Thin LASIK Flap Creation Using the SCHWIND Carriazo-Pendular Microkeratome

Corneal flap thickness with the Moria M2 single-use head 90 microkeratome in 72 consecutive LASIK procedures

Purpose

This study aimed to evaluate the accuracy and consistency of corneal flap thickness in laser-assisted in situ keratomileusis (LASIK) with the Moria M2 single-use head 90 microkeratome.

Methods

The central corneal thickness of 72 (37 right, 35 left) eyes of 37 patients was measured by ultrasonic pachymetry preoperatively and intraoperatively after flap cut. The Moria M2 single-use head 90 microkeratome was used to create a superior hinged flap in all eyes. The right eyes were always operated on before the left eyes in each patient, using the same blade in all bilateral cases. All patients underwent LASIK for myopia and/or myopic astigmatism using VISX Star S4 platform.

Results

The mean preoperative spherical equivalent refraction was −3.55±2.30 D (range: −0.625 to −11.00 D), preoperative central corneal thickness by ultrasonic pachymetry was 541±26.82 µm (490–600 µm) and steepest K was 44.08±1.49 D (40–46.75 D) in all eyes. The mean flap thickness was 136.97±20.07 µm (106–192 µm), 131.2±19.5 µm (91–192 µm), and 134.16±19.85 µm (91–192 µm) in the right, left, and both eyes, respectively. A positive significant relationship was found between flap thickness and preoperative ultrasonic pachymetry thickness. No significant relationship was found between flap thickness and the age, preoperative spherical equivalent, and preoperative steepest K. The difference between the first and second eyes was not significant. There were no major intraoperative and postoperative complications in all eyes.

Conclusion

The Moria M2 single-use head 90 microkeratome cut relatively thicker flaps than were intended. The flap thickness range was quite wide. This was a disadvantage for the accuracy and consistency of corneal flap thickness.

Reproducibility of flap thickness in sub-Bowman keratomileusis using a mechanical microkeratome

PURPOSE

To examine the predictability of flap thickness using a mechanical microkeratome (One Use-Plus) and identify factors related to variations in flap thickness in sub-Bowman keratomileusis (SBK).

SETTING

Tadawi Surgical Center, Taif, Saudi Arabia.

DESIGN

Retrospective case series.

METHODS

Patients with a stable refraction for 1 year, corrected distance visual acuity (CDVA) of at least 20/20 in each eye, and minimum central corneal thickness of 480 μm in each eye had microkeratome-assisted SBK. Parameters included manifest refraction, uncorrected distance visual acuity (UDVA), CDVA, pachymetry, and higher-order aberrations (HOAs).

RESULTS

Seventy eyes (36 patients) were enrolled. The mean flap thickness was 88.74 μm ± 15.40 (SD) and the mean change in HOAs, 0.11 ± 0.30 μm(2). There was no correlation between flap thickness and age (r = -0.10), preoperative manifest refraction spherical equivalent (MRSE) (r = -0.08), preoperative cylinder (r = 0.13), postoperative CDVA (r = -0.17), or postoperative change in HOAs (r = -0.07). A strong positive correlation with preoperative pachymetry (r = 0.41) and a weak negative correlation with preoperative sphere (r = -0.21) were observed. There was no or a moderate negative correlation of pachymetry with age (r = -0.14), preoperative sphere (r = -0.36), cylinder (r = -0.04), or MRSE (r = -0.36).

CONCLUSIONS

The microkeratome was reliable with reasonable predictability for SBK flap creation. Extra caution in handling the flaps to avoid flap striae or tears is advised. Flap thickness correlated positively with preoperative pachymetry; however, the variation in flap thickness did not affect visual outcomes.

FINANCIAL DISCLOSURE

The author has no financial or proprietary interest in any material or method mentioned.

Comparison of corneal flap thickness using a FS200 femtosecond laser and a moria SBK microkeratome

AIM

To evaluate differences in flap thickness resulting from use of an Alcon Wavelight FS200 femtosecond laser and a MORIA SBK microkeratome when making a 110-µm-thick corneal flap and to identify the potential factors that affect corneal flap thickness.

