Laser In Situ Keratomileusis Flap Research Articles

Optimization of femtosecond lasers using porcine and human donor corneas before in vivo use

To demonstrate a safe and effective method of optimizing a femtosecond laser upon installation or for a new procedure before use on patients. In this case, specifically for optimizing settings for intrastromal corneal pocket creation for the presbyopic small-aperture corneal inlay (Kamra) and deep laser insitu keratomileusis (LASIK) flaps for the presbyopic hydrogel corneal inlay (Raindrop). Keil LASIK Vision Center, Grand Rapids, Michigan, USA. Experimental study. Human donor corneas were used to optimize femtosecond laser settings after initial optimization with porcine corneas. The laser used was the Femto LDV Z4. Pocket settings optimized for porcine corneas were 12.0mm/s pocket and tunnel at 105% energy; whereas, settings optimized with human donor corneas were 13.0mm/s pocket and tunnel at 110% energy. Settings optimized with human donor corneas were subsequently applied invivo to create pockets for the small-aperture corneal inlay. Further adjustment of settings to 14.0 mm/s pocket at 110% energy was still necessary to optimize pockets. No change in settings was necessary when creating deeper corneal LASIK flaps (ie, the same settings could be used for flaps of 110μm or 180μm). After settings were optimized for porcine corneas, further optimization was necessary before successful corneal incisions could be created invivo for corneal pockets. No further optimization was required when creating deeper corneal flaps for the hydrogel inlay. It is important to emphasize that settings obtained and reported here are not applicable to other femtosecond lasers.

Long-term safety of laser in situ keratomileusis in eyes with thin corneas: 5-year follow-up.

To investigate the long term (≥5y) efficacy, predictability, and safety of laser in situ keratomileusis (LASIK) in eyes with thin corneas [central corneal thickness (CCT) <500 µm]. A total of 339 patients met the criteria of this study. Finally, 175 eyes of 89 patients who had thin corneas and underwent LASIK≥5y ago returned to our clinic and included in this study. Preoperative parameters recorded included uncorrected visual acuity (UCVA), corrected distance visual acuity (CDVA), manifest refraction, CCT and corneal topography. At returning visits, in addition to visual acuity and manifest refraction, ultrasound CCT and corneal topography were performed. Optical coherence tomography was used to measure the CCT, LASIK flap thickness, and residual stromal bed thickness (RSBT). Safety index, efficacy index, percentage of eyes within ±0.5 D and ±1.0 D of refraction, percent tissue altered (PTA), and percentage stromal bed thickness (PSBT) were calculated. The safety index was 1.09 and efficacy index was 0.99. The percentages of eyes within ±0.5 D and ±1.0 D were 71.2% and 87.7%, respectively. The mean PTA was 40%±6% (range 20% to 55%); 76 eyes (43.4%) had PTA <40% and 99 eyes (56.6%) had PTA≥40%. The mean RSBT was 303±27 µm (range 240 to 390 µm), and 2 eyes had RSBT<250 µm. The mean PSBT was 61%±9% (range 51% to 85%). No eyes developed ectasia. In this cohort with the PSBT of 50% or more, LASIK is safe with follow-up for at least 5y.

Reproducibility of laser in situ keratomileusis flap thickness using a new multifunctional femtosecond laser platform and correlation with clinical preoperative measurements

To analyze the reproducibility of laser insitu keratomileusis (LASIK) flap thickness (target 120μm) using the multifunctional femtosecond laser (Lensx) and correlate postsurgical measurements with preoperative factors. Hospital Oftalmológico Visão Laser, Santos, São Paulo, Brazil. Prospective case series. Patients with stable refraction for over a year were evaluated. Patients who submitted to refractive surgery with -1.25 to -6.00 diopters (D), with or without astigmatism up to -4.00 D, and corneal curvature of 40.00 to 47.00 D were included. At 100days postoperatively, an independent examiner performed 4 high-resolution tomographic sections of the cornea for each eye at 45- to 225-degree, 90- to 270-degree, 135- to 315-degree, and 0- to 180-degree meridians. Two masked experienced observers analyzed each section using measuring points located at the center of the cornea (0.0mm), 2.0mm to the left and to the right of the center, and 4.0mm to the left and to the right of the center. The study comprised 33 patients (63 eyes), aged 21 to 50years. A significant difference from the target flap thickness (120μm) was found in 2 of 20 measurements; however, the actual difference was approximately 2.2μm. Interrater reliability was excellent (ICC>0.75), with an interrater bias close to 0. Clinical measurements were not predictive of the set of 20 postoperative measurements. Reproducibility of the multifunctional femtosecond laser was good for LASIK flap creation and no predictive correlation was found with preoperative clinical factors.

