Microkeratome versus femtosecond flaps: accuracy and complications

Effect of femtosecond laser-assisted arcuate keratotomy versus toric intraocular lens implantation on correction of astigmatism in cataract surgery: a systematic review and meta-analysis

PURPOSE

To compare the efficacy of femtosecond laser-assisted arcuate keratotomy (FSAK) combined with non-toric intraocular lens (IOL) implantation versus Toric IOL (TIOL) implantation in correcting corneal astigmatism in cataract patients.

METHODS

Relevant literature was searched in databases including PubMed, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL), and SinoMed. Data from the included studies were extracted. A meta-analysis was conducted to compare the correction performance of FSAK combined with non-toric IOL implantation and TIOL implantation using postoperative refractive astigmatism, correction index, and uncorrected distance visual acuity (UDVA) outcomes. Publication bias assessment and sensitivity analysis were also performed.

RESULTS

Five comparative studies were ultimately included in the meta-analysis. The TIOL group had smaller postoperative refractive astigmatism and a greater correction index compared to the FSAK group. The mean differences in postoperative refractive astigmatism and correction index between the two groups were - 0.19D (95% CI = 0.12 to 0.26, P < 0.01, I2 = 7%) and - 0.09 (95% CI =  - 0.18 to 0.00, P = 0.04, I2 = 0%), respectively. We found no statistically significant difference in UDVA between the two groups (95% CI =  - 0.01 to 0.11, P = 0.09, I2 = 70%).

CONCLUSIONS

FSAK combined with non-toric IOL implantation was found to be less effective than TIOL implantation in correcting preoperative corneal astigmatism in cataract patients. The difference in the effectiveness of astigmatism correction between the two surgical methods seems to diminish, as the degree of preoperative corneal astigmatism decreases.

Atypical microbial keratitis

Atypical microbial keratitis refers to corneal infections caused by micro-organisms not commonly encountered in clinical practice. Unlike infections caused by common bacteria, cases of atypical microbial keratitis are often associated with worse clinical outcomes and visual prognosis. This is due to the challenges in the identification of causative organisms with standard diagnostic techniques, resulting in delays in the initiation of appropriate therapies. Furthermore, due to the comparatively lower incidence of atypical microbial keratitis, there is limited literature on effective management strategies for some of these difficult to manage corneal infections. This review highlights the current management and available evidence of atypical microbial keratitis, focusing on atypical mycobacteria keratitis, nocardia keratitis, achromobacter keratitis, and pythium keratitis. It will also describe the management of two uncommonly encountered conditions, infectious crystalline keratopathy and post-refractive infectious keratitis. This review can be used as a guide for clinicians managing patients with such challenging corneal infections.

Post photorefractive keratectomy (PRK) infectious keratitis; six-year experience of a tertiary eye hospital

BACKGROUND/OBJECTIVES

As an essential development in the new century, surface ablation procedures have attracted increasing attention. There exists a concern regarding the risk of infectious keratitis. Hence, we aimed to investigate the rate and predisposing factors of infectious keratitis after photorefractive keratectomy (PRK).

SUBJECTS/METHODS

This retrospective study was designed in two phases. First, the rate of post-PRK keratitis of Farabi Eye Hospital was investigated. In other words, the targeted population was the patients who developed keratitis after performing procedure at Farabi Eye Hospital. In the second phase, all the patients with the diagnosis of post-PRK keratitis were studied regardless of the centre where surgery was performed. Patients with the diagnosis of infectious keratitis between 2014 and 2020 were enrolled and following information was analyzed: demographics, presentation time after surgery, perioperative medications, culture results, risk factors, medical treatment, complications, and final visual acuity.

RESULTS

The total number of PRK procedures in our centre was 24,986 (13,253 patients), in which 6 eyes of 5 patients developed keratitis. Beside these 5 patients, 24 referred patients (24 eyes) from the other centres were enrolled. Finally, a total number of 29 patients (30 eyes) were included. Our analysis revealed that manipulation of contact lens, dry eye, and blepharitis were the essential predisposing factors for keratitis development.

CONCLUSION

The overall post-PRK keratitis occurrence rate of our study was 0.02%. Our observation highlighted the importance of preoperative examination and treatment of the lids and dry eye disease.

Changes in aberrations and biomechanics after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in eyes with high astigmatism: a retrospective case control study

BACKGROUND

To compare the 6-month changes in aberration and biomechanics after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for high astigmatism.