METHODS

A prospective case study was performed on 120 eyes of 60 patients who were divided into two groups for LASIK, each group consisting of 60 eyes (30 patients). The corneal flaps were created using an Alcon Wavelight FS200 femtosecond laser or a MORIA SBK microkeratome. The central corneal flap thickness was calculated by subtraction pachymetry. Age, central corneal thickness (CCT), spherical equivalent refraction, mean keratometry, and corneal diameter were recorded preoperatively for analysis.

RESULTS

Cutting of all flaps was easily performed without intraoperative complications. In the Alcon Wavelight FS200 femtosecond laser group, the mean right and left corneal flap thicknesses were 114.0±6.6 µm (range: 98-126) and 111.4±7.6 µm (range: 98-122), respectively. The difference (2.6±9.1 µm) in the corneal flap thickness between the right and left eyes was not significant (t=1.59, P=0.12). Stepwise regression analysis indicated that the resulting corneal flap thickness was unrelated to the patient's age, preoperative CCT, spherical equivalent refraction, mean keratometry, or corneal diameter. In the MORIA SBK microkeratome group, the mean right and left corneal flap thicknesses were 110.6±7.4 µm (range: 97-125 µm) and 108.2±6.1 µm (range: 78-123 µm), respectively. The difference in the corneal flap thickness between the right and left eyes (2.4±6.5µm) was not significant (t=2.039, P=0.0506). The corneal flap thickness was positively correlated with the preoperative CCT through stepwise regression analysis (r=0.297, P=0.021). The corneal flap thickness was not related to age, spherical equivalent refraction, mean keratometry, or corneal diameter. The corneal flap thickness was estimated using the following equation: Tflap=67.77+0.076 CCT (F=5.63, P=0.021).

CONCLUSION

Both the Alcon Wavelight FS200 femtosecond laser and the MORIA SBK microkeratome produced 110-µm-thick corneal flaps. The central corneal flap thickness was positively correlated with the preoperative CCT in MORIA SBK microkeratome surgery.

Influence of microkeratome parameters on the stromal bed and flap edge quality in laser in situ keratomileusis

Purpose

Femtosecond lasers have become the standard for laser-assisted in situ keratomileusis (LASIK) flap creation, but advanced mechanical microkeratomes are still an alternative, more cost-effective way to create the flap. The SCHWIND Carriazo-Pendular microkeratome is one of the most commonly used microkeratomes. The influence of different cutting parameters (head-advance speeds, cutting heads) on morphology of LASIK cuts was investigated.

Setting

Experimental study performed at the University Eye Hospital of the Martin Luther University Halle/Wittenberg, Halle (Saale), Germany.

Methods

The Carriazo-Pendular microkeratome was used on freshly enucleated porcine eyes for lamellar keratotomy. After flap removal, the cutting edge and stromal bed were evaluated from scanning electron micrographs using an individualized scoring system. Four different settings of microkeratome parameters were compared. For each setting, eight cuts were evaluated (n=32).

Results

Different oscillation frequencies and head-advance speeds did not influence the cutting qualities. A higher oscillation/feed rate ratio seemed to be advantageous for a smoother interface. Concerning different cuttings heads, a deeper keratotomy led to sharper cutting edges. The thinner the flap, the more irregularities in the stromal bed appeared. Complications did not occur.

Conclusion

The Carriazo-Pendular microkeratome is a safe tool with which to create a LASIK flap and is a good alternative to a costly femtosecond laser. Deeper keratotomies, as well as the use of a higher oscillation/feed rate quotient, improve the cutting quality.

WaveLight FS200 vs Hansatome LASIK: intraoperative determination of flap characteristics and predictability by hand-held bioptigen spectral domain ophthalmic imaging system

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.

Flap thickness in eyes with ectasia after laser in situ keratomileusis

PURPOSE

To measure central flap thickness in eyes with ectasia after laser in situ keratomileusis (LASIK) and to compare these values with estimated anticipated flap thickness based on mean published values for each device used for flap creation.

SETTING

Emory Vision at Emory University, Atlanta, Georgia, USA.

DESIGN

Retrospective comparative case series, using published data for controls.

