Journal of Refractive Surgery

Review Supplemental Data

Phototherapeutic Keratectomy: Science and Art

Steven E. Wilson, MD; Gustavo K. Marino, MD; Carla S. Medeiros, MD; Marcony R. Santhiago, MD

Abstract

PURPOSE:

To describe, with videos, the principles of excimer laser phototherapeutic keratectomy (PTK) for the treatment of corneal scars, corneal surface irregularity, and recurrent corneal erosions.

METHODS:

Depending on the pathology in a treated cornea, the epithelium is removed either by transepithelial PTK ablation with the excimer laser or thorough scraping with a scalpel blade. Stromal PTK can be performed with or without photorefractive keratectomy (PRK), depending on the refractive status of both eyes. Residual surface irregularity is treated with masking-smoothing PTK. Typically, 0.02% mitomycin C treatment is applied for 30 seconds to corneas treated with PTK for scars and surface irregularity.

RESULTS:

Transepithelial PTK with masking-smoothing typically improves corrected distance visual acuity in the eye even if the entire stromal opacity cannot be removed and can be used to debulk surface irregularity to facilitate subsequent therapeutic customized wavefront-guided or optical coherence tomography-guided PTK or PRK. PTK for recurrent erosion is performed after thorough mechanical epithelial debridement of redundant epithelial basement membrane (EBM) with a scalpel and should only include a dusting of excimer laser to remove residual EBM without inducing central irregular astigmatism or damaging limbal tissues. Meta-analyses are provided for PTK treatment for corneal scars, corneal dystrophies, and recurrent corneal erosions.

CONCLUSIONS:

Excimer laser PTK is a highly effective treatment for superficial corneal scars, central corneal irregular astigmatism, and recurrent corneal erosions unresponsive to medical treatment or mechanical epithelial debridement alone.

[J Refract Surg. 2017;33(3):203–210.]

Abstract

PURPOSE:

To describe, with videos, the principles of excimer laser phototherapeutic keratectomy (PTK) for the treatment of corneal scars, corneal surface irregularity, and recurrent corneal erosions.

METHODS:

Depending on the pathology in a treated cornea, the epithelium is removed either by transepithelial PTK ablation with the excimer laser or thorough scraping with a scalpel blade. Stromal PTK can be performed with or without photorefractive keratectomy (PRK), depending on the refractive status of both eyes. Residual surface irregularity is treated with masking-smoothing PTK. Typically, 0.02% mitomycin C treatment is applied for 30 seconds to corneas treated with PTK for scars and surface irregularity.

RESULTS:

Transepithelial PTK with masking-smoothing typically improves corrected distance visual acuity in the eye even if the entire stromal opacity cannot be removed and can be used to debulk surface irregularity to facilitate subsequent therapeutic customized wavefront-guided or optical coherence tomography-guided PTK or PRK. PTK for recurrent erosion is performed after thorough mechanical epithelial debridement of redundant epithelial basement membrane (EBM) with a scalpel and should only include a dusting of excimer laser to remove residual EBM without inducing central irregular astigmatism or damaging limbal tissues. Meta-analyses are provided for PTK treatment for corneal scars, corneal dystrophies, and recurrent corneal erosions.

CONCLUSIONS:

Excimer laser PTK is a highly effective treatment for superficial corneal scars, central corneal irregular astigmatism, and recurrent corneal erosions unresponsive to medical treatment or mechanical epithelial debridement alone.

[J Refract Surg. 2017;33(3):203–210.]

The U.S. Food and Drug Administration approved phototherapeutic keratectomy (PTK) in 1995 for use in removal of corneal scars or to treat recurrent corneal erosion. The excimer lasers used clinically employ 193-nm wavelength ultraviolet light to break apart molecular bonds in tissue in a low-heat–generating process termed “photoablation.” Although it is possible to use a “small spot” excimer laser such as the Allegretto WaveLight (Alcon Laboratories, Inc., Fort Worth, TX) laser for tissue removal PTK, some components of treatment, such as PTK masking-smoothing, are best performed with a “broad beam” laser such as the VISX S4 IR (Abbott Medical Optics, Santa Ana, CA) with a treatment diameter from 6 to 6.5 mm.

