Laser in situ keratomileusis in United States Naval aviators

Transcription

1 ARTICLE Laser in situ keratomileusis in United States Naval aviators David J. Tanzer, MD, Tyson Brunstetter, OD PhD, Richard Zeber, OD, Elizabeth Hofmeister, MD, Sandor Kaupp, MS, Neil Kelly, PhD, Myah Mirzaoff, William Sray, MD, Mitch Brown, OD, Steven Schallhorn, MD PURPOSE: To evaluate the safety and efficacy of femtosecond-assisted wavefront-guided laser in situ keratomileusis (LASIK) as well as higher-order aberrometric changes in a population of activeduty United States Naval aviators. SETTING: Navy Refractive Surgery Centers, San Diego, California, and Portsmouth, Virginia, USA. DESIGN: Prospective noncomparative 2-site study. METHODS: In this study of femtosecond-assisted wavefront-guided LASIK, 3 groups were differentiated according to the refractive status: myopia, mixed astigmatism, and hyperopia. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction, mesopic low-contrast CDVA, higher-order aberrations (HOAs), and patient satisfaction were evaluated during a 3-month follow-up. RESULTS: The study enrolled, treated, and included for analysis 548 eyes with myopia, 60 eyes with mixed astigmatism, and 25 eyes with hyperopia. The UDVA was 20/20 or better in 98.3% of eyes with myopia and mixed astigmatism at all postoperative visits and in 95.7% of hyperopic eyes 3 months postoperatively. The gain in CDVA was 1 or more lines in 39.2%, 41.1%, and 30.4% of myopic, mixed astigmatic and hyperopic eyes, respectively. Loss of 2 lines of CDVA after surgery occurred in 2 myopic eyes (0.4%). At 3 months, a mean change of C0.03 mm G 0.10 (SD) and C0.05 G 0.08 mm was observed in higher-order root mean square and primary spherical aberration, respectively. Of the patients, 95.9% said they believed that LASIK had helped their effectiveness as Naval aviators and 99.6% would recommend the same treatment to others. CONCLUSION: Femtosecond-assisted wavefront-guided LASIK was an efficacious and safe option for refractive correction in Naval aviators, enabling a quick return to flight status. Financial Disclosure: Drs. Tanzer and Schallhorn are consultants to Abbott Medical Optics, Inc. No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2013; 39: Q 2013 ASCRS and ESCRS Laser in situ keratomileusis (LASIK) is a U.S. Food and Drug Administration approved procedure that has been shown to be safe, effective, and efficient for the correction of refractive errors and has experienced significant advances since the early days of its use. 1,2 This technological development has led to fewer complications related to the excimer laser ablation and creation of the corneal lamellar flap. For this reason, LASIK has been proposed as a valid treatment option for patients with high visual demands seeking spectacle and/or contact lens independence, such as United States Naval aviators. 3 7 The Naval aviator represents one of the highest value personnel assets in the military; it costs approximately $5 million to fully train an aircraft carrier based pilot. Therefore, any elective surgical procedure, such as LASIK, should be carefully evaluated before being performed on these patients. To this end, many military-based studies have been performed to evaluate the safety and efficacy of LASIK, including the quality of vision and unique environmental conditions. 3 6 These reports indicate that LASIK should provide a safe and effective refractive option for Naval aviators. However, it is not known what impact Q 2013 ASCRS and ESCRS Published by Elsevier Inc /$ - see front matter

2 1048 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS LASIK may have on this dynamic population, such as the effect of higher-order aberrometric changes induced by the surgery, the subjective evaluation of the impact of the surgery on activities specific to high-performance flight status, the real improvement of using a wavefront-guided ablation profile, and the potential risk for significant complications. Cases of late traumatic flap displacement and even traumatic flap loss after LASIK have been reported in military personnel. 8,9 The aim of the current study was to evaluate the safety and efficacy of wavefront-guided LASIK using femtosecond technology for flap creation in a large population of active-duty U.S. Naval aviators and to assess the impact of the surgery on the aviators' activities. PATIENTS AND METHODS Patients This prospective noncomparative 2-site study comprised consecutive eyes of U.S. Naval aviators having LASIK surgery. This study was approved by the local ethics committee and was performed in accordance with the ethical standards in the Declaration of Helsinki. Written informed consent was obtained after the nature of the procedure was explained before surgery. Authorization from the patient's commanding officer was also obtained before study enrollment and LASIK treatment. Three groups were differentiated according to Submitted: December 13, Final revision submitted: January 15, Accepted: January 15, From the Navy Refractive Surgery Center (Tanzer, Brunstetter, Zeber, Hofmeister, Kaupp, Kelly, Mirzaoff, Brown, Schallhorn), Naval Medical Center, San Diego, California, and the Navy Refractive Surgery Center (Sray), Naval Medical Center, Portsmouth, Virginia, USA. