Femtosecond laser in situ keratomileusis forconsecutive hyperopia after radial keratotomy

Gonzalo Munoz, MD, PhD, FEBO, Cesar Albarran-Diego, OD, Hani F. Sakla, MD, PhD,Jaime Javaloy, MD, PhD

PURPOSE: To assess the use of the femtosecond laser for laser in situ keratomileusis (LASIK) ineyes with consecutive hyperopia after radial keratotomy (RK).

SETTING: Private ambulatory surgical center, Valencia, Spain.

METHODS: This prospective noncomparative interventional case series study included 13 eyes of 9patients with secondary hyperopia after previous RK. The patients were operated on with theIntraLase femtosecond laser (IntraLase Corp.) and the Star S2 excimer laser (Visx, Inc.). Postop-erative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifestrefraction, flap thickness, flap diameter, and complications were evaluated at 6 months.

RESULTS: The mean spherical equivalent (SE) decreased from 2.00 diopters (D) G 0.40 (SD) to�0.41 G 0.61 D, with 8 eyes (61.5%) within G0.50 D of the targeted refraction. Twelve eyes(92.3%) had a UCVA of 20/40 or better, and 3 eyes (23.1%) lost 1 line of BSCVA. A mean changein SE of 0.10 D was observed at the 6-month follow-up. The mean flap thickness and diameter were117 G 14 mm and 9.18 G 0.12 mm, respectively. Most complications were in eyes with more than8 RK incisions than in eyes with 8 RK incisions. These complications were multiple intraoperativeincision openings (100% versus 28.6%, respectively), interface inflammation (66.6% versus 0%,respectively), haze (83.3% versus 14.3%, respectively), and loss of BSCVA (50% versus 0%,respectively).

CONCLUSIONS: The femtosecond laser provided large, thin corneal flaps for hyperopic LASIK.However, the procedure should be avoided in eyes with more than 8 RK incisions because of theincreased risk for multiple intraoperative incision openings, interface inflammation, haze, andloss of BSCVA.

J Cataract Refract Surg 2007; 33:1183–1189 Q 2007 ASCRS and ESCRS

ARTICLE

Consecutive hyperopia after radial keratotomy (RK) isa relatively common complication that may developmonths to years after the primary procedure.1,2

Several techniques have been used to treat secondaryhyperopia after RK. These include laser thermalkeratoplasty,3 photorefractive keratectomy (PRK),4 andlaser in situ keratomileusis (LASIK).5–10 Laser thermalkeratoplasty shows variable degrees of regression, es-pecially for hyperopia greater than 3.00 diopters (D),3

while PRK carries a risk for haze in eyes with radial in-cisions.11 Hyperopic LASIK has provided predictableresults with long-term stability.5–10 However, mechan-ical LASIK after RK may place the eye at risk for seri-ous complications, including intraoperative incisionopening,5,10 irregular apposition of the flap,5 stromalopacities,7 diffuse lamellar keratitis (DLK),5 epithelialdefects,7 epithelial ingrowth,5,7,10 and corneal ectasia.9

All these complications are mainly attributable to

Q 2007 ASCRS and ESCRS

Published by Elsevier Inc.

imperfect cutting with the microkeratome andmay re-sult in permanent loss of vision.10 Although surfaceablation procedures have been fraught with the riskfor scar formation,11 many surgeons today prefer per-forming PRK over LASIK in RK eyes, especially withthe use of mitomycin-C (MMC).12,13

The femtosecond laser represents a revolutionaryinnovation in the field of refractive surgery.14–16 Thefemtosecond laser corneal flap has advantages overthe classic mechanical keratome corneal flap, includ-ing improved predictability of flap thickness and di-ameter,17–19 astigmatic neutrality,19–21 and reducedincidence of epithelial defects and buttonholes.17–19

However, other complications such as light sensitiv-ity,22,23 corneal folds,24 and increased interface inflam-mation23,25 have been reported.

The purpose of this study was to assess the efficacy,safety, predictability, stability, flap characteristics, and

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1184 FEMTOSECOND LASIK FOR CONSECUTIVE HYPEROPIA AFTER RK

complications after the use of the femtosecond laser forhyperopic LASIK after RK. To our knowledge, thereare no previous peer-reviewed studies of the use ofthe femtosecond laser in creating a flap for hyperopicLASIK in eyes that had RK.

