Douglas D. Koch, MD,1 Robert Maloney, MD,2 David R. Hardten, MD,3 Steven Dell, MD,4 Alex D. Sweeney, MD,1 Li Wang, MD, PhD1

To investigate the outcomes of wavefront-guided photorefractive keratectomy (WG PRK) using prophylactic mitomycin C (MMC) in eyes that had previously undergone radial keratotomy (RK).

Retrospective, observational, consecutive case series.

Thirty-two eyes of 27 patients with previous RK that underwent WG PRK with MMC.

The records were reviewed of consecutive RK patients whose eyes underwent WG PRK with MMC in 4 centers with postoperative follow-up of 6 months or longer (range, 6–21 months). Eyes were divided into myopic WG PRK and hyperopic WG PRK groups based on their preoperative spherical equivalent (SE). Preoperative best spectacle-corrected visual acuity (BSCVA) was compared with postoperative uncorrected visual acuity (UCVA) and BSCVA to ascertain efficacy and safety. Change in SE and attempted versus achieved SE were evaluated. Incidences of haze and other complications were recorded.

Uncorrected visual acuity, BSCVA, SE, corneal haze, and other complications.

In the myopic WG PRK group (n
9), UCVA improved by 3 lines on average (P
0.015) with UCVA of
20/20 in 56% and
20/40 in 100% of eyes; 55% were within 0.5 diopter (D), and 100% were within 1 D of attempted refraction. In the hyperopic WG PRK group (n
23), UCVA improved for 3 lines on average (P0.001), with UCVA of
20/20 in 48% and
20/40 in 100% of eyes; 57% were within 0.5 D and 74% were within 1 D of attempted refraction. One eye lost 2 lines of BSCVA as a result of the development of mild to moderate haze, but recovered in 4 months. No eyes lost more than 2 lines of BSCVA. Six eyes (19%; 6/32) experienced the development of haze in the postoperative course, with mild to moderate haze in 1 eye and trace haze in the other 5 eyes. No other complications were noted.

Wavefront-guided PRK with MMC in eyes with prior RK improved the UCVA significantly and was safe over the short follow-up of this series. Although haze occurred, no eye suffered persistent visual loss of 2 or more lines.

Proprietary or commercial disclosure may be found after the references. Ophthalmology 2009;116:1688–1696 © 2009 by the American Academy of Ophthalmology.

Hyperopic shift is a frequently described complication of radial keratotomy (RK). Long-term follow-up data from the Prospective Evaluation of Radial Keratotomy study demonstrated a hyperopic shift of 1 diopter (D) or more in 43% of eyes between 6 months and 10 years after RK.1 A subsequent investigation identified a similar trend toward hyperopia in as high as 54% of eyes.2 Although there are some indications that the drift rate may slow with time, there is no evidence that the progression is finite.

Several methods have been used to correct hyperopia after RK, including LASIK3–10 and photorefractive keratectomy (PRK).11–14 The main concern of LASIK over RK is the risk of incision separation, whereas PRK carries the risk of inducing corneal haze and scarring. In the Summit therapeutic clinical trial, Maloney et al14 studied the efficacy, stability, and safety of PRK in eyes with prior refractive or cataract surgery and reported that trace haze occurred in 39 (36.4%) of 107 eyes, mild haze occurred in 11 (10.3%) of 107 eyes, moderate haze occurred in 5 (4.7%) of 107 eyes, and marked haze occurred in 3 (2.8%) of 107 eyes 1 year after the PRK. Nassaralla et al12 reported that intraoperative application of mitomycin C (MMC) 0.02% for 2 minutes is effective in preventing subepithelial haze after PRK in patients with previous RK.

Wavefront-guided PRK (WG PRK) has been used widely clinically. The authors are unaware of any studies

investigating WG PRK with prophylactic MMC in eyes after RK. In this multicenter study, the outcomes of WG PRK with prophylactic MMC in eyes with previous RK were evaluated.

Figure 1. Bar graphs showing the cumulative Snellen uncorrected visual acuity (UCVA) before and at the last postoperative visit in (A) the myopic wavefront-guided photorefractive keratectomy (WG PRK) group and (B) the hyperopicWGPRK group. Post-Op
after surgery; Pre-Op
before surgery.

