Journal of Refractive Surgery

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Original Article 

Femtosecond Thin-Flap LASIK for the Correction of Ametropia After Penetrating Keratoplasty

Irina S. Barequet, MD; Ami Hirsh, MD; Samuel Levinger, MD

Abstract

Purpose:

To evaluate the outcomes of LASIK with thin femtosecond laser flaps for the treatment of refractive errors after penetrating keratoplasty (PK).

Methods:

Eleven consecutive eyes underwent femtosecond thin-flap LASIK 51.6±42.1 months (range: 13 to 156 months) after the initial PK. A full ophthalmic assessment was performed before femtosecond LASIK and 6 months after surgery. Postoperative retreatments were also noted.

Results:

No intra- or postoperative complications were observed. The outcomes of nine eyes that completed at least 6 months’ follow-up and had no retreatment during that period were evaluated. Mean preoperative myopia decreased from −3.60±1.60 diopters (D) to +1.00±2.70 D 6 months after surgery, and mean hyperopia decreased from +3.50±1.30 D preoperatively to +0.30±0.70 D 6 months after surgery. Mean preoperative astigmatism decreased from −6.60±3.60 D to −2.90±2.00 D 6 months after surgery. At 6 months, the mean preoperative myopic spherical equivalent refraction (SE) decreased from −6.40±2.00 D to −0.02±2.20 D, and mean hyperopic SE from +0.80±2.80 D to −0.60±0.60 D. At 6 months postoperatively, 67% (6/9) of eyes were within 1 line of preoperative best spectacle-corrected visual acuity and 33% (3/9) gained ≥2 lines.

Conclusions:

Femtosecond thin-flap LASIK is a safe procedure in eyes with previous PK. This procedure is reasonably predictable, especially for the spherical component of the refraction. Creating the flap with the femtosecond laser and performing excimer laser ablation within the corneal graft limits without involving the graft–host junction provides the advantage of performing the entire procedure in one step.

Abstract

Purpose:

To evaluate the outcomes of LASIK with thin femtosecond laser flaps for the treatment of refractive errors after penetrating keratoplasty (PK).

Methods:

Eleven consecutive eyes underwent femtosecond thin-flap LASIK 51.6±42.1 months (range: 13 to 156 months) after the initial PK. A full ophthalmic assessment was performed before femtosecond LASIK and 6 months after surgery. Postoperative retreatments were also noted.

Results:

No intra- or postoperative complications were observed. The outcomes of nine eyes that completed at least 6 months’ follow-up and had no retreatment during that period were evaluated. Mean preoperative myopia decreased from −3.60±1.60 diopters (D) to +1.00±2.70 D 6 months after surgery, and mean hyperopia decreased from +3.50±1.30 D preoperatively to +0.30±0.70 D 6 months after surgery. Mean preoperative astigmatism decreased from −6.60±3.60 D to −2.90±2.00 D 6 months after surgery. At 6 months, the mean preoperative myopic spherical equivalent refraction (SE) decreased from −6.40±2.00 D to −0.02±2.20 D, and mean hyperopic SE from +0.80±2.80 D to −0.60±0.60 D. At 6 months postoperatively, 67% (6/9) of eyes were within 1 line of preoperative best spectacle-corrected visual acuity and 33% (3/9) gained ≥2 lines.

Conclusions:

Femtosecond thin-flap LASIK is a safe procedure in eyes with previous PK. This procedure is reasonably predictable, especially for the spherical component of the refraction. Creating the flap with the femtosecond laser and performing excimer laser ablation within the corneal graft limits without involving the graft–host junction provides the advantage of performing the entire procedure in one step.

From Enaim Refractive Surgery Centers, Jerusalem and Tel Aviv (Barequet, Hirsh, Levinger); and Goldschleger Eye Institute, Sheba Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Hashomer (Barequet), Israel.

The authors have no proprietary interest in the materials presented herein.

Presented in part at the International Society of Refractive Surgery of the American Academy of Ophthalmology Subspecialty Day; October 15–18, 2005; Chicago, Ill.

AUTHOR CONTRIBUTIONS

Study concept and design (I.S.B.); data collection (I.S.B., A.H., S.L.); analysis and interpretation of data (I.S.B., A.H.); drafting of the manuscript (I.S.B.); critical revision of the manuscript (I.S.B., A.H., S.L.)