PTK can be applied to a wide range of corneal pathologies, including anterior scar removal after injury, infection, disease, or surgery, smoothing the corneal surface in eyes with stromal dystrophies or after trauma or surgical complications, or to remove redundant epithelial basement membrane in eyes with recurrent corneal erosions.1–3 There are also some situations where PTK can be applied to temporize patients with bullous keratopathy and other corneal diseases. Thus, this procedure can effectively treat many disorders that would otherwise require manual keratectomy or lamellar or full-thickness corneal transplantation. In our experience, PTK tends to be underused as an optimal treatment for many of these corneal pathologies and surgeons frequently perform a more invasive lamellar or full-thickness corneal transplant when the disorder could have been effectively treated with PTK. It is our hope that this review, along with selected videos, will encourage ophthalmologists to more frequently consider PTK as an option for patients with corneal pathology.

General Principles

When planning and performing PTK surgery, it is critical to have an overall understanding of the effects of the excimer laser on corneal tissue and the refractive status of the eye. These principles will be focused on the use of broad-beam excimer lasers that are optimal for masking-smoothing treatments for corneal scars and irregularities, but scanning-spot or scanning-slit excimer lasers can also be used (Tables AB, available in the online version of this article).


Phototherapeutic Keratectomy for Corneal Scars

Table A:

Phototherapeutic Keratectomy for Corneal Scars


Phototherapeutic Keratectomy for Corneal Dystrophies

Table B:

Phototherapeutic Keratectomy for Corneal Dystrophies

The first helpful guideline for broad-beam excimer lasers is that each pulse of the excimer laser removes approximately 0.25 µm of normal corneal stromal tissue over the ablated zone. Removal varies somewhat between epithelial tissue and stromal tissue, as well as between normal stroma and scarred stroma, but usually these variations minimally affect treatments. The second helpful guideline is that 50 pulses of broad beam excimer laser applied to the stroma produce approximately 1.00 diopter (D) of hyperopic shift in the refractive error of the eye. These guidelines can be used to estimate the number of pulses required to remove a scar and the amount of refractive shift expected from the procedure so that, when necessary, a compensating photorefractive keratectomy (PRK) can be added to optimize the visual outcome of a procedure. Removal of a corneal scar while inducing 5.00 D of hyperopia is often not perceived as a helpful treatment by a patient.

The stromal depth of a scar can be measured with optical coherence tomography (OCT) or estimated at the slit lamp or with an optical pachymeter. Importantly, it is frequently not necessary to completely remove a scar to obtain a substantial improvement in vision, especially when surface irregularity is an important contributor to the decreased vision. Thus, when a deep corneal scar is present, we frequently aim for a final corneal thickness of 400 µm to limit the risk of ectasia while removing a large percentage of the opacity—knowing we could repeat the PTK later if the improvement in vision is insufficient.

Once the surgeon decides what depth PTK will be performed, the resulting expected refractive change can be estimated and used to plan the detailed procedure. For example, if an eye has 9.00 D of myopia and a 100-µm depth scar is to be removed, it can be estimated that 400 pulses of excimer laser must be applied to the stroma and the eye will likely end up with approximately 1.00 D of myopia (induced change of 8.00 D of hyperopic shift). Therefore, in this eye no additional PRK treatment would be applied during the surgery to compensate for the hyperopic shift, although issues with anisometropia may be present after surgery, depending on the refractive status of the opposite eye. Conversely, if the same eye is estimated to have 2.00 D of myopia prior to PTK, then the surgeon can anticipate that the eye will end up with approximately 6.00 D of hyperopia unless PRK treatment for hyperopia is applied during the procedure. We typically do not apply more than 5.00 D of hyperopic PRK treatment during a primary PTK surgery because of the clinically significant optical aberrations commonly produced by such a high hyperopic correction. Sometimes the refractive status of an eye with a corneal scar can only be estimated from that of a normal opposite eye or from medical records. Thus, this is frequently only an approximation, but a useful one so that the patient is prepared for the outcome of PTK and can anticipate that a secondary procedure may be needed later.

