Radial Keratotomy — possible complications

“Life is just one damned thing after another.”

Frank Ward O'Malley

hen dealing with any medical matter, it is quite impossible to list every adverse possibility, thus surgeons can no more list all the possible complications of this procedure than they could for the taking of a single aspirin, a shot of penicillin, the administration of an eye drop, or for that matter, the wearing of glasses. They can tell you that in the many thousands of cases already performed, there have been few serious complications from RK. Part of the surgeon's pre-surgical consultation with you will be devoted to discussing all the possible complications and any other aspect of the surgical procedure to any extent you may desire.

Complications of a surgical procedure are unexpected and/or severe side-effects which may require treatment and which usually lead to a permanent condition. The possible complications of RK are (these are not arranged in any particular order):

Severe scarring

Severe scarring is rare on the cornea following surgery but can occur under certain circumstances. Often such scarring is blamed on the patient's healing response. There is, however, no recorded instance of “corneal keloids”, the hallmark of an overactive healing process. Vigorous scarring can be seen at the corneal limbus which is replete with blood vessels. But the author submits that the limbus, which is a boundary area, is not the cornea in any true sense though it may be continuous with it. Excess scarring is seen, however, when incisions have been re-cut too frequently (twice is usually enough); when incisions gape (as in T-cuts and then usually only those at the lower portion of the cornea; and in instances where the incisions have been placed closely together allowing the healing process to “flash-over” and involve more tissue than usual in the healing (scarring) process. Excess scarring is also seen in cases where tangential incisions have crossed (usually fresh [less than 6 months old]) radials or vice-versa. In cases of macroperforations, a certain amount of sub-endothelial scarring always results which can create a “dimple” or thin spot in the cornea; this also leads to excess scarring in some cases.

Figure 1. Scarring produced when incisions cross.

All instances of excess scarring are associated with some degree of irregular astigmatism. Usually such astigmatism is “local” — that is it does not affect the entire corneal shape. If the scarring is close to the visual axis — as in cases where the surgical clear zone is excessively small — the irregular astigmatism can directly affect vision. Even if the irregular area is in the periphery and away from the visual axis it can still affect vision indirectly by creating disturbances in the tear film and/or tearing or may do so by creating glare. additionally, such areas can make contact lens wearing difficult — not to say impossible.

Intractable glare

Intractable glare of a degree which interferes with a patient's vision to the point of making them functionally blind is always associated with an irregular corneal surface coupled with excess scarring and is almost always seen associated with an optical zone less than 2.75 mm; though it has also been seen in cases of grossly decentered optical clear zones and in cases where one or more incisions have invaded the clear zone and/or visual axis.

Severe glare to the point of making night driving impossible has been reported in rare cases of otherwise uneventful and perfectly performed RK. This is always self-limiting but can last upwards of a month or more.

Intractable glare will sometimes respond to palliative therapy in the form of miotics and dark glasses but can only be completely cured by a corneal transplant — which removes the offending scars. Although lamellar transplants have been attempted with some degree of success, penetrating keratoplasty is recommended.

Under-correction (residual myopia/astigmatism)

Despite the best planning, some cases will end up with residual myopia. In the majority of these cases the cause will be incisions that are too shallow, too few, or too short (optical zone too big).[22, 23] All of these problems can be solved for the most part by correcting the deficiencies. Timing is the essence however, in these corrective efforts.

Generally speaking, shallow incisions should be recut and deepened within the first month of the initial surgery. If not done within the first 30 days, then the deepening should be delayed for at least 4 months — waiting at least 6 months being better. When deepening incisions, the straight or vertical-edged blade should be used and the incisions deepened starting at the limbus and moving toward the center using the previous incision as a guide line. Doubled incisions, with infolding of epithelium, can occur when trying to recut incisions from the center to the periphery. It is not possible to keep the blade within the old incision track unless the incision is made from the limbus to center and even then it is extremely difficult. The knife footplate straddles the old incision — the surgeon using it as a guide. These types of incisions are notoriously unstable.

No more than 8 incisions should be deepened at any one sitting. The eye becomes soft very quickly — thus there is a tendency for the blade to wander when approaching the center. Corneal pachymetry must be repeated because the cornea is always somewhat thicker post-operatively for some months — possibly a year or more.[14, 24] Mapping can be done again between the previous incisions but it is usually enough to get the central pachymetry, adding the increase to the original preoperative readings.

The decision to add incisions should be delayed until the corneas have become stabilized (around 4 to 6 months). The patient should then be re-examined and the parameters re-calculated using the pre-operative K-readings. This holds for astigmatic as well as spherical cases. Expect a correction of between 80 and 90% of the residual myopia and/or astigmatism.

When fitting spectacles, it is wise to wait a minimum of two weeks before doing so. There will be a small percentage of patients who will require a change of lenses within 6 months. Contact lens fitting should be delayed for at least 6 weeks for hard lenses and 8 weeks for soft lenses (including extended wear). There is a increased risk in developing neovascularization if soft lenses are fitted before that time.