Evaluation of femtosecond laser in flap and cap creation in corneal refractive surgery for myopia: a 3-year follow-up.

PurposeTo evaluate femtosecond laser in flap and cap creation, detect some corneal biomechanical changes, and evaluate dry eye after laser in situ keratomileusis (LASIK), Femto-LASIK, and small incision lenticule extraction (SMILE) with 3-year follow-up.Patients and methodsPreoperative evaluation taken: full ophthalmic examination, Pentacam, ocular response analyzer, ocular surface disease index (OSDI), and tear breakup time (TBUT). LASIK flap was created using Moria microkeratome in 30 eyes (LASIK group) and using VisuMax femtosecond laser in 38 eyes (FS-LASIK group) and SMILE was done by VisuMax in 35 eyes (SMILE group). Postoperative evaluation: anterior segment optical coherence tomography to measure flap and cap thickness, ocular response analyzer to measure corneal hysteresis (CH) and corneal resistance factor (CRF), OSDI, and TBUT at 1, 3, 6, 12, 24, and 36 months after surgery.ResultsThis study included 103 eyes of 103 patients. The mean deviation of central cap or flap thickness from intended was statistically higher in the LASIK group (P<0.001). Both CH and CRF showed significant reduction postoperatively but were significantly higher in the SMILE group during follow up (P<0.05). The mean OSDI scores were significantly elevated in all groups postoperatively (P<0.01) but were significantly lower in the SMILE group 3 months postoperatively (P<0.05). The mean TBUT was significantly decreased in all groups postoperatively (P<0.01) but was significantly higher in the SMILE group 6 months postoperatively (P<0.05).ConclusionFemtosecond laser is more accurate than microkeratomes. CH and CRF changes were least after SMILE. The three procedures led to significant dryness but for shorter duration with SMILE.

Evaluation of a multifunctional femtosecond laser for the creation of laser in situ keratomileusis flaps

To characterize the performance of a multifunctional femtosecond laser system (Lensx) for the creation of laser insitu keratomileusis (LASIK) flaps. Two surgical sites in the United States. Prospective case series pilot study. Patients with myopia or hyperopia who were eligible for femtosecond laser-initiated LASIK surgery with corrected distance visual acuities (CDVA) correctable to at least 20/25 were enrolled. Central flap thickness accuracy (desired versus achieved) and precision (flap thickness standard deviation) were measured using anterior segment optical coherence tomography. Flap dissection quality, stromal bed quality, and amount of opaque bubble layer (OBL) formation were graded during surgery, and the refractive outcomes were evaluated postoperatively at 1-month and 3-month follow-ups. The study comprised 30 patients (58 eyes). At 3months postoperatively, the flap thickness accuracy was 1.3μm±2.6 (SD). A total of 78.3% of flaps were lifted with no resistance and 16.7% were lifted with minimal resistance using a blunt instrument. All (100%) stromal beds were determined to have a very smooth surface (grade 5 on a 0 to 5 scale). No OBL was observed in 73.3% of eyes; 26.7% of eyes showed an OBL occurring on less than 24% of the stromal bed surface. At 3months postoperatively, most eyes (84.5%) had an uncorrected distance visual acuity of 20/20 and 98% had a CDVA of 20/20. The most common ocular adverse event was punctate keratitis (11.7%). The multifunctional femtosecond laser system effectively created LASIK flaps that were high quality, accurate, and precise.

The effect of flap thickness on corneal biomechanics after myopic laser in situ keratomileusis using the M-2 microkeratome.

