- Email: [email protected]
Optical Coherence Tomography–Guided Transepithelial Phototherapeutic Keratectomy for the Treatment of Anterior Corneal Scarring
Optical Coherence Tomography–Guided Transepithelial Phototherapeutic Keratectomy for the Treatment of Anterior Corneal Scarring SLOAN W. RUSH, DEREK Y. HAN, AND RYAN B. RUSH PURPOSE: To report the visual and anatomic outcomes of a novel technique for the management of anterior corneal scarring using optical coherence tomography (OCT)–guided transepithelial phototherapeutic keratectomy (transepithelial PTK). DESIGN: Retrospective, consecutive case series. METHODS: The charts of 22 patients with anterior corneal scarring associated with irregularities in the Bowman layer who had undergone transepithelial PTK according to a novel protocol were reviewed. The protocol consisted of a preoperative OCT-measured depth-of-treatment calculation, followed by a dual excimer laser treatment profile set to achieve the desired refractive outcome while eliminating or reducing corneal scarring. The primary outcomes were change in best spectacle-corrected visual acuity (BSCVA) and change in corneal topography indices at 4 months after ablation. RESULTS: BSCVA (in logMAR) improved from a mean of 0.82 (0.61–1.02; 95% confidence interval) preoperatively to a mean of 0.40 postoperatively (0.19–0.61) (P [ 0.0070). All patients gained a minimum of 1 line of BSCVA postoperatively. Preoperative and postoperative corneal topographic indices showed significant improvement in corneal cylinder (P [ 0.0173) and projected visual acuity (P [ 0.0261) but not in the surface asymmetry index (P [ 0.0849) or the surface regularity index (P [ 0.0543). Postoperative spherical equivalent averaged 0.78 diopters (0.49–1.07) of error from the intended target refractive outcome. No complications were associated with the treatment, and no patients required or desired subsequent treatment with either repeat PTK or with more invasive surgery such as lamellar or penetrating keratoplasty. CONCLUSIONS: OCT-guided transepithelial PTK using a dual ablation excimer laser profile can provide favorable results as well as predictable refractive outcomes in the treatment of corneal scarring associated with Bowman layer irregularities. Future investigations
Accepted for publication Jun 17, 2013. From the Panhandle Eye Group, Amarillo, Texas (S.W.R., R.B.R.); the Texas Tech University Health Science Center, Amarillo, Texas (D.Y.H.); and the Southwest Retina Specialists, Amarillo, Texas (R.B.R.). Inquiries to Ryan Rush, Southwest Retina Specialists, 7411 Wallace Boulevard, Amarillo, TX 79106; e-mail: Ryanbradfordrush21@hotmail. com
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are warranted to further validate the technique reported in this study. (Am J Ophthalmol 2013;156:1088–1094. Ó 2013 by Elsevier Inc. All rights reserved.)
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HOTOTHERAPEUTIC KERATECTOMY (PTK) IS A SAFE
and efficacious modality for the treatment of opacities localized to more than one third of the superficial corneal stroma.1–3 In cases with irregular corneal surfaces, PTK may also enhance the cornea’s optical qualities and improve vision by smoothing the irregular corneal surface4,5 as well as avoiding the need for more invasive surgery such as lamellar6 or penetrating keratoplasty.7 Recently, new technologies, such as the Pentacam device (Oculus, Lynnwood, Washington, USA)8 and anterior segment optical coherence tomography (OCT) (Carl Zeiss Meditec, Dublin, California, USA),9 have improved preoperative prediction of the depth of corneal pathology and have determined more accurately the amount of corneal tissue to be removed during PTK. Transepithelial PTK is a technique in which PTK is performed without the manual removal of the epithelium by superficial keratectomy but instead uses the excimer laser to photoablate the epithelial layer, which serves as a natural masking agent. Transepithelial PTK has been used to treat recurrent erosions,10,11 laser in-situ keratomileusis (LASIK) flap macrostriae,12 keratoconus (in combination with corneal collagen crosslinking),13 corneal stromal dystrophies14,15 and, more recently, corneal scarring.16 In cases with anterior corneal scarring or irregularities in the Bowman layer, OCT may provide useful clinical information that helps to determine the appropriate depth of ablation during transepithelial PTK.17 While conventional epithelium-off PTK for anterior corneal scarring is being performed, intraoperative findings may reveal a visible ‘‘crater’’ or ‘‘divot’’ in the Bowman layer. Once the epithelium has been removed and a Bowman irregularity has been revealed, the laser ablation profile will transmit these subtle and focal irregularities down to a deeper level in the stroma, and they will persist to some degree once the cornea re-epithelializes. To mitigate against this problem, investigators have tried using various masking agents (eg, artificial tears or surgical sponges) to fill in or cover the irregular defect in order to provide for a more uniformly distributed ablation profile.18–21
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0002-9394/$36.00 http://dx.doi.org/10.1016/j.ajo.2013.06.026
With the advent of OCT technology, clinicians now have the ability to determine preoperatively which patients are likely to develop intraoperative craters in the Bowman layer if traditional epithelium-off PTK is performed. In these cases, the authors hypothesize that the epithelium itself may act as an effective masking agent and allow for a more even distribution of the ablation pattern if preserved. This could result in lower amounts of postoperative irregular astigmatism by avoiding the propagation of the Bowman layer irregularities to a deeper level in the corneal stroma. In this study, the authors describe a novel technique that uses OCT imaging of the central cornea to guide a transepithelial excimer laser ablation algorithm in order to treat anterior corneal scars associated with an irregular Bowman layer, all while maintaining and controlling for refractive outcomes.
METHODS THE SOUTHWEST RETINA SPECIALISTS INSTITUTIONAL
review board (IORG0007600/IRB00009122) approved this retrospective chart review of consecutive cases in patients who underwent OCT-guided transepithelial PTK for anterior corneal scarring between January 2011 and February 2013. All research components adhered to the tenets of the Declaration of Helsinki and were conducted in accordance with human-subject research regulations and standards. INCLUSION CRITERIA:
Subjects included in the study had undergone complete ophthalmologic examinations and had undergone OCT-guided transepithelial PTK for central corneal scarring that was associated with a significantly irregular Bowman layer. A significantly irregular Bowman layer was defined as follows: spectral domain OCT (Cirrus HD-OCT; Carl Zeiss Meditec, Dublin, California, USA) of the central 3 mm of cornea (1) exhibited a hyperintense signal that corresponded with scarring on clinical examination and (2) was associated with a variation in epithelial thickness by a minimum of a 33% increase from the baseline epithelial thickness, thus giving it the appearance of a crater or a divot scar (Figure 1).