PATIENTS AND METHODS

Study Design

A prospective noncomparative interventional case seriesstudy comprised 13 consecutive eyes of 9 patients who hadfemtosecond hyperopic LASIK for significant hyperopia orhyperopic astigmatism. All eyes had RK for myopia rangingfrom �5.00 to �8.00 D of spherical equivalent (SE) at least10 years previously. All eyes had 3.0 mm optical zone RK.Seven eyes had 8 radial incisions, and 6 eyes had 12 ormore radial incisions. The depth of the incisions, determinedby slitlamp biomicroscopy, ranged from 80% to 90% of totalcorneal depth. Epithelial inclusion cysts and evidence of clin-ical wound gape were ruled out. Before the procedure wasattempted, signs of progressive hyperopic instability werestudied; all patients had a stable refractive history for morethan 2 years, and topography ruled out signs of corneal ecta-sia. The tenets of the Declaration of Helsinki were followed,and informed consent was obtained.

Before the LASIK procedure, patients had a completeophthalmologic examination including manifest and cyclo-plegic refractions, uncorrected visual acuity (UCVA), bestspectacle-corrected visual acuity (BSCVA), computerizedvideokeratography, slitlamp biomicroscopy, Goldmann ap-planation tonometry, binocular indirect ophthalmoscopy,and ultrasonic pachymetry. Postoperative examinationswere performed at 1, 3, and 7 days and 1 and 6 monthsand included UCVA, BSCVA, slitlamp evaluation, applana-tion tonometry, and corneal topography. All patients com-pleted a 6-month follow-up.

Femtosecond Laser In Situ KeratomileusisTechnique

Antibiotic prophylaxis before surgery consisted of topicalciprofloxacin (Oftacilox) every 8 hours for 3 days. Antisepticprophylaxis was performed by applying 1 drop ofpovidone–iodine 5% solution to the conjunctiva immedi-ately before surgery.

The femtosecond laser for flap creation has been de-scribed.17 All surgeries were performed by the same surgeon

Accepted for publication March 6, 2007.

From the Refractive Surgery Department (Munoz, Albarran-Diego),Centro Oftalmologica Marques de Sotelo and Hospital NISA Virgendel Consuelo, Valencia, and the Refractive Surgery Department(Munoz, Sakla, Javaloy), VISSUM Instituto Oftalmologico de Ali-cante, Alicante, Spain.

No author has a financial or proprietary interest in any material ormethod mentioned.

Corresponding author: Gonzalo Munoz, Centro Oftalmologico Mar-ques de Sotelo, Avenida Marques de Sotelo 5, Planta 2a, 46002Valencia, Spain. E-mail: gon.munoz@ono.com.

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(G.M.) using the 15 KHz IntraLase FS laser (IntraLase Corp.).Femtosecond laser flaps were programmed with the follow-ing settings: 110 mm thickness, 9.5 mm diameter, 45-degreehinge angle, 135-degree nasal hinge position (right eyes) or45-degree nasal hinge position (left eyes), 70-degree side-cut angle, 0.2mm stromal pocket, 9.0 mm laser raster patternsfor both spot separation and interbeam separation, and 2.0 mJraster stromal energy with 2.6 mJ side-cut energy. In all eyes,the flap was centered relative to the pupil until a predictedflap of at least 9.0 mm was achieved. Intraoperative pachy-metry was performed after the flap was lifted and beforethe excimer laser ablation.

Excimer laser ablation was performed with the Star S2laser system (Visx, Inc.) with a target of full cycloplegic cor-rection in all eyes. After surgery, topical tobramycin–dexamethasone eyedrops (TobraDex) were used every 2hours for 3 days and then every 8 hours for 4 days.

Statistical Analysis

Statistical analysis was performed using SPSS for Win-dows (version 12.0, SPSS, Inc.). Visual acuity data weretransformed into logMAR notation for means computationand comparison using the t test for paired variables. Differ-ences were considered statistically significant when P!.05.

RESULTS

The mean age of the 7 men and 2 women in the studywas 46.4 years G 4.8 (SD) (range 41 to 53 years). In4 patients, both eyes were treated.