Over-correction (induced hyperopia [farsightedness])

The author reported an incidence of post-operative hyperopia of less than 1% in a series of patients. [25] This phenomenon is more likely to occur in patients over 40 years of age with myopia less than 3 diopters. [26-28] It is also more likely to occur with cases calculated using nomograms that do not take age or scleral rigidity into consideration. It is not unusual, even in well calculated cases using regression formulæ, for patients in this group to show an initial overcorrection lasting upwards of 3 to 4 weeks. Deitz and Waring have noted that a certain percentage of patients undergoing RK have shown a progression of effect, some of whom have shifted to the hyperopic side — others have also reported a sporadic incidence of this complication. [26, 29-31] The author has some patients within his practice that have also shown a shift to the hyperopic side after 4 years post-RK but it is less than the 30% reported by Deitz and Waring. As a matter of fact, some of this so-called progression may be a result of a normal fluctuation in K-readings seen in normal, unoperated patients.

This problem is difficult to recover from although if the hyperopia is less than one diopter it may well be lost eventually through a process called “emmetropization”. Any hyperopia greater than one diopter and lasting more than 6 to eight weeks is likely to remain and poses a problem, especially for older patients.

The use of anti-glaucomatous medication, such as beta-blockers, has proven to be of some value in reducing over-corrections of up to 2 diopters. It may be necessary to continue the use of such therapy for as long as a year. Even then, some cases have been reported in which the hyperopia has returned upon discontinuation the medication. Furthermore, not all normals will respond to beta-blockers with a reduction in IOP. Such response as there is will be variable. However, if there are no contra-indications, it may be worth trying.

Hexagonal incisions (HK) have been advocated for over-corrections up to 4 diopters of hyperopia. [33, 34] The author advises against such application as being fraught with an almost 100% incidence of irregular astigmatism not to mention intractable corneal fluctuation.

Likewise, the author does not recommend the use of thermokeratoplasty advocated by Schachar. [35] Placing the burns in the RK incisions results in a variable outcome often associated with induced astigmatism. This occurs because denaturation of the scar tissue does not appear to be a uniform process and scarring is often much greater than anticipated. Placing the burns between radial incisions often leads to splitting and or widening of the adjacent incisions. Such splitting or widening also results in unpredictable astigmatism — sometimes of the irregular variety.

Recently the author has employed the method of hyperopic lamellar keratotomy (HLK, ALK), performed with the Barraquer micro-keratome to correct induced hyperopia. By making a section of at least 80% in depth and by varying the diameter of the disk of tissue excised, hyperopia of up to 6 D have been predictably reversed. The procedure has the advantage that the cornea has not been materially weakened as is the case in HK. A non-torquing, 14-point suture is emplaced at the time of surgery and is removed within 7 to 14 days. The incidence of induced astigmatism is low. Since no freezing or lathing is involved, visual recovery is rapid.

While ongoing research is being done and success reported with cautious optimism by some investigators, EXCIMER PRK for hyperopia is still problematic and not recommended at this time.

In cases of reversal of the astigmatism where the axis has rotated 90 degrees, other methods must be used. This complication is mostly seen in cases where trapezoidal keratotomy (Ruiz Procedure) has been used. Invariably, the T-incisions are found to be too long or gape during healing producing wide, soft scars. The recommended approach is to strip out the old scar and suture it tightly closed with one or two X-type sutures of 10-0 nylon. The sutures must be placed symmetrically — one on each side of the optic center — otherwise gaping may occur in the un-sutured. The sutures close the gap and reduce the chord length, consequently increasing corneal steepening in that meridian.

The same basic procedure can be employed to correct spherical over-corrections. In these cases, 3 or 4, X-type sutures of 10-0 nylon (EthiconTM CUM-5 or similar) are symmetrically placed across the radial incision. These are placed between a 6 and 8 mm OZ mark made on the cornea in the usual fashion and the knots pulled below the corneal surface. The sutures are tightened sufficiently to produce very slight striations to appear around the suture. These are best seen if the cornea is dry. An over-correction of mild degree is the norm. This reverts within 7 to 10 days. Sometimes it is necessary to remove and replace sutures that are too tight or loose. These can be removed in 9-12 months but if the patient is comfortable the author leaves them in.

Starling and Hoffman have advocated the use of purse-string intrastromal sutures as a way of reducing induced hyperopia.[36] Such a suture is technically difficult to place and inevitably results in some “cheese-wiring” with resultant loss of effect and induced scarring. While no cases of erosion of this suture into the anterior chamber have as yet been reported — the possibility of such a complication exists, particularly if the suture is drawn too tightly.

As always, the best treatment of any complication is prevention. Educated guesswork and making surgical decisions using tables based on one or two preoperative parameters is not the best way to optimize this surgery for each patient. Only the use of computer programs employing algorithms derived from regressive analysis of actual cases can be relied upon to correlate the numerous parameters required for the successful outcome of this surgery.