Institutional review board approval was obtained for this study. All cases that underwent WG PRK with prophylactic MMC in post-RK eyes from 4 study centers were reviewed retrospectively. Eyes were excluded if they were treated for near vision or had fewer than 6 months of postoperative follow up. A total of 32 eyes

Figure 2. Bar graphs showing the change in Snellen lines of best spectaclecorrected visual acuity (BSCVA) from before surgery to the last postoperative visit in (A) the myopic wavefront-guided photorefractive keratectomy (WG PRK) group and (B) the hyperopic WG PRK group.

Figure 3. Bar graphs showing the manifest refractive spherical equivalent (MRSE) at the last postoperative visit in (A) the myopic wavefrontguided photorefractive keratectomy (WG PRK) group and (B) the hyperopic WG PRK group. D
diopters.

of 27 patients were included for analysis. The numbers of RK incisions ranged from 3 to 16. Of the 32 eyes, 7 eyes (22%) had additional astigmatic keratotomy or limbal relaxing incisions, and 10 eyes (31%) had undergone other surgical enhancements, including standard LASIK, PRK, and WG LASIK, after RK and before the WG PRK procedure studied here (Table 1, available at http://aaojournal.org). The minimum time between RK and WG PRK was 6 years.

Informed consent for the WG PRK surgery was obtained from all patients before the procedure. The preoperative measurements

Figure 4. Scattergrams showing attempted correction versus achieved correction at the last postoperative visit in (A) the myopic wavefrontguided photorefractive keratectomy (WG PRK) group and (B) the hyperopic WG PRK group. Dashed lines indicate1 diopter (D) of prediction errors.

included uncorrected visual acuity (UCVA), subjective manifest refraction, best spectacle-corrective visual acuity (BSCVA), intraocular pressure, pachymetry, and corneal topography using either the Humphrey Atlas (Carl Zeiss Meditec, Inc., Pleasanton, CA) or Orbscan (Bausch & Lomb, Rochester, NY). Ocular wavefront aberrations were measured with the WaveScan (Advanced Medical Optics, Inc., Santa Ana, CA). Each WG PRK was performed by 1 of 4 experienced refractive surgeons at 1 of the respective study sites. The corneal epithelium was debrided chemically using 20% alcohol and was irrigated with a balanced salt solution. Wavefront-guided PRK was performed with the AMO VISX Star 4 excimer laser (Advanced Medical Optics, Inc.). For the ablation algorithm, each surgeon adjusted the ablation parameters based on his own experience (Table 1, available at http:// aaojournal.org). Ablation and optical zones were 9.0 and 6.0 mm, repspectively, for hyperopes and 8.0 and 6.0 mm, repspectively, for myopes. At the conclusion of the ablation, 0.02% MMC was used with durations of 10, 15, 20, 30, 45, 60, or 120 seconds. Plano refraction was targeted for all eyes.

At the conclusion of surgery, a bandage contact lens was placed on the cornea. Topical antibiotics were prescribed for 5 to 7 days, and corticosteroid drops were prescribed initially 4 times daily to be discontinued at day 6 or tapered over 2 to 3 months. Follow-up visits were classified as 1 month for postoperative visits between 3 and 5 weeks, 3 months for visits between 10 and 14 weeks, 6 months for visits between 4 and 8 months, and 12 months for visits between 10 and 14 months.

Outcome measures for this study were UCVA, BSCVA, manifest refraction, and corneal haze. Data from all available eyes were included on designated follow-up dates. Geometric visual acuity was converted to the logarithm of the minimum angle of resolution units, and manifest refraction was converted to spherical equivalent refraction where appropriate. Preoperative BSCVA was compared with postoperative UCVA and BSCVA to ascertain efficacy and safety. Preoperative and postoperative refraction data were used for stability and accuracy calculations. Haze was graded as clear cornea, trace haze that could be seen only with broad-beam illumination, mild haze visible by slit-beam illumination, moderate haze somewhat obscuring iris details, or marked haze obscuring iris detail. The paired t test was used to compare the visual acuity in logarithm of the minimum angle of resolution units and the spherical equivalent before and after WG PRK. Statistical analysis was performed with SPSS software version 15.0 for Windows (SPSS, Inc., Chicago, IL), and a P value of 0.05 or less was considered significant.

The mean age of the 27 patients was 519 years (meanstandard deviation; range, 33–64 years). Of the 27 patients, 18 were male and 9 were female.