PurposeThe purpose of this study was to determine the effect of flap thickness on corneal biomechanics after myopic laser in situ keratomileusis (LASIK).MethodsThis is a prospective controlled non-randomized, institutional study. Patients underwent either epi-LASIK with mitomycin (advanced surface ablation [ASA]), thin-flap LASIK (90 µm head), or thick-flap LASIK (130 µm head). In ASA, the Moria Epi-K hydroseparator was used. LASIK flaps were created using the Moria M-2 mechanical microkeratome. The corneal hysteresis (CH) and corneal resistance factor (CRF) were measured preoperatively and 3 months after surgery, using the Ocular Response Analyzer®.ResultsTen patients (19 eyes) underwent ASA, 11 patients (16 eyes) underwent thin-flap LASIK, and 11 patients (16 eyes) underwent thick-flap LASIK. The mean preoperative CH was 10.47±0.88, 10.52±1.4, and 11.28±1.4 mmHg (p=0.043), respectively, decreasing after surgery by 1.75±1.02, 1.66±1.00, and 2.62±1.03 mmHg (p=0.017). The mean reduction of CH per micron of central corneal ablation was 0.031, 0.023, and 0.049 mmHg/µm (p=0.005). Mean preoperative CRF was 10.11±1.28, 10.34±1.87, and 10.62±1.76 mmHg (p=0.66), decreasing after surgery by 2.33±1.35, 2.77±1.03, and 2.92±1.10 mmHg (p=0.308). The mean reduction of CRF per micron of central corneal ablation was 0.039, 0.040, and 0.051 mmHg/µm (p=0.112).ConclusionThick-flap LASIK caused a greater reduction of CH and CRF than thin-flap LASIK and ASA, although this was statistically significant only for CH. ASA and thin-flap LASIK were found to be biomechanically similar.

Effects of ablation depth and repair time on the corneal elastic modulus after laser in situ keratomileusis

BackgroundThe biomechanical properties of the cornea should be taken into account in the refractive procedure in order to perform refractive surgery more accurately. The effects of the ablation depth and repair time on the elastic modulus of the rabbit cornea after laser in situ keratomileusis (LASIK) are still unclear.MethodsIn this study, LASIK was performed on New Zealand rabbits with different ablation depth (only typical LASIK flaps were created; residual stroma bed was 50 or 30% of the whole cornea thickness respectively). The animals without any treatment were served as normal controls. The corneal thickness was measured by ultrasonic pachymetry before animals were humanly killed after 7 or 28 days post-operatively. The corneal elastic modulus was measured by uniaxial tensile testing. A mathematical procedure considering the actual geometrics of the cornea was created to analyze the corneal elastic modulus.ResultsThere were no obvious differences among all groups in the elastic modulus on after 7 days post-operatively. However, after 28th days post-operatively, there was a significant increase in the elastic modulus with 50 and 30% residual stroma bed; only the elastic modulus of the cornea with 30% residual stroma bed was significantly higher than that of 7 days.ConclusionsChanges in elastic modulus after LASIK suggest that this biomechanical effect may correlate with the ablation depth and repair time.

Moria One-Use Plus sub-Bowman’s keratomileusis head: a useful tool in the refractive surgeon’s armamentarium

Patients and methods A total of 500 eyes of 250 patients underwent laser in situ keratomileusis (LASIK) surgery using the One-Use Plus sub-Bowman’s keratomileusis head for the creation of an ultrathin LASIK flap. During the follow-up at 1, 6, 12, and 24 months, both uncorrected visual acuity (UCVA) and best-corrected visual acuity were recorded. A keratoconus screening corneal topography was carried out during the last follow-up visit. Results A total of 500 eyes of 250 myopic patients were included in this study. There were 115 male patients and 135 female patients. The mean age was 27.5 years (range: 18–44 years). The mean preoperative refractive error was −5.0 diopter sphere (DS) (range: −3 to −9 DS). The mean cylindrical error was −2.5 diopter cylinder (DC) (range: −0.75 to −4.5 DC). The mean UCVA was 0.07 (range: 0.01–0.3), and it improved to 1.0 (range: 0.8–1.25) on day 1 postoperatively. At the end of the follow-up, the mean UCVA was 1.0 and the mean best-corrected visual acuity was 1.0. The mean stromal residual bed thickness was 362 μm (range: 304–466 μm), and the mean central flap thickness was 102 μm (range: 82–120 μm). Complications were perilimbal bleeding in 15 eyes and fine irregular stromal edge cuts at the sides of the hinge in 10 eyes. There were no epithelial defects, no epithelial heaping or sliding, no irregular stromal bed surface cuts, no free caps or button holes, or incomplete flaps. Diffuse lamellar keratitis occurred in one eye of one patient, and no slipped flaps, macrostriae or microstriae, or epithelial downgrowth was seen during the follow-up period. At the end of the follow-up period none of our patients had topographic evidence of keratoconus. Conclusion The One-Use Plus sub-Bowman’s keratomileusis head is a safe and effective method for creating an ultrathin LASIK flap and allows the surgeon to treat higher errors of refraction while maintaining a higher safety margin by leaving more residual stromal tissue.