Infection

Fortunately this is a rare problem, possibly because we have tended to be cautious in our follow- up — placing all patients on antibiotic drops following the surgery and covering, with oral antibiotics (in some cases sub-tenons injection), those patients in whom perforations have occurred. It is also a rare happening undoubtedly because we are dealing with young healthy eyes whose tear complex is alive and well. Still the occasional infection does occur and ranges from small areas of epithelialitis to frank endophthalmitis.. In 1980, Gelender reported a case of endophthalmitis immediately following RK in a patient in whom a perforation into the anterior chamber had occurred and who had not been placed on antibiotics. [40] Fortunately that eye was saved by timely intervention with antibiotics and eventually a vitrectomy-lensectomy. At last report this eye had recovered a corrected visual acuity of 20/30.

Another patient was not so fortunate, developing an endophthalmitis 24 hours after surgery. Despite timely intervention, the eye was lost — surely not an expected sequela. Another patient developed a corneal infection approximately one month post-RK following a hair-brush injury. This infection went on to become a frank endophthalmitis without subsequent loss of the eye.

Deep intra-intrastromalitis was reported in three cases by Deitz and Katzen, in 1981.[41] One of these cases was later shown to have had a history of previous Herpetic keratitis. All of these eyes sustained a profound loss of vision (< 20/200) associated with the onset of central stromal clouding some 3 to 4 months post-RK. All cases eventually responded to topical steroid therapy over an 8 to 10 week period with no recurrence reported to date. For this reason, any eye in which previous Herpes keratitis has been documented or suspected is not considered a candidate for this surgery. [42, 43]

Several cases of localized disease seemingly limited to the epithelium have been seen. Some of these occur as persistent optic clear zone marks implying that the marker has either damaged the basement membrane or implanted some foreign substance. Other times the inflammatory process lies between the incisions and filaments may develop.

Fyodorov and his group have reported a case of staphylococcal corneal ulcer occurring in an incision following a re-operation.[44] This patient responded to antibiotics and debridement but was left with a wide scar causing increased glare. No astigmatism resulted and the visual acuity was said to have returned to 20/25.

Iritis beyond a few cells with a trace of cells is unusual in this surgery but of course hypopyon has been reported in the presence of corneal ulcers.

The PERK study has reported on two cases of post-operative intracorneal abscesses, occurring some two years after the initial surgery. All eventually responded to conventional therapy as well. [45-47] Geggel reported a case of sterile keratitis which eventually required a penetrating keratoplasty. The author has also seen one case in which an intra-incisional abscess formed approximately 3 years post-RK. Topical antibiotics cleared the infection within 3 days on CiloxanTM (topical ciprofloxacin). Since then 2 other cases have appeared, 1 occurring at 5 years, and the other at 7 years post-surgery.

It is obvious, since the majority of these cases involve the incisions initially, that the scar formed after an incision of this type is soft and offers little resistance to invasion for some years. It has been suggested that the epithelium over RK scars is somehow abnormal and perhaps more susceptible to the occurrence of infection. How this can be has never been adequately explained nor why these incisions should differ markedly from lacerations or PKP scars. However, there does appear to be, at least initially, disturbance of the corneal wetting mechanism post-RK. [48] While the BUT seems to return to normal in most cases the author has examined, it is possible that this might play a role in allowing an invading organism a foothold. It is evident that the appearance of iron lines in these corneas is somewhat higher than the general population — thus it could be that the mechanism is simply that of a sufficiently irregular surface for organisms to adhere to. [49] Whatever the mechanism might be, it is evident that these patients may be at slightly greater risk for infection and should be advised accordingly.

Irregular astigmatism

Some degree of irregular, transitory, “micro” astigmatism probably occurs in every case following RK — particularly if the patient has had regular astigmatism to begin with. However, this type of irregularity gradually disappears as the healing process goes on.

Figure 2. Irregular astigmatism over a wide incision.

There are many causes for the occurrence of permanent irregular astigmatism following RK. One of these is irregular healing. Irregular healing can be caused by unusual gaping of an incision producing a wider scar. A wider scar may produce a localized area of increased corneal flattening leading to irregular astigmatism. Such gaping is often seen after a T-cut for astigmatism. Another frequent cause of irregular astigmatism is an off-centered surgical clear zone. There are many reasons for such a zone being made off-center. The most frequent of these is the surgeon's reliance on the pupil to place the marker. The pupil is hardly ever concentric with the visual axis and should never be relied on for surgical zone placement. However, even relying on the visual axis is not without hazard especially in a non-cooperative patient who is either incapable or is too stupid to look at the target light . An irregular optic zone is also a frequent cause for irregular astigmatism and is the leading hazard of the so-called Russian or Fyodorov RK technique. This happens because it is next to impossible to stop the blade exactly on the OZ mark. It should be clear by now that the central optic clear zone is vital to the successful outcome of RK surgery. A more detailed discussion follows:

Sub-normal optic clear zones

It is a fact that the amount of correction obtained in radial keratotomy by a given number of incisions is inversely proportional to the size of the optical zone. That is — the smaller the zone, the greater the effect. However, this relationship is non-linear and there is a size beyond which the effect is counter balanced by disability and/or diminishing returns. The problem is related to the concept of effective optical zone size. When an incision is made, the edges of the cut become elevated. Then as the scar matures they become depressed. These edge changes create corneal curvature changes which distort the light striking them. These changes are constant in size. The smaller the OZ, the more effect these edge changes have on the size of the clear zone. For example, the effective zone for a 2.75 mm OZ is close to 2.5 mm. For a 2.5 mm OZ it approaches 2.0 mm. For a 2.0 mm zone it is about 1.25 mm! Centration and radial symmetry of the incisions becomes critical.