Correspondence: Irina S. Barequet, MD, Goldschleger Eye Institute, Sheba Medical Center, Tel Hashomer 52621, Israel. Tel: 972 3 530 2874; Fax: 972 3 530 2822; E-mail: ibarequet@hotmail.com

Received: May 10, 2008
Accepted: February 18, 2009
Posted Online: March 11, 2010

The visual success of corneal transplantation is frequently impaired by high degrees of astigmatism, which, in most cases, is accompanied by large amounts of myopia, anisometropia, and, less commonly, hyperopia. The excimer laser has acquired a significant role in the management of refractive errors after keratoplasty. The results of photorefractive keratectomy (PRK) performed after keratoplasty have been published in several studies, some of which report low predictability of refractive results and a significant incidence of stromal haze.1–10 Haze seems to be related to the magnitude of the ablations necessary for these cases, which usually is coupled with regression of the obtained refractive effect. More recent publications reported improved results of PRK with mitomycin C after deep anterior lamellar keratoplasty for keratoconus and transepithelial PRK after penetrating or deep lamellar keratoplasty.11,12 In addition, some case reports cite excimer photoablation-induced graft rejection.13,14

More recently, several studies have shown that LASIK has advantages over other surgical procedures in the management of refractive errors after penetrating keratoplasty (PK).15–21 However, a lamellar cut at the graft–host junction has limitations and can cause complications such as dehiscence.22 The larger flap may release contractile forces, causing change in the magnitude and axis of astigmatism; therefore, a sequential two-step treatment was advocated.23 However, performing the procedure routinely, along with a flap lift after LASIK, may carry the risks of epithelial ingrowth.24

The femtosecond laser has been gaining popularity, as a replacement for the microkeratome, for creating the lamellar cut. The IntraLase femtosecond laser (Abbott Medical Optics, Santa Ana, Calif) is a solid-state laser used to create flaps in LASIK with an infrared wavelength (1053 nm) to deliver closely spaced, 3-μm spots that can be focused to a preset depth to photodisrupt tissue within the corneal stroma. The IntraLase femtosecond laser software creates a circular cleavage plane starting at one side of the cornea and progressing across the cornea using a raster (back and forth) pattern. It then creates a flap edge of a programmable angle (side-cut angle) using a circumferential pattern of progressively shallower pulses. A predefined arc along the edge is left uncut to create the hinge. The entire process takes place through a glass applanation plate that is fixed to the eye with a low pressure suction ring, providing a significant advantage due to extremely precise cutting beginning at any corneal point.

In this study, we analyzed the safety and predictability of LASIK with thin femtosecond laser flaps confined within the graft margins in the treatment of ametropia in eyes after PK. To the best of our knowledge, this is the first study to report LASIK with femtosecond laser flaps as a primary procedure for this indication.

Patients and Methods

A retrospective chart review was done for LASIK procedures performed with the femtosecond laser to create flaps in eyes with previous PK. Eleven consecutive eyes from 11 patients were identified. The preoperative data included age, sex, ocular history, type of previous ocular surgery, time elapsed between PK and femtosecond LASIK, refractive error, keratometry readings, and central corneal thickness. Intra- and postoperative complications were noted. Postoperative data included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and refraction at 1 day, 1 week, and 1, 2, and 6 months. A written informed consent was provided to all patients, which included information about the procedure itself, possible complications, and other treatment alternatives.

Laser in situ keratomileusis was performed under topical anesthesia with the IntraLase femtosecond laser. The flap diameter was predetermined prior to the initiation of the IntraLase femtosecond laser, so to be confined within the graft margins, and this resulted in creating flaps with a diameter between 7.5 and 7.7 mm. Flap thickness was programmed from 90 to 110 μm. The flap edge angle was programmed to 60°, and the hinge size was set at 45° of arc. All eyes had a pocket and the hinge was programmed at 90°. The flap was lifted as per routine LASIK with femtosecond laser followed by excimer laser ablation using the Technolas 217 laser (Bausch & Lomb, Rochester, NY) with either standard PlanoScan V2.9992 or wavefront-guided ablation using Zyoptix 3.1 software (Bausch & Lomb). Intraoperative pachymetry was not performed. The stromal photoablation was based on the programmed desired refractive error, leaving at least 50% of the total corneal thickness and ≥250 μm of stromal tissue under the treated area. The mean ablation zone was 5.3±0.4 mm and mean ablation depth was 98.7±26.7 μm.