Of the 32 eyes, 9 eyes underwent myopic WG PRK. The mean preoperative spherical equivalent was –1.080.55 D (range, –1.75 to –0.13 D), and astigmatism was 2.111.51 D (range, 0.50 –5.50 D). The mean follow-up was 11.35.8 months (range, 6–21 months). The numbers of eyes available for follow-up were 8 eyes (89%) at 1 month, 6 eyes (67%) at 3 months, 4 eyes (44%) at 6 months, and 5 eyes (56%) at 12 months..

Twenty-three eyes had hyperopic WG PRK. The mean preoperative spherical equivalent was 1.741.00 D (range, 0.00–4.00 D), and astigmatism was 1.230.58 D (range, 0.00 –2.50 D). The mean follow-up was 10.93.3 months (range, 6–18 months). The numbers of eyes available for follow-up were 23 eyes (100%) at 1 month, 20 eyes (87%) at 3 months, 19 eyes (83%) at 6 months, and 17 eyes (74%) at 12 months.

In the myopic WG PRK group, UCVA improved in all eyes from before surgery to the last visit after surgery (Table 2), with an average improvement of 3 lines (P = 0.015). The percentage of eyes with UCVA of 20/20 or better increased from 0% before surgery to 56% after surgery, and the percentage of eyes with UCVA of 20/40 or better increased from 56% before surgery to 100% after surgery (Fig 1A). The efficacy index was 0.89.

In the hyperopic WG PRK group, UCVA improved in all eyes except 1 from before surgery to the last visit after surgery (Table 2), with an average improvement of 3 lines (P0.001). The percentage of eyes with UCVA of 20/20 or better increased from 0% before surgery to 48% after surgery, and the percentage of eyes with UCVA of 20/40 or better increased from 48% before surgery to 100% after surgery (Fig 1B). The efficacy index was 0.85.

In the myopic WG PRK group, 3 eyes (33%) lost 1 line of BSCVA at last visit compared with the preoperative BSCVA (Fig 2A). All these 3 eyes had BSCVA of 20/15 before surgery and BSCVA of 20/20 after surgery. No eyes lost 2 lines or more of BSCVA, and 2 eyes gained 2 lines of BSCVA. The safety index was 1.09.

In the hyperopic WG PRK group, 5 eyes (22%) lost 1 line of BSCVA at last visit compared with the preoperative BSCVA (Fig 2B). Of the 5 eyes, 2 eyes had BSCVA of 20/15 before surgery and BSCVA of 20/20 after surgery. One eye lost 2 lines of BSCVA; this was the eye in which mild to moderate haze developed 12 months after surgery. Four months later, the haze severity diminished to trace, and BSCVA improved 2 lines to the preoperative BSCVA of 20/20. No eyes lost more than 2 lines of BSCVA, and 1 eye gained 2 lines of BSCVA. The safety index was 1.00.

Figure 5. Graphs showing the refractive spherical equivalent in eyes evaluated at 3 and 12 months after surgery: (A) myopic (n = 5) and (B) hyperopic (n = 14). Error bars indicate 1 standard deviation. D = diopters; Pre-Op = before surgery; SE = spherical equivalent.

BSCVA = best spectacle-corrected visual acuity; D = diopters; DLK = diffuse lamellar keratitis; n/a = not applicable; PRK = photorefractive

For the myopic WG PRK group, postoperative manifest refraction is shown in Table 2. At last visit after surgery, 55% of eyes were within 0.50 D of desired postoperative refraction, and 100% of eyes were within 1.00 D of desired refraction (Figs 3A and 4A).

For the hyperopic WG PRK group, postoperative manifest refraction is shown in Table 2. At last visit after surgery, 57% of eyes were within 0.50 D of desired postoperative refraction, and 74% of eyes were within 1.00 D of desired refraction (Figs 3B and 4B).

Refractive stability was seen in the small number of eyes evaluated both at 3 and 12 months after surgery (5 in the myopic group [Fig 5A] and 14 in the hyperopic group [Fig 5B]). In the myopic WG PRK group, none of the 5 eyes had a change of 1.00 D in spherical equivalent between 3 and 12 months (Fig 5A). In the hyperopic WG PRK group, 1 of 12 eyes that was examined at both 6 and 12 months had a change of 1.00 D in spherical equivalent between 6 and 12 months. This eye had manifest refraction of –0.25+0.2560 at 6 months and +1.25+0.2595 at 12 months.