Because this surgery is elective and involves a vital sense organ of the body, the surgeon is held to a higher standard than if the surgery were emergent or the problem life threatening. Consequently, not only must the surgeon exercise considerably greater diligence in the performance of the surgery itself but the duty to inform the patient is also greater.

In order to reduce the side effects of glare and photophobia which typically reduce vision, the surgical clear zone must be precisely centered. There are various methods employed to accomplish this. Most surgeons rely upon the patient to fixate (look) at a guide light from which the surgeon orients his visual axis mark. All OZ's are subsequently centered upon that mark. If the mark is not precisely placed — reduction of vision may occur due to factors mentioned above or through the introduction of asymmetric or irregular astigmatism. The surgeon is in complete control here. If the mark is ill-placed — this is the fault of the surgeon alone. If the patient moved while the mark was being placed it must be remarked. If the patient was not looking at the light — the surgeon must be alert to that fact and insure centration.

Furthermore, the smaller the OZ, the more critical the centration because even a slight mis-alignment can produce greater after effects. There appears to be a limit to the smallness of this OZ. Most refractive surgeons consider a 2.75 mm surgical OZ the absolutely smallest OZ that can be used in RK. A large number of these will use nothing smaller than 3.00 mm. There is no question that smaller zones are accompanied by greater incidence of disabling glare and reduced vision due to this and the greater incidence of irregular astigmatism.

Irregular astigmatism and/or surface distortions occur around all corneal incisions. This is a fact of life and has been known from the days before refractive surgery. The extent of the distortion is related to the quality of the instrument doing the incising. There is no question that thin, smooth, sharp blades produce more regularly shaped incisions and reduce distortion. But the distortion is only reduced in extent not eliminated. There is a finite amount of distortion which persists because of the fact of the incision and the fact that healing processes are underway. These healing processes produce irreducible changes in tissue only some of which are temporary.

Thus, as the optical zone gets smaller, these disturbed areas are brought closer to each other as well as to the center of vision. Hence, even though an OZ might be marked at 2.75 mm, the actual clear zone is smaller — more on the order of 2.5 mm (the effective OZ). As the zone gets even smaller, this clear zone gets disproportionately smaller and the visual disturbance gets greater even if perfectly centered.

Most if not all keratotomy surgeons would declare that a 2.50 mm OZ is smaller than normal. In fact, most surgeons will not use a zone smaller than 3.00 mm and declare the smallest they'd even consider is 2.75 mm. There is a consensus among most experienced surgeons currently performing RK, that the surgical clear zone should not be less than 2.75 mm with the vast majority preferring to go no smaller than 3.0 mm. These surgeons cite difficulty in centering; increased incidence and intensity of glare; loss of best corrected vision; induced irregular astigmatism; and loss of contrast sensitivity in sub-nominal OZ cases. They are correct in this.

The use of optical zones smaller than 2.50 mm in diameter is not considered to be usual and customary and their employment is considered experimental — best case — necessitating a special protocol and informed consent.

However, some surgeons are nonetheless regularly performing RK surgery with zones smaller than 1.75 mm! Some have defended their actions by stating that the increase in acuity offsets the loss of contrast sensitivity! However, it is not possible to suffer loss of contrast sensitivity and maintain good acuity in the real world — the two are tied together.

If zones are used that fall below the standard — the surgeon must not only justify this by the facts of the case but more importantly he must inform the patient that he is doing non-standard surgery and let the patient decide to take the risk. In cases where considerable numbers of patients are undergoing non-standard or investigational surgery — special informed consent forms must be generated for that purpose. This is a standard within the profession.

Induced astigmatism

The incidence of induced irregular astigmatism following RK is, fortunately, quite rare. [20, 21] When it is seen its cause can usually be traced to a problem with the incisions as described above. Regular astigmatism that remains after surgery is most often a result of an incomplete correction or residual myopia either through failure to correct for the astigmatic portion or ignoring it. While it is true that up to 1.50 D of astigmatism may disappear after operating for the sphere alone in 16-incision cases, this is not true for incisions less than 16 in number. The rule of thumb for the author is to compensate for the astigmatism when that component equals or exceeds 20% of the spherical myopia and/or when the astigmatism is “against-the-rule”. Patients will tolerate surprisingly large values of “with-the-rule” astigmatism post-operatively. It is the author's considered opinion that a small residual W-T-R is not a bad thing and may actually improve the patients visual perception.

