Accuracy and precision of the amadeus microkeratome in producing LASIK flaps

Amadeus® II Microkeratome: Optimizing Microkeratome Settings for High Flap Accuracy Using Optical Low Coherence Reflectometry

Purpose

To investigate the impact of various experimental microkeratome settings and blade reuse on the accuracy of the flap thickness created with the new Amadeus® II microkeratome (SIS, Ziemer Ophthalmic, Port, Switzerland).

Methods

In this prospective study, 120 porcine eyes were used to create corneal flaps with the Amadeus® II using 2 different cutting heads (140 μm, 160 μm) with the Surepass® blade. Using each blade twice, a head advance speed of 1.5 mm/s and 3.5 mm/s and oscillation rates of 8000 rpm, 10,000 rpm, and 13,000 rpm were used. Flap thickness was measured by optical low coherence reflectometry (OLCR). Descriptive statistical analysis was based on means, medians, and quartiles, with graphical representation on box plot. Pearson correlation test and Mann-Whitney U-test for unpaired samples were employed to identify the impact of different settings.

Results

Using the 140 μm cutting head, highest precision of the flap thickness was achieved with a head advance rate of 1.5 mm/s and an oscillation rate of 10,000 rpm (mean 132.1±10.0 μm; range 120.2–147.2 μm). Reusing the blade, highest accuracy (mean 130±6.9 μm; range 118.5–135 μm) was achieved with 8000 rpm. Using the 160 μm cutting head, an optimum flap thickness was reached with a head advance rate of 3.5 mm/s and an oscillation rate of 13,000 rpm (mean 162.4±7.7 μm; range 151.9–169.8 μm). Reusing the blade with the 160 μm cutting head, an adjustment to 3.5 mm/s and 10,000 rpm was necessary (mean 157.4±7.7 μm; range 153.7–161.8 μm).

Conclusions

Optimized microkeratome settings lead to minimized deviation from the intended flap thickness and are mandatory to improve flap accuracy. OLCR is an ideal method to proof individualized settings.

Temporal and Spatial Flap Variability in Laser In-Situ Keratomileusis by Optical Coherence Tomography

Purpose:

To study changes in flap thickness made with two different microkeratome heads across different corneal locations using anterior segment optical coherence tomography (OCT).

Methods:

In this prospective, non-randomized, consecutive case series, subjects who had their laser in-situ keratomileusis (LASIK) flaps made using 90 μm (MSU90) or 130 μm (MSU130) disposable M2 microkeratome heads were examined using OCT. The measurements were performed at three locations (central and 2.5 mm to either side) at 1 day, 1 week, and 1 month postoperatively.

Results:

The central flap thickness was 123 ± 15, 130 ± 14, and 127 ± 13 μm, respectively, at 1 day, 1 week, and 1 month postoperatively in the MSU90 group (41 eyes) and 142 ± 20, 147 ± 19, and 143 ± 15 μm, respectively, in the MSU130 group (47 eyes). At 1 month, peripheral flap thickness was 161 ± 17 and 159 ± 13 μm, respectively, at 2.5 mm to the right and left of corneal center in the MSU90 group. The corresponding figures were 170 ± 14 and 167 ± 13 μm, respectively, in the MSU130 group. There was a statistically significant difference between the two groups at all locations (P < 0.001). No statistically significant change in flap thickness was detected in either group at any assessment time. There was a partial positive correlation (after controlling for preoperative manifest refractive spherical equivalent) between central flap thickness and preoperative ultrasound central pachymetry (r = 0.739, P = 0.036) in the MSU90 group but not in the MSU130 group.

Conclusion:

Using OCT, changes in flap thickness were minimal in the first month after LASIK. Flap thickness correlated strongly with central corneal thickness if a 90 μm head was used.

Fibrinogen, riboflavin, and UVA to immobilize a corneal flap--conditions for tissue adhesion

PURPOSE

Laser-assisted in situ keratomileus (LASIK) creates a permanent flap that remains non-attached to the underlying laser-modified stroma. This lack of permanent adhesion is a liability. To immobilize a corneal flap, a protocol using fibrinogen (FIB), riboflavin (RF), and ultraviolet (UVA) light (FIB+RF+UVA) was devised to re-adhere the flap to the stroma.

