Serious complications following Laser Assisted Intrastromal Keratectomy (LASIK) are rare. Assuming a competent, experienced surgeon and a good refractive surgery candidate, the risk of serious complication is less than one percent. Our definition of serious complication is an event that results in the need for surgical intervention and/or loss of best-corrected visual acuity (BCVA). There are a number of other events following LASIK that may require careful patient management, but are not classified as serious complications. We shall begin by addressing these events and then progress to discussing serious complications. Each section below will describe the complication, how it is managed and the most likely outcomes.

LASIK POSTOPERATIVE EVENTS

DEBRIS IN THE INTERFACE

Regardless of the sterility of the surgical suite or the diligence of the surgeon, debris will occasionally be seen under a flap. Fibers are the most common form of debris. If the fiber is not in the visual axis and does not interfere with acuity it should be left alone. A cardinal rule of LASIK is DO NOT MANIPULATE A FLAP UNLESS ABSOLUTELY NECESSARY. If the debris is at the edge of the flap it may cause irritation and can usually be easily removed with a forceps. If the debris is large and/or interferes with vision the patient should be returned to the surgeon immediately to have the flap lifted and the bed irrigated.

Debris left under a flap often results in an inflammatory response. Haze may form around the debris. This is a sterile inflammatory response, which requires monitoring only.

 

Slide #1 Fiber in the Interface

BLOOD IN THE INTERFACE

Neovascularization is common in contact lens wearers and is therefore common in LASIK candidates. With the advent of new microkeratomes and larger flaps, the risk of cutting neovascular vessels has increased. If vessels are cut, blood may be present in the interface postoperatively. The blood usually appears as localized coagulated granules near the cut vessels. Small amounts of blood in the interface resolves in one to two weeks without treatment. Large pools of blood should be monitored frequently and may require prolonged treatment with a topical steroid such as Vexol(tm) or Flarex(tm) to prevent secondary inflammation. For mild amounts of blood the steroid is often used qid and tapered over 1 month. For severe amounts of blood, the steroid can be used as often as eight times a day and may require months of tapering. Blood in the interface should resolve without sequelae.

 

Slide #2 Blood in the Interface from Cut Neovascularization

LIPID IN THE INTERFACE

Lipid is a primary component of tears and may become trapped in the interface during LASIK. Although it is important to differentiate lipid from epithelial cells in the interface, it can be challenging. Lipid presents as isolated circular bodies that sparkle upon slitlamp examination. They are not associated with haze or associated epithelial defects, as is found with epithelial ingrowth.

SUBCONJUNCTIVAL HEMORRHAGES

The suction necessary for microkeratomes to create flaps may break subconjunctival blood vessels resulting in hemorrhages. These hemorrhages resolve without sequelae and require only patient education. Patients should be told that hemorrhages are normal and will completely resolve in days to weeks. It is also important to warn the patient that the hemorrhages may get worse before they resolve.

FE DEPOSIT

As in RK, ALK and other refractive procedures, iron may deposit in the cornea following LASIK. The iron will generally appear centrally and may be visible as early as two to three months postLASIK. This deposit is of no consequence and is detectable only by slit lamp examination.

UNDERCORRECTIONS

Although not considered a LASIK complication, under corrections may be difficult patient management problems. Under corrections occur regardless of laser technology and surgical technique. Although under corrections are more likely for patients with high refractive errors and in hyperopes, all patients should be educated preoperatively that LASIK outcomes vary and results are due, in large part, to individual tissue healing responses.

In most cases undercorrections may be enhanced three to six months from the original surgery. Patient management during the interim may be difficult because these patients are typically not happy about wearing refractive correction. Spectacles are the first choice in managing undercorrections because contact lenses may damage flaps in the early postoperative period. Contact lenses should not be prescribed before one month postop and even then, patients must be educated on careful insertion and removal to avoid damaging the flap. Patients should also be made aware that contact lenses influence refractive and corneal stability and need to be discontinued prior to an enhancement.

As previously mentioned, in order to be successful, enhancements should not be performed before three months post LASIK, and then only if there is corneal and refractive stability. In some cases patients may fluctuate for months following the initial procedure. Corneal thickness and topography are two other variables that determine when and if an enhancement is appropriate. The FDA has recommended that 250 microns be left in the stromal bed following LASIK. To calculate if a patient has enough corneal tissue to support an enhancement you must subtract the depth of the flap usually 180 to 160 microns, and the amount of tissue removed by the laser from the initial central pachymetry reading. The amount of tissue removed is related to the diameter of the ablation zone and the refractive error. For a 6 mm optical zone, approximately 10 microns of thickness is ablated for every diopter of correction. The corneal thickness minus the ablation depth and flap depth should exceed 250 microns by enough tissue to support the enhancement ablation. Measuring central pachymetry postoperatively to determine if a patient can support an enhancement is inaccurate because epithelial hypertrophy may contribute to the postoperative reading.