Options for a young patient with considerably high, topographically stable, astigmatism: December consultation #1

A 21-year-old woman was referred for a refractive surgery evaluation. She has no relevant allergies or medical or family history of keratoconus or corneal transplantation. Spectacle dependence is her chief complaint. She occasionally wears contact lenses but wants to have surgery performed. The corrected near visual acuity and the corrected distance visual acuity (CDVA) are 20/20 in both eyes. The manifest refraction is 5.75 3.25 178 in the right eye and 5.00 3.50 170 in the left eye. The intraocular pressure and the results from a slitlamp examination and a fundus retinoscopy are normal. The ultrasound pachymetry shows the central corneal thickness (CCT) to be 505 mm in the right eye and 508 mm in the left eye. Among all devices used tomeasure the CCT, the thinnest measured point is 504 mm in the right eye and 503 mm in the left eye. Placido-disk corneal topography shows a high regular symmetric astigmatism that was stable over 1 year of follow up, with an insignificant change in keratometry (K) values (Figure 1). The 5 topographies were obtained at 3-month intervals. Scheimpflug and dual Scheimpflug tomography (Figures 2, 3, and 4) are normal with no suspicious pattern except a high regular astigmatism. The pachymetry maps show corneas that, although slightly thin, are within normal limits across the diameter. An excimer laser system predicts a stromal ablation of approximately 127 mm in the right eye and 121 mm in the left eye. For laser in situ keratomileusis (LASIK) with a 110 mm flap thickness, the percentage of tissue altered (PTA) would be 47% in the right eye and 46% in the left eye. The residual stromal bed (RSB) would be 267 mm in the right eye and 272 mm in the left eye. For photorefractive keratectomy (PRK), the PTA would be 25% in the right eye and 24% in the left. What kind of refractive surgery (if any) would you recommend to this patient? If none, why? Would you consider LASIK with a thin, predictable LASIK flap? What data helped you most in making your decision? Did the stability shown by the Placido disk–based corneal topography over 1 year significantly affect your surgery decision?What are your limits for treating a cornea with high regular symmetric astigmatism? If you recommend proceeding with surgery, was age a significant factor in that decision?

Visual outcomes after femtosecond laser in situ keratomileusis flap complications

To compare visual outcomes in normal and complicated laser in situ keratomileusis (LASIK) flaps constructed with a femtosecond laser. Wilford Hall Ambulatory Surgical Center, San Antonio, Texas. Retrospective chart review. The main outcome measures were uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (CDVA) at 1 month post-surgery, which were compared in patients with and without complications during flap creation. This retrospective chart review identified 586 eyes of 293 consecutive patients who had bilateral simultaneous femtosecond LASIK for myopia. A normal flap was attained in 539 (91.8%) of patients. At 1 month postoperatively, the mean UDVA was 20/19.1, and the CDVA was 20/16.8. 3 (0.51%) of patients experienced an incomplete side cut or intraoperative flap tear (the mean 1-month uncorrected distance visual acuity [UDVA] was 20/17.5 and the corrected distance visual acuity [CDVA] was 20/16.9 in both groups). Microstriae were seen in 28 (4.8%) of patients (mean 1-month UDVA, 20/21.7; CDVA, 20/17.4). Diffuse lamellar keratitis appeared in 4 (0.68%) of patients (mean 1-month UDVA, 20/21.7; CDVA, 20/15.6). Epithelial ingrowth developed in 9 (1.5%) of patients (mean 1-month UDVA, 20/18.7; CDVA, 20/16.9). There was no statistically significant difference in UDVA or CDVA at 1 month postoperatively between complicated and uncomplicated flaps (P > .05), and complicated flaps did not lose a statistically significant amount of CDVA or low-contrast acuity (CDVA 5%) compared to preoperative values. Intraoperative and postoperative complications of LASIK flaps created with the femtosecond laser were rare, and their visual outcomes were equivalent to those of normal flaps. Charles D. Reilly is a consultant to Alcon Labs and Abbott Medical Optics at present, but was not at the time of the study. For the remaining authors none are declared.

