Precision of Flap Measurements for Laser in situ Keratomileusis in 4428 Eyes

Comparing pentacam HR screening indices in different normal corneal thicknesses among refractive surgery candidates

Purpose:

To compare Pentacam indices in normal eyes with different corneal thicknesses.

Methods:

It is a retrospective observational study. Ninety-six normal eyes of 96 patients who were referred for refractive surgery in a tertiary university-based hospital from October 2015 to April 2019 were recruited consecutively. Corneal keratometry as well as Pentacam's software Belin-Ambrósio Enhanced Ectasia Display (BAD) parameters including pachymetry progression indices (PPIs), maximum Ambrosio's relational thickness (ART-max), corneal elevations, normalized deviations, BAD total deviation value (BAD-D), and anterior surface indices were measured by Pentacam HR (Type 70900). The included were classified as thin (26 eyes), average (45 eyes), and thick (25 eyes) corneas with the thinnest point thickness of ≤496 μm, 497–595 μm, and ≥596 μm, respectively. The specificities of all parameters were calculated based on routine cut-off values.

Results:

The refraction, keratometry, and elevations were not different (P > 0.05). All PPIs (minimum, average, and maximum) of thick corneas were significantly lower than average and thin corneas (P < 0.001). ART-max increased by thickening of the cornea (P < 0.001). BAD-D score and normalized indices of pachymetric parameters decreased with the increase of thickness (P < 0.001), while specificities of all indices increased with corneal thickening. More than 96% of thick corneas were classified as normal PPI-max (24/25), ART-max (25/25), and BAD-D (25/25), while nearly <54% of thin corneas (14/26 for PPI-max, 9/26 for ART-max, and 12/26 for BAD-D) were normal.

Conclusions:

The pachymetry-related indices and BAD-D were different among normal corneas with various thicknesses. The specificities of PPIs, ART-max, and BAD-D of thin corneas were lower than in thick corneas.

A Comparative Study of Laser In Situ Keratomileusis Flaps Created Using Single-Functional Versus Multifunctional Femtosecond Laser for Refractive Surgery

PURPOSE

To compare laser in situ keratomileusis flaps created at the programmed target thickness of 120 μm using the LenSx multifunctional and the FS200 single-functional femtosecond lasers as evaluated by anterior segment optical coherence tomography (AS-OCT).

METHODS

This was a prospective, comparative, consecutive, blinded, nonrandomized study. Patients with stable refraction for over a year were consecutively allocated to the LenSx group or the FS200 group (n = 66; 33 patients in each group). All the patients underwent refractive surgery in both eyes. Previous eye surgery, ocular pathology associated with refractive errors, pregnancy, breastfeeding, and use of medication that causes ocular adverse effects constituted the exclusion criteria. Corneal topography, corneal tomography, dilated fundoscopy, applanation tonometry, ultrasonic pachymetry, dynamic and static refraction, visual acuity, and AS-OCT were evaluated before and after surgery. AS-OCT flap thickness was measured at 20 points on each cornea.

RESULTS

In the LenSx group, AS-OCT flap thickness differed significantly from the target thickness at 2 of 20 points (mean differences of 2.106 and 1.803 μm). In the FS200 group, 6 of 20 measurements differed significantly (mean differences ranging from 1.121 to 2.121 μm). The 2 lasers were similarly successful in creating regular and uniform flaps. The agreement between the 2 blinded examiners regarding the AS-OCT flap thickness measurements was excellent (intraclass correlation coefficient >0.75) in both groups.

CONCLUSIONS

Both femtosecond lasers were safe and capable of creating highly reproducible, uniform, and regular flaps at the target preoperative thickness of 120 μm. The LenSx multifunctional femtosecond laser offers the advantage of allowing both cataract and corneal surgeries.

Preparation of endothelial keratoplasty lenticules with Gebauer SLc Original versus Moria CBm Carriazo-Barraquer and Moria One-Use Plus microkeratomes

Purpose

To investigate endothelial keratoplasty lenticules prepared from fresh whole eyes via Gebauer SLc Original (SLc) versus Moria CBm Carriazo-Barraquer (CBm), and those prepared from corneoscleral buttons via SLc versus Moria One-Use Plus (OUP) in terms of eye bank preparation criteria.

Methods

Fresh whole eyes-dissected endothelial keratoplasty lenticules with SLc were compared with CBm in terms of thickness profile measurements, over/under dissection values, endothelial cell loss, and postoperative graft failures. A similar comparison was made between corneoscleral buttons-dissected endothelial keratoplasty lenticules with SLc and OUP.

Results

Means of central thicknesses and increase of thickness toward periphery were not significantly different between 33 fresh whole eyes-dissected endothelial keratoplasty lenticules with SLc and 33 fresh whole eyes-dissected ones with CBm. There was no significant difference between 19 corneoscleral buttons-dissected endothelial keratoplasty lenticules with SLc and 19 corneoscleral buttons-dissected ones with OUP in terms of mean central thickness and post-cut endothelial cell loss. However, in the corneoscleral buttons-dissected endothelial keratoplasty lenticules, a mean increase of thickness was significantly different from central to two pericentral locations with OUP (P = 0.001) and from central to two peripheral parts with SLc (P = 0.011). Both CBm and OUP systems showed deeper dissection depths than head descriptions as compared to SLc (P < 0.001).