Postop topography should be evaluated before an enhancement. Flattening or steepening a cornea to an extreme level may result in decreased quality of vision or loss of BCVA. It has been proposed that a cornea not be flattened beyond 35 diopters or steepened beyond 49 diopters. A general rule of thumb for calculating how much flattening will occur from a myopic LASIK ablation is 0.75 keratometric diopters for one refractive diopter of correction. The rule for hyperopic steepening is one keratometric diopter for one refractive diopter of correction. It is always prudent to calculate the residual stromal bed thickness and post LASIK keratometry before scheduling a patient for LASIK.

Enhancements are usually accomplished by lifting the flap. In some cases the flap may be too adherent to lift and a new flap must be cut. If a new flap is cut, it is important that it be cut at the same plane or at a deeper plane than the original flap. Although studies indicate cutting new flaps reduces the risk of epithelial ingrowth, the risks associated with creating a new flap are more serious than the risk of epithelial ingrowth and most surgeons would therefore prefer to lift flaps. Flaps have been successfully lifted years after LASIK surgery.

OVERCORRECTIONS

As laser technology has improved the incidence of overcorrections has decreased, but they are still possible due to individual tissue healing responses. Overcorrections are more likely for patients with high refractive errors, and as in the case of undercorrections, spectacles are the best treatment option for the first month. Contact lenses may be helpful in achieving regression in overcorrected myopes because contact lens wear causes epithelial irritation which may lead to epithelial hyperplasia and regression. As mentioned above, contact lenses should not be prescribed prior to one month postop LASIK to avoid flap damage. Patients wearing contact lenses for regression should be monitored carefully as a hyper response has been reported in some cases. The use of nonsteroidal antiinflammatory (NSAID) drops has been proposed to induce regression in overcorrected myopes. The reports of success have been anecdotal and due to the risk of stromal melt in post surgery patients, NSAIDs are not recommended.

Enhancement criteria is similar to that discussed above and in some cases may not be necessary as healing regression may result in loss of the overcorrection. It is therefore, imperative that overcorrected patients reach a stable refractive endpoint before considering an enhancement.

LASIK COMPLICATIONS

KERATITIS

Keratitis, by definition is inflammation of the cornea and is a common presentation following LASIK. Keratitis may result from a variety of etiologies with dryness being the most common cause. LASIK disrupts the tear cornea interface during the formation of the flap and interrupts innervation to the cornea resulting in less tear/cornea interaction. Keratitis sicca may therefore be a problem, in dry climates it is probably the greatest LASIK postoperative management challenge.

There are a number of ways to manage keratitis sicca post LASIK. The first and most important management technique is to treat any dryness preoperatively. Prophylactic nonpreserved artificial tears four times a day is prudent to insure a moist cornea on the day of surgery. If significant sicca exists, punctal occlusion should be performed. For a mildly to moderately dry cornea, temporary occlusion with collagen plugs is advised. Remember that temporary plugs only last two to four days so the plugs should not be inserted too far in advance of an upcoming procedure. If the patient manifests significant superficial punctate keratopathy (SPK) permanent plugs should be inserted several weeks before the procedure. If the Freeman type of plug is used, the eye must be checked for careful plug positioning to avoid contact of the top of the plug with the globe or cornea. This is not an issue with intracanalicular plugs although they may have the disadvantage of difficult removal. Patients with severe dry eye may not be candidates for LASIK.

Regardless of dry eye treatment preoperatively, many patients will present with dryness following LASIK. These patients typically complain of irritation with blurred vision and are often disappointed by the absence of the proverbial "WOW" experience following LASIK. Immediate and aggressive treatment is therefore critical in managing a potentially unhappy patient.

Postoperative treatment of keratitis due to dryness follows the same course as outlined above with a few caveats. Begin treatment with the least invasive therapy and progress as needed. Do not forget to recommend the obvious therapy such as humidifiers at home and avoiding very dry situations such as wind and excessive exposure to the elements. Nonpreserved artificial tears should be administered frequently; up to every hour. If artificial tears are not sufficient to control the dryness then punctal occlusion should be performed. Occasionally it may be necessary to occlude all four puncta. For the significantly dry cornea, an ointment at night may become necessary. To avoid ointment finding its way under a flap, do not prescribe ointment at night until the flap has firmly adhered, usually two to four days postop. In rare cases, patients may continue to experience dryness even with aggressive therapy and a bandage soft contact lens may be necessary. Do not apply a lens until the flap is well adhered, approximately four weeks postop, and continue to monitor the eye carefully. Except in the driest eyes, the above therapy will be sufficient. Most corneas return to baseline levels of hydration two to three months post LASIK.