Combined intrastromal astigmatic keratotomy and laser in situ keratomileusis flap followed by photoablation to correct post–penetrating keratoplasty ametropia and high astigmatism: One-year follow-up

To evaluate a new technique combining intrastromal astigmatic keratotomy (AK) with a laser in situ keratomileusis (LASIK) flap followed by excimer laser photoablation to correct post-penetrating keratoplasty (PKP) high astigmatism and ametropia. Kasr El Aini Hospital, Cairo University, Cairo, Egypt. Prospective interventional uncontrolled case series. Patients with post-PKP high astigmatism and ametropia had paired intrastromal AK with LASIK flap using the M2 microkeratome followed 2 to 3 months later by excimer laser photoablation. The main outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), mean refractive spherical equivalent (SE), and mean cylinder after each step and at the 1-year follow-up. The study comprised 20 eyes (20 patients). All parameters were significantly improved in all patients by the last follow-up visit. The mean UDVA improved from 1.07 logMAR ± 0.2 (SD) preoperatively to 0.23 ± 0.18 logMAR (P < .001), the mean CDVA improved from 0.79 ± 0.18 logMAR to 0.12 ± 0.12 logMAR (P < .001), the mean refractive SE improved from -5.04 ± 2.62 diopters (D) to -1.47 ± 1.32 D (P = .001), and the mean cylinder reduced from -5.39 ± 0.98 D to -1.05 ± 0.71 D (P < .001). The mean correction index was 0.84 ± 0.10, and the mean flattening index was 0.83 ± 0.10. Thirty-five percent of cases developed microperforations, and 15% developed epithelial ingrowth. This combined approach allowed for the correction of high astigmatism and ametropia following PKP; however, epithelial ingrowth requiring intervention is a complication to be considered. No author has a financial or proprietary interest in any material or method mentioned.

Comparison of the femtosecond laser and mechanical microkeratome for flap cutting in LASIK.

To compare refractive results, higher-order aberrations (HOAs), contrast sensitivity and dry eye after laser in situ keratomileusis (LASIK) performed with a femtosecond laser versus a mechanical microkeratome for myopia and astigmatism. In this prospective, non-randomized study, 120 eyes with myopia received a LASIK surgery with the VisuMax femtosecond laser for flap cutting, and 120 eyes received a conventional LASIK surgery with a mechanical microkeratome. Flap thickness, visual acuity, manifest refraction, contrast sensitivity function (CSF) curves, HOAs and dry-eye were measured at 1wk; 1, 3, 6mo after surgery. At 6mo postoperatively, the mean central flap thickness in femtosecond laser procedure was 113.05±5.89 µm (attempted thickness 110 µm), and 148.36±21.24 µm (attempted thickness 140 µm) in mechanical microkeratome procedure. An uncorrected distance visual acuity (UDVA) of 4.9 or better was obtained in more than 98% of eyes treated by both methods, a gain in logMAR lines of corrected distance visual acuity (CDVA) occurred in more than 70% of eyes treated by both methods, and no eye lost ≥1 lines of CDVA in both groups. The difference of the mean UDVA and CDVA between two groups at any time post-surgery were not statistically significant (P>0.05). The postoperative changes of spherical equivalent occurred markedly during the first month in both groups. The total root mean square values of HOAs and spherical aberrations in the femtosecond treated eyes were markedly less than those in the microkeratome treated eyes during 6mo visit after surgery (P<0.01). The CSF values of the femtosecond treated eyes were also higher than those of the microkeratome treated eyes at all space frequency (P<0.01). The mean ocular surface disease index scores in both groups were increased at 1wk, and recovered to preoperative level at 1mo after surgery. The mean tear breakup time (TBUT) of the femtosecond treated eyes were markedly longer than those of the microkeratome treated eyes at postoperative 1, 3mo (P<0.01). Both the femtosecond laser and the mechanical microkeratome for LASIK flap cutting are safe and effective to correct myopia, with no statistically significant difference in the UDVA, CDVA during 6mo follow-up. Refractive results remained stable after 1mo post-operation for both groups. The femtosecond laser may have advantages over the microkeratome in the flap thickness predictability, fewer induced HOAs, better CSF, and longer TBUT.