Another approach that can be taken is to do the PTK alone, see where the refractive error ends up, and then, in a secondary procedure 3 to 6 months later, apply PRK to correct the residual refractive error, including astigmatism. We often use the latter approach in cases where there is limited predictability due to the extent of pathology. Corneas with severe irregularity that precludes accurate topographic analysis can often have the irregularity “debulked” with traditional PTK followed months later by topography-guided PTK, OCT-guided PTK, or very high-frequency digital ultrasound-guided PTK.4–8 Topography-guided, OCT-guided, or very high-frequency digital ultrasound-guided treatments themselves are beyond the scope of this review, but have been covered in other publications and are included in the meta-analysis in Tables AB.4–8 In cases where there is better predictability, and our initial planning suggests the eye will end up with at least 2.00 D of hyperopia, we often apply compensatory hyperopic PRK correction up to 5.00 D maximum during the primary PTK procedure to improve function—knowing that further treatment in the form of additional PTK or PRK, including topography- or OCT-guided PTK or PRK, may be needed later. We typically wait a minimum of 6 months between PTK or PRK procedures to allow the refractive error of the eye to stabilize. This waiting period usually ensures that the wound healing response from the first procedure is completed before the second procedure is performed.

A third important principle of PTK is to use the corneal epithelium as an initial masking agent when treating corneas with irregular astigmatism, with or without significant stromal scarring. Usually, stromal surface irregularity is at least partially masked by hyperplasia and/or hypertrophy of the epithelium and, therefore, manual removal of the epithelium with a scalpel or ethanol prior to PTK will yield an even more irregular surface. Therefore, transepithelial PTK combined with PTK masking-smoothing is often used in these cases.

Transepithelial PTK is performed by drying the epithelial surface with a surgical sponge and applying 6- to 6.5-mm diameter PTK under dim illumination, usually with the pupil tracker engaged. The epithelium fluoresces cobalt blue while being ablated with a broad-beam excimer laser and a transition to black is noted where the ablation reaches the underlying stroma (Video 1, available in the online version of this article). This transition to black is typically spotty in scarred corneas such that some areas within the ablation zone transition to black, whereas others are blue and additional PTK must be applied before all epithelium is removed from the ablated zone—especially where there has been stromal retraction within a scar. Thus, the surgeon monitors the ablation until the epithelium has been completely removed in the ablated zone and then continues the stromal ablation to the planned depth.

In corneas where there is significant irregular astigmatism, masking-smoothing is the next component of the overall PTK treatment performed after transepithelial ablation (Video 2, available in the online version of this article). The use of masking agents to facilitate PTK for corneal irregularity was first described in 1991.25 Masking agents should have ablation characteristics similar to corneal stromal tissue to be most effective as an adjuvant to PTK. The masking agent that is frequently used for this component of PTK is 1% carboxymethylcellulose, although some surgeons prefer to use 1 mg/mL sodium hyaluronate solution (prepared by sterile dilution of Healon [Pharmacia AB, Uppsala, Sweden]) to 10% with balanced salt solution (BSS; sterile physiological balanced salt solution of 0.64% sodium chloride, 0.075% potassium chloride, 0.048% calcium chloride, 0.03% magnesium chloride, 0.39% sodium acetate, 0.17% sodium citrate, pH 7.4; Alcon Laboratories, Inc., Fort Worth, TX) because it is thought to have ablation characteristics that are most similar to human corneal stroma. Two drops of the masking agent are applied and distributed over the zone of ablation with a Barraquer iris spatula (example, Asico, Westmont, IL, Cat. # AE-2049). PTK excimer laser pulses 6.5 mm in diameter are then delivered onto the masking agent and stromal surface while the Barraquer iris spatula is rapidly and repeatedly slid back and forth completely across the stromal surface of the ablation zone (Video 2).

Typically, we deliver 100 to 200 pulses of excimer laser during this portion of the treatment. Note that most of this ablation is delivered to the masking agent, not the stromal surface, except that peaks of irregularity protruding through the masking agent with each passage of the spatula are progressively reduced (Figure 1). Thus, there is typically little change in the overall refractive error of the eye induced by this portion of the treatment. When done properly, this treatment maneuver markedly reduces surface irregularities within the ablated zone and the surface becomes notably smoother as observed by the surgeon through the operating microscope of the excimer laser once the masking agent is irrigated away. If the surgeon deems the smoothing to be insufficient once the smoothing agent is removed by irrigation with BSS, he or she can immediately repeat the masking-smoothing step in the same manner. Trainees can perfect this method on enucleated pig eyes by scraping away the epithelium with a scalpel and then performing PTK over a fine mesh screen to imprint irregularity on the stromal surface before removing this irregularity completely using the masking-smoothing PTK method.


