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Moshirfar M, Smedley JG, Muthappan V, Jarsted A, Ostler EM. Rate of ectasia and incidence of irregular topography in patients with unidentified preoperative risk factors undergoing femtosecond laser-assisted LASIK. Clin Ophthalmol 2013; 8:35-42. [PMID: 24363553 PMCID: PMC3862735 DOI: 10.2147/opth.s53370] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To report the rate of postoperative ectasia after laser-assisted in situ keratomileusis (LASIK) with femtosecond laser-assisted flap creation, in a population of patients with no identified preoperative risk factors. Methods A retrospective case review of 1,992 eyes (1,364 patients) treated between March 2007 and January 2009 was conducted, with a follow up of over 4 years. After identifying cases of ectasia, all the patient charts were examined retrospectively for preoperative findings suggestive of forme fruste keratoconus (FFKC). Results Five eyes of four patients with post-LASIK ectasia were identified. All eyes passed preoperative screening and received bilateral LASIK. One of the five patients developed ectasia in both eyes. Three patients retrospectively revealed preoperative topography suggestive of FFKC, while one patient had no identifiable preoperative risk factors. Upon review of all the charts, a total 69 eyes, including four of the five eyes with ectasia, were retrospectively found to have topographies suggestive of FFKC. Conclusion We identified four cases of post-LASIK ectasia that had risk factors for FFKC on reexamination of the chart and one case of post-LASIK ectasia with no identifiable preoperative risk factors. The most conservative screening recommendations would not have precluded this patient from LASIK. The rate of purely iatrogenic post-LASIK ectasia at our center was 0.05% (1/1,992), and the total rate of post-LASIK ectasia for our entire study was 0.25% (1/398). The rate of eyes with unrecognized preoperative FFKC that developed post-LASIK ectasia was 5.8% (1/17).
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Affiliation(s)
- Majid Moshirfar
- John A Moran Eye Center, University of Utah, Salt Lake City, UT, USA
| | - Jared G Smedley
- College of Human Medicine, Michigan State University, Lansing, MI, USA
| | | | - Allison Jarsted
- Department of Ophthalmology, State University of New York Upstate Medical University, Syracuse, NY, USA
| | - Erik M Ostler
- John A Moran Eye Center, University of Utah, Salt Lake City, UT, USA
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Shetty R, Malhotra C, D'Souza S, Wadia K. WaveLight FS200 vs Hansatome LASIK: intraoperative determination of flap characteristics and predictability by hand-held bioptigen spectral domain ophthalmic imaging system. J Refract Surg 2013; 28:S815-20. [PMID: 23447894 DOI: 10.3928/1081597x-20121005-01] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To intraoperatively determine and compare the characteristics and predictability of LASIK flaps made by the WaveLight FS200 femtosecond laser (Alcon Laboratories Inc) and Hansatome (Bausch & Lomb) microkeratome using a hand-held spectral domain ophthalmic imaging system (Bioptigen Inc). METHODS Sixty eyes from 30 patients undergoing bilateral LASIK were prospectively evaluated. Patients were divided into two equal groups to undergo flap creation with either 100-microm femtosecond laser flaps (FS flap group) or 120-microm microkeratome flaps (MK flap group). Flap thickness was measured intraoperatively after creation of the flap but prior to lifting using the hand-held probe of the spectral domain imaging system. Geometry of the flap edge and smoothness of the stromal bed after lifting the flap was also evaluated in all cases. RESULTS Mean difference between planned and achieved flap thickness in the paracentral region was 2.84 +/- 3.16 mm for the FS flap group and 11.33 +/- 10.27 mm for the MK flap group, whereas in the periphery, it was 5.72 +/- 3.26 mm in the FS flap group and 24.67 +/- 10.35 mm in the MK flap group. The differences between groups were statistically significant (P < 0.001, Kruskal-Wallis test). The edges of the flaps were vertical in the FS flap group and the stromal bed was smoother, whereas in the MK flap group, the edges were more sloping and the stromal bed more irregular. CONCLUSIONS The WaveLight FS200 femtosecond laser is able to produce planar flaps with a high degree of predictability between the desired and achieved flap thickness. The ability to study the flap characteristics intraoperatively (when flap edema and stromal bed hydration changes have not yet occurred) with the hand-held probe of the Bioptigen imaging system ensures greater accuracy than measurements done postoperatively using other anterior segment optical coherence tomography prototypes.