Options for an eye with a thin cornea: June consultation #1

Journal of Cataract & Refractive Surgery: June 2015 - Volume 41 - Issue 6 - p 1324-1327 doi: 10.1016/j.jcrs.2015.06.006

Changes in Keratocyte Density and Visual Function Five Years After Laser In Situ Keratomileusis: Femtosecond Laser Versus Mechanical Microkeratome

To determine the effects of keratocyte loss on optical properties and vision after laser in situ keratomileusis (LASIK) with the flap created with a femtosecond laser or a mechanical microkeratome. Randomized clinical paired-eye study. Both eyes of 21 patients received LASIK for myopia or myopic astigmatism. One eye of each patient was randomized by ocular dominance to flap creation with a femtosecond laser and the other eye to flap creation with a mechanical microkeratome. Before LASIK and at 1, 3, and 6 months and 1, 3, and 5 years after LASIK, keratocyte density was measured using confocal microscopy, and high-contrast visual acuity and anterior corneal wavefront aberrations were measured by standard methods. At each visit, all variables were compared between methods of creating the flap and to the same variable before treatment using paired tests with Bonferroni correction for multiple comparisons. Keratocyte density in the flap decreased by 20% during the first year after LASIK and remained low through 5 years (P < .001). High-order wavefront aberrations increased and uncorrected visual acuity improved immediately after surgery, but these variables did not change further to 5 years. There were no differences in any variables between treatments. A sustained reduction in keratocyte density does not affect vision or optical properties of the cornea through 5 years after LASIK. The method of creating a LASIK flap does not influence the changes in keratocyte density in the flap.

High-irradiance CXL combined with myopic LASIK: flap and residual stroma biomechanical properties studied ex-vivo

Background/aimsTo evaluate ex vivo biomechanical and enzymatic digestion resistance differences between standard myopic laser in-situ keratomileusis (LASIK) compared with LASIK+CXL, in which high-irradiance cross-linking (CXL) is added.MethodsEight human donor corneas...

One-year eye-to-eye comparison of wavefront-guided versus wavefront-optimized laser in situ keratomileusis in hyperopes.

BackgroundTo compare wavefront (WF)-guided and WF-optimized laser in situ keratomileusis (LASIK) in hyperopes with respect to the parameters of safety, efficacy, predictability, refractive error, uncorrected distance visual acuity, corrected distance visual acuity, contrast sensitivity, and higher order aberrations.MethodsTwenty-two eyes of eleven participants with hyperopia with or without astigmatism were prospectively randomized to receive WF-guided LASIK with the VISX CustomVue S4 IR or WF-optimized LASIK with the WaveLight Allegretto Eye-Q 400 Hz. LASIK flaps were created using the 150-kHz IntraLase iFS. Evaluations included measurement of uncorrected distance visual acuity, corrected distance visual acuity, <5% and <25% contrast sensitivity, and WF aberrometry. Patients also completed a questionnaire detailing symptoms on a quantitative grading scale.ResultsThere were no statistically significant differences between the groups for any of the variables studied after 12 months of follow-up (all P>0.05).ConclusionThis comparative case series of 11 subjects with hyperopia showed that WF-guided and WF-optimized LASIK had similar clinical outcomes at 12 months.

Microkeratome versus femtosecond flaps: accuracy and complications.

To update the knowledge on differences between mechanical microkeratome and femtosecond flaps for laser in-situ keratomileusis (LASIK) in terms of accuracy and complications. Corneal flaps created with the femtosecond laser present a more planar architecture and provide greater precision in flap diameter and thickness; a more uniform flap thickness across the flap diameter and it allows the surgeon to programme the angulation of the flap periphery. Femtosecond LASIK flaps are classically related to complications derived from a more intense inflammatory response, such as diffuse lamellar keratitis and transient light-sensitivity syndrome. Newer femtosecond models allow for much lower energy delivery to cut the flap, to the point the overall inflammatory response is not significantly different from the microkeratome. The incidence of complications such as epithelial defect and flap dislocations is higher with microkeratome flaps. This review examines the accuracy and complications of flaps created with femtosecond and microkeratome. Both femtosecond and microkeratome are able to create accurate LASIK flaps. Femtosecond LASIK flaps represent significant improvement in morphology and predictability with implications for safety.

