Potential Side Effects

8/12/2019 Potential Side Effects

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Potential Side Effects

More Common

Delayed epithelial healingis more typical of flapless procedures, such as PRK, LASEK and

Epi-LASIK because they disturb a large area of epithelium, as opposed to flap procedures,

which leave the epithelium intact.

Normally, the epithelium heals 3 to 5 days after a flapless procedure. During healing, the eyes

are often scratchy and uncomfortable. A delay means that the discomfort lasts longer, and it

also leads to an increased chance of haze.

Delayed epithelial healing can occur during a flap procedure if the epithelium is inadvertently

disturbed during surgery.

Diffuse Lamellar Keratitis (DLK)refers to inflammation beneath a flap, so it is unique to

LASIK and IntraLASIK and impossible with flapless procedures, such as PRK, LASEK and

Epi-LASIK. Microscopically, DLK has a fine, white, sand-like appearance underneath the

flap.

DLK almost always presents on the first postoperative day. Mild cases are treated with anti-

inflammatory eye drops and daily follow-up until the inflammation begins to fade. With

treatment, DLK usually peaks around day 3 to 6, gradually fades over the next few days and

doesn't come back. For rare cases that don't respond adequately to drops, a return trip to the

operating room to lift the flap and rinse away the inflammatory cells is the treatment of

choice.

Dry eyes:Virtually all laser vision correction patients experience dry eyes. For most, the

dryness is moderate for the first month, mild for the next few months and minimal after the

third or fourth month. However, dryness varies widely and ranges from a dry sensation to

filmy, fluctuating vision to continuously blurry vision and in rare instances on to painful,

blurry vision.

The preoperative dryness level is the key predictor of postoperative dryness problems. A

number of tests, such as the tear break-up time, fluorescein, lissamine green or rose bengal

staining, Schirmer's test and biochemical tear analysis are used to quantify preoperative

dryness. When preoperative dryness is severe, surgery is inadvisable.

The choice between a flap procedure such as LASIK or IntraLASIK and a flapless procedure,

such as PRK, LASEK or Epi-LASIK, also affects postoperative dryness. In general, flap

procedures lead to greater dryness, because formation of the flap interrupts more of the

corneal nerves that are responsible for signaling the body to produce tears. These nerves

eventually grow back, but the process takes anywhere from 6 months to 2 years. Flapless

procedures still cause some dryness, because the laser treatment itself interrupts some of the

corneal nerve fibers.

A number of treatments are available for dryness. The first line is artificial tear

supplementation with products such as Systane, Refresh, GenTeal, Soothe, Thera-tears, Tears


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Naturale and others. If necessary, an ointment such as Refresh-PM, Akwa-tears or Lacrilube

can be added at night.

When dryness remains a problem, the next step is often insertion of punctal plugs. These tiny

plastic devices block the outflow of tears by plugging the tear drain in the corner of the eyelid

near the nose. Though punctal plugs sound intimidating, they are easily and painlessly placedin a matter of seconds and work quite well for most patients.

As an alternative to plugs, some surgeons prefer Restasis, a prescription eye drop that

increases natural tearing. Restasis doesn't help everyone, and it can take up to 6 months to

work, but because it is the only available treatment that addresses the underlying problem

behind the dryness, Restasis remains a popular choice.

Epithelial ingrowthis only a concern of the flap procedures, LASIK and IntraLASIK, and

cannot occur with flapless surgery. For a flap to heal, the surface epithelium must seal along

the margin where the flap was lifted. Occasionally, instead of just sealing, the epithelium

migrates underneath the flap. Small amounts of ingrowth usually fade away with time, butlarge amounts necessitate lifting the flap and manually removing the excess epithelium.

Epithelial ingrowth almost never occurs with a first-time treatment, but it is a greater

possibility when an existing flap is lifted for a retreatment. As more time passes between the

initial treatment and the retreatment, epithelial ingrowth becomes more likely.

Although epithelial ingrowth is treatable, it can be frustrating because it occasionally recurs

and necessitates another flap lift. For this reason, there is a slight trend toward retreating

patients who are many years out from LASIK or IntraLASIK directly on the surface of the

flap, as in PRK, rather than lifting the flap.