METHODS

A model flap was created using rabbit (Oryctolagus cuniculus) and shark (Squalus acanthias) corneas. Solutions containing FIB and RF were applied between corneal strips as glue. Experimental corneas were irradiated with long wavelength (365 nm) UVA. To quantify adhesive strength between corneal strips, the glue-tissue interface was subjected to a constant force while a digital force gauge recorded peak tension.

RESULTS

In the presence of FIB, substantive non-covalent interactions occurred between rabbit corneal strips. Adhesiveness was augmented if RF and UVA also were applied, suggesting formation of covalent bonds. Additionally, exposing both sides of rabbit corneas to UVA generated more adhesion than exposure from one side, suggesting that RF in the FIB solution catalyzes formation of covalent bonds at only the interface between stromal molecules and FIB closest to the UVA. In contrast, in the presence of FIB, shark corneal strips interacted non-covalently more substantively than those of rabbits, and adhesion was not augmented by applying RF+UVA, from either or both sides. Residual RF could be rinsed away within 1 hour.

CONCLUSIONS

Glue solution containing FIB and RF, together with UVA treatment, may aid immobilization of a corneal flap, potentially reducing risk of flap dislodgement.

Femtosecond laser-assisted enhancements after laser in situ keratomileusis

We describe a technique of femtosecond laser-assisted enhancement after primary LASIK with a mechanical microkeratome-created flap. The vertical side-cut incision by the femtosecond laser creates a wound configuration that decreases mechanical trauma to the epithelium and prevents epithelial cell migration. These factors may decrease the risk for post-LASIK enhancement epithelial ingrowth.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Femtosecond laser in-situ keratomileusis flap configurations

PURPOSE OF REVIEW

The corneal flap laser in-situ keratomileusis (LASIK) is among the most important determinants in the successful outcome of the surgery. Femtosecond lasers have evolved over the last decade to all but replace the mechanical microkeratome as the preferred method to create these flaps. With improvements in femtosecond laser technology, there has been a reduction in the time taken for the cut and the quality of the stromal bed has improved. Improved predictability has led surgeons to explore the possibility of thin flap LASIK.

RECENT FINDINGS

Corneal flaps created with the femtosecond laser have been shown to be more predictable in depth and have a more desirable planar morphology. Corneal flaps created by the femtosecond laser can be customized according to depth, profile, morphology, and side-cut configuration. Changes in the angulation of the side cut, to reduce the incidence of epithelial ingrowth, have not been corroborated by clinical evidence as yet. Thin flap LASIK, also referred to as sub-Bowman's keratomileusis, has the advantage of preserving more stroma and potentially reducing the incidence of corneal ectasia but seems to be associated with an increased incidence of interface haze.

SUMMARY

This review examines the advantages of creating a flap with the femtosecond laser and the various configurations of these flaps. It also explores the advantages of varying the thickness and profile of femtosecond flaps.

Corneal flap assessment with Rondo microkeratome in laser in situ keratomileusis

PURPOSE

To assess the accuracy of flap thickness in laser in situ keratomileusis (LASIK) with Rondo, Wavelight AG microkeratome and to examine factors that can influence flap thickness (FT).

SETTING

The study took place at the Laser & Ophthalmos Eye Clinic, Thessaloniki, Greece.

MATERIAL AND METHODS

Three hundred and sixty eyes from 180 patients underwent LASIK with Rondo microkeratome. Three surgeons (A, B and C) performed all surgeries with no previous experience of Rondo microkeratome. All patients were treated with the 130 μm plate. Central corneal thickness (CCT) and stromal bed thickness were measured by Scheimpflug and ultrasound pachymetry. Right eye (OD) was treated first.