Schematic of masking-smoothing phototherapeutic keratectomy ablation of irregularity. Note that the masking agent fills and protects depressions from excimer laser ablation while the peaks of irregularity are exposed to the excimer laser beam with each passage of the iris spatula across the ablated zone.

Figure 1.

Schematic of masking-smoothing phototherapeutic keratectomy ablation of irregularity. Note that the masking agent fills and protects depressions from excimer laser ablation while the peaks of irregularity are exposed to the excimer laser beam with each passage of the iris spatula across the ablated zone.

If PRK is to be added to reduce induced hyperopia after the transepithelial PTK followed by masking-smoothing PTK, then the surrounding epithelium is expeditiously removed with a scalpel to yield a 9-mm zone for application of the PRK. Delays should be avoided during the overall PTK or PRK procedure by expeditiously proceeding through the steps to avoid unpredictable changes that can be produced by stromal desiccation—resulting in more tissue removal per pulse of the laser than expected.

The final step in any PTK procedure, with or without masking-smoothing PTK and/or PRK, is treatment with 0.02% mitomycin C for 30 seconds.26 In our experience, extending the exposure time to mitomycin C beyond 30 seconds does not improve the efficacy of this treatment in preventing haze.

If possible, we strive to complete all of the steps of PTK in a particular cornea without reducing the total central corneal thickness to less than 400 µm to try to limit the chances of developing ectasia in a treated cornea. However, in 27 eyes that would otherwise require penetrating keratoplasty, we have reduced total corneal thickness to as low as 250 to 300 µm without the development of ectasia in any of these eyes with more than 5 years of follow-up (Wilson SE, unpublished data, 2013).

Corneal Opacity Removal with PTK

Corneal opacities can result from injury, infection, inflammatory disorders, surgery, dystrophies, riboflavin-ultraviolet cross-linking, and many other etiologies. Separate tables have been provided for meta-analysis for corneal scars (Table A) and corneal stromal dystrophies (Table B) because of differences in the magnitude and extent of irregularity and the potential for recurrence of the stromal dystrophies.27–29 PTK optimally addresses opacity in approximately the anterior 100 to 150 µm of the cornea. This limitation is related to potential for inducing iatrogenic ectasia and induced hyperopic shift that can interfere with visual function despite removal of opacity. Importantly, significant improvement in visual performance can be obtained in many eyes without removing all of the corneal stromal opacity in a particular cornea. Also, in many cases of stromal opacity there is also associated surface irregularity that must be addressed by the masking-smoothing PTK step to achieve the best possible outcome. Importantly, any infectious or disease-related inflammation should be resolved for a period of several months before PTK is performed.

PTK with mitomycin C can be used to address opacity (late haze, Figure 2) occurring after PRK.30 However, in our experience, it is best to wait at least 1 year after the initial PRK procedure to perform PTK because many cases of PRK-associated haze—even though severe—spontaneously resolve over time and, when they do, the refractive state of the eye often returns nearly to the intended correction. Spontaneous regression of late haze is especially likely to occur if mitomycin C was NOT used at the time of the initial PRK procedure. We have termed late haze that occurs after PRK despite the use of mitomycin C during the initial PRK surgery31 “breakthrough haze” and, in our experience, there is less tendency for this type of haze to spontaneously resolve—likely due to mitomycin C–related diminished anterior stromal density of keratocytes that function to both provide critical components to regenerate the defective epithelial basement membrane (EBM) associated with late haze and remove disordered extracellular matrix produced by myofibroblasts once these fibrosis-associated cells undergo apoptosis.31–33 Also, it is best to wait to see whether spontaneous resolution of late haze occurs because, in some cases, PTK worsens the severity of recurrent late haze despite the use of mitomycin C during the PTK procedure. It is our approach to re-treat the cornea with mitomycin C even if the patient developed haze after PRK with mitomycin C treatment as the original procedure.