Postoperatively, patients were instructed to use prednisolone 1% and ofloxacin 0.3% (one drop each six times daily on the day of surgery and the following day, then four times daily for 1 week) and preservative-free artificial tears (as needed). Patients were examined 1 day, 1 week, and 1, 2, and 6 months after surgery, and a complete eye examination was performed. Two eyes (eyes 1 and 2) were identified to have a retreatment procedure <6 months postoperatively. Therefore, the outcome analysis was performed only on the 9 eyes that completed at least 6 months’ follow-up.

Results

Preoperative Data

Mean age of the 11 patients (6 men, 5 women) was 36±9 years (range: 24 to 52 years). All patients had a clear corneal graft that had been transplanted at least 1 year prior to femtosecond LASIK. The mean time from PK to LASIK was 51.6±42.1 months (range: 13 to 156 months). Indications for the corneal graft were keratoconus (n=9) or ectasia (n=2). All eyes had a stable refractive error for at least 6 months after all sutures were removed. Mean preoperative ultrasonic central corneal pachymetry was 540.5±69.2 μm (range: 500 to 650 μm). Complete ocular examination was normal in all eyes except for the presence of a clear corneal graft and insignificant myopic retinal degeneration in some patients. The preoperative data are summarized in Table 1.

Preoperative Data for Eyes that Underwent Femtosecond LASIK After Penetrating Keratoplasty

Table 1: Preoperative Data for Eyes that Underwent Femtosecond LASIK After Penetrating Keratoplasty

Surgical Parameters and Complications

Surgical parameters of the IntraLase femtosecond laser and excimer laser data are presented in Table 2. No intraoperative complications occurred, either related to femtosecond LASIK or to the corneal graft.

Surgical Parameters and Outcome Data at 6 Months Postoperatively for Eyes that Underwent Femtosecond LASIK After Penetrating Keratoplasty

Table 2: Surgical Parameters and Outcome Data at 6 Months Postoperatively for Eyes that Underwent Femtosecond LASIK After Penetrating Keratoplasty

Postoperative Data

Follow-up. Postoperative follow-up was ≥6 months. The analysis of outcome was based on results at the 6-month follow-up visit.

Complications. No postoperative complications were observed related to femtosecond LASIK or to the corneal graft. During the entire follow-up period, no graft rejection, failure, increased graft vascularization, or infections were noted. None of the eyes developed interface epithelial ingrowth.

Visual Outcome. The BSCVA of nine analyzed eyes improved from a preoperative decimal value of 0.56±0.1 (similar to 20/36) to 0.68±0.1 (20/29) at 6 months postoperatively. The safety index (BSCVA postoperatively/BSCVA preoperatively) at final follow-up was 1.31. At 6 months postoperatively, 67% (6/9) of eyes were within 1 line of preoperative BSCVA and 33% (3/9) gained ≥2 lines (Table 2).

Mean preoperative UCVA (decimal) was 0.05±0.04 (20/400) and 0.35±0.14 (20/57) at 6 months. The efficacy index (UCVA postoperatively/BSCVA preoperatively) at 6 months was 0.65. Uncorrected visual acuity improved in all eyes. The differences between UCVA before femtosecond LASIK and at 6 months postoperatively were statistically significant (P=.005).

Six months after surgery, mean preoperative myopia decreased from −3.60±1.60 D to +1.00±2.70 D and mean hyperopia decreased from +3.50±1.30 D preoperatively to +0.30±0.70 D. Mean preoperative astigmatism decreased from −6.60±3.60 D to −2.90±2.00 D 6 months after surgery. At 6 months, mean preoperative myopic spherical equivalent refraction (SE) decreased from −6.40±2.00 D to −0.02±2.20 D and mean hyperopic SE from +0.80±2.80 D to −0.60±0.60 D.