METHODS

Confocal microscopic analysis was performed using the Confoscan 3 device to measure central flap thickness in eyes with ectasia after LASIK. Pre-LASIK records were evaluated for information, including basic patient demographics, preoperative corneal topographies, estimated anticipated flap thickness based on the mean average thickness values, and residual stromal bed (RSB) thickness calculations using measured and estimated flap thicknesses.

RESULTS

Fifty eyes of 29 patients were evaluated. The mean measured flap thickness was 138 μm ± 26 (SD) (range 90 to 220 μm). There were no significant differences between measured and estimated flap thicknesses (138 μm versus 135 μm; P=.5) or RSB thickness (329 μm versus 332 μm; P=.7), nor were there differences in flap thickness between eyes developing ectasia with normal corneal topographies and eyes with abnormal corneal topographies. One eye had a measured flap resulting in an unintended RSB thickness less than 250 μm; this eye also had abnormal topography.

CONCLUSIONS

Measured central flap thickness was not thicker than estimated in most eyes developing ectasia after LASIK. Thus, excessively thick flaps do not appear to be a major contributing factor to the pathogenesis of ectasia after LASIK.

FINANCIAL DISCLOSURE

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

Corneal endothelial cell density after myopic intra-LASIK and the effect of AC gas bubbles on the corneal endothelium

PURPOSE

To evaluate the endothelial cell density (ECD) change after laser-assisted in situ keratomileusis (LASIK) using IntraLase FS30® and the influence of anterior chamber gas bubbles (AC gas bubbles) produced during flap creation on the corneal endothelium during the excimer laser ablation.

METHODS

Myopic LASIK was performed in 436 eyes of 252 patients at Shinagawa LASIK Center. Average age was 32.4±7.05 years. IntraLase FS30® was used for flap creation and Allgretto Wave Eye-Q® 400Hz was used for excimer laser ablation. Preoperative and 3-month postoperative ECD were measured with a noncontact specular microscope (Noncon Robo FA-3509®) and compared. The preoperative and 3-month postoperative ECD changes that developed AC gas bubbles during the flap creation (19 eyes of 18 patients) were also examined. The change of ECD was compared to the group that did not produce AC gas bubbles.

RESULTS

The average ECD reduction after LASIK was -15±102 cells/mm2 for AC gas bubbles (-) group (0.51%, p>0.05) and -35±130 cells/mm2 (1.21%, p>0.05) for AC gas bubbles (+) group. There was no significant ECD change in the AC gas bubbles (-) and AC gas bubbles (+) groups, and no significant difference was observed between AC gas bubbles (-) and AC gas bubbles (+) groups.

CONCLUSIONS

IntraLase FS30® is a safe and effective tool for LASIK operation which does not cause damage to corneal endothelium. Anterior chamber gas bubbles produced during flap creation did not damage corneal endothelial cells and did not interfere with LASIK operations.

Laser in situ keratomileusis flap-thickness predictability with a pendular microkeratome

PURPOSE

To assess flap-thickness predictability with a pendular microkeratome (130 μm head).

SETTING

Eye Institute of Thrace, Democritus University of Thrace, Alexandroupolis, Greece.

DESIGN

Clinical trials.

METHODS

The study comprised 263 eyes (132 patients). Laser in situ keratomileusis was performed using the 130 μm head of the Carriazo pendular microkeratome; right eyes were treated first. Ultrasound pachymetry and topography were used for central corneal thickness (CCT) and keratometry (K) measurements. Evaluation included flap thickness, flap diameter, and flap shape.

RESULTS

The mean flap thickness was 125 μm ± 22 (SD) (range 74 to 187 μm) in right eyes and 112 ± 21 μm (range 61 to 190 μm) in left eyes. Flap thickness was significantly correlated with preoperative CCT (r = 0.271; P<.001) but not with K values or the manifest refraction spherical equivalent (P>.15). Right eyes had thicker flaps than left eyes (P<.001); both were significantly below the 130 μm head thickness (mean flap thickness 119.2 ± 22.8 μm; P<.001). The mean achieved flap diameter was 9.2 mm using the 9.0 ring and 9.8 mm using the 10.0 mm ring. Flap-thickness stabilization and convergence between right eyes and left eyes occurred after 100 consecutive flap cuts.

