes to a focus in front of the retina (Armstrong 51).
A nearsighted person has trouble seeing things that are far away but
can usually clearly see things that are close and can usually see well enough
to read or do other close work (Figure 1).
Hyperopia--Farsightedness.
In farsightedness, the eyeball is shorter than normal, and light
comes to a focus behind the retina (Armstrong 56).
A farsighted person can clearly see things that are far away but has
trouble seeing images that are close, reading, or doing other close work
(Figure 2).
Astigmatism.
In this eye problem, irregularities in the shape of the cornea project
light waves at two points inside the eye rather than one (Armstrong 57).
The result of these misdirected light rays is a distortion or blurring
of both distance and near vision (Figure 3).
Surgical Options
PRK or photorefractive keratectomy has been performed worldwide to
correct myopia, hyperopia and astigmatism.
PRK involves removing the epithelium, the surface layer of the cornea.
Then a computer-controlled excimer laser reshapes the cornea of the
affected eye (Figure 4).
Franette Armstrong, author of Beyond
Glasses! and a PRK patient herself in 1995, claims that the single most
important component of the PRK procedure is an accurate refractive exam.
The results of this exam, she reports, determine exactly how much
tissue will be removed from the cornea.
Because the composition of the epithelium is different from the cornea, it vaporizes at a different rate and must be removed separately before PRK begins. There are several methods of removing the epithelium, including manually scraping it off, using a rotating brush that scrubs the epithelium off, drops of alcohol to soften it so it can be removed with a swab, or the laser method, which Woods called the “no-touch technique” because a laser removes the epithelium in a 6-millimeter zone. Woods went on to say that while individual doctors believe that one method of epithelium removal produces faster healing or faster visual results, there doesn’t appear to be any long-term benefit to one method over the others. According to a study led by H. V. Gimbel of the Gimbel Eye Center, Calgary, Alberta, Canada, comparing the two methods, there wasn’t a statistical difference at six months between eyes treated with the manual and laser removal techniques (41).
Once the epithelium is removed, the laser is then used to reshape the cornea. There is no pain during this process--only an acrid smell similar to burning hair as the tissue from the cornea is vaporized. The total laser time is about 20 to 40 seconds for each eye. When the procedure is finished, a bandage contact lens is placed over the eye along with drops of chilled antibiotics to help prevent swelling (Armstrong 95).
Woods
reported that PRK does have its drawbacks.
Patients do experience discomfort for one to two days while the
epithelium regenerates and some patients may have unstable vision for a few
months. In his interview he reported that others might experience
varying degrees of corneal haze or cloudiness.
He reported that typically both eyes are not treated at the same time,
and patients must use eye drops for four months.
LASIK, or laser in situ keratomileusis, has been used for more than ten
years in Canada to treat myopia, hyperopia and astigmatism, and is nicknamed
“Flap ‘n Zap” (Woods). As
shown in Figure 5, in this procedure a hinged corneal flap composed of the
outermost 25 percent of the cornea’s thickness is produced with the aid of a
microkeratome, an instrument similar to a carpenter’s plane (Armstrong 178).
The microkeratome is used in conjunction with a suction ring, a
stainless steel ring placed over the eye and connected to a vacuum device by
tubing. The ring presses into the
eye, raising it up and flattening out the cornea.
This holds the eye still and allows the microkeratome blade to reach
and cut straight across the front of the cornea.
Once the flap is created, it’s folded to the
side and the underlying cornea is wiped dry in preparation for the laser, as
shown in Figure 6. From this point, the surgical procedure is the same as in PRK.
The computer-controlled excimer laser removes the tissue under the flap
and reshapes the cornea (Armstrong 179).
LASIK
resembles PRK in that both procedures use the excimer laser to change the
refractive error. However, Woods
noted that because the surgeon creates the flap, LASIK preserves the
epithelium and stroma, the outermost 20 to 25 percent of the thickness of the
cornea. As a result, the surfaces
of eyes treated with LASIK heal faster than those treated with PRK. Most patients achieve good vision the day following surgery.
Woods noted that patients experience less discomfort with LASIK than
with PRK. He went on to say that
LASIK requires more instrumentation than PRK, and additional surgical
precision is necessary to handle the microkeratome.
With that in mind, he suggested that those interested in LASIK should
take into consideration the number of actual procedures a surgeon has
performed before making a decision to have eye surgery.
FDA Approval
In October 1995, after ten years of development and six years of clinical trials, the Food and Drug Administration’s ophthalmic devices advisory panel approved Summit Technology’s excimer laser for use in PRK for the correction of nearsightedness. A second laser, developed by VISX, was given FDA approval in March 1996. In October 1999, the FDA gave both Summit and VISX lasers their approval for treating astigmatism and VISX has received additional approval for treating high myopia (FDA Talk Paper). In September 2000, the FDA approved the Summit Autonomous LADARVision for LASIK treatment of hyperopia, hyperopic astigmatism, and mixed astigmatism (FDA, CDRH).