Flap striaeare wrinkles in the flap, so they are unique to LASIK and IntraLASIK and cannot

occur with flapless surgery. Microstriae are fine wrinkles that tend to occur with treatments

for high levels of nearsightedness. Typically, they are not visually significant. Macrostriae

are larger wrinkles that often form a concentric fingerprint-like pattern. Macrostriae are often

caused by inadvertent rubbing or trauma early in the postoperative course and are treated by

lifting the flap and smoothing the wrinkles.

Glare and halosaround lights at night are already a fact of life for many patients who wear

glasses and contact lenses. However, laser vision correction can worsen these complaints or

cause them to develop in previously unaffected eyes.

Unfortunately, no preoperative test can determine with certainty whether glare and halo

problems will develop. For many years, pupil size was thought to be a predictive factor, but a

number of studies have failed to support a relationship between pupil size and night vision

complaints. However, some studies suggest that the following factors are related to night

vision complaints:

High degrees of myopia (>5 diopters)

Age greater than 50 years old

Small diameter treatments (0.50 D) after treatment.


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The above list is derived from papers published before the modern wavefront era. In 2005,

Captain Steve Schallhorn, M.D., of the U.S. Navy Refractive Surgery program presented data

at the Annual Symposium of American Society of Cataract and Refractive Surgery (ASCRS)

from a collaborative armed forces study that showed that wavefront-guided treatments

produce superior night vision and better contrast sensitivity than conventional treatments.

Other studies have shown that some wavefront patients obtain better night vision than theyhad with glasses or contacts. Still, wavefront treatments don't entirely eliminate the

possibility of glare and halos.

Hazeis a potential side effect unique to the flapless procedures PRK, LASEK and Epi-

LASIK. Only in very rare circumstances does it occur with LASIK or IntraLASIK. Haze

appears as lattice-like areas of corneal opacification in the area of the laser treatment. Mild

haze is common and often of no visual significance, while moderate to severe haze is less

common, but more likely to cause blurred vision.

When laser vision correction with PRK was first introduced in the mid 1990's, haze was

common and often problematic. The lack of haze with LASIK was the primary medicalreason that LASIK rapidly became the procedure of choice for most surgeons. The other

reason was thewow factor" patients described from its rapid, overnight recovery.

In the past few years, many surgeons have developed a renewed interest in flapless surgery.

Part of the reason lies in the desire to avoid flap complications altogether and another part lies

in the dramatic decrease in haze possible with modern lasers and surgical techniques. Modern

lasers reshape the cornea more smoothly, which is thought to decrease the stimulus for haze,

and intraoperative treatment of the cornea with a medication known as Mitomycin-C further

reduces the likelihood of haze to a very low level.

Over or undercorrection:All FDA-approved lasers used in laser vision correction are

incredibly accurate and precise. However, variability in biological tissue, healing and other

factors can sometimes lead to undercorrection or overcorrection. For example, a farsighted

patient with +3.00 diopters of farsightedness may achieve +2.00 diopters of effect from the

laser treatment (undercorrection) or +4.00 diopters (overcorrection). Patients who are within

0.50 diopters of the intended target are almost always happy and see well. Those who are

0.75 diopters are usually still pleased, but patients 1.00 diopters or more from the intended

target often request a second laser treatment (a "retreatment" or "enhancement") to further

clear the vision.

Pain and light sensitivity:Mild to moderate pain and light sensitivity are common duringthe first three to five days after the flapless procedures PRK, LASEK and Epi-LASIK.

Though modern surgical techniques such as cooling the cornea after laser treatment and

prescribing dilute anesthetic drops have made flapless surgery more comfortable than in years

past, flap procedures such as LASIK and IntraLASIK are still the most comfortable.

With LASIK, pain and light sensitivity are typically brief and mild. The same is true for most

IntraLASIK patients. However, a small percentage of IntraLASIK patients develop a

syndrome called Transient Light Sensitivity (TLS). TLS typically begins two to eight weeks

after uneventful surgery and manifests as extreme light sensitivity, yet the vision remains

clear. TLS is treated with anti-inflammatory eye drops.