OPTICAL COHERENCE TOMOGRAPHY IMAGING AND MEASUREMENTS: Preoperative Cirrus HD-OCT of the
central 3 mm of the cornea was performed in all subjects as follows. Multiple vertical and horizontal raster line scans (axial resolution 5 mm) were centered over the apex of the cornea and the following measurements were obtained: (1) maximum depth of the opacity; (2) maximum depth of the crater (ie, the depth to the Bowman layer, where the epithelium is at its thickest point); (3) baseline epithelial thickness (as ascertained from an area of the cornea where scarring is absent); and (4) the total central corneal VOL. 156, NO. 6
FIGURE 1. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the hyperintense corneal signal in the anterior stroma as well as >33% variation in epithelial thickness.
thickness. Scans with signal strength less than 8 or scans that were noted to be significantly offset from the central cornea (as determined by inspection of the centration of the raster lines seen on the scout view) were rejected for use in the measurements and the analysis. DUAL EXCIMER LASER PHOTOABLATION TREATMENT ALGORITHM: All photoablations were performed by a single
surgeon (S.W.R.). Off-label use of the Allegretto Wavelight Eye-Q 400 Hz (Alcon, Fort Worth, Texas, USA) platform was used to perform 2 wave-front–optimized ablation treatment profiles.22,23 First, the maximum depth of the patient’s scar (as measured on OCT) was used as the primary target ablation depth. A large optic zone (usually 7 mm) spherical myopic ablation was then calculated to ablate to the desired depth (including the epithelial thickness). Immediately following this, a secondary ablation was performed to control the refractive outcome by using a hyperopic ablation profile. This was calculated in the following way. The ablation depth for the baseline epithelial thickness (which is refractively neutral) was subtracted from the total of the myopic ablation depth. The patient’s preoperative spherical equivalent (SE) was then subtracted from the remaining myopic ablation treatment. Accounting for the surgeon-specific myopic ablation nomograms, the secondary spherical hyperopic ablation profile was used to bring the patient back to an SE near plano or any other desired refractive result. The preoperative SE was ascertained by several methods: (1) previous prescriptions for glasses or contact lenses prior to the corneal scarring events; (2) manifest refraction results in those with good enough preoperative vision; and (3) the refractive status of the fellow eye. Pseudophakic patients were assumed to be plano unless known to be otherwise. All relevant historical data and clinical tests were used in combination to establish the final SE. (Astigmatic correction was not used in the laser ablation profiles because the majority of astigmatisms in these cases were irregular and were assumed to be related to the corneal scarring). Patients were not given ablation treatment profiles that were calculated to leave the cornea with residual stromal beds of less than 275 mm. If the preoperative calculations
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TABLE 1. Transepithelial Phototherapeutic Keratectomy for the Treatment of Anterior Corneal Scarring: Preoperative Diagnoses That Resulted in Anterior Corneal Scarring Preoperative Diagnosis
Number of Patients (n ¼ 22)
Herpes simplex virus keratitis Bacterial keratitis Trauma (including foreign body) Other chronic ocular surface disease
9 9 2 2
anticipated violation of this restriction, the myopic portion of the ablation was decreased to accommodate for the 275 mm residual stromal-bed parameter, and the hyperopic portion of the ablation profile was also adjusted accordingly. If the patient had corneal scarring that was too deep to eliminate entirely despite application of the largest myopic ablation profile allowed by the Allegretto Wavelight laser platform (10 sphere at an optic zone of 7 mm, which ablates 163 mm of tissue), the ablation profile was done as deeply as possible and at least deeply enough to get to the maximal depth of the crater. If the patient had a moderate to high preoperative myopic SE, the patient may not have required the second ablation with the hyperopic treatment profile to achieve the desired refractive outcome. PREOPERATIVE ROUTINE:
All patients with known or suspected herpes simplex virus keratitis were pretreated with oral acyclovir 400 mg by mouth twice daily 1 week prior to transepithelial PTK and continuing for a total of 3 months postoperatively. No cases of herpes zoster were included in the study. TRANSEPITHELIAL PTK SURGICAL TECHNIQUE:
The excimer laser was programmed to deliver two separate ablation profiles, as described above. The patient was given topical anesthetic and prepared using Betadine 5% to the ocular fornices. The myopia profile was delivered first and was immediately followed by the hyperopic ablation (a delay of about 20 seconds between the two ablations). Following both ablations, mitomycin C 0.02% was applied to the stromal bed on an 8 mm diameter circular sponge for a total of 15 seconds, which was followed by vigorous ocular surface irrigation. A bandage contact lens was placed over the cornea at the end of the procedure.
POSTOPERATIVE ROUTINE:
Patients were given ofloxacin 0.3% 1 drop 4 times a day for 1 week and prednisolone acetate 1% 4 times daily for 1 week, then twice daily for 1 week. The bandage contact lens was removed 3 to 5 days postprocedure. Additional follow-up included both 2-week and 4-month postoperative examinations.
DATA COLLECTION: The best spectacle-corrected visual acuity (BSCVA), the indices on the Tomey TMS-4 Corneal Topographer (Phoenix, Arizona, USA), and the maximal
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crater depth on OCT were collected at baseline and at the 4-month postoperative follow-up. The absolute value of the SE on postoperative refraction subtracted from the predicted SE refractive outcome was also recorded. The corneal topography indices measured included cylinder, projected visual acuity, surface asymmetry index, and surface regularity index. STATISTICAL ANALYSIS: One-way analysis of variance was performed to compare the preoperative to the postoperative measurements of the BSCVA (logMAR), corneal topography indices and OCT crater depths. Mathematical software from the SAS Institute (Cary, North Carolina, USA) was used to perform statistical analysis. Results were considered statistically significant at the alpha <0.05 level.