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Affiliation(s)
- Rohit Shetty
- Narayana Nethralaya Eye Hospital, Bangalore, India
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Johnson RD, Nguyen MT, Lee N, Hamilton DR. Corneal biomechanical properties in normal, forme fruste keratoconus, and manifest keratoconus after statistical correction for potentially confounding factors. Cornea 2011; 30:516-23. [PMID: 21045653 DOI: 10.1097/ICO.0b013e3181f0579e] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To evaluate the difference in corneal biomechanical properties, after controlling for potentially confounding factors, along the spectrum of keratoconic disease as measured by the keratoconus severity score. METHODS The corneal biomechanical properties of 73 keratoconic (KCN) eyes of 54 patients, 42 forme fruste keratoconic (FFKCN) eyes of 32 patients, and 115 healthy eyes of 115 age- and sex-matched patients were reviewed retrospectively. The main outcome measures were corneal hysteresis (CH) and corneal resistance factor (CRF). RESULTS In the normal group, the mean CH was 11.0 ± 1.4 mm Hg and mean CRF was 11.1 ± 1.6 mm Hg. The FFKCN mean CH was 8.8 ± 1.4 mm Hg and mean CRF was 8.6 ± 1.3 mm Hg. The KCN mean CH was 7.9 ± 1.3 mm Hg and mean CRF was 7.3 ± 1.4 mm Hg. There were statistically significant differences in the mean CH and CRF in the normal group compared with the FFKCN and the KCN groups (P < 0.001) after statistically controlling for differences in central corneal thickness, age, and sex. CONCLUSIONS There is a significant difference in the mean CH and CRF between normal and FFKCN corneas after controlling for differences in age, sex, and central corneal thickness. However, there is a significant overlap in the distribution of CH and CRF values among all groups. The biomechanical parameters CH and CRF cannot be used alone but may be a useful clinical adjunct to other diagnostic tools, such as corneal tomography, in distinguishing normal from subclinical keratoconic corneas.
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Ruth AL, Lynn MJ, Randleman JB, Stulting RD. Blade source effect on laser in situ keratomileusis flap thickness with the Amadeus I microkeratome. J Cataract Refract Surg 2008; 34:407-10. [PMID: 18299064 DOI: 10.1016/j.jcrs.2007.11.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Accepted: 11/01/2007] [Indexed: 10/22/2022]
Abstract
PURPOSE To determine the effect of different blades on laser in situ keratomileusis (LASIK) flap thickness created with the Amadeus I microkeratome (Ziemer Ophthalmic Systems). SETTING Emory University Department of Ophthalmology and Emory Vision, Atlanta, Georgia, USA. METHODS This retrospective nonrandomized comparative case study from January 2005 through June 2006 compared LASIK flap thickness created with blades from 2 manufacturers: the Surepass from Surgical Instrument Systems and distributed by AMO and the ML7090 CLB distributed by Med-Logics, Inc. Sex, preoperative corneal thickness, surgical-eye sequence, flap thickness and variance, and residual stromal bed were evaluated in each group. RESULTS This study evaluated 424 eyes of 226 patients. Surepass blades were used in 238 eyes and ML7090 CLB blades in 186 eyes. There were no significant differences between the 2 blade groups in preoperative corneal thickness, sex, or cases with corneal thickness greater than 550 microm. Mean flap thickness and variance were significantly lower in the ML7090 CLB group than in the Surepass group (P<.0001). There were no significant differences in flap thickness in either group based on sex; however, in both groups, flap thickness was significantly lower in second eyes and in eyes with a preoperative thickness less than 550 microm (P<.001). CONCLUSIONS The Amadeus I microkeratome created thinner, more consistent LASIK flaps with the ML7090 CLB blade than with the Surepass blade. Preoperative corneal thickness and eye sequence affected flap thickness, while sex did not.