RESULTS

Mean FT for OD: 120 ± 19 μm (range 69-158 μm); for left eye (OS): 106 ± 17 μm (range 70-147 μm). Flaps in OD were significantly thicker than in OS (p < 0.001). FT was significantly correlated to the keratometric reading (K): r = 0.121; p = 0.02. No correlation was found between FT and CCT or between FT and the attempted refractive correction (SE) (p > 0.14). Mean FT was significantly lower than the manufacturer's 130 μm specification (Mean FT = 113 ± 19 μm; p < 0.001). FT between surgeons A, B and C was significantly different (analysis of variance between surgeons; p < 0.001). Scheimpflug and ultrasound CCT measurements were significantly correlated (r = 0.921; p < 0.001) with ultrasound measuring an average 4.5 μm higher than Scheimpflug (CCT (Oculyzer) = 553.96 ± 27 μm; CCT (Ultrasound) = 558.45 ± 28 μm). Mean flap diameter was 9.2 ± 0.2 mm.

CONCLUSIONS

FT with Rondo microkeratome was significantly influenced by the mean preoperative K reading. First treated eye was significantly thicker than the fellow left eye, while both were significantly lower than the recommended 130 μm thickness. Gaining basic experience of Rondo microkeratome required an average of 90 flaps/surgeon.

Lamellar keratoplasty with a novel anterior chamber system and organ cultured donor corneas

PURPOSE

To present a novel artificial anterior chamber system for anterior and posterior lamellar keratoplasty.

METHODS

The artificial anterior chamber system MOZARTTM in conjunction with the AMADEUSTM II microkeratome was evaluated for its applicability in anterior and posterior lamellar keratoplasty using organ cultured donor corneas.

RESULTS

Twelve patients underwent microkeratome-assisted lamellar keratoplasty for corneal opacifications due to either anterior stromal scaring or endothelial decompensation. Eight patients underwent Descemet stripping automated endothelial keratoplasty (DSAEK) and 4 patients underwent anterior lamellar keratoplasty (ALK). A 400-microm and 250-microm cutting head was used for DSAEK and ALK, respectively. In all patients, an 8.5-mm suction ring was applied. For the 250-microm cutting head, a mean anterior lamella thickness of 244+/-12 microm was found. For the 400-microm cutting head, a mean anterior lamella thickness of 390+/-18 microm was found. The graft diameter was 8.85+/-0.5 mm for the 8.5-mm suction ring with both cutting heads. Deswelling of the anterior donor lamella was 11.5% compared to 30% of the posterior lamella transplant after 6 months of follow-up.

CONCLUSION

The AMADEUSTM II microkeratome in conjunction with the MOZARTTM artificial anterior chamber system proved to be a suitable device for modern lamellar keratoplasty. Swelling and deswelling characteristics of organ cultured corneas need to be further investigated to optimize the deswelling time prior to donor cornea sectioning in lamellar keratoplasty.

Corneal flap thickness with the Moria M2 microkeratome and Med-Logics calibrated LASIK blades

PURPOSE

 This study aimed to compare and study potential factors that affect the accuracy of corneal flap thickness created in laser-assisted in situ keratomileusis (LASIK) using the Moria model 2 (M2) head 130 microkeratome with the Med-Logics calibrated LASIK blades Minus 20 (ML -20) and Minus 30 (ML -30).

METHODS

 Corneal thickness in 200 (164 myopic and 36 hyperopic) eyes (100 patients) was measured by ultrasonic pachymetry preoperatively and intraoperatively after flap cutting. A total of 100 eyes were treated with the ML -20 and 100 with the ML -30. The right eye was operated before the left eye in each patient, using the same blade. In an additional group of 40 eyes, the left eye was operated first.

RESULTS

 Mean corneal flap thickness using the ML -20 blade for an intended flap thickness of 140 μm was 129.1 μm (standard deviation [SD] 15.6, range 104-165 μm) in right eyes and 111.5 μm (SD 14.5, range 78-144 μm) in left eyes. Mean corneal flap thickness using the ML -30 blade for an intended flap thickness of 130 μm was 127.1 μm (SD 16.6, range 90-168 μm) in right eyes and 109.9 μm (SD 16.8, range 72-149 μm) in left eyes.