A representative example of the topographic changes induced by the hyperopic WG PRK is shown in Figure 6. Although the simulated keratometry values that measure the power at the 3-mm diameter showed slightly lower values after WG PRK than those before the surgery, the mean powers within the central zones of 2 mm, 3 mm, and 4 mm increased after surgery, and the Q value decreased from 1.19 to 0.74, indicating a less oblate surface after the procedure. Difference maps for both axial and tangential curvatures showed obvious central steepening.

Of the 32 eyes, haze developed in 6 eyes (19%) at some point in the postoperative course (Table 3). Mild to moderate haze formation was noted in 1 eye; the preoperative spherical equivalent was +3.00 D, and MMC was applied for 60 seconds. The haze was noted at 12 months after surgery, and the BSCVA was 20/32; at 16 months, the mild to moderate haze diminished to trace haze, and BSCVA had improved to 20/20. Trace haze was noted in the other 5 corneas (MMC duration of 15 seconds or fewer). In none of the 4 eyes receiving more than 60 seconds of MMC treatment did haze develop. There were no other complications noted at any visits.

Undercorrection and long-term hyperopic shift are frequent complications of radial keratotomy. Previous studies addressed the use of conventional (not WG) LASIK and PRK with MMC in this role. For virgin corneas, the application of wavefront technology to refractive surgery has demonstrated improvements in UCVA, BSCVA, low-contrast acuity, and general patient satisfaction.15 This study evaluated WG PRK using MMC as a possible treatment option for correcting refractive errors in RK eyes.

Haze is a well-recognized complication of surface ablation in post-RK eyes. In the Summit therapeutic clinical develin the Literature

keratectomy; RK = radial keratotomy; UCVA = uncorrected visual acuity.

trial,14 in 107 eyes with prior RK (90.7%), astigmatic keratotomy (6.5%), hexagonal keratotomy (0.9%), or cataract surgery (1.9%), trace haze occurred after PRK in 36.4% of eyes, mild haze occurred in 10.3% of eyes, moderate haze occurred in 4.7% of eyes, and marked haze occurred in 2.8% of eyes. A moderate correlation (r2 = 0.55) was found between the severity of the haze and the number of lines of Snellen visual acuity loss under glare conditions. In this study, 32% of eyes lost 2 lines or more of BSCVA with glare.

Mitomycin C has been shown to be an effective tool to combat the formation of corneal haze after refractive surgery. In the prospective randomized masked study, Carones et al16 reported that prophylactic use of 0.02% MMC applied after PRK for medium and high myopia produced lower haze rates, with none of the eyes in the study group having a haze rate higher than 1, compared with 63% of eyes in the control group (P = 0.01). Nassaralla et al12 demonstrated the safety and efficacy of a 2-minute intraoperative application of 0.02% MMC in 22 eyes receiving PRK after RK.

The present data showed that WG PRK with MMC improved UCVA in 31 of the 32 treated eyes; the average improvement was 3 lines. All eyes had UCVA of 20/40 or better at last visit after surgery, compared with 50% and 48% at baseline in the myopic and hyperopic groups, respectively. Additionally, 13 of the 22 eyes available for follow-up at postoperative month 12 had UCVA of 20/20 or better. By 6 months after surgery, 1 eye transiently lost 2 lines of BSCVA resulting from mild to moderate haze development, but this improved to 20/20 by 4 months later. No eye lost more than 2 lines of BSCVA. In terms of refractive accuracy, 100% of eyes were within +1.00 D of desired refraction in the myopic WG PRK group, and 74% of eyes were within 1 D of attempted refraction in the hyperopic WG PRK group. Stability was good over the short interval of this study, with only 1 eye (from the hyperopic WG PRK group) experiencing a change of >1.00 D in spherical equivalent between 6 and 12 months. Trace corneal haze developed in 5 of 32 eyes, and mild to moderate haze was noted in 1 cornea at 12 months after surgery. Fortunately, this faded to trace 4 months later. No other complications were reported.

Table 4 summarizes the results from studies that evaluated the efficacy and safety of conventional LASIK and PRK for treatment of residual myopia or hyperopia in RK eyes. Compared with these other studies, higher percentages of eyes in the present WG PRK patients achieved UCVA of >20/20 and >20/40.