Healthcare and a holiday: the risks of LASIK tourism

Medical tourism is the practice of travelling overseas for surgery. We describe a patient with low myopia who underwent laser in situ keratomileusis (LASIK) while on holiday in India. She presented to local hospital eye services six weeks post‐LASIK with discomfort and reduced vision. She reported three previous LASIK flap lifts in the right eye. Clinical assessment, optical coherence tomography and confocal microscopy demonstrated moderate epithelial ingrowth and reduced visual acuity. Epithelial ingrowth after LASIK may be associated with visual impairment and management is determined by location, magnitude and effect on vision. LASIK tourism may mean patients are less well‐informed of risks and lose continuity of professional care.

Comparison of biomechanical effects of small-incision lenticule extraction and laser in situ keratomileusis: Finite-element analysis

To theoretically compare the corneal stress distribution of laser in situ keratomileusis (LASIK) with the stress distribution of small-incision lenticule extraction. Cleveland Clinic Cole Institute, Cleveland, and The Ohio State University, Columbus, Ohio, USA. Computational modeling study. A finite-element anisotropic collagen fiber-dependent model of myopic surgery using patient-specific corneal geometry was constructed for LASIK, small-incision lenticule extraction, and a geometry analog model with unaltered material properties from preoperative but with postoperative geometry including thickness. Surgical parameters, magnitude of myopic correction, LASIK flap thickness, and lenticule depth in small-incision lenticule extraction were varied. Two sets of models, 1 with uniform and 1 with depth-dependent material properties, were constructed. Stress distribution between small-incision lenticule extraction simulations and the geometry analog model were similar. In contrast, LASIK consistently reduced stress in the flap and increased stress in the residual stromal bed (RSB) compared with the geometry analog model. An increase in flap thickness or lenticule depth resulted in a greater increase in RSB stress in the LASIK model than in the small-incision lenticule extraction model. Small-incision lenticule extraction may present less biomechanical risk to the residual bed of susceptible corneas than comparable corrections involving LASIK flaps. Deeper corrections in the stroma may be possible in small-incision lenticule extraction without added risk for ectasia. Proprietary or commercial disclosures are listed after the references.

Comparison of Ziemer FEMTO LDV "Classic" and "Crystal Line" femtosecond laser flap quality by Fourier-domain optical coherence tomography.

To compare the regularity and accuracy of laser in situ keratomileusis (LASIK) flaps created by the Ziemer FEMTO LDV "Classic" (Ziemer "Classic") and Ziemer FEMTO LDV Crystal Line femtosecond laser (Ziemer Crystal Line). Fourier-domain optical coherence tomography (RTVue OCT) was used to measure the morphology of 200 LASIK flaps of 100 consecutive patients created with the Ziemer Classic (100 flaps) or the Ziemer Crystal Line (100 flaps) at one week postoperatively. Flap thickness was evaluated at 36 specified measurement points on each flap. For all procedures with both lasers, the nominal flap thickness was 110µm. The mean flap thickness of the Ziemer Crystal Line group (102.49±2.68µm) was thinner than that of the Ziemer Classic group (107.65±5.09µm) (P<0.01). Average thickness of all flaps was uniform within 4µm at all measurement points. The flaps in the Ziemer Crystal Line group were more regular than those in the Ziemer Classic group when measured from the center to the periphery. The maximum deviation from the nominal 110µm of 36 measurements was 8µm in the Ziemer Classic group, while in the Ziemer Crystal Line group it was 9µm. Within the 3 600 measurements on the 100 eyes, differences greater than 20µm were observed 0.14% in the Ziemer Classic group, and 0.04% in the Ziemer Crystal Line group. The flaps created with the Ziemer FEMTO LDV Crystal Line femtosecond laser are more uniform and thinner than those created by the Ziemer FEMTO LDV Classic femtosecond laser.