CONCLUSIONS

Both microkeratome blade types cut thinner flaps than were intended. There was substantial variation in flap thickness. The first flap to be cut with a particular blade was considerably thicker than the second flap cut with the same blade. Based on these data, we recommend the use of disposable single-use microkeratomes rather than these ML blades.

Analysis of actual corneal flap thickness and confounding factors between first and second operated eyes

BACKGROUND AND OBJECTIVE

To calculate the actual corneal flap thickness during laser in-situ keratomileusis.

PATIENTS AND METHODS

Fifty-four women and 26 men with refractive error were enrolled in the study. Flaps were created using a MK-2000 microkeratome (Nidek, Gamagori, Japan) with a 130-microm head. The comparisons between both operated eyes of a patient and the correlations between flap thickness and confounding factors were analyzed.

RESULTS

The average flap thicknesses were 134.0 + or - 16.5 and 112.3 + or - 14.4 microm in the first and second operated eye groups, respectively, and the data showed a significant difference between the two groups (P < .001). There were positive correlations between central corneal thickness and flap thickness (first group, P = .017; second group, P = .041).

CONCLUSION

The flap thicknesses of the first operated eye group were thicker than those of the second operated eye group and there was a positive correlation between the flap thickness and central corneal thickness. The coefficient of variation of the flap thickness was greater in the second group than in the first group.

Accuracy of corneal flap thickness achieved by two different age MK-2000 microkeratomes

AIMS

To investigate the accuracy of corneal flap thickness (FT) using two different age MK-2000 microkeratomes.

METHODS

The prospective cohort study enroled 260 patients with refractive error. Flaps were created using two microkeratomes A and B (new and aged, respectively) with 130-mum heads in two patient groups and two times the same blade in both treated eyes of each patient. The variations in FTs were compared between two groups and between both operated eyes of each patient. The correlations were analysed between FT and CCT or keratometric power.

RESULTS

In the A and B groups, the average FTs were 123.3+/-18.7 and 147.5+/-19.1 mum respectively. Difference in measurements between the actual FTs of first eye operations in the A group and intended 130 mum of FTs was not significant (P=0.462), but those of second operated eyes in the A group and both treated eyes in the B group were significant (P<0.001). Second cut achieved a thinner flap and increased the variability in FT, and an aged microkeratome achieved a thicker flap than a new microkeratome and than that claimed by the manufacturer. Positive correlations were observed between preoperative CCT and FT (P<0.05).

CONCLUSIONS

The first eye operation by a new MK-2000 microkeratome achieves the accuracy of the intended FT. FTs varied between first and second cuts of each patient and between two different age MK-2000 microkeratomes. LASIK surgeons should compare FT when using an aged MK-2000 microkeratome, and frequent and periodic comparison of FT achieved by all microkeratomes may be also recommended.

Microkeratome blades and corneal flap thickness in LASIK

BACKGROUND AND OBJECTIVE

To determine the corneal flap thickness produced by using two different types of blades on the same microkeratome for LASIK, comparing flap thickness in the first and second eyes.

PATIENTS AND METHODS

The corneal flap thickness was measured in two sets of 100 consecutive patients undergoing bilateral LASIK procedures using the Moria M2 microkeratome with a 110 head (Moria, France) and either Moria or CLB blades (Med-Logics Inc., Laguna Hills, CA). Corneal flap thickness was determined by intraoperative pachymetry using an ultrasonic pachymeter.

RESULTS

The mean corneal flap thickness was 138.95 +/- 21.6 microm (range: 75-205 microm) with Moria blades and 115.07 +/- 16.0 microm (range: 70-153 microm) with CLB blades, which is a significant difference (P < .001). The difference in flap thickness between the first and second eyes was not significant with the Moria blades (141.46 +/- 21.46 microm vs 136.45 +/- 21.55 microm, P = .965), but it was when the CLB blades were used (123.21 +/- 12.07 microm vs 106.93 +/- 15.51 microm; P= .013).

CONCLUSION

In LASIK surgery using a Moria M2 microkeratome, blades from different manufacturers may produce significantly different corneal flap thicknesses, as well as differences between the first and second eyes.

Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery

Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery today. The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. This way, we are able to change the refractive status of the patient, providing better unaided vision. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are the responsible for new surgical instrumentation, which makes the surgical procedure easier for the surgeon, and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. This article aims to describe the more relevant advances in LASIK that have played an important role in the spread and popularity of this technique.

Photorefractive keratectomy for refractory laser in situ keratomileusis flap striae

Photorefractive keratectomy (PRK) with mitomycin-C (MMC) was performed in 2 patients with visually significant, complicated laser in situ keratomileusis flap striae. These striae had been resistant to multiple treatments, including stretching, suturing, and PRK. The visual symptoms in both patients resolved after PRK with MMC, and both patients were stable 1 year later. Wavefront-guided PRK with MMC may be a viable treatment for patients who have complicated flap striae resistant to standard measures.

Blade source effect on laser in situ keratomileusis flap thickness with the Amadeus I microkeratome

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.

Corneal flap thickness with the Moria M2 single-use head 90 microkeratome

PURPOSE

To analyse the accuracy of corneal flap thickness created in laser-assisted in situ keratomileusis (LASIK) using the Moria Model 2 (M2) single-use head 90 microkeratome.

METHODS

The corneal thickness of 300 (266 myopic and 34 hyperopic) eyes of 150 patients was measured by ultrasonic pachymetry preoperationally and intraoperationally after flap cut. The Moria M2 single-use head 90, intended to create a flap with a thickness of 120 microm, was used in all eyes. The right eye was always operated first and the left eye second, using the same blade.

RESULTS

Mean corneal flap thickness was 115.4 microm (standard deviation [SD] 12.5) in the two eyes, 115.7 microm (SD 12.4, range 73-147 microm) in right eyes and 115.1 microm (SD 12.6, range 74-144 microm) in left eyes. Mean horizontal flap diameter was 9.1 mm (SD 0.2) and mean hinge length 4.1 mm (SD 0.1). There were no free flaps, incomplete flaps or flaps with buttonholes in the study. Occasional iron particles were observed in three (1.0%) eyes.

CONCLUSIONS

As with most microkeratomes, the single-use head 90 microkeratome cut thinner flaps than were intended. The range of the cuts was relatively wide. However, thin flaps did not increase the rate of flap-related complications. The difference between the first and second eyes was not significant.

Corneal flap thickness during laser in situ keratomileusis

To analyze the actual corneal flap thickness (FT) after flap making by MK-2000 microkeratome during laser in situ keratomileusis (LASIK), 42 females and 20 males with myopia or myopic astigmatism were enrolled in this study. FTs were created using a microkeratome with a 130 microm head. Corneal thickness was measured by ultrasonic pachymeter. The correlations between FT and central corneal thickness (CCT), keratometric power and age were analyzed. The mean age at operation for all study subjects was 27.6+/-4.9 years. The average FT was 133.2+/-15.4 microm. The average CCT was 540.+/-30.3 microm. The average keratometric power was 43.66+/-1.32 D. There was a positive correlation between FT and CCT and no correlation between FT and keratometric power or between FT and age. We recommend that LASIK surgeons inspect the actual FT when using microkeratome.

Probability Model of the Inaccuracy of Residual Stromal Thickness Prediction to Reduce the Risk of Ectasia After LASIK Part I: Quantifying Individual Risk

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.

Probability Model of the Inaccuracy of Residual Stromal Thickness Prediction to Reduce the Risk of Ectasia After LASIK Part II: Quantifying Population Risk

PURPOSE

To derive a statistical model to estimate the rate of excessive keratectomy depth below a selected cut-off residual stromal thickness (RST) given a minimum target RST and specific Clinical Protocol; apply the model to estimate the RST below which ectasia appears likely to occur and back-calculate the safe minimum target RST that should be used given a specific Clinical Protocol.

METHODS

Myopia and corneal thickness distribution were modeled for a population of 5212 eyes that underwent LASIK. The probability distribution of predicted target RST error (Part I) was used to calculate the rate of excessive keratectomy depth for this series. All treatments were performed using the same Clinical Protocol; one surgeon, Moria LSK-One microkeratome, NIDEK EC-5000 excimer laser, Orbscan pachymetry, and a minimum target RST of 250 microm--the Vancouver Clinical Protocol. The model estimated the RST below which ectasia appears likely to occur and back-calculated the safe minimum target RST. These values were recalculated for a series of microkeratomes using published flap thickness statistics as well as for the Clinical Protocol of one of the authors-the London Clinical Protocol.