METHODS

In this retrospective case control study, 47 eyes with high astigmatism (≥ 2.5 D, HA group) and 47 eyes with low astigmatism (≤ 1.0 D, LA group) underwent FS-LASIK. Preoperative and follow-up examinations included visual outcomes, higher order aberrations (HOAs) and biomechanics. Biomechanical parameters include a deformation amplitude ratio of 2 mm (DA ratio 2 mm), integrated inverse radius (IIR), stiffness parameter at first applanation (SP-A1), and ambrosio relational thickness through the horizontal meridian (ARTh).

RESULTS

Six months postoperatively, there was no significant difference in the efficacy and safety index (both P > 0.05) between the two groups, but the cylinder was higher in the HA group. The HOAs increased significantly after surgery in both groups (all P < 0.05). Six months postoperatively, the changes in spherical aberration and HOAs were larger in the HA group (both P < 0.005), but there was no significant difference between the changes in coma (P > 0.05). Significant decreases in SP-A1 and ARTh and significant increases in the IIR and DA ratio of 2 mm (all P < 0.05) were observed after surgery in both groups. The changes in the DA ratio 2 mm, IIR, SP-A1, and ARTh were not significantly different between the groups.

CONCLUSION

FS-LASIK had relative comparable efficacy and safety in correcting high and low myopic astigmatism, with higher astigmatic under-correction in eyes with high astigmatism. High astigmatism in eyes after FS-LASIK could introduce larger corneal aberrations, but the impact on corneal stiffness was the same as that in eyes with low astigmatism.

Early LASIK flap displacement without signs of infection

A 37-year-old woman was referred for refractive surgery evaluation. Poor visual quality in her left eye is her chief concern. The patient had undergone laser in situ keratomileusis (LASIK) in both eyes 3 days previously. Detailed history revealed that the patient underwent surgery to correct low myopia and astigmatism (-2.50 -2.75 × 180 in the right eye and -1.25 -2.75 × 180 in the left eye). The preoperative evaluation corrected distance visual acuity (CDVA) was 20/20 in the right eye and 20/20 in the left eye. The surgery was performed with a mechanical microkeratome and was uneventful. The patient reports that after her vision improved on the first day, she woke up with blurry vision in her left eye on the second day and it remained that way until the third day when she sought medical help. The slitlamp examination showed LASIK flap displacement without signs of infection ( Figure 1JOURNAL/jcrs/04.03/02158034-202212000-00023/figure1/v/2022-12-01T092452Z/r/image-tiff ). The patient was using topical corticosteroids and topical antibiotics every 6 hours. Considering the likely stromal exposure time, what would be the best approach for this case? Does the probable time of displacement of this flap change its behavior? In what way? If you decide to reposition the flap, would it be interesting to use fibrin glue or suture? Considering that there was no major trauma in the patient's report, what is the importance of the LASIK flap having been created by a mechanical microkeratome and not by a femtosecond laser in the displacement of the flap?

Quality of Vision After LASIK, PRK and FemtoLASIK: An Analysis Using the Double Pass Imaging System HD AnalyzerTM®

Purpose

Analyze and compare the quality of vision of Photorefractive keratectomy (PRK), LASER in situ keratomileusis with mechanical microkeratome (LASIK) and femtosecond-assisted LASIK (FS-LASIK) using the double-pass imaging system HD AnalyzerTM^®.

Setting

Ophthalmology department of Centro Hospitalar Universitário do Porto (CHUPorto).

Design

Retrospective, non-randomized, single center study.

Methods

Analysis of three equivalent groups of patients submitted to PRK, LASIK and FS-LASIK at our department. The objective quality of vision assessment included the objective scatter index (OSI), the modular transfer function cutoff frequency (MTF) and the predicted visual acuity within the 100% (PVA), 20% (PVA20) and 9% contrast levels (PVA9) that were evaluated at baseline, 1st week, 1 and 6 months after surgery.

Results

118 eyes were included: 40 underwent LASIK, 43 FS-LASIK and 35 PRK. The mean age was 30.6±4.6 years old and 56% were female. There was a significant impact concerning the type of procedure in the objective quality of vision analysis (Repeated measures ANOVA): the FS-LASIK group showed lower OSI values overtime [F(1,2)=4.566, p=0.012, OSI 0.83±0.53 (FS-LASIK) vs 0.87±0.47 (PRK) and 1.21±1.44 (LASIK)], higher MTF values [F(1,2)=6.569, p=0.002, MTF 40.17±8.33 vs 32.37±11.4 (PRK) and 30.26±10.28 (LASIK)], higher PVA 100% [F(1,2)=10.871, p<0.001], PVA 20% [F(1,2)=9.737, p<0.001] and PVA 9% [F(1,2)=6.335), p=0.003].