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Affiliation(s)
- Adrienne L Ruth
- Emory University Department of Ophthalmology, Rollins School of Public Health at Emory University, Atlanta, Georgia, USA
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Alió JL, Piñero DP. Very High-frequency Digital Ultrasound Measurement of the LASIK Flap Thickness Profile Using the IntraLase Femtosecond Laser and M2 and Carriazo-Pendular Microkeratomes. J Refract Surg 2008; 24:12-23. [PMID: 18269144 DOI: 10.3928/1081597x-20080101-03] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Jorge L Alió
- Vissum/Instituto Oftalmológico de Alicante, Alicante, Spain.
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Binder PS, Sarayba M, Ignacio T, Juhasz T, Kurtz R. Characterization of submicrojoule femtosecond laser corneal tissue dissection. J Cataract Refract Surg 2008; 34:146-52. [PMID: 18165095 DOI: 10.1016/j.jcrs.2007.07.056] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2007] [Accepted: 07/30/2007] [Indexed: 11/18/2022]
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Sonmez B, Doan MP, Hamilton DR. Identification of scanning slit-beam topographic parameters important in distinguishing normal from keratoconic corneal morphologic features. Am J Ophthalmol 2007; 143:401-8. [PMID: 17224117 DOI: 10.1016/j.ajo.2006.11.044] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Revised: 11/02/2006] [Accepted: 11/03/2006] [Indexed: 11/24/2022]
Abstract
PURPOSE To identify morphologic parameters obtained using scanning slit-beam topography that help distinguish normal from keratoconic corneal morphologic features. DESIGN Observational, retrospective, cross-sectional study. METHODS This retrospective review examined 207 normal eyes of patients undergoing an initial consultation for primary refractive surgery and 42 eyes with clinical keratoconus (KCN). The following parameters were examined and compared between the two groups: astigmatism, central corneal power, irregularity indices at 3 mm (II3) and 5 mm (II5), maximal posterior elevation (MPE) magnitude and location, thinnest optical pachymetry (TOP) magnitude and location, anterior elevation best-fit sphere (ABFS), posterior elevation best-fit sphere (PBFS), the ratio of ABFS to PBFS, the difference between average inferior and average superior K values at 3 mm and 5 mm in both keratometric (I-S K3 and I-S K5) and tangential (I-S T3 and I-S T5) topographic maps, and skewed radial axis at 3 mm (SRAX3) and 5 mm (SRAX5) of the keratometric topography map. RESULTS The II3, II5, MPE magnitude, TOP magnitude, ABFS, PBFS, ABFS-to-PBFS ratio, I-S K at both 3 mm and 5 mm, I-S T at both 3 and 5 mm, and SRAX at 3 mm and 5 mm values were significantly different among the two groups (P < .001). The least-correlated parameters were SRAX3, TOP magnitude, and II3 in the KCN group and I-S K3, amount of astigmatism and MPE magnitude in the normal group. CONCLUSIONS Parameters obtained using scanning slit-beam topography may allow improved differentiation of keratoconic from normal corneal shapes, especially when the poorly correlated intragroup parameters are used.