Calculation of the predictability of correction at 6 months showed that 78% of eyes (7/9) were within ±1.50 D of sphere, 33% of eyes (3/9) were within ±1.50 D of refractive astigmatism, and 56% of eyes (5/9) were within ±1.50 D of SE. Also, 67% of eyes (6/9) were within ±1.00 D of sphere, 22% (2/9) within ±1.00 D of refractive astigmatism, and 22% (2/9) within ±1.00 D of SE; 44% (4/9) were within ±0.50 D of sphere, 0 within ±0.50 D of refractive astigmatism, and 22% (2/9) within ±0.50 D of SE.

Enhancements. After 6 months, two of nine eyes underwent laser retreatment procedures (Table 2), one eye underwent surface ablation, and one eye had laser retreatment by flap relift surgery. No eye underwent repeat PK.

Discussion

We report the safety and efficacy of LASIK with femtosecond laser flaps to correct residual ametropia after keratoplasty. Our series included patients with a high magnitude of astigmatism, which evidently affected visual and refractive outcomes. These were the first reported cases after PK to undergo femtosecond LASIK in an attempt to correct ametropia. Although excimer laser treatment of higher degrees of astigmatism (6.00 to 7.00 D) is possible, it is less beneficial. Additional procedures such as relaxing incisions or wedge resections with compression sutures can be added later after stabilization of the refraction, or conversely, attempted prior to the laser procedure.

Several studies report that astigmatic correction with LASIK after keratoplasty remains the dominant issue. Arenas and Maglione15 observed poor effectiveness of LASIK for the correction of astigmatism in four patients. Forseto et al18 noticed a tendency toward undercorrection (42%). The attempted cylindrical correction was higher in the Forseto et al study, and some patients had more than 6.00 D of preoperative astigmatism. Güell et al19 reported satisfactory results in spherical as well as cylindrical residual errors. In their study, the cylinder treated with LASIK was ≤6.00 D; higher degrees of astigmatism were treated with relaxing incisions first and with LASIK 3 to 4 months later. Our cases had a large amount of preoperative astigmatism and 67% of the eyes had >5.00 D of astigmatism. Predictability of the intended refractive correction was relatively accurate in seven of nine eyes, and less accurate in two eyes (eyes 3 and 7). Incisional correction of astigmatism is an additional option that can be considered either before or after femtosecond LASIK to enhance the refractive results.

In our series, retreatment was performed in two (22%) eyes. However, the two additional eyes excluded from analysis underwent retreatment at 2 and 4 months postoperatively by arcuate incision and laser ablation with flap relift (a total retreatment rate of 36%). Rashad22 reported a retreatment rate of 52.6% by relifting the flap and re-ablation of the stromal bed. The surgery was uneventful with no loss of BSCVA. Laser in situ keratomileusis retreatment for residual myopia and astigmatism has been described as 9.1% in the series of Donnenfeld et al.21 Kwitko et al23 reported retreatment in 42.9% of eyes due to cylindrical undercorrection.

Although successful LASIK procedures have been reported in patients with PK for keratoconus, there is a risk for wound dehiscence related to the reduced stromal bed thickness of the keratoconic host. Ranchod and McLeod24 reported a case of wound dehiscence shortly after LASIK performed after PK for keratoconus. In patients with keratoconus who have undergone full-thickness grafting, the graft–host junction consists of thinned host stroma fused to a normal thickness graft. A LASIK flap created larger than the graft requires the flap to cross the graft–host junction into the thinned keratoconic host. As a result, the already limited adherence between host and graft is reduced by the thickness of the flap, thereby increasing the risk of dehiscence either at the time of surgery or following minor trauma. One potential advantage of the femtosecond laser flap is the ability to program a reduced flap diameter in an attempt to be within the graft–host junction, which may reduce the risk of graft dehiscence.

The safety results of our series demonstrate that no patient lost >1 line of BSCVA after 6 months; 66% of eyes were within 1 line of preoperative BSCVA and 33% gained ≥2 lines. This can be demonstrated by the centration of the ablation such as shown in the Figure. Alió et al25 reported improved accuracy of excimer laser correction of astigmatism after PK using a two-step technique of lamellar cut and then ablation in two successive procedures. However, lifting the flap may be associated with an increased risk of epithelial ingrowth.26 We did not observe flap wrinkles or epithelial ingrowth even after the retreatments. Moreover, no other complications such as corneal decompensation or graft rejection occurred in our study.

Corneal Topography for Eye #11. Upper Left) Preoperative Topography. Bottom Left) 6-Month Postoperative Topography Showing Regularity of the Astigmatism. Right) Subtraction Map Demonstrating Good Centration of the Laser Ablation.