Conclusion

Unlike fresh whole eyes-dissected endothelial keratoplasty lenticules with SLc or CBm, thickness profiles of corneoscleral buttons-dissected endothelial keratoplasty lenticules with both SLc and OUP systems showed a partial asymmetric increase of thickness toward the periphery. A high agreement was observed between endothelial keratoplasty lenticules thicknesses and SLc nomograms.

Laser-assisted in-situ keratomileusis (LASIK) with a mechanical microkeratome compared to LASIK with a femtosecond laser for LASIK in adults with myopia or myopic astigmatism

BACKGROUND

Laser-assisted in-situ keratomileusis (LASIK) is a surgical procedure that corrects refractive errors. This technique creates a flap of the outermost parts of the cornea (epithelium, bowman layer, and anterior stroma) to expose the middle part of the cornea (stromal bed) and reshape it with excimer laser using photoablation. The flaps can be created by a mechanical microkeratome or a femtosecond laser.

OBJECTIVES

To compare the effectiveness and safety of mechanical microkeratome versus femtosecond laser in LASIK for adults with myopia.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (2019, Issue 2); Ovid MEDLINE; Embase; PubMed; LILACS; ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We used no date or language restrictions. We searched the reference lists of included trials. We searched the electronic databases on 22 February 2019.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of LASIK with a mechanical microkeratome compared to a femtosecond laser in people aged 18 years or older with more than 0.5 diopters of myopia or myopic astigmatism.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 16 records from 11 trials enrolling 943 adults (1691 eyes) with spherical or spherocylindrical myopia, who were suitable candidates for LASIK. Five hundred and forty-seven participants (824 eyes) received LASIK with a mechanical microkeratome and 588 participants (867 eyes) with a femtosecond laser. Each trial included between nine and 360 participants. In six trials, the same participants received both interventions. Overall, the trials were at an uncertain risk of bias for most domains. At 12 months, data from one trial (42 eyes) indicates no difference in the mean uncorrected visual acuity (logMAR scale) between LASIK with a mechanical microkeratome and LASIK with a femtosecond laser (mean difference (MD) -0.01, 95% confidence interval (CI) -0.06 to 0.04; low-certainty evidence). Similar findings were observed at 12 months after surgery, regarding participants achieving 0.5 diopters within target refraction (risk ratio (RR) 0.97, 95% CI 0.85 to 1.11; 1 trial, 79 eyes; low-certainty evidence) as well as mean spherical equivalent of the refractive error 12 months after surgery (MD 0.09, 95% CI -0.01 to 0.19; 3 trials, 168 eyes [92 participants]; low-certainty evidence). Based on data from three trials (134 eyes, 66 participants), mechanical microkeratome was associated with lower risk of diffuse lamellar keratitis compared with femtosecond laser (RR 0.27, 95% CI 0.10 to 0.78; low-certainty evidence). Thus, diffuse lamellar keratitis was a more common adverse event with femtosecond laser than with mechanical microkeratome, decreasing from an assumed rate of 209 per 1000 people in the femtosecond laser group to 56 per 1000 people in the mechanical microkeratome group. Data from one trial (183 eyes, 183 participants) indicates that dry eye as an adverse event may be more common with mechanical microkeratome than with femtosecond laser, increasing from an assumed rate of 80 per 1000 people in the femtosecond laser group to 457 per 1000 people in the mechanical microkeratome group (RR 5.74, 95% CI 2.92 to 11.29; low-certainty evidence). There was no evidence of a difference between the two groups for corneal haze (RR 0.33, 95% CI 0.01 to 7.96; 1 trial, 43 eyes) and epithelial ingrowth (RR 1.04, 95% CI 0.11 to 9.42; 2 trials, 102 eyes [50 participants]). The certainty of evidence for both outcomes was very low.

AUTHORS' CONCLUSIONS

Regarding the visual acuity outcomes, there may be no difference between LASIK with mechanical microkeratome and LASIK with femtosecond laser. Dry eye and diffuse lamellar keratitis are likely adverse events with mechanical microkeratome and femtosecond laser, respectively. The evidence is uncertain regarding corneal haze and epithelial ingrowth as adverse events of each intervention. The limited number of outcomes reported in the included trials, some with potentially significant risk of bias, makes it difficult to draw a firm conclusion regarding the effectiveness and safety of the interventions investigated in this review.

Modeling Changes in Corneal Parameters With Age: Implications for Corneal Disease Detection

PURPOSE

To apply computational methods to model normal age-related changes in corneal parameters and to establish their association with demographic factors, thereby providing a framework for improved detection of subclinical corneal ectasia (SCE).

DESIGN

Cross-sectional study.

METHODS

One hundred seventeen healthy participants were enrolled from Centre for Eye Health (Sydney, Australia). Corneal thickness (CT), front surface sagittal curvature (FSSC), and back surface sagittal curvature (BSSC) measurements were extracted from 57 corneal locations from 1 eye per participant using the Pentacam HR. Cluster analyses were performed to identify locations demonstrating similar variations with age. Age-related changes were modeled using polynomial regression with sliding window methods, and model accuracy was verified with Bland-Altman comparisons. Pearson correlations were applied to examine the impacts of demographic factors.

RESULTS

Concentric cluster patterns were observed for CT and FSSC but not for BSSC. Sliding window analyses were best fit with quartic and cubic regression models for CT and FSSC/BSSC, respectively. CT and FSSC sliding window models had narrower 95% limits of agreement compared with decade-based models (0.015 mm vs 0.017 mm and 0.14 mm vs 0.27 mm, respectively), but were wider for BSSC than decade-based models (0.73 mm vs 0.54 mm). Significant correlations were observed between CT and astigmatism (P = .02-.049) and FSSC and BSSC and gender (P = <.001-.049).