RESULTS A TOTAL OF 22 EYES OF 20 PATIENTS MET CRITERIA FOR
inclusion in the study. The various underlying pathologies responsible for the corneal scarring are detailed in Table 1. The mean age of the subjects was 58.6 years (50.4–66.8; 95% CI); 59% were male and 41% female. Table 2 details the pertinent findings of the study. BSCVA (in logMAR) improved from 0.82 (0.61–1.02) to 0.40 (0.19–0.61) (P ¼ 0.0070). The mean baseline epithelial thickness was 51.6 mm, and the mean baseline maximum crater depth was 114.8 mm. This represented an overall average of a 55% variation in the baseline central corneal epithelial thicknesses. There was an 80% improvement in maximum crater depth postoperatively, with a mean of 12.5 mm residual crater depth, and 36% (8/22) of patients had resolution of the crater scar in its entirety. The mean postoperative SE was 0.78 (0.49–1.07) diopters (D) in error from the intended postoperative refractive target. All patients experienced a gain of at least 1 logMAR line of BSCVA during the study interval, and none of the patients experienced visually significant anisometropia or the effects of aniseikonia postoperatively. The corneal topography–measured cylinder and the projected visual acuity significantly improved, but the other corneal topographic indices were not statistically significant (although they trended toward improvement). None of the study subjects required (or requested) an additional treatment with repeat PTK or lamellar/penetrating keratoplasty. In addition, there were no cases of herpes simplex reactivation in any of the subjects during the study interval. In a subset analysis that excluded the 6 patients with poor visual potential unrelated to the cornea (three with advanced macular degeneration, two with dense cataracts, and one with a prior macula-off retinal detachment), the mean postoperative BSCVA improved from 0.54 to 0.20 (P < 0.0001). CASE EXAMPLE #1: TRAUMATIC CORNEAL FOREIGN BODY: A 53-year-old male with a history of a metallic
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TABLE 2. Transepithelial Phototherapeutic Keratectomy for the Treatment of Anterior Corneal Scarring: Preoperative versus Postoperative Outcomes Using 1-Way Analysis of Variance Outcome Measurement
Best spectacle-corrected visual acuity in LogMAR Topographic cylinder in diopters Topographic surface asymmetry index Topographic surface regularity index Topographic projected visual acuity in LogMAR Crater depth by optical coherence tomography in mm
Postoperative Means (with 95% CI)
0.82 (0.61–1.02)
0.40 (0.19–0.61)
0.0070
4.42 (3.54–5.30) 3.29 (2.58–4.01) 1.63 (1.37–1.90) 0.36 (0.30–0.43)
2.90 (2.02–3.78) 2.41 (1.69–3.12) 1.27 (1.00–1.53) 0.26 (0.19–0.32)
0.0173 0.0849 0.0543 0.0261
61.4 (49.5–73.5)
12.5 (0.8–24.2)
FIGURE 2. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the preoperative corneal scar of the patient in Example #1 following a metallic foreignbody injury. The maximum crater depth was measured at180 mm with a total corneal thickness of 584 mm and a baseline epithelial thickness of 60 mm.
corneal foreign body injury presented with monocular diplopia and 20/30 Snellen BSCVA in the affected eye. The patient’s preoperative OCT demonstrated a large corneal scar with crater formation (Figure 2). To get as deeply as possible to the bottom of the crater, the initial myopic ablation profile was set at the maximum depth ablation profile for the excimer platform of 10.00 sphere with an optic zone of 7 mm, which removes a predicted total of 163 mm of tissue. Accounting for the baseline epithelial thickness, the first 3.25 D of this myopic ablation removed only epithelium (projected to be 58 mm) and did not contribute to the overall postoperative refractive outcome. Using our surgeon-specific nomogram, the remaining 6.75sphere myopic ablation profile with an optic zone of 7 mm was calculated to result in an effective correction of 7.25 D of myopic treatment, which thereby induced 7.25 D of hyperopia in the patient. The operative eye was determined to have a preoperative SE of þ1.00 D according to both the preoperative refraction and the historical refraction prior to injury. Therefore, the second ablation profile was set at maximum hyperopic correction for the excimer platform at þ6.0 D at an optic zone of 6.5 mm, which provided exactly 6 D of correction according to our surgeon-specific nomogram. The mathematics anticipated that the resulting dual treatment excimer laser ablation VOL. 156, NO. 6
P value
Preoperative Means (with 95% CI)
<0.0001
FIGURE 3. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the cornea of the patient in Example #1 just seconds after the dual laser photoablation. Notice that no epithelial layer is visible and that the Bowman layer is markedly improved in uniformity. The bandage contact lens can be seen as the white line above the approximately 80 mm tear film layer. The remaining residual stromal bed depth is measured at 412 mm (584 initial corneal thickness; calculated 163 mm total myopic ablation depth for a projected residual stromal bed of 421 mm [plus the minor contribution from the hyperopic ablation]).
profile would result in a total postoperative SE of 7.25 D of hyperopia induced, added to the 1.00 D of preoperative existing hyperopia and then subtracted from the 6 D of induced myopia in the second treatment, thereby equaling 2.25 D of postoperative hyperopia. The second (hyperopic) ablation was not expected to contribute much to the total ablation depth because the treatment was predominantly peripheral to the central 3 mm of the cornea (Figure 3 and Figure 4). In the postoperative period, the patient experienced resolution of the monocular diplopia, and the Snellen BSCVA improved to 20/20 with a refraction of þ1.00 þ1.75 3081, or an SE of þ1.88, which correlated well with the anticipated SE refractive result of þ2.25 D. Spectacles worked well for this patient without the presence of anisometropia (the fellow eye had a refraction of þ0.50 þ1.00 3076). CASE EXAMPLE #2: HERPES SIMPLEX VIRUS KERATITIS:
A 52-year-old male with a history of herpes simplex virus disciform keratitis presented with visual distortion and
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FIGURE 4. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the postoperative cornea of the patient in Example #1 after the epithelium has healed. The epithelium has regenerated uniformly to a baseline thickness of 60 mm with complete resolution of the crater.
FIGURE 5. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the preoperative cornea of the patient in Example #2. The maximum crater depth was measured to be 104 mm, and the maximum scarring depth was 128 mm. The baseline epithelium depth was 50 mm, and the total central corneal thickness was 624 mm.
a Snellen BSCVA of 20/50 in the affected eye. The patient’s preoperative OCT demonstrated prominent anterior corneal scarring (Figure 5). The myopic ablation profile was done at 5.50 sphere with an optic zone of 8 mm for a total projected ablation depth of 123 mm. The first 2 D of this ablation (a projected depth of 47 mm) were refractively neutral because only the 50 mm of baseline epithelium were removed. Using our surgeonspecific nomogram for myopic ablations at an optic zone of 8 mm, the remaining 3.50 D of myopic treatment provided an effective postoperative refractive correction of 4 D. The second laser ablation was set at þ5 sphere to produce an offset of the newly induced 4 D of hyperopia. The patient’s preoperative refractive status had an SE of þ1 D, so the refractive changes anticipated postoperatively were: 4 D of induced hyperopia from the myopic ablation treatment added to the 1 D of existing hyperopia preoperatively, subtracted from the 5 D of induced myopia from the hyperopic ablation profile equal the total expected refractive outcome of plano (Figure 6 and Figure 7). Following treatment, the preoperative distortion resolved, and the patient ended up with 20/30 Snellen BSCVA and an SE of 1 D. 1092
FIGURE 6. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the cornea of the patient in Example #2 just seconds after the dual laser photoablation. The residual stromal depth was measured at 506 mm after the 123 mm ablation (624 mm preoperative; 123 mm myopic ablation [ anticipated residual stromal depth of 501 mm ). Notice that the preoperative Bowman layer irregularities have been eliminated.