RESULTS

In the series of 5212 eyes, 6 (0.12%) cases of ectasia occurred. The model predicted an RST of 191 microm for ectasia to occur and that a minimum target RST of 329 microm would have reduced the -rate of ectasia to 1: 1,000,000 for the Vancouver Clinical Protocol. The model predicted that the choice of microkeratome varied the rate of ectasia between 0.01 and 11,623 eyes per million and the safe minimum target RST between 220 and 361 microm. The model predicted the rate of ectasia would have been 0.000003: 1,000,000 had the London Clinical Protocol been used for the Vancouver case series.

CONCLUSIONS

There appears to be no universally safe minimum target RST to assess suitability for LASIK largely due to the disparity in accuracy and reproducibility of microkeratome flap thickness. This model may be used as a tool to evaluate the risk of ectasia due to excessive keratectomy depth and help determine the minimum target RST given a particular Clinical Protocol.

Evaluating Microkeratome Efficacy by 3D Corneal Lamellar Flap Thickness Accuracy and Reproducibility Using Artemis VHF Digital Ultrasound Arc-scanning

PURPOSE

To present a method that determines the efficacy of flap creation using a microkeratome.

METHODS

Thirty-six eyes of 18 patients were included in the study, operated by two experienced surgeons using the Moria LSK-One microkeratome. Very high-frequency (VHF) digital ultrasound arc-scanning using Artemis technology was used to measure the Reinstein Flap Thickness Profile created by addition of the preoperative epithelial thickness profile to the postoperative stromal component of the flap. Descriptive statistics revealed central flap thickness accuracy and reproducibility. Univariate and multivariate regression analysis was used to determine correlations between central flap thickness and preoperative clinical parameters. Three-dimensional flap thickness maps demonstrated the mean, median, standard deviation, and range of thickness.

RESULTS

Intended flap thickness was 160 microm. Mean central flap thickness was 161 microm in the right eye and 166 microm in the left eye. Central reproducibility (standard deviation of the mean) was 30.3 microm, with a range of 106 to 228 microm. Central flap thickness correlated to preoperative corneal thickness measured by VHF digital ultrasound but not by Orbscan. On qualitative analysis, no consistency among eyes was observed in the three-dimensional flap thickness map. Flaps were on average thinner in the center, but not in all cases.

CONCLUSIONS

A systematic qualitative and quantitative statistical evaluation of microkeratome accuracy and reproducibility can be performed by measuring corneal flap thickness with arc-scanning VHF digital ultrasound.

Corneal Ectasia After Laser In Situ Keratomileusis in Patients Without Apparent Preoperative Risk Factors

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.

Bilateral Comparison of Corneal Flap Dimensions With the Moria M2 Reusable Head and Single Use Head Microkeratomes

PURPOSE

To compare the Moria (Antony, France) M2 automated microkeratome with the head 130 to a new disposable single use head to evaluate complications, accuracy, and safety of the procedure.

METHODS

Ninety-eight eyes of 49 consecutive patients were operated with the Moria M2 microkeratome. One eye was operated with the metallic head 130 and the other with a plastic single use head, both designed to create a 160-microm flap. Intraoperative flap dimensions were correlated to preoperative parameters and evaluated 1 month postoperatively.

RESULTS

With the head 130, mean thickness was 153.3 microm (standard deviation [SD] 13.3, range: 102 to 179 microm). When using a single use head, mean thickness was 148.0 microm (SD 9.8, range: 120 to 170 microm). Occasional iron particles were observed in one eye with both head types. No true epithelial ingrowth was detected in any of the eyes, but epithelial dots at the wound edge occurred in one eye, when using the head 130, but not in the eyes operated with a single use head.