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government. The Commander, Naval Air Forces and the Force Medical Officer, Captain Kris Belland, MC (FS), USN, provided operational guidance and funding throughout the duration of the study. Past research directors of the Navy Refractive Surgery Center, Naval Medical Center San Diego (John Laurent, OD, PhD, Corina van de Pol, OD, PhD, Andy Engle, OD) contributed to protocol development and study execution. Numerous fleet Navy optometrists referred patients for surgery and provided postoperative support after their return to their parent command. Presented at ASCRS Symposium on Cataract, IOL, and Refractive Surgery, San Diego, California, USA, April Corresponding author: David J. Tanzer, MD, 8910 University Center Lane, Suite 800, San Diego, California 92122, USA. djtanzermd@yahoo.com. the refractive status: myopia group, hyperopia group, and mixed astigmatism group. Inclusion criteria consisted of myopic spherical equivalent (SE) up to diopters (D) with no more than 3.50 D of refractive astigmatism, hyperopic SE up to C3.75 D with no more than 2.75 D of refractive astigmatism, corrected distance visual acuity (CDVA) of 20/20 or better in both eyes, demonstrated refractive stability (spherical and cylindrical changes less than 0.50 D for myopic patients and 0.75 D for hyperopic patients during the 12 months immediately preceding the preoperative examination), and age at least 21 years to ensure documentation of refractive stability. Exclusion criteria were concurrent topical or systemic medications that might impair healing, including corticosteroids, antimetabolites, isotretinoin (Accutane), amiodarone hydrochloride (Cordarone), and/or sumatriptan (Imitrex) or any other tryptan; medical conditions that might impair healing, such as collagen vascular disease, autoimmune disease, immunodeficiency diseases, or ocular herpes zoster or simplex; active ophthalmic disease; neovascularization of the cornea within 1.0 mm of the intended ablation zone; clinically significant lens opacity; evidence of glaucoma or intraocular pressure greater than 22 mm Hg at baseline; evidence of keratoconus, corneal irregularity, or abnormal videokeratography in either eye; corneal thickness insufficient to allow a residual remaining stromal bed of no less than 275 mm in each eye; history of recurrent erosions or epithelial basement dystrophy; and any physical or mental impairment that would preclude participation in any of the examinations. Soft contact lens wearers were asked to discontinue use at least 1 week before the preoperative examination. Poly(methyl methacrylate) or rigid gas-permeable hard contact lens users were asked to remove their lenses at least 3 weeks before baseline measurements and had 2 central keratometry readings and 2 manifest refractions taken at least 1 week apart that did not differ by more than 0.50 D in either meridian. Examination Protocol In all cases, a comprehensive visual and ocular examination was performed preoperatively that included manifest and cycloplegic refractions; uncorrected (UDVA) and CDVA testing (4 m logmar back-illuminated eye chart, Precision Vision); pupil diameter measurement under dim light (!5 lux, 0.1 candelas [cd]/m 2 ) with the patient fixating on a distant target using the Colvard pupillometer (Oasis Medical); slitlamp biomicroscopy; applanation tonometry; corneal topography; mesopic low-contrast CDVA with a back-illuminated chart (4 m, 25% contrast Early Treatment of Diabetic Retinopathy Study back-illuminated chart, Precision Vision) using a neutral density filter to dampen emitted light to 1 cd/m 2 in a darkened examination lane, with patients dark-adapting for at least 5 minutes; ultrasound pachymetry; and wavefront aberration measurement with the Wavescan aberrometer (Abbott Medical Optics, Inc.). The wavefront data obtained preoperatively with this instrument were used for planning the optimum ablation profile in each case (wavefront-guided ablation profile) using the Customvue system (Abbott Medical Optics, Inc.). Physician adjustment of between G0.75 D sphere was used to match the aberrometry measurement to the manifest sphere; the postoperative refraction was targeted to be between emmetropia and C0.25 D sphere in all eyes.