FIGURE 7. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the postoperative cornea of the patient in Example #2 after the epithelium has healed. Complete resolution of the preoperative corneal scar is evident. The epithelium has regenerated uniformly to a baseline thickness of 52 mm.
DISCUSSION ANTERIOR CORNEAL SCARRING WITH CRATER FORMATION
presents a significant treatment challenge for the clinician, and currently no consensus exists regarding the best treatment option. The ideal strategy should aim not only to eliminate the corneal opacity but also to improve the overall anatomic shape of the cornea, thereby minimizing postoperative irregular astigmatism and improving BSCVA. The marked distortion and flattening present on corneal topography in patients with anterior corneal scarring is often indicative of an irregular Bowman layer, which may be readily identified on OCT imaging. For many patients with anterior stromal scarring, their reduced visual acuity can be attributed to the anatomic disruption of the cornea rather than the physical opaqueness of the scar itself. In theory, PTK techniques that remove much (or all) of the corneal opacity but transmit the Bowman layer irregularities to a deeper level in the corneal stroma could produce less gain in BSCVA compared to PTK techniques that aim to normalize the shape and anatomy of the cornea. A variety of PTK techniques for the treatment of anterior corneal scars have been reported, with mixed visual
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and anatomic results.1–5,24,25 Campos and associates1 reported that 7 of 18 patients failed to improve or had worsened BSCVA after PTK. Two of their subjects had significantly increased postoperative irregular astigmatism. Maloney and associates2 reported improvement in BSCVA in only 45% of subjects after PTK. Hafner and associates25 reported better visual outcomes following PTK, with 87% achieving improved postoperative BSCVA. To date, only a single case report is found in the literature concerning transepithelial PTK for anterior corneal scarring.16 OCT-guided transepithelial PTK in our study population resulted in improved BSCVA in all patients. The improvement in BSCVA correlated well with the anatomic improvement on OCT as measured by the changes in the maximum crater depth as well as the corneal topography indices. The postoperative BSCVA improved not only because the scarring and overall astigmatism were significantly reduced, but also because the residual astigmatism of the corneal topography appeared much more regular and was therefore more readily correctable with spectacles alone. In clinical practice, many patients with significant amounts of post-PTK irregular astigmatism are left needing rigid gas-permeable contact lenses to improve their vision. However, this option is not always viable, especially in elderly patients and those who developed corneal scarring secondary to contact lens–associated corneal ulceration. Therefore, the long-term visual rehabilitation of the post-PTK patient may be greatly facilitated by decreasing the amount of residual irregular astigmatism. All of the patients in our study required only spectacle correction at the end of the study period.
The visual and anatomic outcomes of this study suggest that careful calculations during the dual myopic/hyperopic excimer laser ablation profile can safeguard against the possibility of a postoperative ‘‘hyperopic surprise’’ as well as effectively eliminate the possibility of postoperative anisometropia. The final BSCVA results of all study subjects were within 1.5 D spherical equivalent of the target refractive outcome, and 23% (5/22) were within 0.25 D of the target. Weaknesses of our study include the retrospective collection of data, the relatively small number of study subjects, the use of logMAR visual acuity, the relatively short follow-up study period, and the lack of a control group. Without a control group, it cannot be determined how our OCT-guided transepithelial PTK algorithm would compare to other strategies for anterior corneal scar treatment such as topography-guided ablations. In summary, the OCT-guided transepithelial PTK algorithm described in this study can result in excellent visual and anatomic outcomes in patients with anterior corneal scars, particularly with crater formation. The algorithm in this study may also restore the uniformity of the Bowman layer and normalize the epithelial thickness, thereby reducing postoperative residual irregular astigmatism. Because the corneal epithelium is photoablated at a rate similar to that of the corneal stroma, the corneal epithelium may effectively act as a masking agent during transepithelial PTK, obviating the need for masking agents such as sodium hyaluronate or biomask. Future controlled studies are needed to further validate these results and establish the place of the OCT-guided transepithelial PTK algorithm in the management of crater anterior corneal scars.
ALL AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE FORM FOR DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST, and none were reported. Design and conduct of study (S.W.R., R.B.R.); Collection, management, analysis, and interpretation of data (S.W.R., D.Y.H., R.B.R.); and Preparation, review, or approval of manuscript (S.W.R., D.Y.H., R.B.R.).
REFERENCES 1. Campos M, Nielsen S, Szerenyi K, Garbus JJ, McDonnell PJ. Clinical follow-up of phototherapeutic keratectomy for treatment of corneal opacities. Am J Ophthalmol 1993;115(4): 433–440. 2. Maloney RK, Thompson V, Ghiselli G, Durrie D, Waring GO 3rd, O’Connell M. A prospective multicenter trial of excimer laser phototherapeutic keratectomy for corneal vision loss (The Summit Phototherapeutic Keratectomy Study Group). Am J Ophthalmol 1996;122(2):149–160. 3. Fagerholm P. Phototherapeutic keratectomy: 12 years of experience. Acta Ophthalmol Scand 2003;81(1):19–32. 4. Starr M, Donnenfeld E, Newton M, Tostanoski J, Muller J, Odrich M. Excimer laser phototherapeutic keratectomy. Cornea 1996;15(6):557–565. 5. Dogru M, Katakami C, Yamanaka A. Refractive changes after excimer laser phototherapeutic keratectomy. J Cataract Refract Surg 2001;27(5):686–692.