Conclusion

In our study, FS-LASIK showed an excellent optical performance through the HD AnalyzerTM technology, with significantly lower OSI and higher MTF, PVA100, PVA20 and PVA9 values. According to our results, this procedure seems to be superior to PRK and LASIK regarding visual quality objective parameters.

A prospective randomized self-controlled study of LASIK combined with accelerated cross-linking for high myopia in Chinese: 24-month follow-up

Background

To assess the visual and refractive outcomes of femtosecond laser-assisted in situ keratomileusis (FS-LASIK) concurrent with accelerated cross-linking (LASIK Xtra) compared with conventional FS-LASIK (convLASIK) for high myopia in Chinese individuals.

Methods

In this prospective, randomized, fellow-eye comparison study, 25 patients with high myopia were treated randomly with LASIK Xtra in one eye and convLASIK in the other. A 24-month follow-up was conducted, and the main outcome measures included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE) and corneal tomography.

Results

The UDVA was 0.09 ± 0.15 logMAR in the LASIK Xtra group, which was significantly worse than that in the convLASIK group 1 day postoperatively (P = .001), but the difference became nonsignificant from 1 week after surgery. The efficacy index was 0.88 ± 0.18 in the LASIK Xtra eyes and 0.99 ± 0.13 in the convLASIK eyes at 24 months (P = .028). Throughout the follow-up period, a slight myopic shift in the MRSE and keratometry values were observed in both groups without significant intergroup differences. The coefficient of determination was 0.9982 in the LASIK Xtra eyes and 0.9987 in the convLASIK eyes. The corneal density was significantly higher, and demarcation lines were visible in the first 6 months in LASIK Xtra eyes, but both signs of cross-linking gradually disappeared during follow-up. No severe complications were detected in either group.

Conclusions

LASIK Xtra showed comparable safety and predictability with convLASIK for high myopia in Chinese, but lower efficacy and no greater stability was observed up to 24-month follow-up.

Refractive outcomes of femtosecond laser-assisted cataract surgery with arcuate keratotomy and standard phacoemulsification with toric intraocular lens implantation

PURPOSE

Femtosecond laser arcuate keratotomy (FS-AK) and toric intraocular lens (IOL) implantation are effective for the correction of eyes with corneal astigmatism. In this study, the postoperative refractive outcomes of patients receiving femtosecond laser-assisted cataract surgery (FLACS) with FS-AK and patients receiving standard phacoemulsification with toric IOL implantation were evaluated.

METHODS

This retrospective study reviewed the postoperative outcomes of patients undergoing FLACS with FS-AK (the FS-AK group) and patients undergoing standard phacoemulsification with toric IOL implantation (the toric IOL group). The main outcome measures were uncorrected and corrected visual acuities, keratometric and refractive astigmatism, and vector analysis.

RESULTS

The FS-AK group included 41 eyes with preoperative keratometric astigmatism of - 1.64 ± 0.42 diopters (D), and the toric IOL group included 53 eyes with preoperative keratometric astigmatism of - 2.29 ± 0.91 D (P < 0.001). Postoperative refractive astigmatism was comparable between the two groups. Compared with the FS-AK group, postoperative uncorrected visual acuity was significantly better (P = 0.005) and corrected visual acuity was marginally better in the toric IOL group (P = 0.051). The absolute angles of error were 9.95° ± 9.57° and 5.08° ± 4.94° (P = 0.02) in the FS-AK and the toric IOL groups, respectively.

CONCLUSION

Both FLACS with FS-AK and standard phacoemulsification with toric IOL implantation are safe and effective methods for astigmatism correction during cataract surgery. Standard phacoemulsification with toric IOL implantation achieves better visual acuity than FLACS with FS-AK at the 6-month follow-up.

Thin-Flap Laser In Situ Keratomileusis-Associated Dry Eye: A Comparative Study Between Femtosecond Laser and Mechanical Microkeratome-Assisted Laser In Situ Keratomileusis

OBJECTIVE

To assess and compare postlaser in situ keratomileusis (LASIK) dry eye after LASIK with planned thin flaps created by a femtosecond laser (FS) and mechanical microkeratome (MK).

METHODS

Patients were stratified according to the flap creation technique into FS and MK groups with planned 100 μm flap thickness in all eyes. Dry eye parameters including tear film break-up time (TBUT), Schirmer I test, ocular surface disease index (OSDI), and lower tear meniscus height and area (tear meniscus height [TMH] and tear meniscus area [TMA]) were assessed before surgery and at 3 and 6 months after surgery.