Late haze developed 3 months after photorefractive keratectomy for −9.00 diopters of myopia without the use of mitomycin C.

Figure 2.

Late haze developed 3 months after photorefractive keratectomy for −9.00 diopters of myopia without the use of mitomycin C.

It follows that in any cornea treated for stromal opacity with PTK, including late haze after PRK, it is important to use the masking-smoothing step in the procedure to facilitate regeneration of the EBM over the smooth corneal surface. Abnormal EBM regeneration associated with stromal irregularity is a major factor leading to the development of myofibroblasts34 and recurrence of opacity because of ongoing penetration of epithelium-derived cytokines such as transforming growth factor beta through defective EBM.31–33 In many cases of corneal opacity due to microbial infections, including herpes simplex keratitis, there is associated irregularity of the stromal surface at the site of the prior infection that is discovered if the corneal epithelium is removed manually with a scalpel. This corneal surface irregularity not only decreases vision directly, but can also trigger increased haze development following PTK. For this reason, it is usually recommended in these cases that the initial PTK procedure be performed by a transepithelial approach prior to the masking-smoothing maneuver.

PTK for scars resulting from herpes simplex virus keratitis are a special case due to the likelihood of recurrent herpes simplex virus early or late after surgery. Ultraviolet light such as that emitted by the excimer laser can reactivate herpes simplex virus infection.35 Thus, we recommend prophylactic anti-viral treatment beginning at least 1 week prior to PTK and continuing anti-viral treatment indefinitely after surgery in any case of corneal opacity thought to be related to herpes simplex virus.

When PTK is used for corneal dystrophies with opacity confined primarily to the anterior stroma, such as Reis–Buckler dystrophy (Table B), that may have associated recurrent corneal erosion and anterior stromal surface irregularity, we recommend performing PTK by a transepithelial approach followed by masking-smoothing PTK. Typically, it is not necessary or helpful to remove more than 50 to 100 µm of anterior stromal tissue to markedly improve vision as long as the stromal surface is smooth at the end of the treatment. Unfortunately, most of these cases will suffer a recurrence of the opacity over the ensuing 2 to 5 years, but the PTK treatment can often be repeated to improve vision and reduce recurrent corneal erosions.

PTK/PRK for Buttonhole LASIK Flaps, Irregular LASIK Flaps, or Stromal Intrusions in Epi-LASIK

Another special case where PTK can be highly useful is in the treatment of buttonhole (donut-shaped) LASIK flaps, partial LASIK flaps, and stromal intrusions in epithelial LASIK (epi-LASIK). In LASIK, this complication is usually associated with the use of microkeratomes and has been rarely reported with femtosecond lasers.36–39 When these complications are noted at the time of LASIK or epi-LASIK, it is important that the surgeon replace the flap or stromal tissue fragment without performing excimer laser ablation on the day of the initial surgery. Some have advocated repeating the LASIK or epi-LASIK procedure several months later.40 Unfortunately, however, there can be an even more severe flap or epi-LASIK complication at the follow-up procedure because many of these eyes have undetected predisposing anatomical abnormalities.41 Also, many of these eyes develop clinically significant patchy haze due to resulting irregularity of the corneal surface at the site of stromal penetration (resulting from interference with full regeneration of the EBM) and/or epithelial ingrowth at the site of stromal penetration. We advocated early transepithelial PTK/PRK treatment to avoid both of these potentially severe complications.36 Our approach is to replace the corneal tissue without excimer laser ablation, protect the surface with a bandage contact lens, and then proceed with PTK or PRK as soon as the epithelium repairs to the point the corrected distance visual acuity returns close to the preoperative value in 1 to 2 weeks after the initial complication—allowing time for the regenerating epithelium to smooth over most of the surface irregularity produced by the LASIK or epi-LASIK complication. This treatment is always done transepithelial with a masking-smoothing step and the use of mitomycin C. It is critical that the ablation completely removes the interface from the original complicated LASIK or epi-LASIK procedure in the central cornea or severe haze is likely to result due to augmented keratocyte apoptosis and an increased late wound healing response with generation of large numbers of myofibroblasts.41

The advantage of early treatment in these cases is not only faster visual recovery for the patient but also complete removal of the buttonhole (donut-shaped) flap or intrusion (that are typically thin) prior to the development of corneal scarring and epithelial ingrowth that locally alter excimer laser ablation properties that can therefore induce irregular astigmatism.41 This is why, contrary to what others have recommended,38 we typically do not wait more than 2 weeks to proceed with this follow-up treatment. Conversely, performing excimer laser ablation on the irregular epithelial surface immediately after the complicated LASIK or epi-LASIK procedure39 runs the risk of imprinting irregularity on the stroma to a degree it is not easily removed later with a PTK masking-smoothing treatment.