Efficacy

The UCVA (Snellen decimal) improved in all eyesfrom preoperatively to 6 months postoperatively(Table 1), with an efficacy index of 0.79 in the wholegroup (Figure 1). The percentage of eyes witha UCVA of 20/40 or better was 92.3% (Table 1). Strat-ifying by number of radial incisions, the efficacy indexwas 0.83 for eyes with 8 RK incisions and 0.76 for eyeswith more than 8 RK incisions.

Safety

Six months after surgery, 3 eyes (23.1%) lost 1 line ofBSCVA and 10 eyes (76.9%) had no change. The safetyindex ratio was 0.98 in the whole group, and therewere no differences in mean BSCVA before and aftersurgery in the whole group (P Z .50, Student t test).Stratifying by number of radial incisions, none of the7 eyes with 8 RK incisions lost a line of BSCVA,whereas 3 of the 6 eyes (50%) with more than 8 RK in-cisions lost 1 line of BSCVA. The safety index ratio was1 for eyes with 8 RK incisions and 0.94 for eyes withmore than 8 RK incisions.

Predictability

Table 1 shows the mean preoperative and 6-monthpostoperative SE and astigmatism. Eight eyes(61.5%) were within G0.50 D and 10 eyes (76.9%)

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within G1.00 D of the targeted refractive change. Post-operative astigmatism was within G0.50 D of the in-tended astigmatic correction in 8 eyes (61.5%) andwithin G1.00 D in 13 eyes (100%).

Stability

The mean SE changed from �0.51 G 0.72 D at1 month to �0.41 G 0.61 D at 6 months. Data forthe 3-month follow-up were not obtained. Therewas a mean change in SE of 0.10 G 0.23 D between1 month and 6 months; in all eyes, the change was0.25 D or less.

The Flap

The mean achieved flap thickness was 117 G 14 mm(range 96 to 138 mm) for a planned thickness of 110 mm.The mean flap diameter was 9.18 G 0.12 mm. As astromal pocket of 0.2 mm was used, the maximum

Table 1. Results of femtosecond LASIK in eyes with consecutivehyperopia after RK.

Parameter Preop6 MonthsPostop

Sphere (D) 2.65 G 0.50 �0.17 G 0.64Astigmatism (D) �1.31 G 0.80 �0.48 G 0.33SE (D) 2.00 G 0.40 �0.41 G 0.61G0.50 D SE (%) 0 61.5UCVA R 20/40 (%) 46 92.3Mean decimal UCVA (lines) 0.41 G 1.12 0.68 G 1.21Mean decimal BSCVA (lines) 0.86 G 0.60 0.84 G 0.65Mean logMAR UCVA C0.39 G 0.11 C0.17 G 0.12Mean logMAR BSCVA C0.06 G 0.06 C0.08 G 0.07

BSCVA Z best spectacle-corrected visual acuity; SE Z spherical equiva-lent; UCVA Z uncorrected visual acuity

Cumulative Decimal Visual Acuity0,40,50,60,70,80,91,0

Perc

enta

ge o

f Eye

s

0

20

40

60

80

100Pre-surgery BCVAPost-surgery UCVA

Figure 1. Efficacy: postoperative UCVA versus preoperativeBSCVA.

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achieved flap diameter was 9.3 mm. A diameter of9.3 mm was achieved in 4 of the 13 eyes; in the other9 eyes, the achieved flap diameter was between 9.0 mmand 9.2 mm. The planned diameter had to be reducedfrom the attempted diameter when the applanationcone was decentered in respect to the pupil.

Intraoperative Complications

Lifting the flap was the most difficult part of the in-tervention. In all eyes, separation of at least 1 radial in-cision was observed intraoperatively. It was especiallydifficult to lift the flap in eyes with more than 8 RK in-cisions. Two or more incisions opened in all 6 eyeswith more than 8 RK incisions and in 2 eyes (28.6%)with 8 RK incisions (Table 2). In some eyes, the open-ing of the RK incision was produced during the femto-second ablation and it was detected by a suddenchange in the homogeneous pattern of the intrastro-mal bubbles to a nonhomogeneous pattern, with verti-cal lines following the direction of the laser beam. Inmost eyes, incision opening occurred during flap lift-ing (Figure 2). The radial incisions closer to the hingeopened first. For instance, with a nasal hinge in theleft eye, the radial incisions that opened were mainlyat the 7 to 8 o’clock position or the 10 to 11 o’clock po-sition. In the right eye, they gaped primarily at the 1 to2 o’clock position or at the 4 to 5 o’clock position.