3 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS 1049 Postoperatively, patients were examined the day after surgery and then during follow-up visits at 1 week, 2 weeks, and 1 and 3 months. On the first postoperative day, a detailed slitlamp examination was performed to evaluate the flap position and integrity of the cornea. At the remaining postoperative visits, the same examinations as preoperatively (excluding cycloplegic refraction) were performed. A psychometric questionnaire developed for previous aviation-related research protocols was administered at the initiation of the study (before surgery) and 1, 2 and 3 months post-lasik. The questionnaire was given at the beginning of the examination with sufficient time allotted to ensure completion. The questionnaire assessed satisfaction after the procedure and the impact of surgery on the patient's activities. The questionnaire was self-administered and reviewed for completion before the examination was concluded. Surgical Technique All LASIK procedures were performed by experienced surgeons who were certified to use the requisite equipment (D.J.T., E.H., W.S., S.S.). For all procedures, the limbus was marked at 3 o'clock and 9 o'clock with a sterile marking pen at a slitlamp immediately before treatment. The treatment designed according to the preoperative refraction and aberrometric profile was loaded into the excimer laser computer and reviewed by the surgeon to confirm the data. The excimer laser used in this study was operated while maintaining the environmental conditions for appropriate use during surgery (relative humidity 40% to 45%; temperature 68 Fto72 F). After patient positioning and ablation profile confirmation by the surgeon, a corneal flap was created with a femtosecond laser (Intralase 60 or 150 khz, Abbott Medical Optics, Inc.) and lifted before corneal laser ablation. The femtosecond laser system was programmed to create a flap between 8.5 mm and 9.0 mm or greater at a target depth between 110 mm and 120 mm. The 60 khz laser was programmed to create a side-cut angle of 70 degrees, while the 150 khz laser created side-cut angles between 120 degrees and 140 degrees (ie, reverse bevel). All flaps were created with superior hinges. After the flaps were lifted, the programmed treatment was applied to the exposed stroma after iris registration was attempted/ achieved. All wavefront-guided ablations had an optical zone (minor axis) of 6.0 mm with a transition zone extending to a minimum of 8.0 mm for myopic ablations and 9.0 mm for hyperopic and mixed astigmatism ablations. All surgical procedures were performed under topical anesthesia. Regular topical postoperative treatment was administered to all patients in the form of moxifloxacin (Vigamox) 1 drop 4 times a day for 7 days, prednisolone acetate 1.0% 1 drop 4 times a day for 7 days, cyclosporine 0.05% (Restasis) 1 drop twice a day for 1 month, and preservative-free artificial tear drops 1 drop 4 times a day for 2 weeks and then as needed. the Kolmogorov-Smirnov test. The Student t test for paired data was used for comparisons between preoperative and postoperative data. Differences were considered statistically significant when the associated P value was less than The standard graphs for reporting the outcomes of refractive surgery according to the Waring protocol 10 were used for displaying and summarizing the main outcomes in this study. Safety of the procedures was evaluated using the following variables: corneal clarity, induction of higher-order aberrations (HOAs), preservation of CDVA, and the occurrence of adverse events. Efficacy was assessed by the improvement in UDVA, achievement of intended refractive correction, and patient satisfaction/visual complaints. Refractive stability was assessed by the change in manifest refraction over time. RESULTS The study enrolled 651 eyes of 330 patients, 100 Class I pilots in actual control of aircraft and 230 Class II aircrew. Surgical procedures were performed in 633 eyes with the Visx Star S4 IR excimer laser (Abbott Medical Optics, Inc.) (included in data analysis) and in 17 eyes with the Allegretto 400 Hz IQ Wavelight laser (Alcon) (excluded from data analysis). One eye required a Visx conventional ablation and was also excluded from data analysis. Thus, the results are reported for 633 eyes receiving wavefront-guided LASIK. Due to high military demands, not all patients were available to return to the clinic for every followup visit. Therefore, analyses were performed on the data available from each visit; the sample sizes are shown in the figures. Three groups were differentiated in the sample of 631 eyes according to the refractive status (SE range C4.1 to 8.6 D): myopia group (544 eyes, mean age 33 years, mean SE 2.56 D), hyperopia group (30 eyes, mean age 36 years, mean SE C1.86 D), and mixed astigmatism group (57 eyes, mean age 36 years, mean SE 0.34 D). Figure 1 shows the distribution of preoperative SE in the overall sample. Statistical Analysis Data analysis was performed using SPSS for Windows software (version 19.0, International Business Machines Corp.). Normality of data samples was confirmed using Figure 1. Distribution of preoperative SE in the overall sample.