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6. Lyall DA, Tarafdar S, Gilhooly MJ, Roberts F, Ramaesh K. Long-term visual outcomes, graft survival and complications of deep anterior lamellar keratoplasty in patients with herpes simplex related corneal scarring. Br J Ophthalmol 2012;96(9): 1200–1203. 7. Al-Fawaz A, Wagoner MD. King Khaled Eye Specialist Hospital Corneal Transplant Study Group. Penetrating keratoplasty for trachomatous corneal scarring. Cornea 2008; 27(2):129–132. 8. O’Donnell C, Maldonado-Codina C. Agreement and repeatability of central thickness measurement in normal corneas using ultrasound pachymetry and the OCULUS Pentacam. Cornea 2005;24(8):920–924. 9. Li EY, Mohamed S, Leung CK, et al. Agreement among 3 methods to measure corneal thickness: ultrasound pachymetry, Orbscan II, and Visante anterior segment optical coherence tomography. Ophthalmology 2007;114(10):1842–1847. 10. Holzer MP, Auffarth GU, Specht H, Kruse FE. Combination of transepithelial phototherapeutic keratectomy and
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autologous serum eyedrops for treatment of recurrent corneal erosions. J Cataract Refract Surg 2005;31(8):1603–1606. Kymionis GD, Grentzelos MA, Mikropoulos DG, Rallis KI. Transepithelial phototherapeutic keratectomy for recurrent corneal erosions in a patient with previous corneal collagen cross-linking. J Refract Surg 2012;28(10):732–734. Ibarz Barbera´ M, Garcı´a Gonza´lez M, Teus Guezala M. Transepithelial phototherapeutic keratectomy to treat chronic laser in situ keratomileusis-flap macrostriae: a case review. Arch Soc Esp Oftalmol 2012;87(12):407–410. Kymionis GD, Grentzelos MA, Kounis GA, Diakonis VF, Limnopoulou AN, Panagopoulou SI. Combined transepithelial phototherapeutic keratectomy and corneal collagen cross-linking for progressive keratoconus. Ophthalmology 2012;119(9):1777–1784. Reddy JC, Rapuano CJ, Nagra PK, Hammersmith KM. Excimer laser phototherapeutic keratectomy in eyes with corneal stromal dystrophies with and without a corneal graft. Am J Ophthalmol 2013;155(6):1111–1118. Mori H, Miura M, Iwasaki T, et al. Three-dimensional optical coherence tomography-guided phototherapeutic keratectomy for granular corneal dystrophy. Cornea 2009;28(8):944–947. Ma JJ, Tseng SS, Yarascavitch BA. Anterior segment optical coherence tomography for transepithelial phototherapeutic keratectomy in central corneal stromal scarring. Cornea 2009;28(8):927–929. Ventura BV, Moraes HV Jr, Kara-Junior N, Santhiago MR. Role of optical coherence tomography on corneal surface laser ablation. J Ophthalmol 2012;2012:676–740. Kremer F, Aronsky M, Bowyer B, Stevens SX. Treatment of corneal surface irregularities using biomask as an adjunct to
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excimer laser phototherapeutic keratectomy. Cornea 2002; 21(1):28–32. Khoury JM, Salti H, El-Haibi C, Noureddin B. Modified phototherapeutic keratectomy technique for the treatment of elevated corneal opacities. Ophthalmic Surg Lasers Imaging 2009;40(2):203–206. Alio´ JL, Belda JI, Shalaby AM. Correction of irregular astigmatism with excimer laser assisted by sodium hyaluronate. Ophthalmology 2001;108(7):1246–1260. Kornmehl EW, Steinert RF, Puliafito CA. A comparative study of masking fluids for excimer laser phototherapeutic keratectomy. Arch Ophthalmol 1991;109(6): 860–863. Gambato C, Catania AG, Vujosevic S, Midena E. Wavefront-optimized surface ablation with the Allegretto Wave Eye-Q excimer laser platform: 12-month visual and refractive results. J Refract Surg 2011;27(11):792–795. Stonecipher KG, Kezirian GM. Wavefront-optimized versus wavefront-guided LASIK for myopic astigmatism with the Allegretto Wave: three-month results of a prospective FDA trial. J Refract Surg 2008;24(4):S424–430. Awdeh RM, Abbey AM, Vroman DT, et al. Phototherapeutic keratectomy for the treatment of subepithelial fibrosis and anterior corneal scarring after descemet stripping automated endothelial keratoplasty. Cornea 2012;31(7): 761–763. Hafner A, Seitz B, Langenbucher A, Naumann GO. Phototherapeutic keratectomy (o-PTK) with 193 nm excimer laser for superficial corneal scars: prospective long-term results of 31 consecutive operations. Ophthalmologe 2004;101(2): 135–139.
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Accepted for publication Jun 17, 2013. From the Panhandle Eye Group, Amarillo, Texas (S.W.R., R.B.R.); the Texas Tech University Health Science Center, Amarillo, Texas (D.Y.H.); and the Southwest Retina Specialists, Amarillo, Texas (R.B.R.). Inquiries to Ryan Rush, Southwest Retina Specialists, 7411 Wallace Boulevard, Amarillo, TX 79106; e-mail: Ryanbradfordrush21@hotmail. com
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are warranted to further validate the technique reported in this study. (Am J Ophthalmol 2013;156:1088–1094. Ó 2013 by Elsevier Inc. All rights reserved.)
P
HOTOTHERAPEUTIC KERATECTOMY (PTK) IS A SAFE
and efficacious modality for the treatment of opacities localized to more than one third of the superficial corneal stroma.1–3 In cases with irregular corneal surfaces, PTK may also enhance the cornea’s optical qualities and improve vision by smoothing the irregular corneal surface4,5 as well as avoiding the need for more invasive surgery such as lamellar6 or penetrating keratoplasty.7 Recently, new technologies, such as the Pentacam device (Oculus, Lynnwood, Washington, USA)8 and anterior segment optical coherence tomography (OCT) (Carl Zeiss Meditec, Dublin, California, USA),9 have improved preoperative prediction of the depth of corneal pathology and have determined more accurately the amount of corneal tissue to be removed during PTK. Transepithelial PTK is a technique in which PTK is performed without the manual removal of the epithelium by superficial keratectomy but instead uses the excimer laser to photoablate the epithelial layer, which serves as a natural masking agent. Transepithelial PTK has been used to treat recurrent erosions,10,11 laser in-situ keratomileusis (LASIK) flap macrostriae,12 keratoconus (in combination with corneal collagen crosslinking),13 corneal stromal dystrophies14,15 and, more recently, corneal scarring.16 In cases with anterior corneal scarring or irregularities in the Bowman layer, OCT may provide useful clinical information that helps to determine the appropriate depth of ablation during transepithelial PTK.17 While conventional epithelium-off PTK for anterior corneal scarring is being performed, intraoperative findings may reveal a visible ‘‘crater’’ or ‘‘divot’’ in the Bowman layer. Once the epithelium has been removed and a Bowman irregularity has been revealed, the laser ablation profile will transmit these subtle and focal irregularities down to a deeper level in the stroma, and they will persist to some degree once the cornea re-epithelializes. To mitigate against this problem, investigators have tried using various masking agents (eg, artificial tears or surgical sponges) to fill in or cover the irregular defect in order to provide for a more uniformly distributed ablation profile.18–21
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With the advent of OCT technology, clinicians now have the ability to determine preoperatively which patients are likely to develop intraoperative craters in the Bowman layer if traditional epithelium-off PTK is performed. In these cases, the authors hypothesize that the epithelium itself may act as an effective masking agent and allow for a more even distribution of the ablation pattern if preserved. This could result in lower amounts of postoperative irregular astigmatism by avoiding the propagation of the Bowman layer irregularities to a deeper level in the corneal stroma. In this study, the authors describe a novel technique that uses OCT imaging of the central cornea to guide a transepithelial excimer laser ablation algorithm in order to treat anterior corneal scars associated with an irregular Bowman layer, all while maintaining and controlling for refractive outcomes.