CONCLUSIONS

The developed models robustly described aging variations in CT and FSSC; however, other mechanisms appear to contribute to variations in BSSC. These findings and the identified correlations provide a framework that can be applied to future model development and establishment of normal databases to facilitate SCE detection.

Evaluation of the percentage tissue altered as a risk factor for developing post-laser in situ keratomileusis ectasia

PURPOSE

To assess the currently recommended percentage tissue altered (PTA) metric for its ability to screen for ectasia after laser in situ keratomileusis (LASIK).

SETTING

Gavin Herbert Eye Institute, University of California, Irvine, California, USA, and Rothschild Foundation, Paris, France.

DESIGN

Retrospective case series.

METHODS

The study used a LASIK database created by 1 surgeon for LASIK cases with normal preoperative topography that had a minimum follow-up of 24 months with complete preoperative and intraoperative data to permit the calculation of PTA values to detect eyes at risk for developing ectasia.

RESULTS

Of the eyes, 593 eyes had complete data and met the inclusion criteria. Based on measured flap thickness, 126 eyes (21%) had a PTA value of 40% or more (mean 44) and a percentage of that flap thickness accounted for the PTA (mean 66.7%; range 34% to 92%). The mean attempted laser ablation was 79.8 μm ± 29.2 (SD), and the mean residual bed thickness was 304.4 ± 29.2 μm (range 212 to 369 μm). No eye developed ectasia over a mean follow-up of 30 months.

CONCLUSIONS

The current PTA calculation when applied to a LASIK population with normal preoperative topography and flap thickness measured with ultrasound did not predict the risk for ectasia. Differences between study populations and assumptions might have accounted for the different outcomes obtained in the initially published PTA study.

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.

Gebauer SLc Original and Moria One-Use Plus automated microkeratomes for ultrathin Descemet's stripping automated endothelial keratoplasty preparation

PURPOSE

We compared the SLc Original (SLc) and One-Use Plus (OUP) microkeratomes for ultrathin Descemet's stripping automated endothelial keratoplasty (DSAEK) lamella preparation and storage, vis-à-vis accuracy, endothelial cell loss (ECL) and lamellar surface roughness (LSR).

METHODS

Twenty-five human corneas were dissected with single-use heads of different sizes aiming for a posterior lamella (PL) thickness of 85 μm, after which they were incubated for 6 days in a 5% dextran medium. Before preparation (0 hr) and 1, 24, and 144 hr after dissection, ECL and corneal thickness (CCT) were measured by ultrasound pachymetry (USP) and optical coherence tomography (OCT). Lamellar surface roughness (LSR) was assessed by scanning electron microscopy (SEM) and evaluated by two masked observers.

RESULTS

Prior to cutting, CCTs did not differ between OCT and USP measurements, with a high correlation between the two modalities (r²  = 0.8; p < 0.0001). Both systems succeeded in UT lamella preparation (CCT 40-130 μm) in 88% of cases. The OUP heads cut significantly deeper than the according SLc counterparts (p = 0.001), while the variance did not differ. The mean PL thickness increased significantly in the following incubation period (p = 0.01) with no difference between the keratome groups. Endothelial cell density (ECD) decreased significantly from before to 1 hr after preparation (-5.6%; p = 0.04), with no changes in the following 144-hr incubation period and no differences between the OUP and SLc group. Lamellar surface roughness (LSR) did not differ between both systems.

CONCLUSIONS

The SLc and the OUP system are both suited for the preparation of UT-DSAEK lamellae. Neither system differed significantly in variability, LSR or ECL, which did not increase during a 6-day incubation period.

Flap-induced astigmatism in eyes with sphere myopia correction: Superior hinge using a rotating microkeratome versus nasal hinge using a linear microkeratome

PURPOSE

To compare the effect of a rotating microkeratome (M2) and a linear microkeratome (SBK) on the change in the astigmatic component in eyes with preoperative plano refractive cylinder.

SETTING

University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.

DESIGN

Retrospective case series.

METHODS

An Allegretto excimer laser was used to perform laser ablation in myopic eyes of consecutive patients. The laser in situ keratomileusis (LASIK) procedure included mechanical flap preparation using a microkeratome, either a linear type with a single-use 90 μm head to create a nasal hinge or a rotating type with a single-use 90 μm head to create a superior hinge. The Alpins vector method was applied to describe the effects of LASIK on postoperative refractive cylinder.

RESULTS

The study evaluated 1045 eyes of 852 patients. Although the mean overall efficacy and safety indices indicate the procedure was highly precise, safe, and efficient, there were statistically significant differences in surgically induced astigmatism (SIA) between the microkeratomes (P = .002). The postoperative refractive cylinder (ie, SIA) was 0.75 diopter (D) or more in 116 eyes (11.1%), 44 (12.8%) of 344 linear cases and 72 (10.3%) of 701 rotating cases. Independent of the type of microkeratome used, the SIA was slightly higher in eyes treated first; the mean magnitude of the induced astigmatism was 0.35 D.

CONCLUSIONS

In approximately 10% of eyes with preoperative plano refractive myopia, the astigmatic component tended to be overcorrected. Nevertheless, independent of the type of microkeratome, the maximum mean magnitude of refractive cylinder documented was 0.35 D.