Small epithelial irregularities were produced at thejunctions between themargin of the flap and the radialincisions. There were no cases of free caps, button-holes, or suction loss during the femtosecond ablation,and a smooth stromal bed was obtained in all cases.

Postoperative Complications

Four eyes (30.8%) presented with moderate DLKbetween 1 and 3 days postoperatively. These cases

Figure 2. The opening of 2 RK incisions next to the hinge in a case offemtosecond hyperopic LASIK after RK.

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Table 2. Complications based on number of RK incisions.

Number

Eye RK Incisions Intraoperative RK Incision Openings Loss of 1 Line of BSCVA Interface Inflammation Postoperative Haze

1 16 3 Yes C C

2 12 3 Yes C C

3 12 3 Yes C C

4 12 3 No C C

5 12 2 No � C

6 12 2 No � �7 8 2 No � C

8 8 2 No � �9 8 1 No � �10 8 1 No � �11 8 1 No � �12 8 1 No � �13 8 1 No � �

BSCVA Z best spectacle-corrected visual acuity; Pt Z patient; RK Z radial keratotomy

responded well to topical TobraDex every 2 hours for7 days. This complication did not require lifting of theflap. All eyes that developed DLK had more than 8 RKincisions. Postoperatively, all RK incisions looked wellaligned with no signs of progressive fibrosis or epithe-lial ingrowth despite the opening of the incision. Theflap margin showed a degree of fibrosis typical of fem-tosecond flaps that was no different from that in non-RK eyes. There was no epithelial ingrowth despite thesmall epithelial irregularities produced intraopera-tively at the junctions between the margin of the flapand the radial incisions. Diffuse interface haze andsmall particles at the interface were present in 6 eyes(46.2%) at final follow-up. Haze was present in 5eyes (83.3%) with more than 8 RK incisions and 1eye (14.3%) with 8 RK incisions. In these cases, confo-cal microscopy showed keratocyte activation andhighly reflective particles at the level of the interfacewith normal epithelium, posterior stroma, and endo-thelium. Many oval cells (keratocytes) with diametersof approximately 10 to 12 mmwere detected; they werediffusely distributed or arranged in lines (Figure 3, A).Also, clusters and lines of small, highly reflective par-ticles were seen (Figure 3, B).

There were no cases of epithelial ingrowth at themargin of the flap despite the epithelial irregularitiesproduced when the flap was lifted. There were nocases of decentered ablations or transient light sensi-tivity in any eye.

DISCUSSION

Our study found that the efficacy, safety, predictabil-ity, and stability of the femtosecond hyperopic

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LASIK procedure were comparable to those of hyper-opic LASIK using mechanical microkeratomes afterRK,5–10 with 92.3% of eyes having a UCVA of 20/40or better and nearly two thirds within G0.50 D ofthe targeted refraction. The stability index at 6 monthswas excellent, with a mean change in SE of 0.10 D.These results should be viewed within the context ofeyes previously operated on using radial incisions.

The main finding in the present study was the in-creased risk for developing complications in eyeswith more than 8 RK incisions. Complications mainlyaffected eyes with more than 8 RK incisions versuseyes with 8 RK incisions and included difficulty liftingthe flap with multiple incision openings (100% versus28.6%), interface inflammation (66.6% versus 0%),haze (83.3% versus 14.3%), and loss of BSCVA (50%versus 0%).

A main difficulty when performing LASIK in eyeswith previous RK is the creation of a large enoughcorneal flap.5–10 A eye that has had RK has a flat cornearesulting from the incisional procedure; when me-chanical microkeratomes are used, the incidence ofsmall and free caps is higher in the presence of lowkeratometric values.26 Because stromal ablation in hy-peropic LASIK is mainly peripheral, a large flap isneeded to prevent peripheral haze and regression. Infact, hyperopic LASIK in the presence of a small flaphas been related to a higher incidence of undercorrec-tion, regression, epithelial ingrowth, and peripheralhaze.5,8 In the present study, the mean preoperativeK-value was low (mean 39.40 G 1.50 D) for a groupof eyes that had previous RK for myopia rangingfrom �5.00 to �8.00 D. The femtosecond laser usesan applanation glass contact lens cone to create