Whether transepithelial PTK or PRK with PTK masking-smoothing is used to treat LASIK buttonhole flaps or epi-LASIK complications depends on the refractive status of the eye prior to the initial surgery. If the eye had moderate to high myopia, then we typically perform transepithelial PRK (the epithelium is still ablated with PTK until the cobalt blue of the epithelium ablation transitions fully to black of the stromal ablation) aiming to correct approximately 80% of the original refractive error. If the eye has less than 3.00 D of myopia or has hyperopia, then we use PTK and decide whether PRK for hyperopia should also be included in this initial treatment to limit anisometropia—depending on the refractive status of the opposite eye. Whichever approach is used, PRK with mitomycin C can be used 6 or more months later to address the residual refractive error in the eye. Care should be taken not to excessively flatten or steepen the cornea to the point that vision quality is compromised. Many surgeons aim not to steepen greater than 48.00 to 49.00 D nor flatten to less than 34.00 D, although these are only guidelines and some eyes with corneas outside these limits have been noted by the authors to have good visual outcomes.

PTK for Central Islands, Peninsulas, or Decentered Refractive Ablations

PTK can be a useful treatment for topographic central islands, peninsulas, or decentration occurring after PRK or LASIK.42 The use of traditional PTK can often at least reduce the level of surface irregularity associated with each of these complications and improve corrected distance visual acuity and decrease complications such as distortion, multiple images, glare, or halos. In some cases, imaging modalities such as corneal OCT or topography can be used to design customized treatments to address some of these problems. For example, if OCT shows that a central island is approximately 2.5 mm in diameter and has approximately 30 µm of elevation, PTK with an ablation diameter of 2.5 mm can be applied to treat the central island followed by the application of mitomycin C. However, as the irregularity increases in topographic peninsulas and decentrations, it becomes increasingly more difficult to successfully apply traditional PTK methods and there is a high risk the situation will only be worsened. In such cases, treatment is likely to be more successful with topography-guided PTK, OCT-guided PTK, or very high-frequency digital ultrasound-guided PTK.4–8

PTK for Salzmann's Nodular Degeneration

PTK performed in corneas with Salzmann's nodular degeneration is also a special case. We do not recommend PTK of the nodules themselves because this degree of irregularity is almost impossible to remove even with aggressive masking-smoothing PTK. Also, residual fibrous tissue provides fibroblastic progenitor cells to re-accumulate and extend the Salzmann's fibrous tissue. Usually, after the overlying corneal epithelium has been removed with a scalpel, the Salzmann's nodules themselves can be easily stripped from the cornea with 0.12-mm forceps because there is a plane between the fibrotic tissue and the underlying Bowman's layer/corneal stroma (Video 3, available in the online version of this article). This plane is found by teasing at the edge of the fibrous elevations with the forceps, grasping the superficial fibrotic tissue, and firmly stripping the tissue en block off the corneal surface. In our experience, it is rarely necessary to use a lamellar dissecting scalpel to remove nodules43,44 where no plane is detected beneath the fibrous tissue. When dissection with a blade is necessary, much more surface irregularity is usually produced and should be treated with masking-smoothing PTK to improve surface smoothness and corrected vision. Once the nodules are removed mechanically, masking-smoothing PTK can be used to polish the central cornea overlying the entrance pupil to improve corrected vision. Mitomycin C (0.02%) treatment is typically applied for 30 seconds to the central cornea while sparing 1.5 mm at the limbus. In our experience, this treatment seems to help retard recurrence of the Salzmann's nodules.