FINANCIAL DISCLOSURE

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

Using femtosecond laser to create customized corneal flaps for patients with low and moderate refractive error differing in corneal thickness

This study is designed to evaluate the visual outcomes, accuracy, and predictability of corneal flaps with different thicknesses created by 60-kHz femtosecond laser according to different corneal thicknesses in the patients with low and moderate refractive error. A total of 182 eyes were divided according to the central corneal thickness (470 μm-499 μm in Group A, 500 μm-549 μm in Group B, and 550 μm-599 μm in Group C) and underwent femtosecond laser-assisted LASIK for a target corneal flap thickness (100 μm for Group A, 110 μm for Group B, and 120 μm for Group C). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and refractive status were examined. The flap thickness of each eye was measured by anterior segment optical coherence tomography (AS-OCT) on 30 points at 1-month follow-up to assess the accuracy and predictability. Postoperatively, at least 75% of eyes had a UDVA of 20/16 or better, less than 2% of eyes lost one line, over 30% of eyes gained one or more lines in CDVA, at least 95% of eyes had astigmatism of less than 0.25 D, all eyes achieved a correction within ± 1.00 D from the target spherical equivalent refraction. The visual and refractive outcomes did not differ significantly in all groups (P >0.05). The mean flap thickness was 100.36 ± 4.32 μm (range: 95-113 μm) in Group A, 111.64 ± 3.62 μm (range: 108-125 μm) in Group B, and 122.32 ± 2.88 μm (range: 112-128 μm) in Group C. The difference at each measured point among the three groups was significant (P < 0.05). The accuracy and predictability were satisfactory in all three groups. In conclusion, this customized treatment yielded satisfactory clinical outcomes with accurate and predictable flap thickness for patients with low and moderate refractive error.

Comparison of Gebauer SLc and Moria CBm Carriazo-Barraquer ALK Microkeratomes for Descemet's Stripping Automated Endothelial Keratoplasty Preparation

PURPOSE

We compared the hand-guided Moria Carriazo-Barraquer (CBm) microkeratome with the fully automatic SLc microkeratome for Descemet's stripping automated endothelial keratoplasty (DSAEK)-lamella preparation and storage, vis-à-vis accuracy, endothelial cell loss (ECL), and lamellar surface roughness (LSR).

METHODS

A total of 18 human corneas were dissected with both the 300 μm CBm multi-use (n = 9) and the 300 µm SLc (n = 9) single-use heads, after which they were incubated for 6 d in a 5% dextran medium. Before preparation (0 h) and 1, 24, and 144 h after dissection, ECL and corneal thickness (CT) were measured by ultrasound pachymetry (USP) and optical coherence tomography (OCT). LSR was assessed by scanning electron microscopy (SEM) and evaluated by three masked observers.

RESULTS

Prior to cutting, CTs did not differ significantly between OCT or USP measurements, with a high correlation between the two modalities (r(2)= 0.94, p < 0.0001). One hour after preparation the anterior lamella showed a significantly higher dissection depth with the CBm (429.4 ± 21.8 µm) than the SLc (311.7 ± 54.8 µm, p = 0.0006), with the variance of the SLc system showing a trend towards higher values (p = 0.07). Anterior and posterior lamellae swelled significantly in the subsequent culture period. Both groups showed a significant ECL 1 h after preparation (p < 0.0001) with no significant difference between the systems (1 h: p = 0.44; CBm: - 9.4%, SLc: -11.7%), which stabilized over 144 h (144 h CBm: -13.9%, 144 h SLc: -10.3%). LSR did not differ significantly between both systems (p = 0.60).

CONCLUSIONS

The SLc system agrees more with the designated cutting depth than the CBm. The dissection produced a comparable LSR and a ∼10% ECL independently of the system. Further incubation of the prepared lamellae led to a swelling, but no further ECL.

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.

Randomized, contralateral eye study to evaluate the effect of standard and inverted side-cut angle on corneal biomechanical properties during femtosecond laser-assisted in situ keratomileusis

PURPOSE

To evaluate the effect of side-cut angle profile on corneal biomechanical properties after femtosecond laser in situ keratomileusis (FS-LASIK).

METHODS

Ninety-six myopic eyes of 48 patients underwent FS-LASIK. One eye of each patient was randomized to flap creation with a side-cut angle of 115°. The fellow eye flap side-cut angle was adjusted to 70°. Mean absolute error of flap diameter and mean change in Goldmann-correlated intra-ocular pressure (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), corneal resistance factor (CRF), p1 area, p2 area, p1 area 1 and p2 area 1 were compared between both groups.

RESULTS

Overall, the mean IOPg and CRF showed significant reduction at the end of 1 and 3 months, as well as between 1 and 3 months postoperatively (p ≤ 0.03). The mean IOPcc and CH showed significant reduction (p < 0.001) at the end of 3 months postoperatively. The parameters p1 area, p2 area, p1 area 1 and p2 area 1 changed significantly at the end of 1 and 3 months postoperatively (p < 0.001). There was no significant difference between both groups with regards to the mean change of IOPg, IOPcc, CH, CRF, p1 area, and p1 area 1. In 115° group, the mean absolute error in flap diameter was greater compared with 70° group (p = 0.014).

CONCLUSIONS

The stability of IOP and corneal biomechanical properties were not enhanced in FS-LASIK flaps with an inverted side-cut angle. The size of corneal flap created with 70° side-cut angle was more accurate compared with 115° side-cut angle.