CONCLUSIONS

Flap-thickness predictability was influenced by preoperative CCT only. All cuts were significantly thinner than the head thickness regardless of the suction ring size. Second surgical eyes had thinner flaps, possibly from blade deterioration from the first cut. Approximately 100 flaps were required as a learning curve.

Femtosecond sub-bowman keratomileusis: a prospective, long-term, intereye comparison of safety and outcomes of 90- versus 100-μm flaps

PURPOSE

To analyze the long-term safety profile, visual and refractive results, and incidence of complications between sub-Bowman keratomileusis with 90- and 100-μm flaps.

DESIGN

Prospective, randomized, comparative clinical study.

METHOD

A total of 385 candidates (770 eyes) underwent bilateral, single-sitting, sub-Bowman keratomileusis, with flap creation (90 or 100 μm) on IntraLase 60-kHz (Abott Medical Optics) and ablation on Technolas 217z100 (Technolas PV) . Right and left eyes were randomized to undergo 90- or 100-μm flap procedures. Preoperative and postoperative assessment included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refraction, and topographic analysis. All cases were followed up until 12 months after surgery. After excluding cases lost to follow-up, a final analysis of 368 patients was carried out (368 eyes in each of the 2 groups). The main outcome measures were BSCVA, UCVA, complication rates, and residual spherical equivalent refractive error.

RESULTS

The mean preoperative values were: spherical equivalent, -6.08 ± 2.7 diopters (D; 90-μm group) and -5.99 ± 2.8 D (100-μm group; P = .7); and logarithm of the minimal angle of resolution BSCVA, 0.01 ± 0.03 (90-μm group) and 0.01 ± 0.04 (100-μm group: P = .8). Postoperative 12-month values were: spherical equivalent, -0.02 ± 0.4 D (90-μm group) and -0.01 ± 0.4 D (100-μm group; P = .8); logarithm of the minimal angle of resolution BSCVA, -0.05 ± 0.07 (90-μm group) and -0.04 ± 0.07 (100-μm group; P = .8); and logarithm of the minimal angle of resolution UCVA, 0.012 ± 0.01 (90-μm group) and 0.017 ± 0.02 (100-μm group; P = .2). No loss of BSCVA was seen in any case. The efficacy indices were 1.039 ± 0.21 (90-μm group) and 1.014 ± 0.24 (100-μm group; P = .2); safety indices were 1.163 ± 0.21 (90-μm group) and 1.158 ± 0.22 (100-μm group; P = .6); and vision difference indices were 0.09 ± 0.14 (90-μm group) and 0.10 ± 0.15 (100-μm group; P = .1). Both groups had a low but comparable incidence of diffuse lamellar keratitis and microstriae. However, the incidence of microstriae (although visually asymptomatic) was significantly higher in ablation with spherical equivalent of -9 D or more compared with lesser ablations (6.7% vs 0.8%; P < .001).

CONCLUSIONS

The 1-year follow-up of femtosecond sub-Bowman keratomileusis with 90- and 100-μm flaps suggests that both the flap options have comparable outcomes.

Comparison of residual stromal bed thickness measurement among very high-frequency digital ultrasound, intraoperative handheld ultrasound, and optical coherence tomography

PURPOSE

To compare residual stromal thickness (RST) measurement by three methods: very high-frequency digital ultrasound (VHFDU), intraoperative handheld ultrasound (US), and optical coherence tomography (OCT).

METHODS

This was a retrospective analysis of 93 eyes (55 patients) that underwent LASIK retreatment by flap lift where VHFDU and OCT measurements were obtained before the retreatment and intraoperative US RST measurement was performed after lifting the flap. Corneal vertex RST measurements for intraoperative US and OCT were compared with the VHFDU measurement. Linear regression and Bland-Altman analysis were performed.

RESULTS

Mean corneal vertex RST was 327±53 μm for VHFDU, 338±54 μm for intraoperative US, and 326±43 μm for OCT. Mean difference between VHFDU and intraoperative US was 11±11 μm (range: -12 to 46 μm). Mean difference between VHFDU and OCT was -2±23 μm (range: -53 to 57 μm). The coefficient of determination (R(2)) was 0.96 between VHFDU and intraoperative US and 0.82 between VHFDU and OCT. Intraoperative US was on average 11 μm thicker than VHFDU independent of RST value. Optical coherence tomography was on average thicker than VHFDU for low RST values (250 to 300 μm) and thinner than VHFDU for high RST values (>350 μm). The RST was thicker than VHFDU by >10 μm in 50% and >20 μm in 21% of eyes measured with intraoperative US and by >10 μm in 32% and >20 μm in 18% of eyes measured with OCT.