PTK for Recurrent Corneal Erosions

PTK is highly effective in treating recurrent corneal erosions that are recalcitrant to medical treatment or mechanical epithelial debridement with a scalpel (Table C, available in the online version of this article). When PTK is used for this disorder, it is important to realize that the objective of surgery is to remove any remnants of redundant EBM, associated with poor adherence of the corneal epithelium to the underlying stroma, that remain after thorough debridement of the epithelium and underlying basement membrane with a scalpel.58 Thus, unless there is associated stromal haze, the PTK treatment should be limited to only a small number of pulses (typically 8 to 10 pulses) to each location on the exposed stromal surface after thorough epithelial debridement. In this way, refractive shifts can be avoided.


Phototherapeutic Keratectomy for Recurrent Erosions

Table C:

Phototherapeutic Keratectomy for Recurrent Erosions

It is often possible to perform a localized treatment of the stromal surface in cases where the recurrent corneal erosion is due to corneal injury without associated epithelial basement membrane dystrophy. Thus, if epithelial defects are always located in the same position on the corneal surface, then treatment with epithelial debridement and localized PTK of approximately 10 pulses can be performed.

Frequently, however, especially in eyes with corneal epithelial basement membrane dystrophy, recurrent erosions either are not seen during examination or recurrences are noted in several locations in the same cornea. In this case, we prefer to treat the entire corneal surface, sparing 1 mm at the limbus (Video 4, available in the online version of this article). Thus, epithelial debridement can be performed over the entire corneal surface up to 1 mm within the limbus with a 6400 Mini-Blade (Beaver-Visitec International, Inc., Waltham, MA). Care should be taken to remove all redundant EBM to expose the smooth underlying Bowman's layer. Then, approximately 10 pulses of 6.5-mm diameter excimer laser are delivered centered overlying the entrance pupil so that clinically significant central irregular astigmatism is not induced. The remainder of the exposed stroma is also treated with 10 pulses of excimer laser. This can be done by reducing the diameter of the excimer laser beam to 2 to 3 mm, disengaging the tracker, and moving around the peripheral cornea with the smaller beam either by using the joystick or moving the patient's head (Video 4). Alternatively, especially for less experienced surgeons, a 6.5-mm mask for the central cornea and a peripheral mask for the limbus can be cut from sterile drape and placed in position to protect these areas during ablation. Then, the large diameter beam is painted around the peripheral stroma so that approximately 8 to 10 pulses of excimer laser are applied to each area of the peripheral cornea by moving the joystick or the patient's head in a circular path. Mitomycin C is typically not needed for PTK performed purely for recurrent erosions because the stromal ablation depth is minimal.

It is important to consider that it usually takes 1 to 2 weeks for the corneal epithelial basement membrane and anchoring fibrils to fully regenerate after epithelial debridement or excimer laser ablation (Marino GK and Wilson SE, unpublished data, 2015).31,32 Therefore, after PTK for recurrent corneal erosions, our preference is to retain the bandage contact lens for 3 weeks after the procedure to prevent adhesion of the tarsal conjunctiva to the corneal surface and recurrence of erosions. Prophylactic antibiotic treatment is continued during this time. After removal of the bandage contact lens, the patient should also continue non-preserved ointment in the eye at bedtime for at least several months after surgery to limit adhesion of the tarsal conjunctival epithelium of the eyelid to the newly regenerated epithelial surface.

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Phototherapeutic Keratectomy for Corneal Scars

AuthorJournalYearCountryDiseasesnExcimer Laser% Success
Rush et al.6Am J Ophthalmol2013USAHK (9), BK (9), T (2), U (2)22Allegretto WaveLight100%
Rashad9Clin Ophthalmol2012EgyptK (5), CD (2), PPt (1), U (5)11Allegretto WaveLight100%
Arfaj et al.10Ophthalmol Eye Dis2011USAK, CB, PPt, CD, PP28VISX85.7%
Hafner et al.11Ophthalmologe2004GermanyHK, PPt, T, AK31MEL 6087%
Dogru et al.12Eye (Lond)2000JapanHK, T, K, U14EC-500043.2%
Rao et al.13Indian J Ophthalmol1999IndiaHK, CD, T, PPt, K11Summit57.1%
Migden et al.14Ophthalmic Surg Lasers1996USAT, K2239%
Badr et al.15J Refract Surg1996Saudi ArabiasCDK, iCDK75SummitsCDK (61.8%), iCDK (21.2%)