Figure 3. The surgeon put the original incisions in the wrong axis.

One common cause of induced regular astigmatism is making astigmatism incisions in the wrong axis. This has happened to experienced surgeons as well as neophytes. It is a very real danger and the risk of this happening should not be minimized. This can occur due to misunderstanding of the principles of astigmatic correction and confusion of the axis with the meridian. All practitioners are advised to map out the incisional configuration well before, and not during, the day of surgery. If changes are believed to be required at the time of surgery be sure that such a change is absolutely correct before proceeding. If still confused or if any doubt exists — do not do the case. In fact a good watchword for this surgery is: when in doubt — don't!

Use an optical device such as an eyepiece reticule or surgical protractor to mark the plus axis with the marker designed for this purpose. Before making the first incision, double check the axis, preferably with one of your knowledgeable staff. When in doubt — bail out.

If more than one month has elapsed since the surgery, then the surgeon is advised to wait a minimum of 4 to 6 months to re-operate — preferably the latter. Sutures or intra-incisional debris should be removed immediately and the epithelium allowed to heal completely before proceeding. In unusual cases it may be necessary to perform additional incisions to relax or further modify the corneal shape to relieve the irregularity. Corneal topography may be helpful here. In these cases the full waiting time of 6 months should be allowed to elapse before further surgery is done. It should be apparent that the timing of any additional surgery is predicated on stability of the cornea. If change is still occurring, then further waiting is mandatory.

It may be necessary to curette and suture tightly, the incisions in the axis of greatest flattening in order to reduce the chord length, thereby steepening the corneal curvature. This is especially helpful in cases involving “T” (transverse) incisions (see also Over-corrections).

The correction of induced irregular astigmatism is a specialized problem requiring tailored approaches based upon extensive experience. The less experienced surgeon is advised to seek consultation in all such cases.

While waiting for the cornea to stabilize or as an alternative to further surgery it may be advisable to fit a hard or gas permeable contact lens. The usual rules apply. However, such a fitting should be delayed until 6 to 8 weeks have elapsed. This delay will minimize any tendency toward developing neovascularization.

Residual or induced regular myopic astigmatism can be treated as outlined in Undercorrections. The best treatment is, as always, prevention by careful pre-operative evaluation and planning and the use of ultra-sharp blades set at maximum depth with careful blade placement and incision control.

Perambulating astigmatism

In those cases with pre-existing astigmatism or in “spectacle sphere” cases with corneal astigmatism and occasionally in purely spherical cases, induced regular astigmatism may be seen post-operatively. The axis of this astigmatism will change from day to day toward “with-the-rule” but may change course willy-nilly — hence its name: perambulating (or wandering) astigmatism. By itself it is a transient problem and in operated astigmatism cases is a good prognostic sign. Associated with residual myopia it accounts for much of the fluctuation seen in these cases. It may aggravate other side effects, notably glare and ghost images. Unless severe, treatment is not recommended and of little use since the situation is rapidly changing. Furthermore, re-operating astigmatism under these circumstances is highly dangerous.

Neovascularization (blood vessels forming in the incisions)


Figure 4. Neovascularization of multiple radial incisions.
The patient ultimately required a corneal transplant
to restore useful vision.

The author was the first to report the occurrence of this complication following the use of a soft contact lens immediately after surgery to stabilize the cornea.[37] These cases are evidenced by vessels running along incisions in the superficial part of the scar. [19] Typically the encroachment is no more than 1 millimeter central to the capillary arcade. However, one case has occurred in which the vessels reached the edge of the optical zone.[38] There have been few reported cases of neovascularization after RK except those associated with early daily wear soft contact lens wearing. [2] With the exception of the one case reported by Fyodorov, all have responded to removal of the lenses and the application of topical steroids. All patients have eventually been able to wear contact lenses on a limited basis. [39] No cases have been reported while wearing disposable soft contacts but such patients still require careful follow-up and fitting should be delayed unless there is a therapeutic reason for their being worn.

Neovascularization is not inherent in the procedure of radial keratotomy even in cases where incisions crossed the limbus. Except for some conjunctival “peaks”, in the absence of some inciting factor, neovascularization does not occur. The author has performed RK in two cases of superior limbic pannus after performing superficial keratectomies of the pannus. The pannus has not recurred nor has there been any evidence of new vessel growth in the area.

Intra-incisional opacities or inclusions


Figure 5. Mascara in an incision.

These have been reported with decreasing frequency as more attention has been paid to post- surgical incision irrigation and the practice of keeping the cornea dry during surgery. [50] If blood is left within the incisions it is possible that the keratocytes will break it down into refractile lipid deposits. Generally these are unsightly but pose no problem. Occasionally it has been found necessary to remove these deposits with a sharp blade to reduce the glare that they can produce. Sometimes they can become quite large. If air is left within the wounds, encysted areas will result. These collapse in time but may need to be assisted by decompressing them with a needle tip. Rarely, meibomian secretions as well as other things can find their way into a partially open incision. These may have to be excised as well.