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Affiliation(s)
- Baris Sonmez
- The Jules Stein Eye Institute, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095, USA
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Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, Sutton H, Coleman DJ. Probability Model of the Inaccuracy of Residual Stromal Thickness Prediction to Reduce the Risk of Ectasia After LASIK Part I: Quantifying Individual Risk. J Refract Surg 2006; 22:851-60. [PMID: 17124879 DOI: 10.3928/1081-597x-20061101-04] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To measure the imprecision of microkeratome cuts, preoperative corneal pachymetry, and laser ablation depth and develop a statistical model to describe the probability of the residual stromal bed thickness (RST) after myopic LASIK being significantly thinner than predicted. METHODS Preoperative corneal thickness, flap thickness, ablation depth, and RST were measured in 36 eyes by a prototype three-dimensional very high-frequency (VHF) 50 MHz digital ultrasound scanning device (<1.2 microm precision), precursor to the commercially available Artemis 2. All eyes had undergone LASIK with the Moria LSK-One microkeratome and the NIDEK EC-5000 excimer laser. Based on the statistically combined uncertainty (standard deviation) and bias (accuracy to intended value) of corneal thickness measurement, flap thickness, and ablation depth, a continuous probability function was devised describing the chance of obtaining an actual RST less than a specified "cut-off". The model was applied using the data collected from the cohort of eyes. The model was also applied using published flap thickness statistics on a series of microkeratomes. RESULTS Precision (standard deviation) was 0.74 microm for VHF digital ultrasound measurement of pachymetry, 30.3 microm for Moria LSK-One flap thickness, and 11.2 microm for NIDEK EC-5000 ablation depth. Assuming negligible laser ablation depth bias, the model found the probability that the actual RST will be <200 pmicromgiven a target RST of 250 microm is 7.56% with the Moria LSK-One. The model applied to published flap statistics revealed a range of probabilities of leaving <200 microm given a target RST of 250 microm from <0.01% to 33.6%. CONCLUSIONS The choice of microkeratome, laser, and pachymeter has a significant impact on the variation of the depth of keratectomy and thus on the risk of ectasia. This model together with high-precision microkeratomes, preoperative pachymetry, and knowledge of laser ablation precision would enable surgeons to determine the specific imprecision of RST prediction for individual LASIK cases and minimize the risk of ectasia.
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Affiliation(s)
- Dan Z Reinstein
- London Vision Clinic, 8 Devonshire Place, London W1G 6HP, United Kingdom.
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Stonecipher K, Ignacio TS, Stonecipher M. Advances in refractive surgery: microkeratome and femtosecond laser flap creation in relation to safety, efficacy, predictability, and biomechanical stability. Curr Opin Ophthalmol 2006; 17:368-72. [PMID: 16900030 DOI: 10.1097/01.icu.0000233957.88509.2d] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW Methods of flap creation have changed over the years from the evolution of the mechanical microkeratome to the introduction of the IntraLase femtosecond laser keratome, both of which have different mechanisms of action to create corneal resections. Previous studies report the advantages and disadvantages of the mechanical microkeratome and the IntraLase femtosecond laser. The critical components in laser in-situ keratomileusis surgery remain the same, however: safety, efficiency, predictability, and biomechanical stability. RECENT FINDINGS Keratoectasia and flap efficiency remain a constant safety concern in laser in-situ keratomileusis surgery. Unexpectedly thick flaps as well as variable thickness continue to be a concern with safety in relation to microkeratome technology. Epithelial preservation, flap complications, and newer issues such as Transient Light Sensitivity Syndrome are safety concerns of flap creation. Improved outcomes with regards to vision, induced astigmatism, induced higher-order aberrations, and enhancement rates are seen to favor predictability of femtosecond technologies over the microkeratome. Recent biomechanical studies show improved healing with femtosecond laser flap creation compared with blade-assisted flap creation. SUMMARY The aim of this review is to summarize the key components for both the microkeratome and the femtosecond laser and to update on the recent advances reported on these topics.