4 1050 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS Visual Outcomes The UDVA was 20/20 or better in 558 (98.2%) of 568 treated eyes 3 months after wavefront-guided LASIK. Ten of 560 eyes seen at the final visit had a UDVA worse than 20/20 (9 myopic and 1 hyperopic treatments); however, all eyes had a CDVA of 20/20 or better. The postoperative UDVA was 20/20 or better in more than 98.0% of eyes at all visits in the myopia group (range 537 [98.0%] of 548 eyes to 518 [99.4%] of 521 eyes) (Figure 2, A) and mixed astigmatism group (range 59 [98.2%] of 60 eyes to 56 [100%] of 56 eyes) (Figure 2, B). In the hyperopia group, the postoperative UDVA was 20/20 or better in 19 (76.0%) of 24 eyes at 1 week. This increased to 22 (95.7%) of 23 eyes at the end of the follow-up period (Figure 2, C). Three months postoperatively, the UDVA was 20/10 in 113 (22.7%) of 497 eyes in the myopia group, 4 (8.3%) of 48 eyes in the mixed astigmatism group, and 3 (13.0%) of 23 eyes in the hyperopia group. The CDVA was maintained at 20/20 or better in 604 of 605 eyes (99.8% through the 4-week postoperative examination). By the final examination, all eyes Figure 2. Distribution of postoperative UDVA at different follow-up visits in the myopia (A), mixed astigmatism (B), and hyperopia (C) groups. Figure 3. Distribution of postoperative CDVA at different follow-up visits in the myopia (A), mixed astigmatism (B), and hyperopia (C) groups.

5 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS 1051 Figure 4. Distribution of changes in postoperative CDVA 1 month (A) and 3 months (B) after surgery (Chg Z change). had a CDVA of 20/20 or better. Figure 3, A to C, shows the subgroup analysis in each refractive group. In all groups, gains of 1 or more lines of CDVA were observed in more than 23% of cases (208 [39.2%] of 527 eyes in myopic group, 22 [41.1%] of 53 eyes in mixed astigmatism group, and 7 [30.4%] of 23 eyes in hyperopic group 1-month postoperative visit) during the follow-up (Figure 4, A and B). At the end of the follow-up, a loss of 1 line of CDVA was observed in 13 (2.6%) of 498 eyes and 1 (4.3%) of 23 eyes in the myopia group and hyperopia group, respectively (Figure 4, B). No loss of CDVA was observed in any case in the mixed astigmatism group. A loss of 2 lines of CDVA after surgery was observed in 2 eyes (0.4%) in the myopia group (Figure 4, B). Regarding mesopic low-contrast (25%), CDVA test retest variability analysis performed at the Navy Refractive Surgery Center found that a significant change was outside G0.8 line. A Therefore, lowcontrast CDVA improved significantly in a number of cases, with more than 40% of eyes in all groups (202 [41.4%] of 486 eyes in myopic group, 23 [47.5%] of 48 eyes in mixed astigmatism group, and 12 [52.6%] of 23 eyes in hyperopic group) gaining at the end of the follow-up period (Figure 5, A and B). After 3 months, loss of low-contrast CDVA was observed in 25 (5.1%) of 486 eyes in the myopic group, 5 (10.4%) of 48 eyes in the mixed astigmatism group, and 4 (17.4%) of 23 eyes in the hyperopia group (Figure 5, B). The efficacy index, defined as the ratio of postoperative UDVA to preoperative CDVA, averaged 90% in all groups at 3 months after surgery (Figure 6). This index was lower in the hyperopia group during the initial postoperative period (36% at day 1), with an increase afterward to the levels in the myopia and mixed astigmatism groups (91% at 3 months) (Figure 6). Refractive Outcomes In all groups, almost all eyes maintained a postoperative SE within G1.00 D during the entire follow-up Figure 5. Distribution of changes in postoperative low-contrast CDVA 1 month (A) and 3 months (B) after surgery (Chg Z change).

6 1052 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS Figure 6. Efficacy index by group. (Figure 7, A to C). The mean SE was close to zero at all follow-up visits, with a slight trend toward a myopic SE during the initial postoperative period in the hyperopia group, which stabilized at the 1-month postoperative examination (Figure 7, C). Aberrometric Outcomes Table 1 shows the ocular aberrometric outcomes obtained postoperatively in the 3 groups. A mean change of C0.03 mm G 0.10 (SD) and C0.05 G 0.08 mm was observed in higher-order root mean square and primary spherical aberration, respectively, compared with preoperative levels. These changes, although small in magnitude and not believed to be clinically relevant, were statistically significant (P!.01) (Figure 8, A and B). Subjective Questionnaire Outcomes Two hundred eighty-nine (94.9%) of 305 patients reported that vision was much better (238 patients [78.1%]) or better (51 patients [16.8%]) than they expected after surgery. Sixteen patients [5.1%] said that their vision remained unchanged relative to the use of spectacles and/or contact lenses, and no one said that their vision was worse after LASIK. Regarding the impact on the patient's activities, 292 (95.8%) of 305 patients reported that LASIK had helped their effectiveness as Naval aviators, with 258 patients (84.5%) stating that LASIK had definitely helped. Thirteen patients (4.2%) reported the same level of effectiveness before and after surgery. Three hundred one (99.6%) of 305 patients would recommend LASIK treatment to naval aviators, with 300 patients (98.2%) stating they would definitely recommend LASIK to a fellow Naval aviator. One patient (formerly myopic and pre-presbyopic) became slightly farsighted after surgery and had mild near-vision fatigue. Despite having 20/16 UDVA, this patient would not recommend LASIK to a fellow aviator. Figure 7. Change in manifest refraction SE during postoperative follow-up in the myopia (A), mixed astigmatism (B), and hyperopia (C) groups (CI Z confidence interval). Complications No retreatments were required in any case during the follow-up period. One patient had epithelial ingrowth in 1 eye that was limited to within 1.0 mm of the flap edge and was not visually significant. It did not progress, no intervention was performed, and the final UDVA was 20/12.5. In 1 patient, the flap in the right eye was created and lifted, but no treatment was applied due to an excimer laser malfunction. In this case, the flap was replaced and photorefractive keratectomy (PRK) was planned. This eye maintained a CDVA of 20/12.5 at the final examination (before PRK).