The Medical Devices Act of 1976 required that all medical equipment sold in the U.S. be tested in clinical trials. Those already in existence, such as other lasers used for eye surgery, heart pacemakers, and kidney dialysis machines, were grandfathered into approval (Armstrong 279). The FDA does not become involved in surgical procedures unless they involve a new medical device, consequently other treatments for nearsightedness, such as LASIK, have never been FDA-approved. Armstrong further notes that the microkeratome used during LASIK is considered a cutting instrument; thus, new models go through only a brief review, not long clinical trials. By contrast, Armstrong notes that the original excimer laser for PRK had to prove itself to the FDA for safety, predictability, and effectiveness. In addition to the FDA, all lasers are regulated under the Radiation Control for Health and Safety Act, which governs the way lasers are manufactured and labeled and how defects are reported.
Once a device is approved, the FDA monitors manufacturing quality and responds to consumer complaints. The FDA has the power to enforce compliance and can halt production, prevent shipping, and fine companies. Armstrong warns, however, that the FDA does not go out to doctors’ offices to watch procedures and consequently individual doctors can do what they want with their lasers unless someone files a complaint.
Who Is a Candidate
In August 2000 the Federal Trade Commission issued a brochure entitled
Basik Lasik: Tips on Lasik Eye Surgery
that included the following guidelines
for prospective candidates to help determine their eligibility for LASIK:
Candidates
should be at least 18 years old since the vision of people younger than 18
usually continues to change.
Candidates
should not be pregnant or nursing as these conditions might change the
measured refraction of the eye.
Candidates
should not be taking certain prescription drugs, such as Accutane or oral
prednisone.
The eyes must
be healthy and the prescription stable.
Candidates should be in good general health. LASIK may not be recommended for patients with diabetes, rheumatoid arthritis, lupus, glaucoma, herpes infections of the eye, or cataracts.
The Canadian Ophthalmological Society has similar guidelines, but notes that suitable candidates for the surgery must have a reasonable expectation of success. Woods reported that presbyopic patients, a normal aging condition of those over 40 years of age whose eyes have lost their ability to focus on near objects, must be made aware that they will require reading glasses unless they elect to undergo surgical procedures to reverse presbyopia.
Complications and Risks
Haze is part of the healing process after surgery and results from the superficial cornea’s healing reaction. It causes temporary optical side effects and is rarely a long-term visual problem. Haze is significantly lower with LASIK than with PRK and less of an inflammatory response, but a longer period of sensory corneal denervation. In a study done by Jorge L. Alio, he reported that the keratome wound at the flap margin healed at a different rate than that of the intrastromal wound under the flap, accounting for the subsequent development of postoperative haze (524).
Decreased night or low-light vision is characterized by symptoms such
as glare, halos, and starbursts that are seen around objects at night or in
dim-light conditions. Although
these symptoms don’t necessarily interfere with visual acuity as it is
measured by an eye chart, for some patients the experience can interfere with
daily activities and driving at night. Those
patients who experience persistent glare, halos, or starbursts do have several
treatment options, including prescription eye drops to help constrict the
pupil at night to reduce the symptoms of decreased night vision. However, this approach is not successful for all people, and
it also can represent a significant expense over time. Similarly, enhancement procedures may be an option, but not
everyone is eligible for an additional procedure. Eligibility for enhancements depends on a number of factors
that a physician must evaluate (Woods).
The depth
and size of the ablation can result in complications related to decreased
night vision. A study of 120 eyes
of 60 myopic patients conducted by M.A. El Danasoury evaluated glare using two
different ablation zone diameters on each patient.
One eye of each patient had a single ablation zone and the other eye
had the same size removal zone but with a transition zone of 1.0 mm diameter
larger. At six months a spot
light test showed that 74.1 percent of patients perceived more glare in the
eye without the transition zone. Participants
were also administered a subjective questionnaire and 40.7 percent indicated
that they perceived more glare in the eye without the transition zone.
Similarly, the Comprehensive Refractive Surgery Study on LASIK lead
by Charles Casebeer, M.D. has suggested that controlling the ablation depth
can prevent such complications that can contribute to night vision
difficulties. This study noted
significant glare in only 0.2 percent of the study population.