Cataract formation

There have been a small number of cases of cataract formation reported to date. Five followed perforation into the anterior chamber. Four of these showed frank evidence of direct lens injury. [24, 69] It is presumed that the fifth lens was also injured but no injury site could be unequivocally identified. [70] It is difficult to postulate how entry into the AC of the blade tip alone without trauma to the lens could produce a cataract in the immediate post-operative period. Unless withdrawal of the blade is instantaneous in the event of a microperforation, the chamber can deflate sufficiently to allow contact of the blade tip with the lens capsule. That this can occur without notice of the physician and in the absence of evident lens trauma is borne out by the case of Nozik. In this instance, phakoanaphylaxis occurred in a female patient some considerable time after a 16 incision RK was performed. The surgeon acknowledged that a microperforation had occurred but that the chamber had not flattened in any way. Care in blade setting, reduced blade speed, avoidance of manipulation of the incision when the chamber is shallow (free-hand deepening), and an undilated pupil should prevent the occurrence of this major complication.

Two cases of steroid induced cataract formation have been reported. In each case the surgeon was attempting to enhance the effect of his surgery by inducing an intra-intraocular pressure rise with topical steroids. [46] It has not been shown that increasing the IOP above normal has any permanent effect upon the outcome of the surgery, nonetheless some surgeons persist in this attempt. Because of the serious side-effects reported with long term topical steroid usage — this method of “treating” undercorrection is not recommended. Additionally, the steroid itself may interfere with the healing process and negate any possible gain. Our experience with the use of steroids at 8 weeks in which the correction was consequently reduced leads us to believe that the hazards of the long term use of steroids far outweigh its possible benefits. Furthermore, it does not seem logical to induce a disease (glaucoma) in order to cure another (myopia).

Hudson-Stähli (iron) lines

These areas of small brownish pigment deposits are sometimes seen in the inferior aspect of the optic zone, and are due to pooling of tears admixed with various electrolytes — especially iron. [49, 71-73] They are less often seen with well irrigated incisions and do not appear to degrade vision. They do not progress but may be quite large. Such lines have been seen after other forms of refractive surgery as well. [74, 75]

Recurrent corneal erosions

Punctate Keratopathy

Punctate staining of the cornea along the incisions is seen in all cases in the immediate post- operative period. The staining pattern is linear and begins to disperse at 48-72 hours. Some clusters of punctate staining areas can be seen grouped near the inner ends of the incisions for as long as 14 days. Persistent punctate (non-dispersed) is associated with tearing, increased photophobia, a foreign body sensation and is self-limiting. This is not the same thing as recurrent erosion but can recur after many months have elapsed. (see also Recurrent Corneal Erosion, below).

Recurrent Corneal Erosion


Figure 6. Map-dot corneal dystrophy.

Epithelial defects associated with basement membrane disease — such as recurrent corneal erosion and map-fingerprint-dot changes — have been reported following RK. [30, 53] It is unclear what mechanism would account for the appearance of map-dot changes — the one case can be seen to exist between incisions. No note was made whether or not stripping of epithelium had occurred during surgery. As to the recurrent erosions, these are often associated with foreign material embedded in Bowman's layer — which probably explains why many respond to mechanical or chemical debridement. Some of the micro-wipes used in RK surgery are notorious for leaving behind particles of cellulose or other material. Perhaps such detritus is responsible for the incomplete detachment of the epithelium in these cases.

Perforation of the cornea during surgery

There are two types of perforation, micro in which only the very tip of the blade has entered the anterior chamber; and macro, in which the opening is a frank incision involving the anterior chamber. The latter occurs either because the incision is being made too rapidly when a thin spot or “dimple” is encountered or the micro-perforation went unnoticed and the incision was extended. These may occur initially at the edge of the optic zone with the first entry of the blade — in which case the blade was obviously set too long; or anywhere along an incision. The more likely spot for the latter event will be in the inferior-temporal quadrant where such dimples are frequently encountered. The most common place along the incision for this to occur is at the mid-periphery especially at the beginning of the second stepped incision in a multi-stepped incision case.

The incidence of surgical invasion of the anterior chamber in RK has been reported to vary from 6 to 33%.[17] The author has found the incidence to vary depending upon the blade used, the position on the learning curve for that blade the case was performed with and the degree of myopia present. The highest incidence of penetration in the author's series occurred with the use of Sputnik steel blades about one month after beginning the use of ultrasonic pachymetry. This was 23% and occurred because of the practice of oversetting the blade 10 to 15% in each case. It could also have been due to an erroneous setting for the speed of sound through the cornea. When the author switched to the use of the sapphire blade the incidence dipped to 8% after only a few months of trial and error adjustment of the blade depth to obtain the optimum settings.

Do not be quick to envy the surgeon whose reported perforation rate is low without examining his technique and results. It is a small thing to obtain a zero incidence of microperforation — simply set the blade too shallow. There are those who advocate just such an approach. [18] The problem with perforations is not the perforation itself, but the failure to accord sufficient significance to the puncture — it is a potentially serious invasion of the body's defenses. A small percentage of microperforation, however, is acceptable as an indication that the blade depth is close to optimum. The surgery works best with deep incisions and each surgeon should make the deepest incisions possible without incurring too great an incidence of perforation. In this authors opinion, an 8 to 10% incidence of micro-perforation is an acceptable incidence for the average surgeon. For the expert it could be slightly higher.