CONCLUSIONS

On average, both head types created thinner flaps than attempted. Single use heads produced thinner flaps than the head 130. Accuracy in flap thickness in terms of standard deviation was significantly better in single use heads than in the head 130. Single use heads also had fewer microkeratome-related complications. In clinical practice, the single use head was easier to use because no assembly was required. Plastic single use heads also worked more smoothly than the metallic head 130.

Amadeus microkeratome: experience with the first 2000 cases and lessons learned

BACKGROUND

To assess the safety and efficacy of the Amadeus microkeratome and to report on lessons learnt in optimizing results from its use.

METHODS

A retrospective review of the flap-related complications of 2000 laser in situ keratomileusis (LASIK) procedures performed by one surgeon using the Amadeus microkeratome (AMO, Irvine, CA, USA) was conducted. One hundred consecutive cases had preoperative and intraoperative pachymetry to evaluate the relationship between flap thickness, corneal thickness and reuse of the blade.

RESULTS

There were 35 cases of minor epithelial defects (1.8%) and four eyes with major epithelial defects (0.2%). There were no cases of suction loss, buttonholes, or incomplete or damaged flaps. There were four free caps (0.2%). Twenty-five cases had minor wrinkles and two cases had significant folds requiring relifts. Thinner corneas resulted in thinner flaps (P < 0.0001). Reuse of the blade resulted in thinner flaps (P = 0.0001).

CONCLUSION

The Amadeus is a safe and reliable microkeratome. Although short, there is a learning curve with use of the instrument. Corneal thickness and reuse of the blade affect flap thickness.

Factors Predictive of LASIK Flap Thickness With the Hansatome Zero Compression Microkeratome

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.

Pachymetric evaluation prior to laser in situ keratomileusis

PURPOSE

To determine whether deviations in the localization of the cornea's thinnest point or the magnitude and localization of posterior corneal ectasia is associated with deviations in the spherical equivalent, the astigmatism, or the magnitude of an anterior corneal ectasia and whether corneas at risk for iatrogenic keratectasia can be identified without a pachymetry map of the cornea.

SETTING

University hospital eye clinic.

METHODS

Three hundred eight eyes of 156 healthy volunteers with various refractive errors were examined with Orbscan II and autorefractometer-keratometer. The corneal thickness was registered at the fixation point, at the geometrical center, and at the thinnest point of the cornea. Keratometry and refraction were determined for all subjects.

RESULTS

The thinnest point of the cornea was predominantly located in the inferotemporal quadrant, and was significantly thinner than the fixation point (539.6 +/- 35.8 microm and 548.0 +/- 35.4 microm, respectively, P<.001). Interestingly, the larger this difference was, the longer the distance between these points. No relationship was found between the refractive or external surface measurements and the internal surface measurements.

CONCLUSIONS

The absence of a clear relationship between the shape of the anterior corneal surface or the refractive error, and the shape of the posterior corneal surface, necessitates a thorough pachymetric evaluation of the cornea before a laser in situ keratomileusis procedure, with special attention to the inferotemporal area.

Photoablative inlay laser in situ keratomileusis (PAI-LASIK) in the rabbit model

PURPOSE

To evaluate the suitability, biocompatibility, and efficacy of a proprietary hydrogel photoablative inlay (PAI) for use during laser in situ keratomileusis (LASIK).

SETTING

Laboratory study, Tulane University Health Sciences Center, New Orleans, Louisiana, USA.

METHODS

Eight rabbits (1 eye each) underwent the PAI-LASIK procedure; 4 eyes had a disk-shaped inlay and 4, a donut-shaped inlay. Preoperatively, the hydrogel material was ablated with a programmed correction of 5.0 diopters of hyperopia or myopia.

RESULTS

The eyes were followed for 1 to 16 months. No eye showed signs of rejection or extrusion of the PAI. There was no significant difference in corneal clarity or the healing rate between eyes with donut-shaped PAIs and those with disk-shaped PAIs. One eye with a donut-shaped PAI had minimal corneal haze. The remaining inlays did not opacify or fracture during ablation.

CONCLUSION

The hydrogel material can be used for the proposed PAI-LASIK procedure.

Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes

PURPOSE

To measure and compare the changes in objective wavefront aberration and subjective manifest refraction after laser in situ keratomileusis (LASIK) flap creation with a mechanical microkeratome and a femtosecond laser.

SETTING

Private practice refractive surgery center, Irvine, California, USA.

METHODS

This randomized prospective study comprised 9 patients (18 eyes) treated with a 2-step LASIK procedure: lamellar keratectomy with a Hansatome microkeratome (Bausch & Lomb) or the IntraLase femtosecond laser in fellow eyes followed by non-wavefront-guided (standard) excimer laser treatment with the Technolas 217A (Bausch & Lomb) excimer laser 10 weeks later. Fellow eyes were matched to within 0.75 diopter (D) sphere and 0.50 D cylinder. Patients were followed for 3 months after excimer laser treatment. Preoperative and post-flap creation wavefront aberrometry using a Hartmann-Shack aberrometer and manifest refraction were compared between the 2 groups. The same tests were performed 3 months after excimer laser ablation.

RESULTS

Statistically significant changes were seen in defocus wavefront aberrations after Hansatome (P=.004) and IntraLase (P=.008) flap creation. A hyperopic shift in manifest refraction was noted in the Hansatome group after the creation of the corneal flap (P=.04); no statistically significant changes in manifest refraction were seen in the IntraLase group. Statistically significant changes in total higher-order aberrations (HOAs) (trefoil and quadrafoil Zernike terms) were seen after flap creation in the Hansatome group (P=.02). No significant changes in HOAs were noted after flap creation in the IntraLase group. After the flap was relifted and standard excimer laser ablation was performed, a statistically significant increase in coma occurred in the Hansatome group (P=.008). Standard refractive outcomes in the 2 groups were similar.

CONCLUSIONS

The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was seen in the Hansatome group but not in the IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation.

Flap thickness accuracy

PURPOSE

To determine the flap thickness accuracy of 6 microkeratome models and determine factors that might affect flap thickness.

SETTING

Magill Research Center for Vision Correction, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

This multicenter prospective study involved 18 surgeons. Six microkeratomes were evaluated: AMO Amadeus, Bausch & Lomb Hansatome, Moria Carriazo-Barraquer, Moria M2, Nidek MK2000, and Alcon Summit Krumeich-Barraquer. Eyes of 1061 consecutive patients who had laser in situ keratomileusis were included. Age, sex, surgical order (first or second cut), keratometry (flattest, steepest, and mean), white-to-white measurement, laser used, plate thickness, head serial number, blade lot number, and occurrence of epithelial defects were recorded. Intraoperative pachymetry was obtained just before the microkeratome was placed on the eye. Residual bed pachymetry was measured after the microkeratome cut had been created and the flap lifted. The estimated flap thickness was determined by subtraction (ie, mean preoperative pachymetry measurement minus mean residual bed pachymetry).

RESULTS

A total of 1634 eyes were reviewed. Sex distribution was 54.3% women and 45.7% men, and the mean age was 39.4 years +/- 10.6 (SD). In addition, 54.5% of the procedures were in first eyes and 45.5%, in second eyes. The mean preoperative pachymetry measurement was 547 +/- 34 microm. The mean keratometry was 43.6 +/- 1.6 diopters (D) in the flattest axis and 44.6 +/-1.5 D in the steepest axis. The mean white-to-white measurement was 11.7 +/- 0.4 mm. The mean flap thickness created by the devices varied between head designs, and microkeratome heads had significant differences (P<.05). Factors that explained 78.4% of the variability included microkeratome model, plate thickness, mean preoperative pachymetry, Kmin, surgery order, head serial number, blade lot number, and surgeon. Factors such as age, sex, Kmax, Kaverage, white to white, and laser had no significant correlation to flap thickness.

CONCLUSIONS

The results demonstrated variability between the 6 microkeratome models. Device labeling did not necessarily represent the mean flap thickness obtained, nor was it uniform or consistent. Thinner corneas were associated with thinner flaps and thicker corneas with thicker flaps. In addition, first cuts were generally associated with thicker flaps when compared to second cuts in bilateral procedures.