7 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS 1053 Table 1. Mean preoperative and postoperative ocular aberrometric data stratified by preoperative refractive status. Myopia Group Hyperopia Group Mixed Astigmatism Group Parameter Preop 1 Mo Postop 3 Mo Postop Preop 1 Mo Postop 3 Mo Postop Preop 1 Mo Postop 3 Mo Postop HO RMS (mm) Mean G SD C0.26 G 0.08 C0.29 G 0.10 C0.29 G 0.09 C0.26 G 0.06 C0.37 G 0.13 C0.37 G 0.13 C0.26 G 0.07 C0.27 G 0.09 C0.24 G 0.06 Range 0.10, , , , , , , , , 0.38 Coma RMS (mm) Mean G SD C0.15 G 0.07 C0.16 G 0.09 C0.16 G 0.09 C0.15 G 0.06 C0.17 G 0.05 C0.18 G 0.09 C0.11 G 0.04 C0.12 G 0.08 C0.16 G 0.08 Range 0.01, , , , , , , , , 0.15 Trefoil RMS (mm) Mean G SD C0.13 G 0.07 C0.11 G 0.08 C0.11 G 0.06 C0.13 G 0.06 C0.11 G G 0.09 C0.16 G 0.09 C0.16 G 0.09 C0.21 G 0.14 Range 0.01, , , , , , , , , 0.28 SA (mm) Mean G SD C0.06 G 0.09 C0.12 G 0.09 C0.11 G 0.12 C0.10 G G G 0.20 C0.09 G 0.08 C0.06 G 0.09 C0.05 G 0.07 Range 0.33, , , , , , , , , 0.20 HO Z higher order; RMS Z root mean square; SA Z spherical aberration DISCUSSION Photorefractive keratectomy has been evaluated extensively for Naval aviation 4,7,11 and has been shown to be efficacious in reducing refractive errors and improving uncorrected vision. Indeed, PRK has been approved as a waiverable procedure for Naval aviators. One of its potential limitations is a relatively slow visual recovery, requiring at least 3 months of down time before an aviator can return to flight status. Laser in situ keratomileusis has been proposed as an alternative for refractive correction in Naval aviators, 3,4 with the potential of providing a faster visual recovery and return to full duty. However, not only is the surgical technique an important factor in the refractive correction of Naval aviators; the ablation profile is also a key component to consider in the safety and efficacy of LASIK in this unique patient population. In a previous study, 3 our research group found that night-driving visual performance after wavefront-guided LASIK to correct myopia combined with a femtosecond laser flap was significantly better than after conventional LASIK using a mechanical microkeratome. Wavefront-guided LASIK is effective not only in correcting the spherocylindrical error but also in minimizing HOAs The current study was aimed at evaluating the results of wavefront-guided LASIK using femtosecond technology for flap creation in a large population of activeduty U.S. Naval aviators. Analysis included visual and refractive outcomes as well as evaluation of mesopic low-contrast acuity, induction of HOAs, and the impact of surgery on the aviator's activities. The goal was to obtain a general overview of the safety, efficacy, and performance of wavefront-guided LASIK in this type of patient. In the current series, the postoperative UDVA was 20/20 or better in the majority of all eyes treated in Figure 8. Distribution of the changes in aberrometric parameters evaluated in the analyzed sample. A: Higher-order RMS. B: Primary spherical aberration.