METHODS THE SOUTHWEST RETINA SPECIALISTS INSTITUTIONAL
review board (IORG0007600/IRB00009122) approved this retrospective chart review of consecutive cases in patients who underwent OCT-guided transepithelial PTK for anterior corneal scarring between January 2011 and February 2013. All research components adhered to the tenets of the Declaration of Helsinki and were conducted in accordance with human-subject research regulations and standards. INCLUSION CRITERIA:
Subjects included in the study had undergone complete ophthalmologic examinations and had undergone OCT-guided transepithelial PTK for central corneal scarring that was associated with a significantly irregular Bowman layer. A significantly irregular Bowman layer was defined as follows: spectral domain OCT (Cirrus HD-OCT; Carl Zeiss Meditec, Dublin, California, USA) of the central 3 mm of cornea (1) exhibited a hyperintense signal that corresponded with scarring on clinical examination and (2) was associated with a variation in epithelial thickness by a minimum of a 33% increase from the baseline epithelial thickness, thus giving it the appearance of a crater or a divot scar (Figure 1).
OPTICAL COHERENCE TOMOGRAPHY IMAGING AND MEASUREMENTS: Preoperative Cirrus HD-OCT of the
central 3 mm of the cornea was performed in all subjects as follows. Multiple vertical and horizontal raster line scans (axial resolution 5 mm) were centered over the apex of the cornea and the following measurements were obtained: (1) maximum depth of the opacity; (2) maximum depth of the crater (ie, the depth to the Bowman layer, where the epithelium is at its thickest point); (3) baseline epithelial thickness (as ascertained from an area of the cornea where scarring is absent); and (4) the total central corneal VOL. 156, NO. 6
FIGURE 1. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the hyperintense corneal signal in the anterior stroma as well as >33% variation in epithelial thickness.
thickness. Scans with signal strength less than 8 or scans that were noted to be significantly offset from the central cornea (as determined by inspection of the centration of the raster lines seen on the scout view) were rejected for use in the measurements and the analysis. DUAL EXCIMER LASER PHOTOABLATION TREATMENT ALGORITHM: All photoablations were performed by a single
surgeon (S.W.R.). Off-label use of the Allegretto Wavelight Eye-Q 400 Hz (Alcon, Fort Worth, Texas, USA) platform was used to perform 2 wave-front–optimized ablation treatment profiles.22,23 First, the maximum depth of the patient’s scar (as measured on OCT) was used as the primary target ablation depth. A large optic zone (usually 7 mm) spherical myopic ablation was then calculated to ablate to the desired depth (including the epithelial thickness). Immediately following this, a secondary ablation was performed to control the refractive outcome by using a hyperopic ablation profile. This was calculated in the following way. The ablation depth for the baseline epithelial thickness (which is refractively neutral) was subtracted from the total of the myopic ablation depth. The patient’s preoperative spherical equivalent (SE) was then subtracted from the remaining myopic ablation treatment. Accounting for the surgeon-specific myopic ablation nomograms, the secondary spherical hyperopic ablation profile was used to bring the patient back to an SE near plano or any other desired refractive result. The preoperative SE was ascertained by several methods: (1) previous prescriptions for glasses or contact lenses prior to the corneal scarring events; (2) manifest refraction results in those with good enough preoperative vision; and (3) the refractive status of the fellow eye. Pseudophakic patients were assumed to be plano unless known to be otherwise. All relevant historical data and clinical tests were used in combination to establish the final SE. (Astigmatic correction was not used in the laser ablation profiles because the majority of astigmatisms in these cases were irregular and were assumed to be related to the corneal scarring). Patients were not given ablation treatment profiles that were calculated to leave the cornea with residual stromal beds of less than 275 mm. If the preoperative calculations
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TABLE 1. Transepithelial Phototherapeutic Keratectomy for the Treatment of Anterior Corneal Scarring: Preoperative Diagnoses That Resulted in Anterior Corneal Scarring Preoperative Diagnosis
Number of Patients (n ¼ 22)
Herpes simplex virus keratitis Bacterial keratitis Trauma (including foreign body) Other chronic ocular surface disease
9 9 2 2
anticipated violation of this restriction, the myopic portion of the ablation was decreased to accommodate for the 275 mm residual stromal-bed parameter, and the hyperopic portion of the ablation profile was also adjusted accordingly. If the patient had corneal scarring that was too deep to eliminate entirely despite application of the largest myopic ablation profile allowed by the Allegretto Wavelight laser platform (10 sphere at an optic zone of 7 mm, which ablates 163 mm of tissue), the ablation profile was done as deeply as possible and at least deeply enough to get to the maximal depth of the crater. If the patient had a moderate to high preoperative myopic SE, the patient may not have required the second ablation with the hyperopic treatment profile to achieve the desired refractive outcome. PREOPERATIVE ROUTINE:
All patients with known or suspected herpes simplex virus keratitis were pretreated with oral acyclovir 400 mg by mouth twice daily 1 week prior to transepithelial PTK and continuing for a total of 3 months postoperatively. No cases of herpes zoster were included in the study. TRANSEPITHELIAL PTK SURGICAL TECHNIQUE:
The excimer laser was programmed to deliver two separate ablation profiles, as described above. The patient was given topical anesthetic and prepared using Betadine 5% to the ocular fornices. The myopia profile was delivered first and was immediately followed by the hyperopic ablation (a delay of about 20 seconds between the two ablations). Following both ablations, mitomycin C 0.02% was applied to the stromal bed on an 8 mm diameter circular sponge for a total of 15 seconds, which was followed by vigorous ocular surface irrigation. A bandage contact lens was placed over the cornea at the end of the procedure.
POSTOPERATIVE ROUTINE:
Patients were given ofloxacin 0.3% 1 drop 4 times a day for 1 week and prednisolone acetate 1% 4 times daily for 1 week, then twice daily for 1 week. The bandage contact lens was removed 3 to 5 days postprocedure. Additional follow-up included both 2-week and 4-month postoperative examinations.