Keratitis following LASIK may also be the result of pharmaceutical toxicity. In these cases the SPK will be diffuse over most of the corneal surface. Changing topical drops should eliminate the keratitis. Remember, the patient should remain on an antibiotic and a steroid for at least four days following surgery. Fluoroquinolones (Ciloxan and Ofloxacin) are rarely associated with toxicity and Flarex and/or Vexol are good choices for alternate steroids.

EPITHELIAL DEFECTS

Epithelial defects may occur in conjunction with formation or manipulation of the flap. Epithelial defects are more common in older patients and patients with compromised epithelium. Once again, it is prudent to treat any keratitis preoperatively to avoid epithelial defects. Patients with epithelial basement membrane dystrophy (EBMD) are not LASIK candidates. In these patients, manipulation of the cornea often results in large, slow healing abrasions that are prone to recurrent erosions. Phototherapeutic Keratectomy (PTK) may be a better treatment option for patients with EBMD.

The majority of epithelial defects post LASIK occur at the edge of the flap and do not require special treatment. If the abrasion is large or results in patient discomfort, therapy may be required. Nonpreserved artificial tears administered copiously are often all that is necessary to improve comfort and promote quick reepithelialization. For larger abrasions, a bandage contact lens may need to be applied. A disposable contact lens with a flat base curve works well as a bandage. If a contact lens is placed on a fresh LASIK cornea care must be taken to keep the lens moist to avoid dehydration and subsequent wrinkling of the flap. Punctal occlusion and artificial tears in conjunction with bandage contact lenses generally results in quick epithelial healing and improved comfort. In cases of large, slow healing abrasions, a bandage contact lens may need to be left on the eye for more than one day. In these cases, the patient must be monitored daily to insure that the cornea is healing and that the lens is not damaging the flap or causing inflammation. A mydriatic may occasionally be necessary to increase patient comfort during reepithelialization. For large or slow healing abrasions, a decrease in the topical steroid from four times a day to two times a day may speed wound healing.

 

 SLIDE #3 Large Epithelial Abrasion

With the exception of large epithelial defects, reepithelialization should occur within twenty-four to forty-eight hours post LASIK. All epithelial defects provide potential access through the flap for epithelium to reach the stromal bed. Patients with epithelial defects must be monitored for epithelial ingrowth.

EPITHELIAL INGROWTH

Epithelial cells gain access to the stromal bed through defects in the flap or by being washed in during irrigation of the stromal bed. Ingrowth is evident days to weeks after surgery and does not occur late in recovery unless trauma results in a fresh defect to the flap. Once under the flap, epithelial cells may progress or remain stable.

Epithelial cells in the interface have a variety of appearances and can be graded on a scale from 1 to 3. Grade 1 cells are almost transparent and may be difficult to detect. They are generally near the edge of the flap and have clearly delineated borders. Grade 1 cells are nonprogressive and do not require surgical intervention. Grade 2 cells may be associated with mild haze and are seen in nests or groups of cells without distinct borders. Grade 2 cells may progress and require treatment. Grade 3 cells are characterized by haze, opaque areas of ingrowth and stromal melt. They require immediate surgical intervention.

 SLIDE #4 Grade 3 Epithelial Cells

Treatment for epithelial ingrowth involves lifting the flap and wiping the epithelial cells out of the interface. Epithelial cells are typically easy to remove with a wick cell followed by copious irrigation of the bed to remove any residual cells. The earlier a flap is lifted following surgery the less trauma results to the flap and the easier the cells are to remove.

All epithelial cells require diligent monitoring for progression. Epithelial ingrowth should be monitored weekly and carefully documented until stability is established. Photodocumentation is useful, but if unavailable diagrams of size and position help to determine if cells are progressing. Epithelial cells in the visual axis result in decreased uncorrected visual acuity (UCVA) and/or decreased BCVA and require treatment. Astigmatism and flap melt may also be caused by epithelial ingrowth and indicate that the patient should be referred back to the surgeon for cell removal.

STRIAE

Striae, or wrinkles in the flap, may occur from misalignment of the flap during surgery, from displacement of the flap after LASIK or from "tenting" of the flap into the stromal bed following a deep ablation.

Flap wrinkles are classified as either macrostriae or microstriae. Macrostriae are easily identified by slit lamp examination and may be associated with misalignment of flap edges. Patients with macrostriae complain of distorted and blurred vision and may experience pain or discomfort. Macrostriae are usually associated with trauma to the flap and patients often describe a specific event that resulted in ocular injury. Macrostriae require urgent attention. Patients with macrostriae should be referred back to the surgery center as soon as possible. Delay in referring patients for striae removal may result in permanent wrinkles in the flap. The longer striae remain in a flap the more difficult they are to remove.