Figure. Corneal Topography for Eye #11. Upper Left) Preoperative Topography. Bottom Left) 6-Month Postoperative Topography Showing Regularity of the Astigmatism. Right) Subtraction Map Demonstrating Good Centration of the Laser Ablation.

In this small number of eyes, femtosecond LASIK after PK appears to be safe but longer follow-up and a larger series of eyes is needed. This surgery provides an important tool to improve ametropia after keratoplasty; however, it does not correct high astigmatism after keratoplasty, which is one of the common complications of this surgery. Femtosecond LASIK after PK within the corneal graft limits without involving the graft–host junction provides the advantage of performing the entire procedure in one step in many eyes.

References

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  6. Tuunanen TH, Ruusuvaara PJ, Uusitalo RJ, Tervo TM. Photoastigmatic keratectomy for correction of astigmatism in corneal grafts. Cornea. 1997;16:48–53. doi:10.1097/00003226-199701000-00010 [CrossRef]
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  11. Leccisotti A. Photorefractive keratectomy with mitomycin C after deep anterior lamellar keratoplasty for keratoconus. Cornea. 2008;27:417–420. doi:10.1097/ICO.0b013e318164e4b8 [CrossRef]
  12. Pedrotti E, Sbabo A, Marchini G. Customized transepithelial photorefractive keratectomy for iatrogenic ametropia after penetrating or deep lamellar keratoplasty. J Cataract Refract Surg. 2006;32:1288–1291. doi:10.1016/j.jcrs.2006.03.032 [CrossRef]
  13. Hersh PS, Jordan AJ, Mayers M. Corneal graft rejection episode after excimer laser phototherapeutic keratectomy. Arch Ophthalmol. 1993;111:735–736.
  14. Epstein RJ, Robin JB. Corneal graft rejection episode after excimer laser phototherapeutic keratectomy. Arch Ophthalmol. 1994;112:157.
  15. Arenas E, Maglione A. Laser in situ keratomileusis for astigmatism and myopia after penetrating keratoplasty. J Refract Surg. 1997;13:27–32.
  16. Parisi A, Salchow DJ, Zirm ME, Stieldorf C. Laser in situ keratomileusis after automated lamellar keratoplasty and penetrating keratoplasty. J Cataract Refract Surg. 1997;23:1114–1118.
  17. Zaldivar R, Davidorf J, Oscherow S. LASIK for myopia and astigmatism after penetrating keratoplasty. J Refract Surg. 1997;13:501–502.
  18. Forseto AS, Francesconi CM, Nosé RA, Nosé W. Laser in situ keratomileusis to correct refractive errors after keratoplasty. J Cataract Refract Surg. 1999;25:479–485. doi:10.1016/S0886-3350(99)80043-1 [CrossRef]
  19. Güell JL, Gris O, de Muller A, Corcostegui B. LASIK for the correction of residual refractive errors from previous surgical procedures. Ophthalmic Surg Lasers. 1999;30:341–349.
  20. Webber SK, Lawless MA, Sutton GL, Rogers CM. LASIK for post penetrating keratoplasty astigmatism and myopia. Br J Ophthalmol. 1999;83:1013–1018. doi:10.1136/bjo.83.9.1013 [CrossRef]
  21. Donnenfeld ED, Kornstein HS, Amin A, Speaker MD, Seedor JA, Sforza PD, Landrio LM, Perry HD. Laser in situ keratomileusis for correction of myopia and astigmatism after penetrating keratoplasty. Ophthalmology. 1999;106:1966–1974. doi:10.1016/S0161-6420(99)90410-4 [CrossRef]
  22. Rashad KM. Laser in situ keratomileusis for correction of high astigmatism after penetrating keratoplasty. J Refract Surg. 2000;16:701–710.
  23. Kwitko S, Marinho DR, Rymer S, Ramos Filho S. Laser in situ keratomileusis after penetrating keratoplasty. J Cataract Refract Surg. 2001;27:374–379. doi:10.1016/S0886-3350(00)00642-8 [CrossRef]
  24. Ranchod TM, McLeod SD. Wound dehiscence in a patient with keratoconus after penetrating keratoplasty and LASIK. Arch Ophthalmol. 2004;122:920–921. doi:10.1001/archopht.122.6.920 [CrossRef]
  25. Alió JL, Javaloy J, Osman AA, Galvis V, Tello A, Haroun HE. Laser in situ keratomileusis to correct post-keratoplasty astigmatism; 1-step versus 2-step procedure. J Cataract Refract Surg. 2004;30:2303–2310. doi:10.1016/S0886-3350(04)00666-2 [CrossRef]
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Preoperative Data for Eyes that Underwent Femtosecond LASIK After Penetrating Keratoplasty