CONCLUSIONS

Residual stromal thickness measured by both intraoperative US and OCT was thicker than VHFDU in a significant number of eyes, which could have resulted in retreatment being performed in an eye with insufficient RST.

Analysis of microkeratome thin flap architecture using Fourier-domain optical coherence tomography

PURPOSE

To assess the corneal architecture and reproducibility of LASIK flap thickness created by the Amadeus II mechanical microkeratome (Ziemer Ophthalmic Systems AG) using Fourier-domain optical coherence tomography (OCT; Optovue Inc).

METHODS

Anterior segment Fourier-domain OCT was used to analyze the morphology of 58 LASIK flaps from 30 patients created with the Amadeus II microkeratome 140-μm head and ML7090CLB blades (Med-Logics Inc) at 2 weeks postoperatively. Flap thickness was assessed at 10 points across the central 6 mm of the cornea (horizontal and vertical meridians). Postoperative central corneal flap thickness measured by Fourier-domain OCT was compared with intraoperative ultrasound pachymetry measurements.

RESULTS

No significant difference was noted between central flap thickness measured by intraoperative pachymetry (107.2 ± 14 μm) and postoperative OCT (111.7 ± 11 μm; P=.07, correlation coefficient=0.86). Fourier-domain OCT measurements demonstrated functionally planar flap architecture (standard deviation [SD] of thickness across the flap=4.9 μm, SD range across the flap=2 to 9 μm) for the microkeratome flaps.

CONCLUSIONS

The Amadeus II microkeratome with Med-Logics blades created thin, reproducible, functionally planar flaps as measured by Fourier-domain OCT. Central flap thickness measured by intraoperative ultrasound pachymetry was equivalent to that measured 2 weeks postoperatively by OCT.

Influence of flap thickness on visual and refractive outcomes after laser in situ keratomileusis performed with a mechanical keratome

PURPOSE

To study the effect of flap thickness on visual acuity and refractive outcomes after laser in situ keratomileusis (LASIK) using 2 blade types with a mechanical microkeratome.

SETTING

Emory Vision, Atlanta, Georgia, USA.

METHODS

This retrospective analysis was of LASIK cases performed between January 2005 and June 2006 using an Amadeus I microkeratome and an ML7090 CLB blade (blade A) or a Surepass blade (blade B). Outcomes analyzed included flap thickness, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE), the enhancement rate, and surgical complications 3 months postoperatively.

RESULTS

Two hundred sixty-three eyes of 153 patients were analyzed; blade A was used in 158 eyes and blade B, in 105 eyes. The mean flap thickness was significantly thinner with blade A than with blade B (107 microm +/- 12 [SD] versus 130 +/- 20 microm) (P<.0001). There was no overall correlation with either blade between flap thickness and UDVA, CDVA, or MRSE (all r<0.2). At 3 months, there was no statistically significant difference in UDVA, CDVA, or MRSE between the 2 blade groups at 3 months (all P > .10), and there was no difference in the complication rates.

CONCLUSION

Flap thickness did not affect visual or refractive outcomes with a mechanical microkeratome with either blade type.

Interface Haze Formation After Ultra Thin Flap Laser in Situ Keratomileusis

In this case series, five patients (10 eyes) underwent laser in siter keratomileusis (LASIK) for the correction of moderate myopia and astigmatism with the Schwind Carriazo Pendular microkeratome 90 mum head. Flap (superior hinged) thickness measured intraoperatively was assessed less than 70 mum in all eyes. On first month's postoperative examination, subepithelial mild corneal haze with consequent myopic regression was found in all patients. A significant improvement of haze formation and residual refractive error were observed during the following postoperative months. In conclusion, post-LASIK subepithelial corneal haze after thin flap creation is a temporarily potential complication that could affect patient's refractive error during the first postoperative month.