SLIDE #5 Macrostriae

 

Microstriae may be difficult to detect and usually have no effect on vision. They may be present following a deep ablation in which the flap does not lie smoothly in the stromal bed. Microstriae appear as fine lines in the flap and are best detected with retroillumination. Fine wrinkles presenting immediately postop may smooth out with time. Rarely do microstriae require surgical intervention, as they are not associated with loss of acuity or misalignment of the flap. Microstriae should, however not be overlooked as a potential etiology for unexplainable loss of BCVA following LASIK. Retroillumination with a dilated pupil may reveal microstriae that are otherwise undetectable and may be contributing to an irregular flap. If microstriae are suspected of causing visual loss the patient should be referred back to the surgery center for evaluation. As previously mentioned, a cardinal rule of LASIK is DO NOT MANIPULATE A FLAP UNLESS ABSOLUTELY NECESSARY.

SLIDE #6 Striae with Retroillumination

To avoid striae patients should protect new flaps from mechanical manipulation. All patients must be instructed to avoid rubbing their eyes following LASIK. Lubrication is critical in preventing lids from wrinkling dry flaps. All patients should wear plastic shields during sleep for the first week following LASIK to prevent trauma to the cornea from pillows, blankets, etc. Eye protection for high-risk activities is mandatory for the first year following LASIK and it is prudent to recommend eye protection for all activities with risk of ocular injury for the rest of a patient's life. Ocular trauma has been reported to cause striae in eyes six to nine months post LASIK.

Surgical intervention for striae involves lifting, stretching and smoothing the flap or refloating the flap. One lift and stretch technique is to lift the flap and allow it to dry slightly before stretching and smoothing it into place. Stretching and smoothing is usually accomplished by using canulas and dry wick cells and may result in epithelial defects. As previously mentioned, the longer the duration of striae, the harder they are to remove.

A less invasive procedure for removing striae is to refloat the flap. This technique is effective for recently and mildly wrinkled flaps. In this procedure saline is injected under a flap. The flap expands up and is then gently smoothed into place with a wick cell. This procedure results in less trauma to the flap than lifting, stretching and smoothing.

LASIK INTERFACE KERATITIS (LIK)

LIK also known as: Sands of the Sahara (SOS), Drifting Sands, Sands, Diffuse Lamellar Keratitis, LASIK Interface Inflammation, and Non-specific Diffuse Interface Keratitis, is a sight threatening LASIK complication. The inflammation is usually unilateral and outbreaks are often reported in clusters. LIK is characterized by interface haze that is confined to the stromal bed. The haze is typically diffuse and scattered with faint foci and as the name Drifting Sands implies, may shift to different areas of the stromal bed.

LASIK Interface Keratitis is a noninfectious inflammation of the stromal bed that has been reported to have an incidence ranging from one in three hundred to one in ten thousand cases of LASIK. The etiology of the inflammation is unknown. It has recently been suggested that an external environmental trigger activates an immune response in susceptible individuals. Proposed causes include bacterial spores in microkeratome tubing, povidone iodine scrubs, and contaminated microkeratomes.

LIK usually presents one day postop, but may develop within the first postoperative week. It has also been reported following LASIK enhancements and post surgery trauma to the flap. Patients typically present with blurred vision, decreased BCVA, hyperopic refractions and mild discomfort.

A grading scale from I to IV is used to classify LIK. Partial interface haze and excellent vision characterize grade 1. Grade II LIK is defined by partial to complete stromal bed haze with good vision. In grade III interstitial keratitis the entire stromal bed is hazy and vision is foggy. Grade IV LIK presents with complete interface haze, foggy vision, conjunctival injection, anterior chamber inflammation and lid edema.

 

SLIDE #7 Grade II LIK

 

SLIDE #8 Grade III LIK

Successful treatment of interface keratitis is dependent upon quick diagnosis and aggressive therapy. LIK is treated with high potency, high frequency topical steroids such as pred acetate 1% used from 4 times a day to every hour for 1-2 weeks. Patients with LIK should be monitored daily. Culturing is not generally necessary as interstitial keratitis is a sterile inflammation and does not yield growth on culturing. A topical antibiotic, such as a fluoroquinolone bid to qid, may be used in addition to the steroid for additional coverage.

Aggressive treatment generally results in resolution of the haze and hyperopia with return of UCVA and BCVA. The duration of treatment varies, but in most cases LIK will resolve within days to weeks of the initial presentation. In rare cases where the haze does not resolve, the flap can be lifted and the interface irrigated. Not to belabor the point, but DO NOT MANIPULATE A FLAP UNLESS ABSOLUTELY NECESSARY.

Although serious complications following LASIK are rare, appropriate treatment administered in a timely manner generally results in good vision and happy patients.

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Page Last Updated: May 8, 2003
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