Comparing the safety of LASIK versus PRK, the primary complications of LASIK are RK incisional separation during the flap manipulation and epithelial ingrowth. With PRK, the major reported complication has been haze, although no central or optically significant corneal haze was reported by Joyal et al11 in their retrospective review of 53 eyes that underwent PRK to correct hyperopic shift after RK. In this study, the authors did not grade the haze, nor did they define the area and extend of central or optically significant haze. Using an application of MMC 0.02% solution for 2 minutes, Nassaralla et al12 reported haze development in 5 (22.7%) of 22 eyes.

Figure 6. Representative examples of topographic changes induced by the hyperopic wavefront-guided photorefractive keratectomy: (A) axial curvature maps and (B) tangential curvature maps. (Top left) Preoperative map; (Bottom left) 6-month postoperative map; and (Right) difference map (postoperative–preoperative).

In the present study, 0.02% MMC was used with durations of 10 to 120 seconds, and trace haze was noted in 5 (16%) of 32 eyes, and mild to moderate haze was noted in 1 (3%) of 32 eyes. Of 32 eyes, no eye experienced persistent visual loss from haze. Haze formation in RK eyes may be affected by many factors, possibly the number of RK cuts and the amount of attempted correction. In this cohort, the 5 eyes that experienced trace haze had MMC use of 15 seconds, 4 and 8 RK cuts, and relatively small attempted correction (0.25 to 1.75 D spherical equivalent in magnitude). The eye in which moderate haze developed had received MMC for 60 sec-onds, indicating that the MMC obviously is not the only factor that determines the haze response; this eye had a relatively high intended correction (+3 D). In none of the 4 eyes receiving MMC for 120 seconds did haze develop. More studies are required to elucidate the factors that predispose eyes to postoperative haze and to define the appropriate duration of MMC use in these RK eyes.

Ocular integrity after refractive procedures has been investigated. The RK eyes ruptured with significantly less energy than did normal eyes.17,18 Eyes that have undergone the RK procedure are predisposed to rupture resulting from blunt trauma. Additional procedures carried out on a cornea that already has been treated with the RK may increase the likelihood of rupture in blunt trauma.19 Patients with RK and additional corneal procedures should be informed of this possible risk and complication.

Limitations of this study include: (1) the relatively small number of eyes; (2) follow-up being relatively short to determine the stability, given the known long-term hyperopic shift that can occur in RK eyes; (3) follow-up rates being relatively low, so there could be bias regarding the outcomes of the subgroup of patients who returned for later visits; and (4) changes in wavefront aberrations not being investigated because of lack of wavefront measurements during follow-up visits.

In summary, these preliminary results demonstrated that the WG PRK with MMC in eyes with prior RK significantly improved UCVA, and 74% of eyes were within 1 D of attempted refraction. At last visit, BSCVA lost 1 Snellen line in 33% and 22% of myopic and hyperopic eyes, respectively. Sight-threatening haze was rare and produced no persistent visual loss. Additional work is desirable to investigate the safety, efficacy, and long-term benefits of this approach.

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Originally received: August 28, 2008.
Final revision: May 8, 2009.
Accepted: May 8, 2009.
Available online: July 29, 2009.      Manuscript no. 2008-1036.

• Department of Ophthalmology, Baylor College of Medicine, Houston, Texas.


• Maloney Vision Institute, Los Angeles, California.


• Minnesota Eye Consultants, Minneapolis, Minnesota.


• Dell Laser Consultants, Austin, Texas.

Presented in part at: American Society of Cataract and Refractive Surgery Annual Meeting, April 2008, Chicago, Illinois.

Financial Disclosure(s):
The author(s) have made the following disclosure(s):

Douglas D. Koch - Consultant - Alcon Surgical, Inc; Speaker’s Bureau - Abbott Medical Optics Inc.

Robert Maloney - Consultant - Advanced Medical Optics, Inc.; Equity Holder and Consultant - Calhoun Vision, Inc.; Speaker’s Bureau - Optos, Inc.

David R. Hardten - Consultant - Advanced Medical Optics.

Steven Dell - Consultant - Advanced Medical Optics.

Drs Sweeney and Wang do not have financial interests in any material or method mentioned.

Supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York.

Correspondence:
Douglas D. Koch, MD, Cullen Eye Institute, Baylor College of Medicine, 6565 Fannin Street, NC 205, Houston, TX 77030. E-mail: dkoch@ bcm.tmc.edu.

D = diopters.
*Eyes that had other surgical enhancements before the wavefront-guided photorefractive keratectomy treatment.