DATA COLLECTION: The best spectacle-corrected visual acuity (BSCVA), the indices on the Tomey TMS-4 Corneal Topographer (Phoenix, Arizona, USA), and the maximal
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crater depth on OCT were collected at baseline and at the 4-month postoperative follow-up. The absolute value of the SE on postoperative refraction subtracted from the predicted SE refractive outcome was also recorded. The corneal topography indices measured included cylinder, projected visual acuity, surface asymmetry index, and surface regularity index. STATISTICAL ANALYSIS: One-way analysis of variance was performed to compare the preoperative to the postoperative measurements of the BSCVA (logMAR), corneal topography indices and OCT crater depths. Mathematical software from the SAS Institute (Cary, North Carolina, USA) was used to perform statistical analysis. Results were considered statistically significant at the alpha <0.05 level.
RESULTS A TOTAL OF 22 EYES OF 20 PATIENTS MET CRITERIA FOR
inclusion in the study. The various underlying pathologies responsible for the corneal scarring are detailed in Table 1. The mean age of the subjects was 58.6 years (50.4–66.8; 95% CI); 59% were male and 41% female. Table 2 details the pertinent findings of the study. BSCVA (in logMAR) improved from 0.82 (0.61–1.02) to 0.40 (0.19–0.61) (P ¼ 0.0070). The mean baseline epithelial thickness was 51.6 mm, and the mean baseline maximum crater depth was 114.8 mm. This represented an overall average of a 55% variation in the baseline central corneal epithelial thicknesses. There was an 80% improvement in maximum crater depth postoperatively, with a mean of 12.5 mm residual crater depth, and 36% (8/22) of patients had resolution of the crater scar in its entirety. The mean postoperative SE was 0.78 (0.49–1.07) diopters (D) in error from the intended postoperative refractive target. All patients experienced a gain of at least 1 logMAR line of BSCVA during the study interval, and none of the patients experienced visually significant anisometropia or the effects of aniseikonia postoperatively. The corneal topography–measured cylinder and the projected visual acuity significantly improved, but the other corneal topographic indices were not statistically significant (although they trended toward improvement). None of the study subjects required (or requested) an additional treatment with repeat PTK or lamellar/penetrating keratoplasty. In addition, there were no cases of herpes simplex reactivation in any of the subjects during the study interval. In a subset analysis that excluded the 6 patients with poor visual potential unrelated to the cornea (three with advanced macular degeneration, two with dense cataracts, and one with a prior macula-off retinal detachment), the mean postoperative BSCVA improved from 0.54 to 0.20 (P < 0.0001). CASE EXAMPLE #1: TRAUMATIC CORNEAL FOREIGN BODY: A 53-year-old male with a history of a metallic
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TABLE 2. Transepithelial Phototherapeutic Keratectomy for the Treatment of Anterior Corneal Scarring: Preoperative versus Postoperative Outcomes Using 1-Way Analysis of Variance Outcome Measurement
Best spectacle-corrected visual acuity in LogMAR Topographic cylinder in diopters Topographic surface asymmetry index Topographic surface regularity index Topographic projected visual acuity in LogMAR Crater depth by optical coherence tomography in mm
Postoperative Means (with 95% CI)
0.82 (0.61–1.02)
0.40 (0.19–0.61)
0.0070
4.42 (3.54–5.30) 3.29 (2.58–4.01) 1.63 (1.37–1.90) 0.36 (0.30–0.43)
2.90 (2.02–3.78) 2.41 (1.69–3.12) 1.27 (1.00–1.53) 0.26 (0.19–0.32)
0.0173 0.0849 0.0543 0.0261
61.4 (49.5–73.5)
12.5 (0.8–24.2)
FIGURE 2. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the preoperative corneal scar of the patient in Example #1 following a metallic foreignbody injury. The maximum crater depth was measured at180 mm with a total corneal thickness of 584 mm and a baseline epithelial thickness of 60 mm.
corneal foreign body injury presented with monocular diplopia and 20/30 Snellen BSCVA in the affected eye. The patient’s preoperative OCT demonstrated a large corneal scar with crater formation (Figure 2). To get as deeply as possible to the bottom of the crater, the initial myopic ablation profile was set at the maximum depth ablation profile for the excimer platform of 10.00 sphere with an optic zone of 7 mm, which removes a predicted total of 163 mm of tissue. Accounting for the baseline epithelial thickness, the first 3.25 D of this myopic ablation removed only epithelium (projected to be 58 mm) and did not contribute to the overall postoperative refractive outcome. Using our surgeon-specific nomogram, the remaining 6.75sphere myopic ablation profile with an optic zone of 7 mm was calculated to result in an effective correction of 7.25 D of myopic treatment, which thereby induced 7.25 D of hyperopia in the patient. The operative eye was determined to have a preoperative SE of þ1.00 D according to both the preoperative refraction and the historical refraction prior to injury. Therefore, the second ablation profile was set at maximum hyperopic correction for the excimer platform at þ6.0 D at an optic zone of 6.5 mm, which provided exactly 6 D of correction according to our surgeon-specific nomogram. The mathematics anticipated that the resulting dual treatment excimer laser ablation VOL. 156, NO. 6
P value
Preoperative Means (with 95% CI)
<0.0001
FIGURE 3. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the cornea of the patient in Example #1 just seconds after the dual laser photoablation. Notice that no epithelial layer is visible and that the Bowman layer is markedly improved in uniformity. The bandage contact lens can be seen as the white line above the approximately 80 mm tear film layer. The remaining residual stromal bed depth is measured at 412 mm (584 initial corneal thickness; calculated 163 mm total myopic ablation depth for a projected residual stromal bed of 421 mm [plus the minor contribution from the hyperopic ablation]).
profile would result in a total postoperative SE of 7.25 D of hyperopia induced, added to the 1.00 D of preoperative existing hyperopia and then subtracted from the 6 D of induced myopia in the second treatment, thereby equaling 2.25 D of postoperative hyperopia. The second (hyperopic) ablation was not expected to contribute much to the total ablation depth because the treatment was predominantly peripheral to the central 3 mm of the cornea (Figure 3 and Figure 4). In the postoperative period, the patient experienced resolution of the monocular diplopia, and the Snellen BSCVA improved to 20/20 with a refraction of þ1.00 þ1.75 3081, or an SE of þ1.88, which correlated well with the anticipated SE refractive result of þ2.25 D. Spectacles worked well for this patient without the presence of anisometropia (the fellow eye had a refraction of þ0.50 þ1.00 3076). CASE EXAMPLE #2: HERPES SIMPLEX VIRUS KERATITIS:
A 52-year-old male with a history of herpes simplex virus disciform keratitis presented with visual distortion and
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FIGURE 4. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the postoperative cornea of the patient in Example #1 after the epithelium has healed. The epithelium has regenerated uniformly to a baseline thickness of 60 mm with complete resolution of the crater.