Figure 7. Suturing can have undesirable side effects.
Here a faint-hearted surgeon sutured without cause.
Note the gaping of adjacent wounds. Had this been left
alone irregular astigmatism would have resulted.

In cases of micro-perforation, pressure patching over-night is usually enough to allow the perforation to seal and the leak to stop. In most cases, the anterior chamber is of normal depth and absolutely quiet the following day. In those eyes that show a positive Seidel's (leakage demonstrated after topical fluorescein) repeat patching will solve the problem — in the majority of instances. The author has had to resort to use of a “bandage” contact lens in the face of persistent leak — twice, and sutures once, in over 20 years experience with this surgery.

A macro-perforation will announce itself by a sudden gush of aqueous and collapse of the anterior chamber. More than one suture may be needed to close such an incision. In rare cases such sutures may have to be left in place after the surgery. However, it is not recommended that they be left longer than one week. They should then be removed one at a time, allowing any subsequent leak to seal before removing another one. In no case should less than 24 hours elapse between removals.

Most of these perforations will seal-off spontaneously with a deep chamber forming within the first 24 hours. Attempting to re-inflate the anterior chamber using BSSTM or HealonTM (or other viscoelastic) is not recommended for the reason that there is a risk of introducing contamination. Further, there is a good possibility that this manipulation may cause the wound to leak even more. In addition, the risk of injuring internal structures is increased as well as the possibility of creating an epithelial ingrowth. If the leak is bad enough to require refilling the anterior chamber it is time to abort the case and possibly introduce sutures. Most of these perforation spots heal without excessive scarring. However, an occasional small area of sub-endothelial fibrosis may be seen. This process is, fortunately, self-limiting and only rarely interferes with vision.

This complication can be minimized by careful ultrasonic pachymetric “mapping” of the cornea; using ultra sharp blades that plunge and cut to a known setting; and precise blade setting. Gauges used to set blades should be checked with known standards to “calibrate” each one individually. An optical or shadowgraph gauge (such as the DGH-800) will help to reduce the incidence of such perforations.

It is recommended that all patients in whom perforations have occurred be started on oral broad spectrum antibiotics such as cephalosporin for a period of 5 to 7 days (see also Infections, in this section). If the chamber has been widely opened or if influx of fluid has occurred or is suspected (such as by seeing blood in the anterior chamber), it is advised that a sub-tenons injection of gentamycin (or equivalent) be done on the operating table at the close of the case.

Antibiotic drops should be used in all cases of actual or suspected corneal perforation in any event.

Corneal rupture


Figure 8. Ruptured radial incision. A half-axle fell onto the patient's eye.

Numerous cases of severe trauma occurring to eyes at various periods post-operatively, have been reported following RK. [54-62] One such case involved a direct hit from a racket ball in an eye one month post-surgery. The patient sustained a mild hyphema and a recession of the angle. [61] There was a transient decrease in visual acuity secondary to an associated corneal abrasion. No incisions were found to have opened and the anterior chamber remained full and deep with no evidence of leakage or secondary glaucoma.

On the other hand, a female patient one-and-one-half years post-RK, was thrown through the windshield of an automobile during an accident sustaining severe head trauma. The cornea of one eye was found to have ruptured along the 12 to 6 o'clock meridian in the incisions and ocular contents herniated anteriorly. Several of the other incisions were said to have been split as well. The eye was not lost but vision was reduced to Count Fingers. A similar case involved a male approximately one year post-RK. Again, the eye was not lost but vision was impaired.

Recently a case of a rupture following a blow from an elbow was reported; the eye was saved. The latest incident involved a case of the author's in which a macro-perforation had occurred during a re-operation and which required suturing. Approximately three months after suture removal, the patient was struck in the face by an automobile “half-axle” while repairing his car. The axle fell some 12 inches and struck the eye directly. In this instance the previously sutured (but currently unsutured) wound opened and the chamber collapsed. The patient sought consultation after three days only because of persistent irritation and mild tearing. The unaided visual acuity was 20/60, corrected to 20/20 on the initial visit. Re-suturing of the wound with re-positioning of the iris was accomplished with minimal trauma. The anterior chamber was clear and full by the next day. The patient retains good unaided vision to this day (20/25) and is correctable to 20/20. No lens complications have occurred in this patient to date — 7 years post-trauma.

Figure 9. Patient thrown through windshield. Note laceration running
through the RK incisions. None of these incisions opened.