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a 0.00 D K-cornea, thus avoiding the K-factor. A recentstudy by Binder18 of his first 1000 consecutive femto-second laser LASIK cases found preoperative cornealcurvature had no impact on flap dimensions. In ourstudy, we were able to consistently create at leasta 9.0 mm diameter flap and a small, predictable hingein all the eyes. This is important inmaximizing stromalexposure for the excimer laser ablation. There were nocases of suction loss during the procedure. Anotheradvantage of the femtosecond laser is that in the eventof suction loss, the focal plane shifts to the epithelialsurface, avoiding vertical lacerations and irregular orbuttonholed flaps.

Regarding predictability of flap thickness, intrao-perative pachymetry showed a mean flap thicknessof 117 mm for a planned thickness of 110 mm with

Figure 3. Confocal microscopy of interface showing activated kera-tocytes (A) and highly reflective particles (B).

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a low standard deviation of G14 mm. Binder17 reportsa standard deviation of G12 mm when a 110 mm thickflapwas attempted using the femtosecond laser in nor-mal eyes, which is similar to the results in the presentstudy. The smaller range in the achieved flap thicknessand the smaller standard deviation are superior resultsin comparison with current microkeratomes.27–29 Stro-mal bed thickness before excimer ablation rangedfrom 382 to 500 mm, well above 350 mm in all cases.The preservation of a stromal bed that is as thick aspossible may reduce the incidence of postoperativeregression and keratectasia. The incidence of post-LASIK keratectasia in eyes with previous RK repre-sents more than 3 times the expected incidence fornon-RK eyes according to previous studies.30,31

We had significant problems creating the flap insome eyes, especially those with more than 8 RK inci-sions. We previously reported the intraoperativeopening of a radial incision during femtosecond laserLASIK ablation in eyes with myopic regression afterprevious RK.32 That every eye in the present studyhad an opening of at least 1 radial incision duringflap separation and lifting suggests that this proceduremay pose a significant risk for epithelial ingrowth andother complications. However, the LASIK procedureusing the femtosecondwas still safe, effective, and pre-dictable in the 13 eyes in our study. There were nocases of epithelial ingrowth, buttonhole, or a freecap; however, our series was small. The number ofeyes with more than 8 RK incisions was low (n Z 6);thus, that none of these complications occurred doesnot mean theywould not in a series with a larger num-ber of eyes. It seems that more than 8 radial incisionsincreases the risk for complications. In all 6 eyes withmore than 8 radial incisions, 2 or more incisionsopened, while this occurred in only 2 of the 7 eyeswith 8 radial incisions. The relative importance of thenumber of incisions that open during the proceduremust be determined with a larger series; however, dif-ficulty lifting the flap was definitely proportional tothe number of radial incisions. The efficacy indexand the safety index were better in eyes with 8 RK in-cisions than in eyes with more than 8 RK incisions.

It is well documented that the radial incisions neverheal completely.1,2 A mechanical keratome completelyseparates the flap from the stromal bed; conversely,with the femtosecond laser, the surgeon dissects theflap by breaking the intrastromal adhesion remainingafter the femtosecond ablation. The greater amount ofstrength that must be applied to the flap may increasethe risk for intraoperative RK incision opening duringfemtosecond LASIK compared with mechanicalLASIK. This issue should be clarified in future studiesthat compare the 2 techniques. In our experience, inmost eyes, the RK incisions open during flap lifting

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and the radial incisions closer to the hinge are morelikely to open first. For instance, when a nasal hingewas used in the left eye, the radial incisions thatopened were mainly at the 7 to 8 o’clock position orthe 10 to 11 o’clock position. If the surgeon had chosena superior hinge, the RK incisions at the 10 o’clock and1 o’clock positions would likely separate first.