FIGURE 5. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the preoperative cornea of the patient in Example #2. The maximum crater depth was measured to be 104 mm, and the maximum scarring depth was 128 mm. The baseline epithelium depth was 50 mm, and the total central corneal thickness was 624 mm.
a Snellen BSCVA of 20/50 in the affected eye. The patient’s preoperative OCT demonstrated prominent anterior corneal scarring (Figure 5). The myopic ablation profile was done at 5.50 sphere with an optic zone of 8 mm for a total projected ablation depth of 123 mm. The first 2 D of this ablation (a projected depth of 47 mm) were refractively neutral because only the 50 mm of baseline epithelium were removed. Using our surgeonspecific nomogram for myopic ablations at an optic zone of 8 mm, the remaining 3.50 D of myopic treatment provided an effective postoperative refractive correction of 4 D. The second laser ablation was set at þ5 sphere to produce an offset of the newly induced 4 D of hyperopia. The patient’s preoperative refractive status had an SE of þ1 D, so the refractive changes anticipated postoperatively were: 4 D of induced hyperopia from the myopic ablation treatment added to the 1 D of existing hyperopia preoperatively, subtracted from the 5 D of induced myopia from the hyperopic ablation profile equal the total expected refractive outcome of plano (Figure 6 and Figure 7). Following treatment, the preoperative distortion resolved, and the patient ended up with 20/30 Snellen BSCVA and an SE of 1 D. 1092
FIGURE 6. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the cornea of the patient in Example #2 just seconds after the dual laser photoablation. The residual stromal depth was measured at 506 mm after the 123 mm ablation (624 mm preoperative; 123 mm myopic ablation [ anticipated residual stromal depth of 501 mm ). Notice that the preoperative Bowman layer irregularities have been eliminated.
FIGURE 7. Transepithelial phototherapeutic keratectomy for the treatment of anterior corneal scarring. Corneal optical coherence tomography demonstrates the postoperative cornea of the patient in Example #2 after the epithelium has healed. Complete resolution of the preoperative corneal scar is evident. The epithelium has regenerated uniformly to a baseline thickness of 52 mm.
DISCUSSION ANTERIOR CORNEAL SCARRING WITH CRATER FORMATION
presents a significant treatment challenge for the clinician, and currently no consensus exists regarding the best treatment option. The ideal strategy should aim not only to eliminate the corneal opacity but also to improve the overall anatomic shape of the cornea, thereby minimizing postoperative irregular astigmatism and improving BSCVA. The marked distortion and flattening present on corneal topography in patients with anterior corneal scarring is often indicative of an irregular Bowman layer, which may be readily identified on OCT imaging. For many patients with anterior stromal scarring, their reduced visual acuity can be attributed to the anatomic disruption of the cornea rather than the physical opaqueness of the scar itself. In theory, PTK techniques that remove much (or all) of the corneal opacity but transmit the Bowman layer irregularities to a deeper level in the corneal stroma could produce less gain in BSCVA compared to PTK techniques that aim to normalize the shape and anatomy of the cornea. A variety of PTK techniques for the treatment of anterior corneal scars have been reported, with mixed visual
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and anatomic results.1–5,24,25 Campos and associates1 reported that 7 of 18 patients failed to improve or had worsened BSCVA after PTK. Two of their subjects had significantly increased postoperative irregular astigmatism. Maloney and associates2 reported improvement in BSCVA in only 45% of subjects after PTK. Hafner and associates25 reported better visual outcomes following PTK, with 87% achieving improved postoperative BSCVA. To date, only a single case report is found in the literature concerning transepithelial PTK for anterior corneal scarring.16 OCT-guided transepithelial PTK in our study population resulted in improved BSCVA in all patients. The improvement in BSCVA correlated well with the anatomic improvement on OCT as measured by the changes in the maximum crater depth as well as the corneal topography indices. The postoperative BSCVA improved not only because the scarring and overall astigmatism were significantly reduced, but also because the residual astigmatism of the corneal topography appeared much more regular and was therefore more readily correctable with spectacles alone. In clinical practice, many patients with significant amounts of post-PTK irregular astigmatism are left needing rigid gas-permeable contact lenses to improve their vision. However, this option is not always viable, especially in elderly patients and those who developed corneal scarring secondary to contact lens–associated corneal ulceration. Therefore, the long-term visual rehabilitation of the post-PTK patient may be greatly facilitated by decreasing the amount of residual irregular astigmatism. All of the patients in our study required only spectacle correction at the end of the study period.
The visual and anatomic outcomes of this study suggest that careful calculations during the dual myopic/hyperopic excimer laser ablation profile can safeguard against the possibility of a postoperative ‘‘hyperopic surprise’’ as well as effectively eliminate the possibility of postoperative anisometropia. The final BSCVA results of all study subjects were within 1.5 D spherical equivalent of the target refractive outcome, and 23% (5/22) were within 0.25 D of the target. Weaknesses of our study include the retrospective collection of data, the relatively small number of study subjects, the use of logMAR visual acuity, the relatively short follow-up study period, and the lack of a control group. Without a control group, it cannot be determined how our OCT-guided transepithelial PTK algorithm would compare to other strategies for anterior corneal scar treatment such as topography-guided ablations. In summary, the OCT-guided transepithelial PTK algorithm described in this study can result in excellent visual and anatomic outcomes in patients with anterior corneal scars, particularly with crater formation. The algorithm in this study may also restore the uniformity of the Bowman layer and normalize the epithelial thickness, thereby reducing postoperative residual irregular astigmatism. Because the corneal epithelium is photoablated at a rate similar to that of the corneal stroma, the corneal epithelium may effectively act as a masking agent during transepithelial PTK, obviating the need for masking agents such as sodium hyaluronate or biomask. Future controlled studies are needed to further validate these results and establish the place of the OCT-guided transepithelial PTK algorithm in the management of crater anterior corneal scars.
ALL AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE FORM FOR DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST, and none were reported. Design and conduct of study (S.W.R., R.B.R.); Collection, management, analysis, and interpretation of data (S.W.R., D.Y.H., R.B.R.); and Preparation, review, or approval of manuscript (S.W.R., D.Y.H., R.B.R.).
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