Femtosecond laser-assisted lamellar keratoplasty (FSLK) for anterior corneal stromal diseases

Our objective was to study the outcome of femtosecond-assisted lamellar keratoplasty (FSLK) in stromal corneal diseases. This is a retrospective chart review of 17 patients (20 eyes) who underwent FSLK for anterior corneal pathologies. Main outcome measures were refractive results following FSLK, complications, and graft survival. Mean follow-up time was 42 ± 15 (7-58) months. Preoperative best spectacle-corrected visual acuity (BSCVA) was ≤20/40 in 17 eyes. Postoperative BSCVA ≥ 20/40 was achieved in 12/14 at 12 months, 11/12 at 24 months, and 10/12 eyes at 36 months; postoperative BSCVA ≥ 20/25 was achieved in 8/14, 8/12, and 5/12 eyes at 12, 24, and 36 months, respectively. One eye had vertical gas break through the epithelium during the FSLK. One eye had postoperative epithelial rejection and two eyes had stromal rejection treated successfully with topical steroids. Another eye had epithelial ingrowth that was not progressive; however, the same eye developed bacterial keratitis and scarred graft 32 months post-FSLK. One eye had graft dehiscence and one eye developed excessive interface fibrosis. Five out of 20 grafts failed due to the recurrence of the original disease (3), corneal scarring (1), and excessive interface fibrosis (1). FSLK provides many advantages over conventional PK and DALK, with faster visual rehabilitation and emmetropization of the manifest refraction rather than inducing ametropia and irregular astigmatism.

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.

Post-LASIK keratectasia triggered by eye rubbing and treated with topography-guided ablation and collagen cross-linking--a case report

PURPOSE

To report a case of unilateral post-laser-assisted in situ keratomileusis (LASIK) keratectasia in a 35-year-old woman who had no known predisposing risk factors but who rubbed her affected eye frequently and vigorously in response to allergic conjunctivitis.

METHODS

Case report with relevant literature review.

RESULTS

A 35-year-old woman, with a cumulative risk scale score of 0 (according to the Randleman criteria), who underwent bilateral LASIK developed unilateral post-LASIK keratectasia 32 months later. She presented with a history of vigorous eye rubbing of the affected eye since about a year after allergic conjunctivitis. The fellow eye, which was not rubbed, remained normal. She complained of glare, halos, and ghost images in her affected eye. She underwent transepithelial topography-guided customized ablation with simultaneous UV-A corneal collagen cross-linking, after which she improved symptomatically and topographically.

CONCLUSIONS

Eye rubbing could contribute to the development of keratectasia, even in an eye that has no subclinical features of the disease. When detected early, a simultaneous combined topography-guided customized ablation treatment and collagen cross-linking is effective in improving the irregular corneal contour and restoring biomechanical stability.

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.

Repeatability of intraoperative central corneal and residual stromal thickness measurement using a handheld ultrasound pachymeter

PURPOSE

To determine and compare the repeatability of intraoperative central corneal thickness (CCT) and residual stromal bed thickness measurements using a handheld ultrasound (US) pachymeter.

SETTING

London Vision Clinic, London, United Kingdom.

DESIGN

Comparative evaluation of a diagnostic test or technology.

METHODS

This study comprised eyes that had laser in situ keratomileusis retreatment by flap lift in which handheld US pachymetry (Corneo-Gage Plus 50 MHz) had been performed intraoperatively. In each case, 5 consecutive measurements were obtained centrally immediately before and after the flap was lifted. The within-eye repeatability was calculated as the standard deviation of the 5 repeated measurements for the CCT measurements and the central residual stromal thickness (RST) measurements.

RESULTS

The study evaluated 134 eyes (79 patients). The mean CCT was 467 μm ± 40 (SD) (range 393 to 577 μm). The repeatability of CCT measurements was 6.83 μm, the coefficient of repeatability was 13.40 μm, and the coefficient of variation (CoV) was 1.46%. The mean central RST was 335 ± 46 μm (range 259 to 465 μm). The repeatability of central RST measurements was 4.91 μm, the coefficient of repeatability was 9.62 μm, and the CoV was 1.46%.

CONCLUSION

The repeatability of intraoperative handheld US pachymetry was similar between measurements of CCT and measurements of central RST; the CoV was 1.46% in both cases.

Outcomes of Retreatment after Aborted Laser In Situ Keratomileusis due to Flap Complications

Purpose:

To determine the refractive outcomes and complications of retreatment after aborted primary laser in situ keratomileusis (LASIK) due to flap complications.

Materials and Methods:

This retrospective study evaluated 50 retreated eyes that had flap complications during primary LASIK at the Eye Consultants Center in Riyadh, Saudi Arabia. Data were analyzed for patients with at least 3 months follow-up post retreatment.

Results:

Thirty-three eyes of 31 consecutive patients with 3 months follow-up or later post retreatment were included. The primary LASIK was aborted due to incomplete flaps in 22 eyes (66.7%), buttonhole flaps in 7 eyes (21.2%), free partial flaps in 3 eyes (9.1%), and a free complete flap in 1 eye (3.0%). Twenty-two eyes (66.7%) were retreated with LASIK, and 11 eyes (33.3%) were retreated with surface ablation. The mean spherical equivalent (SE) was –0.23 ± 0.72 D, the mean astigmatism was –0.65 ± 0.89 D, and the mean loss of the best corrected visual acuity (BCVA) was 0.78 lines at the final postoperative visit. At the last postoperative visit, 20/30 or better BCVA was achieved in 90.1% of eyes that underwent retreatment with LASIK and in 91% of eyes that were retreated with surface ablation. There was no statistical difference in postoperative SE between eyes retreated with LASIK and eyes retreated with surface ablation (P = 0.610). There was no statistical difference in postoperative BCVA between eyes retreated with LASIK and those retreated with surface ablation (P = 0.756). There were no intraoperative complications and no eyes required a second retreatment.