8 1054 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS each refractive group analyzed, especially by the end of the follow-up period. Our myopic group had excellent UDVA outcomes, with 98.0% of eyes having a UDVA of 20/20 or better beginning the first postoperative day. This outcome was even better than that reported in previous studies using similar, as well as alternative, excimer laser platforms (Table ,17 22 ). It should be considered that differences in sample size, excimer laser technology, patient age, and examination protocols between studies may have accounted for some of the differences observed in Table 2. Jabbur et al. 17 found results relatively similar to those obtained in the current study in a sample of 351 eyes having wavefront-guided LASIK with the same laser platform used in our patients (Visx Star S4 with iris registration), with 94% of eyes and 74% of eyes achieving a UDVA of 20/20 and 20/16, respectively, 6 months after surgery. The excellent uncorrected visual outcome obtained in the myopia group was consistent with the significant reduction in the SE observed beginning the first day after LASIK and the stability of the correction achieved during the entire follow-up. Indeed, an efficacy index of more than 90% was observed beginning the second postoperative week. The standards of the Naval Aerospace Medical Institute (NAMI) consider the presence of 20/20 vision (uncorrected or corrected), refractive stability (defined as no change greater than 0.50 D in sphere or cylinder over 2 examinations separated by at least 1 week), no subjective visual complaints (eg, glare, halo, starbursts, ghosting, dryness), and a normal slitlamp examination consistent with post- LASIK conditions for a safe return to flight status after excimer laser refractive surgery. B Following the guidance established by NAMI, the outcomes obtained in our myopia group support a return to full flight status for Naval aviators having myopic wavefront-guided LASIK as soon as 2 weeks after surgery, which represents a return to flight duty 6 times faster than that of aviators having PRK. 7 This interval is consistent with a case report describing the return to flight status of an Israeli military jet pilot after conventional LASIK. 6 Having an aviator return to flight status as soon as possible after surgery has significant benefit to the warfighter community and to the operational readiness of the aviator. The UDVA results in the mixed astigmatism group were quite similar to those in the myopia group, confirming the excellent performance of wavefrontguided LASIK for patients with such a refractive error. Our outcomes were slightly better than those reported previously by Khalifa et al. 20 for mixed astigmatism, who also used the Visx laser platform. The better uncorrected visual outcomes were consistent with the refractive results obtained in this group, with stability occurring 2 weeks after LASIK. The iris-registration feature of the excimer laser used, which is designed to compensate for any torsional change between the sitting position and the supine Table 2. Visual and refractive outcomes obtained by other studies after wavefront-guided LASIK. Percentage Study*/Year Eyes Mean G SD or Range of Preop SE (D) Excimer Laser Postop UDVA 20/20 or Better Postop SE G0.50 D Loss 2 lines CDVA FU (Mo) Current , 7.00 Visx Star S d C1.00, C d 0 57 d 92.3 d 0 Keir 21 / C1.00, C5.00 Ladarvision Perez-Straziota 12 / , 9.75 Visx Star S Moshirfar 13 / , 8.07 Visx Star S Khalifa 20 / C1.00 G 1.69 sph Visx Star S G 5.60 cyl Keir 14 / , 6.50 Ladarvision Schallhorn 15 / , , 6.00 VISX Star S Awwad 22 / , 7.25 Ladarvision , 7.50 Visx Star S Jabbur 17 / , 6.50 Visx Star S Kanjani 18 / , Technolas Kohnen 19 / , 9.00 Technolas cyl Z cylinder; FU Z follow-up; SE Z spherical equivalent; sph Z sphere; UDVA Z uncorrected distance visual acuity *First author

9 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS 1055 position and for pupil centroid shift, which occurs in varying lighting conditions between the aberrometer and actual laser ablation, contributes to the effective correction of astigmatism, as shown previously. 20 According to the visual and refractive results in this group of mixed astigmatic aviators, a short return to flight status of approximately 2 weeks is supported, comparable to that in the myopic group. The recovery interval was slightly longer in the hyperopia group than in the other 2 groups. Visual improvement was progressive during the first postoperative month due to an initial slight myopic shift (mean 0.21 D 1 week postoperatively and improving to C0.005 D by 3 months), with 92.3% of eyes achieving a UDVA of 20/20 or better 3 months postoperatively. This result is consistent with that reported by Keir et al. 21 after hyperopic wavefrontguided LASIK. Several factors may account for this relatively slower recovery process compared with that in the myopic and mixed astigmatic groups. There may be differences in the biomechanical corneal response to increasing the relative prolate nature of the cornea inherent in a hyperopic ablation. 