No study was found showing a correlation between developing dry-eye
syndrome and PRK or LASIK. However,
an article in Ocular Surgery News discussed the attention
ophthalmologists are paying to the possible connection between LASIK and
dry-eye. According to the
December 1999 article entitled LASIK-Dry Eye Connection Gets Attention at
AAO-PAAO, a good deal of attention was paid to dry-eye at the 1999 joint
meeting of the American Academy of Ophthalmology and the Pan-American
Association of Ophthalmology. In
the article, Dr. Robert Maloney reported the results of a survey of 550
patients after LASIK. Forty to fifty percent experienced dry eyes three months
post-operatively. Dr. Richard Lin
noted that while the overall frequency of complications after LASIK is
decreasing, the incidence of dry-eye after LASIK is increasing.
Ophthalmic literature breaks complications into two categories: intra-operative, surgical complications that occur during the procedure itself, and post-operative, healing complications that arise after the procedure has been completed. Table 1 below summarizes the intra-operative complication rate in two studies on LASIK.
Table 1
Intra-Operative Complication Rate
Study |
Complication Rate |
|
CRS-USA
LASIK Study (n=1,800) |
1.2% |
|
Lin
& Maloney (n=1,019) |
2.2% |
Source: “Risk & Complications.” LASIK Institute. 1999: 42 pars. Online. Available: http://www.lasikinstitute.org/risk.html. 2 Nov. 2000.
The 1998 CRS-USA LASIK Study of 1,800 eyes noted two intra-operative complications that arose resulting from the microkeratome--irregular cuts that damaged the stromal bed (0.03%) or damage to the epithelium (0.47%). This noted 1.2 percent complication rate produced temporary effects and after three months the visual results of the group experiencing intra-operative complications were no different from the group who experienced no such complications. In 1999 Lin and Maloney studied 1,019 eyes for which the flap was created by a microkeratome and noted a 2.2 percent intra-operative complication rate. Lin and Maloney reported that flap complications after refractive surgery are relatively common but rarely lead to a permanent decrease in visual acuity. Physician experience with the microkeratome and with the handling of the corneal flap decreased the incidence of flap complications.
The CRS-USA LASIK Study noted that overall, 5.8 percent of LASIK patients experienced post-operative complications at the three-month follow up examination that did not result from complications during the procedure itself. These complications included corneal edema (0.6%), corneal scarring (0.1%), persistent epithelial defect (0.5%), significant glare (0.2%), persistent discomfort or pain (0.5%), interface epithelium (0.6%), cap thinning (0.1%), and interface debris (3.2%).
In 1998 J.S. Vidaurri-Leal published a study, Complications in 5000
LASIK Procedures, that supports the existence of a learning curve
with LASIK. His data was broken
into two categories: his first 200 cases performed in 1995 and his 4,800
following cases. In Vidaurri-Leal’s
later 4,800 cases, less than 1 percent experienced intra-operative
complications. Post-operatively,
7.98 percent of these cases experienced complications, with a loss of
best-corrected visual acuity in 0.81 percent.
This compares with complications 4.5 percent intra-operatively, 38.8
percent post-operatively, and a loss of best corrected visual acuity in 3
percent of his first 200 cases (see Table 2, below).
Table
2
Risks More Prevalent in
Vidaurri-Leal’s First Cases
|
|
First
Cases (n=200) |
Following
Cases (n=4,800) |
|
Intra-operative
complications |
4.5% |
0.87% |
|
Post-operative
complications |
38.8% |
7.98% |
|
Loss of
BCVA |
3.0% |
0.81% |
Source: “Risk & Complications.” LASIK Institute. 1999: 42 pars. Online. Available: http://www.lasikinstitute.org/risk.html. 2 Nov. 2000.
Conclusion
Refractive surgery is a low-risk alternative to wearing glasses for those with myopia, hyperopia, and astigmatism. Research indicates there are two methods currently in use for this surgical vision correction. In the photorefractive keratectomy method, the epithelium of the cornea is removed, in contrast to laser in situ keratomileusis where the epithelium is cut as a hinged flap that remains attached to the cornea. Once the epithelium is removed, both methods then use the excimer laser to reshape the cornea. While the U.S. Food and Drug Administration has approved specific lasers for PRK and LASIK, it should be noted that no follow up is conducted with individual surgeons in their use of the equipment. Candidacy for either procedure requires good health and stability of vision. Numerous studies indicate that a very small percentage of patients experience temporary haze, glare, halos, or starbursts as complications and these effects rarely remain a long-term visual problem.
Due to the additional instrumentation required for the epithelial-hinged flap
in the LASIK method of surgery, those contemplating PRK or LASIK refractive
surgery should conduct additional research into a surgeon’s actual
experience before making their decision.
REFRACTIVE SURGERY:
A LOW RISK ALTERNATIVE TO GLASSES
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