Conclusion:

Creation of a flap after a previous intraoperative flap complication was not associated with any complications. The refractive outcomes of retreatment with LASIK or surface ablation were comparable and reasonably favorable.

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.

Novel pachymetric parameters based on corneal tomography for diagnosing keratoconus

PURPOSE

To describe pachymetric progression indices (PPI) of the Pentacam HR (Oculus Optikgeräte GmbH) and the concept of relational thickness, and to test their accuracy for differentiating keratoconic and normal corneas compared with single-point thickness values.

METHODS

One hundred thirteen individual eyes randomly selected from 113 normal patients and 44 eyes of 44 patients with keratoconus were studied using the Pentacam HR by acquiring central corneal thickness (CCT), thinnest point (TP), position of the TP and PPI at minimal (PPI Min) and maximal (PPI Max) meridians, and the average (PPI Ave) of all meridians. Relational thickness parameters were calculated as the ratios of TP and CCT and PPI values. Mann-Whitney U test assessed differences in groups for each variable. Receiver operating characteristic (ROC) curves were calculated for all variables and pairwise comparisons were performed.

RESULTS

Statistically significant differences were noted between normal and keratoconic eyes for all parameters (P<.001), except for horizontal position of TP (P=.79). The best parameters, named Ambrósio's Relational Thickness (ART), were ART-Ave (TP/PPI Ave) and ART-Max (TP/PPI Max) with areas under the ROC curves of 0.987 and 0.983, respectively. The best cutoffs were 424 μm and 339 μm for ART-Ave and ART-Max, respectively. Pachymetric progression indices and ART had a greater area under the curve than TP and CCT (P<.001); TP (0.955) had a greater area under the curve than CCT (0.909; P=.002).

CONCLUSIONS

Tomographic-derived pachymetric parameters were better able to differentiate normal and keratoconic corneas than single-point pachymetric measurements. Further studies are needed to evaluate the role of tomography in identifying early forms of ectasia as well as ectasia risk among LASIK candidates.

Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome

PURPOSE

To evaluate the thickness and side-cut angle of laser in situ keratomileusis (LASIK) flaps created by 1 of 3 femtosecond lasers or a microkeratome using Fourier-domain optical coherence tomography (OCT).

SETTING

Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea.

DESIGN

Comparative case series.

METHODS

Flap creation for bilateral LASIK was performed using an IntraLase (femtosecond group 1), VisuMax (femtosecond group 2), or Femto LDV (femtosecond group 3) femtosecond laser or an M2 microkeratome. Flap thickness was determined at 14 points. The side-cut angle was measured in 4 directions at the margin interface. Measurements were taken 2 months postoperatively using an RTVue Fourier-domain OCT device and integrated software.

RESULTS

Femtosecond group 1 comprised 50 eyes; femtosecond group 2, 40 eyes; femtosecond group 3, 64 eyes; and the microkeratome group, 52 eyes. Eyes in femtosecond groups 1 and 2 had relatively even flap configuration. Flaps in femtosecond group 3 and the microkeratome group had a meniscus shape. Flaps in femtosecond group 1 had the least difference between the mean peripheral and the central flap thickness (P<.001). The greatest flap thickness predictability (measured versus intended thickness) was in femtosecond group 3 (P<.001). Flaps in femtosecond group 1 had a side-cut angle closest to 90 degrees (P<.001).

CONCLUSIONS

Flap morphology differed according to the system used. The 3 femtosecond laser systems appeared to be superior to the microkeratome system generally. The 3 femtosecond laser systems also produced different flap configurations depending on their individual mechanisms.

Factors influencing corneal flap thickness in laser in situ keratomileusis with a femtosecond laser

Purpose

To evaluate factors responsible for the variability between intended and achieved corneal-flap thickness during femtosecond laser-assisted laser in situ keratomileusis (LASIK).

Methods

A prospective, nonrandomized, case study was performed on 35 eyes of 18 consecutive patients who underwent LASIK surgery using the 60 kHz femtosecond laser microkeratome. Eyes were assigned to three different thickness groups, with 110-, 120-, or 130-µm cut depths. Anterior segment optical coherence tomography was used to assess the morphology of 35 LASIK flaps at postoperative one week postoperatively. The flap thickness was assessed at seven measuring points across each flap. Patient age, preoperative spherical equivalent, manual keratometry, preoperative central pachymetry, and regional variability of the cornea were evaluated to determine where they influenced the achieved corneal flap thickness.

Results

Cuttings of all flaps were easily performed without any intraoperative complications. Flap-thickness measurements had a mean of 115.21 ± 4.98 µm (intended thickness, 110 µm), 121.90 ± 5.79 µm (intended, 120 µm), and 134.38 ± 5.04 µm (intended, 130 µm), respectively. There was no significant difference between the 110-µm and 120-µm groups when compared with the 130-µm group (one-way analysis of variance test, p > 0.05). Patients' age, preoperative spherical equivalent, manual keratometry, and preoperative central pachymetry did not affect the achieved flap thickness (Pearson correlations test, p > 0.05). The reproducibility of flap thickness in the central 1.5-mm radius area was more accurate than that in the peripheral 3.0 to 4.0-mm radius area (paired samples t-test, p < 0.05).