23,24 Another factor may be persistent accommodative ciliary muscle tone in younger hyperopic patients that relaxes over time. These visual results suggest the need for a longer return to flight (approximately 4 weeks) in hyperopic patients having wavefront-guided LASIK to achieve postoperative stability. Preservation of the CDVA is crucial for the safety of LASIK, especially in aviators, and it was evaluated in detail. Postoperative CDVA was maintained at 20/20 or better in all eyes except 1 (a hyperopic ablation that required 5 weeks to achieve 20/20 CDVA). This confirms the safety of the myopic, mixed astigmatism, and hyperopic wavefront-guided treatments in the population analyzed, as seen in previous studies evaluating the outcomes of wavefront-guided LASIK Three months after LASIK, 2 eyes had a loss of 2 lines of CDVA, for an incidence of 0.4% in the myopia group. In these 2 cases, the preoperative and postoperative CDVA was 20/20 or better; therefore, the postoperative level of visual acuity was acceptable. This outcome is consistent with results in previous studies of myopic wavefrontguided LASIK, which report an incidence of this occurrence between 0% and 2%. These losses may be attributed to uncommon induction of HOAs due to slight decentrations 25 or to corneal alterations such as punctate keratitis. 26 More than 38% of myopic eyes, 37% of mixed astigmatism eyes, and 26% of hyperopic eyes gained CDVA 3 months after wavefront-guided LASIK. A minimal incidence of loss of lines of mesopic low-contrast CDVA was also observed 3 months after surgery (1% of myopic eyes and 3% of mixed astigmatism eyes losing 2 lines of low contrast CDVA). Ten percent of myopic eyes, 13% of mixed astigmatism eyes, and 16% of hyperopic eyes gained 2 or more lines of low-contrast CDVA. This is consistent with the excellent aberrometric outcomes obtained, with a minimum mean change in primary spherical aberration and also in higher-order RMS. After wavefront-guided LASIK using the Visx laser platform, Jabbur et al. 17 also found a minimal change in some higher-order aberrometric coefficients, including primary spherical aberration (change from C0.11 G 0.08 mm preoperatively to C0.12 G 0.09 mm 6 months postoperatively). Therefore, the use of wavefront-guided ablation profiles is an excellent option for the correction of spherocylindrical errors, preserving CDVA and the eye's optical quality. Also, the creation of the flap with femtosecond technology contributed to the better aberrometric outcomes as a result of better control of flap creation (planar configuration) 27 and a minimization of the induction of aberrations associated with this process. 28 The synergistic effect of wavefront-guided ablations and femtosecond laser flap creation makes this type of treatment (wavefront-guided femtosecond laser facilitated LASIK) the preferred choice for the refractive correction of patients with high visual demands who require a relatively short visual recovery period, such as Naval aviators. In our sample, gains of 2 or more lines of CDVA were observed 3 months after surgery in 3.8% of eyes in the myopia and 4.1% in the mixed astigmatism groups; improvement of 3 lines was observed in 0.4% of myopic eyes. These percentages of gains were higher when mesopic low-contrast CDVA was analyzed. Other studies also report cases of CDVA improvement after wavefront-guided LASIK; however, the percentages vary from 1 study to another, mainly due to differences in the visual acuity scale used (Snellen or logmar) and in the examination protocols. In a sample of myopic eyes having wavefront-guided LASIK with the Visx laser platform, Schallhorn and Venter 15 found that 1.0% of eyes gained 2 lines of CDVA. In contrast, Jabbur et al., 17 using the same laser technology and for the same myopia range, report that 9.7% of eyes gained 2 lines of CDVA and 0.7% gained more than 2 lines. On the subjective questionnaire, a significant proportion of patients (95%) said their postoperative vision was better than preoperatively. This is undoubtedly due to several factors, including improved in-flight UDVA, gains of lines of CDVA, the

10 1056 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS reduction in spectacle-induced minification, and the reduction in the level of HOAs (17% at 3 months). On the questionnaire, 96% of patients said that LASIK had helped their effectiveness as Naval aviators and no one said that they were hindered by the procedure. This is due, in large part, to achieving spectacle and/or contact lens independence. Awwad et al. 22 evaluated quality-of-life changes after wavefront-guided LASIK in patients with myopia from 1.00 to 7.50 D and found a significant improvement in the quality of life after surgery, with the main changes pertaining to psychological wellbeing and social role more than to changes in visual function. In our sample, problems or limitations with spectacles and contact lenses for performing some professional activities may be the main reason a large proportion of patients believed their effectiveness as Naval aviators after surgery was improved. Technological advancements over the past decades have resulted in more sophisticated and specialized weapon systems and headgear that are essentially incompatible with spectacle wear. Other problems with spectacles include restricted peripheral vision, fogging, incompatibility with swimming/diving, laser eye protection, helmet displays, chemical/biological masks, discomfort during prolonged wear, displacement under positive acceleration, reduced clarity in inclement weather, and their immediate removal from U.S. prisoners of war. Regarding contact lens wear, soft contact lenses can absorb noxious fumes or gases and act as a reservoir for the slow release of the substance. Rigid gas-permeable contact lenses can easily dislodge while maneuvering under positive acceleration, gas bubbles can form underneath