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Abstract
PURPOSE To evaluate patients who developed ectasia with no apparent preoperative risk factors. METHODS Potential cases of patients who developed ectasia without apparent risk factors were identified by contacting participants in the Kera-Net (n = 580), ASCRS-Net (n = 450), and ISRS/AAO ISRS-Net (n = 525) internet bulletin boards from April to October 2003. Cases were included if ectasia developed after laser in situ keratomileusis in the absence of apparent preoperative risk factors. Reported cases were excluded for the following reasons: (1) calculated residual stromal bed less than 250 microm, (2) preoperative central pachymetry less than 500 microm, (3) any keratometry reading greater than 47.2 diopters (D), (4) a calculated inferior-superior value greater than 1.4, (5) more than 2 retreatments, (6) attempted initial correction greater than -12.00 D, (7) an Orbscan II "posterior float" (if obtained) greater than 50 microm, and (8) surgical/flap complications. RESULTS A total of 27 eyes of 25 patients were submitted for consideration. Eight eyes (8 patients) met our inclusion criteria. Mean age was 27.7 years (range, 18-41 years). Preoperative manifest refraction spherical equivalent was -4.61 D (range, -2.00 to -8.00 D); steepest keratometric reading was 43.86 D (range, 42.50-46.40 D); keratometric astigmatism was 0.93 D (range, 0.25-1.90 D); and preoperative central pachymetry was 537 microm (range, 505-560 microm). The mean calculated ablation depth was 82.8 microm (range, 21-125.4 microm), and mean calculated residual stromal bed was 299.5 microm (range, 254-373 microm). Mean time to recognition of ectasia onset was 14.2 months (range, 3-27 months) postoperatively. At the time of ectasia diagnosis, the mean manifest refraction spherical equivalent was -1.23 D (range, +0.125 to -3.00) with a mean of 2.72 D (range, 0.75-4.00 D) of astigmatism. CONCLUSIONS Ectasia can occur after an otherwise uncomplicated laser in situ keratomileusis procedure, even in the absence of apparent preoperative risk factors.
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Affiliation(s)
- Shawn R Klein
- Cornea Service, Department of Ophthalmology, Rush University Medical Center, Chicago, IL 60612, USA
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Abstract
PURPOSE To determine the explanatory power of preoperative variables and comeal flap thickness in laser in situ keratomileusis (LASIK) using the Hansatome zero compression microkeratome (Bausch & Lomb, Rochester, NY). METHODS A prospective, nonrandomized, comparative interventional case study was performed on 250 eyes of 129 consecutive patients who underwent LASIK surgery using the Hansatome zero compression microkeratome. A 160-microm or 180-microm microkeratome head and an 8.5- or 9.5-mm suction ring were used in the procedures. Preoperative measurements included refraction, spherical equivalent, keratometry, intraocular pressure, corneal white-to-white, anterior chamber depth, and corneal eccentricity. Corneal thickness was measured intraoperatively using ultrasonic pachymetry before and after flap creation, and the difference was taken as flap thickness. Flap diameter was measured with a corneal gauge. Data were analyzed using simple, multiple, stepwise linear and non-linear regression analyses and two-tailed t tests. RESULTS The mean flap thickness was 124 +/- 17 microm with the nominal 160-microm head and 142 +/- 20 microm with the nominal 180-microm head. One third (33%) of the total variation in flap thickness could be accounted for by three preoperative variables: average corneal thickness, spherical equivalent refraction, and choice of 160- or 180-microm microkeratome head. A simple correlation of 0.114 was noted between corneal eccentricity and flap thickness, but this variable did not add significant explanatory power on multiple regression analysis. Linear regression analysis allowed determination of a flap thickness nomogram with a standard error of the estimate of 16.9 microm and a 95% confidence interval of +/- 33.1. CONCLUSIONS Comeal thickness is the most systematic predictor of corneal flap thickness using the Hansatome microkeratome. Because three preoperative variables account for only 33% of the range in flap thickness, future studies should focus on variations in blade extension and corneal biomechanical factors, which may also play an important role in determining flap thickness.