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Recent upgrades to the Intralase laser are thought to reduce the likelihood of TLS. Instead of

large, high-energy laser spots spaced widely apart, the current protocol calls for small, low-

energy spots spaced more closely together.

Less Common

Loss of best-corrected vision:Best-corrected vision refers to visual acuity, at any moment in

time, while wearing the best possible eyeglasses. Therefore, best-corrected vision can be

measured both before and after laser vision correction.

Prior to surgery, laser vision correction patients typically have a best-corrected vision of

20/20 or slightly better (20/15). While most achieve 20/20 without correction, of those who

don't, it is important to document whether 20/20 is still possible with eyeglasses. If 20/20

with eyeglasses remains intact, uncorrected 20/20 vision can usually be achieved with a

second laser treatment. However, if 20/20 is no longer possible, even with eyeglasses,

retreatment is more problematic and occasionally not advisable. Patients who have had laservision correction, are no longer able to see 20/20 with glasses, and can't have another laser

treatment are said to have lost best-corrected vision.

The laser manufacturers are required to document the incidence of loss of best-corrected

vision as part of the FDA approval process. The standard is to report patients whose vision

decreases by two or more lines on the eye chart. This occurs in roughly 1 out of 500 cases

with modern lasers. Patients with high degrees of nearsightedness/astigmatism and those who

are farsighted are at higher risk.

Decreases in best-corrected vision are typically mild. Some patients are aware of a loss of

sharpness and clarity, while others don't notice the decrease, even though it is measurable onthe eye chart.

Decentrationrefers to placement of the laser treatment off-center from the optimal centration

point. Visually significant decentrations are extremely rare when experienced surgeons use

modern lasers.

Flap dislocationis another issue unique to the flap procedures LASIK and IntraLASIK.

While flaps heal quite effectively for everyday life, extreme trauma, such as a punch to the

eye or an automobile airbag deployment, could conceivably dislodge a previously healed

flap. For this reason, police officers, prison guards, military personnel, boxers and others

whose activities put them at risk for extreme eye trauma sometimes elect for flaplessprocedures.

Ectasiais one of the more significant potential complications of laser vision correction.

Ectasia occurs when the cornea is thinned too much and a region of it begins to bulge

forward, leading to a distorted, irregular contour. Mild ectasia causes visual distortion that

can still be corrected with glasses. With moderate disease, gas permeable or hard contact

lenses are necessary to mask the distortion, and advanced cases are treated with corneal

transplantation.


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The risk of ectasia is correlated with the initial corneal thickness, the presence or absence of a

flap and the amount of laser correction needed. These issues are discussed in greater detail

under the topic of thin corneas.

Bad flaps:One of the reasons LASIK is so popular, is that complications during the actual

procedure are quite rare. However, out of the entire procedure, LASIK surgeons worry aboutthe flap creation step the most, as a bad flap means the procedure must be aborted without

doing the laser treatment. Bad flap examples include flaps that are too small, off-center or

ones that have a ridge, buttonhole or tear.

An aborted surgery naturally leads to a very disappointed and worried patient. Fortunately,

most bad flaps heal so that the vision returns back to the way it was before anything was

done. If desired, another flap can often be made after three months of healing or a flapless

procedure such as PRK, LASEK or Epi-LASIK can be considered.

LASIK surgeon experience plays a considerable role in the frequency of flap problems.

Experienced surgeons with modern equipment have reported flap complication rates around 1in 1000. Inexperienced surgeons can have rates closer to 1 in 150 and sometimes higher.

Flap creation with the Intralase laser may be of benefit when potential flap complications are

of particular concern. While bad flaps are still possible with the Intralase, proponents believe

they occur less often than with the standard microkeratome. On the other hand, flaplesssurgery is undergoing a mini-renaissance, in part because flap complications are impossible

when no flap is made.

Infectionis an extremely rare but serious potential complication of all vision correction

procedures. The rate of infection with LASIK has been estimated at 1 to 2 per 10,000 cases.

By comparison, a recent study published in Ophthalmologyby Johns Hopkins Wilmer Eye

Institute showed an infection rate of 18 per 10,000 per year with CIBA Vision Night and Day

contact lenses.

Potential Side Effects

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