Conclusions

Femtosecond laser-assisted LASIK is likely to reproduce a reliable thickness of the corneal flap, which is independent of corneal shape factors or refractive status. Future studies should focus on variations in corneal biomechanical factors, which may also play an important role in determining flap thickness.

Biomechanical corneal changes induced by different flap thickness created by femtosecond laser

OBJECTIVE

To evaluate the impact of the creation of corneal flaps at different thicknesses on the biomechanical properties of swine corneas.

METHOD

Twelve swine eyes were obtained to form two groups: 100 μm flap thickness and 300 μm flap thickness. Each eye was submitted to the following examinations: raster topography to investigate corneal curvature alterations, ocular response analyzer to investigate corneal hysteresis change, optical coherence tomography to measure central corneal and flap thickness and sonic wave propagation velocity as a measure of stiffness, before and immediately after flap creation. After flap amputation, surface wave velocity measurements were repeated.

RESULTS

Measured flap thicknesses were statistically different for thin and thick flap groups, with an average of 108.5 + 6.9 and 307.8 + 11.5 μm respectively. Hysteresis and corneal resistance factor did not change significantly after flap creation in the thin flap group. With thicker flaps, both parameters decreased significantly from 8.0 +1.0 to 5.1 +1.5 mmHg and from 8.2 + 1.6 to 4.1 +2.5 mmHg respectively. Simulated keratometry values increased in the thick flap group (from 39.5 + 1 D to 45.9+1.2 D) after flap creation but not in the thin flap group (from 40.6 + 0.6 D to 41.4+ 1.0 D). Regarding surface wave velocity analysis, the surgical procedures induced statistically lower results in some positions.

CONCLUSION

In the experimental conditions established by this model, thicker flaps presented a greater biomechanical impact on the cornea.

Anterior segment optical coherence tomography measurement of LASIK flaps: femtosecond laser vs microkeratome

PURPOSE

To compare the uniformity and accuracy of LASIK flaps created with a femtosecond laser versus a mechanical microkeratome using optical coherence tomography (OCT).

METHODS

A prospective study was performed on 72 consecutive patients who underwent LASIK in both eyes in alternating fashion with either the AMO IntraLase FS60 (72 eyes) or the Moria M2 microkeratome (72 eyes). One month after surgery, anterior segment OCT was performed on each eye to measure flap thickness at 20 locations and the results were assessed for uniformity and accuracy.

RESULTS

At 1 month after surgery, the microkeratome group flap ranges were greater than those found in the femtosecond laser group (P<.05). The meridian and radial flap uniformity in the femtosecond laser group were better, showing an almost planar configuration, than the meniscus-shaped flaps created with the microkeratome. Comparison of the nasal and temporal flap thickness revealed more regularity in the femtosecond laser group than the microkeratome group. The maximum deviation from the intended flap thicknesses was 7 μm in the femtosecond laser group compared to 26 μm in the microkeratome group. During the 1440 measurements of the 72 eyes, a difference >20 μm was observed in 0.42% of eyes in the femtosecond laser group and 15% of eyes in the microkeratome group.

CONCLUSIONS

LASIK flaps made with the IntraLase FS60 were more uniform with more accurate thickness than those created by the Moria M2 microkeratome.

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.

Efficacy, safety, and flap dimensions of a new femtosecond laser for laser in situ keratomileusis

PURPOSE

To evaluate the clinical results of a preproduction femtosecond laser for flap creation in laser in situ keratomileusis (LASIK).

SETTING

Private practice, Brussels, Belgium.

METHODS

This study comprised myopic eyes with a plano target refraction and a target flap thickness of 110 microm. The LASIK flap was created with a Ziemer LDV femtosecond laser. Prospective evaluation included flap dimensions, intraoperative and postoperative complications, and visual outcomes.

RESULTS

Sixty-three patients (111 eyes; mean age 37.2 years) were evaluated. Preoperatively, the mean corrected distance visual acuity (CDVA) was 1.34 (Snellen) and the mean manifest refraction spherical equivalent (MRSE), -4.91 diopters (D) +/- 2.45 (SD). Six months postoperatively, the mean CDVA was 1.33; the mean MRSE, -0.05 +/- 0.3 D; and the mean uncorrected distance visual acuity (UDVA), 1.27. The UDVA was 20/25 or better in 98.2% of eyes and 20/20 or better in 94.6% of eyes. The MRSE was within +/-0.50 D in 95.5% of eyes and within +/-1.00 D in 99.1% of eyes. The cylinder was 0.50 D or less in 99.1% of eyes. The mean flap thickness was 106.6 +/- 12.6 microm. The most frequent complications were epithelial sloughing (10.8%), a decentered cut (4.5%), flap adhesions (5.4%), a slightly irregular flap border (5.4%), and microstriae (5.4%); all were mild.

CONCLUSIONS

Overall, the flap dimensions and refractive results were predictable and the complication rate was acceptable after LASIK using the new femtosecond laser for flap creation.

Comparison of laser in situ keratomileusis reoperation outcomes with the Moria M2 head 90 and 130 following previous photorefractive keratectomy or laser in situ keratomileusis

PURPOSE

To compare the Moria Model Two (M2) automated microkeratome with the head 90 (intended to create a 120-microm flap) to the head 130 (intended to create a 160-microm flap) in reoperations following previous photorefractive keratectomy (PRK) or laser-assisted in situ keratomileusis (LASIK) in terms of accuracy, predictability, safety and complications of the procedure.