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Liu Q, Gong XM, Chen JQ, Yang B, Ge J, To CH. Laser in situ keratomileusis induced corneal perforation and recurrent corneal epithelial ingrowth. J Cataract Refract Surg 2005; 31:857-9. [PMID: 15899469 DOI: 10.1016/j.jcrs.2004.09.027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/09/2004] [Indexed: 10/25/2022]
Abstract
We report a rare complication of recurrent corneal epithelial cell ingrowth after corneal perforation induced by laser in situ keratomileusis. A corneal flap was made uneventfully with an automatic SCMD microkeratome (Howard Instruments, Inc.). During laser ablation, instead of random burning over the stromal bed, repeated ablation at a single location occurred because of a machine malfunction, resulting in corneal perforation. The flap was replaced and sutured to prevent leakage of aqueous humor. As the cornea healed, the patient's vision was compromised by scar formation, high irregular astigmatism, and epithelial ingrowth. The flap was reopened, and the epithelial cells were removed by thoroughly scraping the flap and stromal bed. However, corneal epithelial ingrowth recurred within a week. The recurrent and progressive epithelial ingrowth further decreased vision, and penetrating keratoplasty was recommended.
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Affiliation(s)
- Quan Liu
- Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, People's Republic, China
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Giledi O, Mulhern MG, Espinosa M, Kerr A, Daya SM. Reproducibility of LASIK flap thickness using the Hansatome microkeratome. J Cataract Refract Surg 2004; 30:1031-7. [PMID: 15130640 DOI: 10.1016/j.jcrs.2003.09.070] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/16/2003] [Indexed: 11/23/2022]
Abstract
PURPOSE To evaluate the actual versus the expected thickness of laser in situ keratomileusis (LASIK) flaps and to determine the factors that affect flap thickness. SETTING Centre For Sight, Queen Victoria Hospital, East Grinstead, United Kingdom. METHODS A retrospective analysis of LASIK procedures in 757 consecutive eyes was done. The surgery was performed by a single surgeon using 2 Hansatome microkeratomes (Bausch & Lomb) with 160 microm and 180 microm heads. Patient age, preoperative manifest refraction, automated keratometry, preoperative central pachymetry, and intraoperative stromal pachymetry were evaluated to determine whether they influenced the actual flap thickness. RESULTS Bilateral LASIK was performed in 343 patients (686 eyes). The 160 microm head was used in 641 eyes (84.6%) (Group 1) and the 180 microm head, in 116 eyes (15.4%) (Group 2). The mean preoperative manifest refraction spherical equivalent (SE) was -3.9 diopters (D) +/- 4.5 (SD) (range +7.4 to -25.0 D) in Group 1 and -4.4 +/- 3.7 D (range +7.1 to -12.9 D) in Group 2. The mean preoperative keratometry reading was 43.6 +/- 1.8 D (range 36.0 to 48.6 D) and 43.6 +/- 1.8 D (range 35.9 to 47.0 D), respectively; the mean preoperative central pachymetry was 543 +/- 35 microm (range 447 to 643 microm) and 548 +/- 31 microm (range 453 to 613 microm), respectively; and the mean flap thickness was 116.4 +/- 19.8 microm and 117.3 +/- 18.0 microm, respectively. The difference between the actual and the expected flap thickness in each group was statistically significant (P<.001). There was no significant difference in the actual flap thickness between the 2 Hansatomes. The preoperative SE and central pachymetry were the only factors that influenced the actual flap thickness (P<.05); thin flaps were more common with increasing myopia and increasing corneal thickness. CONCLUSIONS Spherical equivalent and preoperative pachymetry were the principal factors that influenced flap thickness. Preoperative keratometry values and patient age did not influence the actual flap thickness.
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Affiliation(s)
- Osama Giledi
- Corneoplastic Unit, Queen Victoria Hospital NHS Trust, East Grinstead, West Sussex, United Kingdom
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