the lens during low atmospheric pressure. Likewise, solutions and replacement of contact lenses, as well as hygienic conditions, can be difficult to obtain during deployments to remote locations. Consistent with the high levels of patient satisfaction in our sample, almost all patients (99.6%) stated that they would recommend LASIK treatment to other Naval aviators. This correlates with the results of Yu et al., 29 who found that 95% of myopic patients having wavefront-guided LASIK were satisfied with the surgery and would recommend the operation to a friend or family member. There are 2 potential criticisms of the current study. First, we evaluated the outcomes of femtosecond-assisted wavefront-guided LASIK only up to 3 months after surgery. This can be considered a relatively short follow-up. Future studies with a longer follow-up would be necessary to analyze the long-term outcomes obtained with this surgery. However, as shown in Figure 7, refractive stability was achieved by 1 month in all refractive groups evaluated. Second, the study cohort included a group of healthy, motivated, intelligent, and highly competitive individuals who were required to faithfully attend all follow-up visits. As such, this group may overachieve on the visual acuity tests, trying harder than a similar age-matched group not on flight status and not in the military. It could be considered that the results in this study represent the best-case scenario; however, they represent the potential any surgeon has using similar technology. In conclusion, wavefront-guided LASIK combined with femtosecond technology for flap creation was an efficacious and safe option for the correction of the spherocylindrical error in U.S. Naval aviators, preserving CDVA, controlling ocular aberrations, and providing outstanding patient satisfaction. This technique provided a rapid visual recovery period, allowing a quick and safe return to flight status for Naval aviators (as soon as 2 weeks for myopic and mixed astigmatism patients and 4 weeks for hyperopic patients). An aviator is currently medically grounded for at least 3 months after PRK due to the prolonged visual recovery associated with this procedure. When it is considered that approximately refractive surgical procedures are performed in the U.S. military per year, the cost savings of LASIK compared with PRK in returning a military member to full-duty status is impressive. Although no significant complications or adverse events occurred in this study, potentially sight- and career-threatening complications are possible. These risks must be included in the informed consent process and must be accepted by the aviator. Acknowledgement of these risks is evidenced by LASIK having been accepted by the Naval aerospace medical and operational communities as allowable for designated and student Naval aviators. The results in this study confirm the assumption made by the National Aeronautics and Space Administration and other military entities that femtosecond laser assisted LASIK is a safe, effective, and appropriate procedure for U.S. military personnel, especially those on flight status, as well as for astronauts. 4 Furthermore, wavefront-guided LASIK combined with femtosecond technology has the potential to reduce preexisting HOAs and improving CDVA (performance-enhancing) in many Naval aviators, allowing them to perform their aviation duties more effectively after surgery. Femtosecond laser assisted LASIK represents the preferred refractive surgical procedure for U.S. Naval aviators today. Future studies evaluating the long-term stability of outcomes with this technique are necessary, as is the analysis of outcomes in a larger sample of hyperopic patients.

11 EVALUATION OF LASIK IN U.S. NAVAL AVIATORS 1057 WHAT WAS KNOWN Photorefractive keratectomy is a safe and efficacious technique for reducing refractive errors and improving uncorrected vision in Naval aviators, and it has been approved as a waiverable procedure for them. The limitation of this technique is the relatively long period of recovery and therefore the delay in the safe return to flight of aviators. Laser in situ keratomileusis has also been proposed as an alternative for refractive correction in Naval aviators, with the potential of providing significantly faster visual recovery and return to flight status. Night-driving visual performance after wavefront-guided LASIK to correct myopia combined with a femtosecond laser flap is considerably better than that after conventional LASIK using a mechanical microkeratome. WHAT THIS PAPER ADDS Femtosecond-assisted wavefront-guided LASIK was efficacious and safe for the correction of myopia, mixed astigmatism, and hyperopia in Naval aviators. This technique preserved CDVA due to the improved accuracy in correcting lower-order aberrations (spherocylindric errors) and because it corrects or minimizes the induction of HOAs. It provided a fast visual recovery period for Naval aviators, allowing a rapid and safe return to flight status for aviators after 2 weeks for myopic and mixed astigmatism patients and after 4 weeks for hyperopic patients. It had a positive impact on the daily activities of Naval aviators, improving their effectiveness in most cases. REFERENCES 1. Maldonado MJ, Nieto JC, Pi~nero DP. Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery. Expert Rev Med Devices 2008; 5: Sakimoto T, Rosenblatt MI, Azar DT. Laser eye surgery for refractive errors. 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