METHODS

Eighty-five eyes of 70 consecutive patients received LASIK with the Moria M2 microkeratome. Nine previously PRK-operated eyes were reoperated with the head 90 and 37 eyes were reoperated with the head 130. Repeated LASIK was performed on 16 eyes with the head 90 and on 23 eyes with head the 130. Flap dimensions were measured and correlated to preoperative parameters.

RESULTS

The average flap thickness in the previously PRK-operated eyes was 115.1 microm [range 82-137 microm, standard deviation (SD) 17.9] with the head 90 and 131.2 microm (range 105-171 microm, SD 19.8) with the head 130. In the previously LASIK-operated eyes, the mean flap thickness was 139.2 microm (range 92-182 microm, SD 23.8) with the head 90 and 141.9 microm (range 109-179 microm, SD 15.2) with the head 130. There were no free or incomplete flaps or flaps with buttonholes in the study. There was no statistically significant difference in postoperative uncorrected visual acuity (UCVA) between the groups.

CONCLUSION

In eyes with previous PRK or LASIK, LASIK reoperation offers a safe alternative for improving refractive outcomes. The Moria M2 head 90, especially in LASIK-operated eyes, does not cut thinner flaps compared to the head 130.

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.

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.

High myopia as a risk factor for post-LASIK ectasia: a case report

Purpose

To describe the case of a patient developing corneal ectasia following LASIK for the correction of myopic astigmatism.

Materials and Methods

A 39-year-old man underwent bilateral uneventful LASIK for myopic astigmatism of -10.25 -1.75 ×040 OD and -8.00 -2.50 ×005 OS. Preoperative corneal pachymetry was 542 micrometers OD and 543 micrometers OS. Preoperative corneal topography showed bilateral oblique bow-tie patterns. Central keratometry measurements were 45.12 D @ 124 / 43.87 D @ 34 OD and 44.87 D @ 78 / 43.12 D @ 168 OS. Keratoconus or forme fruste keratoconus were not present preoperatively.

Results

The residual stromal bed was 314 micrometers OD and 295 micrometers OS. Increasing astigmatism was documented progressively after LASIK. Central keratometry and topography were performed with evidence of ectasia OD at 17 months post-operatively and early evidence of ectasia OS at last follow-up of 58 months.

Conclusion

High myopia appears to be a predisposing factor in this patient. High myopia may need to be considered as an ectasia risk factor independent of amount of ablation or residual stromal bed thickness and in the absence of forme fruste keratoconus. The possibility remains that ectasia was due to an unidentified risk factor or an intrinsic corneal problem with this patient's right eye.

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.

Thin-flap (sub-Bowman keratomileusis) versus thick-flap laser in situ keratomileusis for moderate to high myopia: case-control analysis

PURPOSE

To compare the refractive and visual outcomes of sub-Bowman keratomileusis (SBK) and thick-flap laser in situ keratomileusis (LASIK) for moderate to high myopia and evaluate the effect of corneal flap thickness on outcomes.

SETTING

Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA.

METHODS

Two studies were performed. In the first study, the refractive and visual outcomes in 33 eyes that had SBK (flap thickness 82 to 120 microm) and 62 eyes that had thick-flap LASIK (flap thickness >or=160) were retrospectively analyzed. Inclusion criteria were spherical equivalent -4.0 to -10.0 diopters (D), astigmatism 3.0 D or less, and follow-up 3 months or more. In the second study, the influence of flap thickness was evaluated. A case-control matched study (21 pairs) that controlled for residual stromal bed (RSB) thickness was performed.

RESULTS

The mean flap thickness was 110.2 microm+/-9.2 (SD) in the SBK group and 179.2+/-19.5 microm in the thick-flap LASIK group. There were no significant differences in visual outcomes. In the second study with equivalent RSB thickness, case-control matched comparisons between SBK (mean 108.6+/-8.0 microm) and thick-flap LASIK (mean 165.7+/-12.6 microm) showed no differences in preoperative and postoperative refractive and visual outcomes. Comparison of the intended versus achieved correction showed no significant differences between the 2 groups.

CONCLUSION

Retrospective analyses showed that the safety, efficacy, and predictability of SBK were similar to those of conventional thick-flap LASIK in corneas with equivalent RSB thickness.

Thin-flap laser-assisted in situ keratomileusis

PURPOSE OF REVIEW

Concerns regarding the increasing incidence of corneal ectasia following laser in situ keratomileusis procedures, together with increased understanding of the biomechanics of the cornea, has resulted in many refractive surgeons returning to surface ablation techniques such as photorefractive keratectomy. Even if surface ablation techniques offer a higher degree of safety than LASIK, they are associated with more pain and a slower visual recovery in the immediate postoperative period. This highlights the need for alternative procedures that offer the combined advantages of laser in situ keratomileusis and photorefractive keratectomy.

RECENT FINDINGS

Sub-Bowman's keratomileusis is a new procedure that provides the biomechanical stability and associated safety of photorefractive keratectomy with the visual results and reduced pain experience of laser in situ keratomileusis. This technique involves the use of the femtosecond laser to create a customized corneal flap of between 90 and 110 mum with a diameter based on the requirements of the individual patient and the type of excimer laser being used.

SUMMARY

This review outlines the rationale for sub-Bowman's keratomileusis and describes the efficacy, tolerability and safety of the procedure compared with photorefractive keratectomy.