EyeIndication for PKGraft Size (mm)
Refractive ErrorBSCVA (decimal)UCVA (decimal)RefractionCorneal Thickness (μm)Time From PK to LASIK (mo)
DonorRecipient
1*Keratoconus87.75Astigmatism0.80.05−1.00 −6.50 × 7252738
2*Ectasia8.258Astigmatism0.670.3+3.50 −5.00 × 18053630
3Keratoconus7.757.5Hypermetropia, astigmatism0.70.1+5.00 −2.25 × 10556725
4Keratoconus7.757.5Astigmatism0.30.050.00 −15.00 × 7860034
5Keratoconus87.75Myopia, astigmatism0.670.01−5.00 −8.00 × 6255437
6Keratoconus8N/AAstigmatism0.60.1+2.50 −7.00 × 4650048
7Ectasia after LASIK8.258Anisometropia0.70.01−4.00 −4.50 × 6853919
8Keratoconus87.75Astigmatism0.670.05−1.25 −5.75 × 11050013
9Keratoconus8N/AAstigmatism0.60.10.00 −7.00 × 30650156
10Keratoconus7.75N/AMyopia, astigmatism0.40.01−4.00 −4.25 × 4560972
11Keratoconus7.75N/AAstigmatism0.40.05+3.00 −6.00 × 3256492

Surgical Parameters and Outcome Data at 6 Months Postoperatively for Eyes that Underwent Femtosecond LASIK After Penetrating Keratoplasty

EyeFemtosecond Laser Flap Parameters
Excimer Laser Ablation Parameters
Wavefront-guided6 Months Postoperative
Enhancements
Diameter (mm)Programmed Thickness (μm)Optical Zone (mm)Ablation Depth (μm)RefractionBSCVA (decimal)UCVA (decimal)RefractionProcedureTime (mo)
1*7.71106.0940.00 −5.50 × 69No0.70.15−2.50 −1.50 × 11Flap lift, laser4
2*7.71105.5154+3.00 −4.00 × 0No0.670.15+4.50 −5.00 × 10Arcuate incisions2
37.71105.574+2.50 +2.00 × 15No0.60.4+0.50 −1.75 × 100
47.71005.01040.00 −8.00 × 85No0.50.1+0.00 −6.00 × 100LASEK8
57.71104.5120−4.00 −3.00 × 56Yes0.70.3+4.50 −4.00 × 56
67.71105.578+3.00 −5.00 × 46No0.60.3−0.50 −1.50 × 43
77.71105.5106−2.50 −4.50 × 68No0.70.33−2.00 −0.75 × 125
87.61005.5100−0.75 −5.75 × 110No0.80.50.00 −2.50 × 150Flap lift, laser6
97.7905.577−4.00 +6.00 × 120No0.50.2+1.00 −6.00 × 38
107.51105.0120−4.00 −4.25 × 45Yes1.00.5+1.50 −0.75 × 65
117.51105.559+2.50 −5.50 × 28Yes0.70.5+1.00 −2.50 × 52
Authors

From Enaim Refractive Surgery Centers, Jerusalem and Tel Aviv (Barequet, Hirsh, Levinger); and Goldschleger Eye Institute, Sheba Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Hashomer (Barequet), Israel.

The authors have no proprietary interest in the materials presented herein.

Presented in part at the International Society of Refractive Surgery of the American Academy of Ophthalmology Subspecialty Day; October 15–18, 2005; Chicago, Ill.

Correspondence: Irina S. Barequet, MD, Goldschleger Eye Institute, Sheba Medical Center, Tel Hashomer 52621, Israel. Tel: 972 3 530 2874; Fax: 972 3 530 2822; E-mail: ibarequet@hotmail.com

10.3928/1081597X-20100224-05

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