Difficulties in flap-lifting techniques for experiencedfemtosecond laser users are related to instrumentationused to lift the flap and how femtosecond laser energyis delivered. Strategies to improve flap lifting could in-clude decreasing the distance between spots of thesame line or raster spot separation, decreasing the dis-tance between lines of spots or raster interbeam sepa-ration, or increasing the raster energy. One could alsouse a double-pass technique, which consists of per-forming the femtosecond ablation twice in the sameplane.However, all these approacheswouldusehigherlevels of energy, which may increase the postopera-tive inflammatory reaction as well as other complica-tions such as transient light-sensitivity syndrome(TLSS).22,23 We believe that increasing the flap thick-ness would also decrease the risk for wound separa-tion; now we use a 160 to 180 mm flap instead of a 110mm flap in selected cases. This does not contradict ouroriginal statement on the issue of ectasia with thickerflaps in patients with RK after mechanical LASIK.9

Increasing the depth of the femtosecond ablation mayaffect the biomechanical properties of the cornea andincrease the risk for future ectasia; thus, the depth ofthe femtosecond ablation should be considered ona case-by-case basis taking into account corneal thick-ness, the depth of excimer laser ablation, and the num-ber of RK incisions. One advantage of the femtosecondlaser is the better predictability of the corneal flapthickness compared with that with mechanical kera-tomes; this avoids creating a corneal flap that is toothick.17,28,29

In some cases, a semi-sharp or sharp corneal dissec-tor could be used when separation is difficult becauseof incomplete cuts; this would also decrease the diffi-culties with both flap lifting and wound separation.A dissector used for lamellar keratoplasty could beadequate and should be available when dealing withthese eyes.

Radial keratotomy wound integrity should be ex-amined clinically before surgery. Epithelial inclusioncysts or evidence of clinical wound gape should beruled out at the slitlamp. Before the LASIK procedure,any sign of progressive hyperopic instability should beruled out. If in doubt, any attempt at improvementshould be done with a procedure that has a minimalbiomechanical impact such as surface ablation withMMC.12,13 Surgeons performing femtosecond laser ormicrokeratome LASIK surgery in RK eyes must

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evaluate these clinical findings and determinewhetherthey will perform LASIK or surface ablation.

It is noteworthy that 4 eyes (30.8%) developed mod-erate postoperative DLK and 6 eyes (46.2%), diffusehaze and small particles in the interface. Confocal mi-croscopy showed activated keratocytes and highly re-flective particles, suggesting there is more interfacereaction in eyes that have had radial incisions beforefemtosecond laser application. Postoperative interfaceinflammation after femtosecond LASIK in eyes withprevious RK incisions may represent a relative disad-vantage compared with mechanical LASIK, especiallyin the presence of more than 8 radial incisions. This is-sue should be studied further by comparing femto-second LASIK and mechanical LASIK.

The femtosecond laser has been associated witha higher post-LASIK inflammatory reaction and fibro-sis.23,25,33 We used the 15 kHz femtosecond laser;however, new lasers that work at 30 or 60 kHz woulddeliver much less energy to the eyes, causing fewer in-flammatory side effects. In our study, DLK after fem-tosecond laser LASIK responded well to topicalsteroids and did not require flap lifting. At the finalfollow-up, diffuse haze and small particles in the inter-face were present in a significant number of eyes,causing a subtle loss of transparency that may explainthe loss of 1 line of BSCVA in some eyes. These parti-cles have been described as cell-degradation prod-ucts.25 Causes other than the femtosecond ablationmay be related to the high incidence of postoperativeDLK and small particles in the interface. Difficult flaplifting may cause more reflux of tears into the inter-face, and oil from the tear film could explain the bio-microscopic and confocal findings. Thus, it could bea technique-related complication rather than some-thing unique to the femtosecond laser. Despite the as-sociation between DLK and TLSS,23 no patientreported increased photophobia during the follow-up period.

In conclusion, the femtosecond laser provided largeand thin flaps for hyperopic LASIK with a range offlap thickness smaller than that reported with conven-tional microkeratomes. The procedure proved to besafe, effective, predictable, and stable for the treatmentof consecutive hyperopia after RK, especially in eyeswith 8 or less RK incisions. Femtosecond laser ablationfor LASIK should be avoided in eyes with more than 8RK incisions as there is an increased risk for complica-tions such as multiple intraoperative incision open-ings, DLK, haze, and loss of BSCVA.

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First author:Gonzalo Munoz, MD, PhD, FEBO

Refractive Surgery Departments, CentroOftalmologica Marques de Sotelo andHospital NISA Virgen del Consuelo,Valencia, and VISSUM InstitutoOftalmologico de Alicante, Alicante, Spain

RG - VOL 33, JULY 2007