Phototherapeutic Keratectomy for Corneal Dystrophies

AuthorJournalYearCountryDiseasesnExcimer Laser% SuccessCDVA Change
Reddy et al.16Am J Ophthalmol2013USAGD (19), MCD (2), SCD (1)22VISX50%0.46 to 0.16
Hieda et al.17Am J Ophthalmol2013JapanTB10EC-500050%0.57 to 0.04
Arfaj et al.10Ophthalmol Eye Dis2011USAGD (10), LD (2), FD (1), AD (1), MDF (9)21VISX85.95%0.2 to 0.1
Gruenauer-Kloevekorn et al.24Graefes Arch Clin Exp Ophthalmol2009GermanyTGFBI20Technolas 217100%0.4 to 0.18
Pogorelov et al.18Cornea2006GermanyMDF15MEL 60/700.9 to 0.7
Hafner et al.19Am J Ophthalmol2005GermanyMCD10MEL 6010%0.3 to 0.6
Stewart et al.20Eye (Lond)2002UKMDF (9), RBD (8), LD (5), GD (5), FD (2)29Technolas 11682.75%0.4 to 0.2
Dogru et al.Ophthalmology2001JapanGD, AD5EC-50000%0.58 to 0.15
Paparo et al.22Cornea2000USASCD4VISX100%1.0 to 0.3
Dinh et al.23Ophthalmology1999USAMDF, RBD, GD, LD, SCD43VISXMDF (50%), RBD (55.5%), GD (45.4%), LD (100%), SCD (100%)0.5 to 0.18

Phototherapeutic Keratectomy for Recurrent Erosions

AuthorJournalYearCountryDiseases or InjurynExcimer Laser% Success
Mehlan et al.45Graefes Arch Clin Exp Ophthalmol2016GermanyT, EBMD48Allegretto93.7%
Dedes et al.46Graefes Arch Clin Exp Ophthalmol2015GermanyT, EBMD, U89Technolas 21772%
Chan et al.47Br J Ophthalmol2014AustraliaT, EBMD, U16Zyoptix62.5%
Eschstruth et al.48Ophthalmologe2006GermanyT, EBMD5094%
Chow et al.49J Cataract Refract Surg2005ChinaT, EBMD13Schwind84.6%
Sridhar et al.50Ophthalmology2002USAEBMD42VISX73.3%
Giessler & Duncker51Ophthalmologe2001GermanyT45Technolas 21791.1%
Rashad et al.52J Refract Surg2001EgyptRecurrent corneal erosion43Technolas 117C90.7%
Cavanaugh et al.53Ophthalmology1999USAEBMD48Summit86.2%
Orndahl et al.54Cornea1998SwedenEBMD3090%
Morad et al.55J Cataract Refract Surg1998IsraelU (39%), T (35%), EBMD (17,4%), ECS (4.3%), DE (4,3%)23MEL 7083%
Forster et al.56Graefes Arch Clin Exp Ophthalmol1997HungaryT, U103Schwind91%
O'Brart et al.57Eye (Lond)1994UKT (52.9%), U (47,1%)17Summit76.4%
Authors

From Cole Eye Institute, The Cleveland Clinic, Cleveland, Ohio (SEW, GKM, CSM); and the University of São Paulo, São Paulo, Brazil (GKM, MRS).

Supported in part by a departmental grant from Research to Prevent Blindness, Inc., New York, New York.

Dr. Wilson has been a trainer for the Abbott VISX. The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (SEW, MRS); data collection (SEW, GKM, CSM); analysis and interpretation of data (SEW, GKM, CSM); writing the manuscript (SEW, GKM, MRS); critical revision of the manuscript (CSM, MRS); statistical expertise (SEW, GKM, MRS); administrative, technical, or material support (SEW, GKM); supervision (SEW, MRS)

Correspondence: Steven E. Wilson, MD; Cole Eye Institute, i-32, The Cleveland Clinic, 9500 Euclid Ave., Cleveland, OH 44195. E-mail: wilsons4@ccf.org

Received: July 18, 2016
Accepted: October 31, 2016

10.3928/1081597X-20161123-01

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