Forstot and Damiano have reported 8 cases of ocular trauma following RK in 7 accident prone patients in their own practice; one patient got hit with a tennis ball — twice. All patients retained the same visual acuity post-trauma that they had pre-trauma. Only 2 of the 8 cases received direct injury which opened one incision in each case resulting in flat chambers. Both of these were 16 incision cases; only one incision opened at the site of a microperforation. In one of the other cases, the laceration was oblique to the RK incisions. [60]

Spivack reported a case in which a women had received severe facial trauma consequent to a plane crash in which the globes remained intact. [62] That these corneas may be vulnerable for some time is shown by the case reported by McDermott and colleagues. A woman suffered corneal rupture after trauma in an eye that had RK 10 years previously. [56]

Ocular injury accounts for a considerable number of accident cases each year. Visual loss occurs in an appalling number of these. It is obvious that RK does not necessarily predispose the patient to such a sad fate, however. Still, in both rupture cases described by Forstot, each occurred in eyes that had 16 incisions. Is this evidence that 16-incision eyes are more vulnerable than those with fewer incisions? Possibly, but both of these cases were in eyes injured within 1 year of the original surgery — one of them at 2 weeks. It is possible that while the shear strength of an eye which has had 16 incisions is less than one with 8 or fewer incisions, it is also true that such eyes tend to be easily distorted thus possibly absorbing the shock of trauma through that distortion.

At least one rupture has been reported following blunt trauma after HK. [63] Approximately 6 months post-HK the patient's left eye collided with a fist. Both nasal and temporal transverse incisions had opened. It was noted that incisions at the apices were joined (some overlapped). The patient never regained useful vision in the damaged eye.

Critics of RK have pointed to the work of Larson showing that eyes do not regain normal tensile strength even after 3 months and are prone to rupture along the incisions. [64] This study, while interesting, used rabbit eyes and each eye was subjected to repeated trauma until rupture occurred. Rabbits do not have a Bowman's layer in any event, which adds considerably to the integrity of the human cornea. Thus all we can conclude from this study is that rabbit eyes undergoing RK should not be exposed to repeated blunt trauma. Luttrull's study, on the other hand, is more significant. [65] The safety of deep corneal incisions in radial keratotomy was evaluated in a porcine model. All eyes were subjected to standard blunt trauma. Control eyes ruptured at the equatorial sclera. Eyes with radial incisions cut through approximately 70% of corneal thickness also ruptured at the equator. When incisions of this depth (70%) were extended across the limbus rather than stopping at the corneal-scleral junction, all ruptures occurred at the limbal portion of the incisions — which further reinforces our decision not to carry the incisions across the limbus. Eyes cut 95% to 100% of corneal thickness tended to rupture at the incisions as would be expected. However, this tendency in pig eyes does not explain the oblique lacerations in Forstot's cases nor does it explain an RK eye which received severe blunt trauma in which the resultant laceration crosses the RK incisions — none of which opened.

Patients in whom transverse incisions cross radials may be more vulnerable to such injury nonetheless. Karr, et al, reported persistent wound gape in a patient in a patient with just such an incisional pattern. [66] This patient's case was complicated by a sterile keratitis. Girard described a patient in whom the radials reopened 6 months post-operatively when a circumferential incision was made in an effort to correct post-operative astigmatism. [67]

All this means is that RK eyes may be vulnerable to trauma and patients should be cautioned. Still how to explain the author's patient who, 1 month after bilateral RK surgery, completed a free ocean descent with scuba equipment to a depth of 435 feet. Despite the enormous pressures to which he was subjected during the dive and the hours spent in the decompression chamber, he experienced only mild, transient blurring of vision upon surfacing. No evidence of ocular injury was found.

Retinal detachment

Only one case of this complication has been reported to date. In this case the patient had been placed on a strong miotic (phospholine iodide) post-operatively in an attempt to ameliorate an over- correction. [46] Strong miotics, particularly PI, have been implicated in numerous instances of retinal detachment in myopic patients and their usage in these cases is decried. [76-78] retinal detachments have not been recorded as being caused by mild miotics such as 1% pilocarpine.

Optic Atrophy and/or blindness

The use of retrobulbar anesthesia in this surgery has led, tragically, to acute optic atrophy in a number of cases. [79] In each instance, irretrievable visual loss has occurred. In at least three of these cases, penetration of the globe has been demonstrated.[80] The myopic eye, being long and thin, is much more vulnerable to this hazard than the older, shorter, cataractous eye. The use of this type of anesthesia, indiscriminately, has never been advocated in this surgery for the reason that it is fraught with known hazard and inappropriate to the situation. The fact that thousands of patients have had this surgery performed under topical anesthesia alone and under all sorts of differing conditions strengthens this viewpoint.

The author recognizes that there may be those occasions where the use of local, injectable anesthesia may be appropriate. In those rare instances, the surgeon is advised to use peri-bulbar anesthetic administration which has been put forward as an effective and less hazardous alternative to retrobulbar injection. The author would agree with this point of view but it is this author's strong recommendation that injectable anesthetics be avoided in these cases. In the unlikely event that such type of anesthesia must be used, the patient should look down toward the needle thus swinging the posterior pole away from the tip instead of toward it — which would be the case if the patients is instructed to look up as usual.

© Leo D. Bores, MD - 2002