RESULTS

The study included 102 eyes of 55 patients (52 eyes underwent FS-LASIK/50 eyes underwent MK-LASIK). The preoperative characteristics including age, gender, and spherical equivalents were similar in both groups (P>0.05). The difference in postoperative flap thickness was statistically significant (P<0.05). In each group, dry eye parameters showed a statistically significant worsening (P value<0.001) at 3 months with later significant improvement at 6 months but did not return to baseline. The mean TBUT, Schirmer I, and lower TMH and TMA were statistically higher, and the mean OSDI was statistically lower in FS-LASIK than the MK-LASIK group at both 3 and 6 months (P value<0.001). The depth of ablation had a statistically significant correlation with Schirmer I at 6 months and OSDI at both 3 and 6 months post-LASIK (P<0.05).

CONCLUSION

The use of femtosecond laser technology in performing thin-Flap LASIK eye surgeries has improved the outcome of post-LASIK dry eye when compared with the mechanical microkeratome.

Flap Thickness and the Risk of Complications in Mechanical Microkeratome and Femtosecond Laser In Situ Keratomileusis: A Literature Review and Statistical Analysis

INTRODUCTION

A recent Cochrane review found no difference in visual acuity outcomes between femtosecond-assisted laser in situ keratomileusis (LASIK) and LASIK using mechanical microkeratomes (MMKs). This study compares the flap thickness and risk of complications related to flap creation using femtosecond lasers and MMKs.

METHODS

PubMed and the Web of Science are used to search the medical literature. An extensive search is performed to identify the flap thickness and complications of LASIK as reported up to 15 July 2021. The following keywords are used in various combinations: Corneal flap, femtosecond laser, laser in situ keratomileusis, laser-assisted in situ keratomileusis, LASIK, mechanical microkeratome.

RESULTS

After removing duplicates and irrelevant studies, 122 articles were included for review. Pooled differences for intended vs. postoperative flap thickness using MMKs and femtosecond laser were -4.07 μm (95% CI: -19.55, 3.24 μm) in studies on the MMK and 5.43 μm (95% CI: 2.30, 7.84 μm; p < 0.001), respectively. After removing the studies evaluating outcomes of the old generation Hansatome MMKs (which had a significantly greater variation of flap thickness), the pooled difference for newer MMKs was 4.97 μm (95% CI: 0.35, 9.58 μm; p < 0.001), but the results still favored the femtosecond laser. Uncommon and mild complications unique for the femtosecond LASIK are epithelial gas breakthrough, opaque bubble layer, transient light sensitivity syndrome, and rainbow glare. A single study reported a very low, but stastically different risk of postoperative flap slippage (0.033% for MMK LASIK, and 0.003% for femtosecond LASIK, respectively).

CONCLUSION

In both manual microkeratome and femtosecond LASIK, intra- and postoperative complications were uncommon. The evidence of the superiority of one technique in terms of complications over another cannot be indisputably stated.

Femtosecond LASIK for the correction of low and high myopic astigmatism

INTRODUCTION

Higher preoperative myopic astigmatism is associated with a higher probability of retreatment due to patient dissatisfaction as a result of residual cylindrical error. Nonetheless, retreatment is safe and the final clinical results are comparable to those of patients with lower preoperative astigmatism who were satisfied with the primary treatment. Our purpose is to compare the efficacy and safety of femtosecond LASIK (FS-LASIK) for the refractive correction of patients with low (< 1.5 Diopters (D) versus high (≥ 1.5 D) myopic astigmatism.

METHODS

Retrospective observational study of 841 eyes of 825 eligible patients treated with FSLASIK for the correction of simple or compound myopic astigmatism. Outcome measures included residual error, best corrected and uncorrected distance visual acuity (BCVA and UCVA), efficacy and safety 3 months after the primary procedure or the retreatment.

RESULTS

Of 841 eyes in total, 432 (51.37%) had < 1.5 D (Group 1) and 409 (48.63%) had ≥ 1.5 D (Group 2) preoperative myopic astigmatism. The efficacy index of primary treatment was 0.94 ± 0.18 in Group 1 and 0.89 ± 0.22 in Group 2 (P = 0.001). Of 138 eyes (16.41%) that were retreated due to dis-satisfaction related to residual refractive error, 28 belonged to Group 1 (6.5%) and 110 (26.9%) to Group 2 (P < 0.001). Following retreatment, small but statistically significant differences in the residual mean postoperative cylinder (-0.08 ± 0.24 vs -0.27 ± 0.46 D, P = 0.001) and UCVA (1.11 vs 0.96, P = 0.0001) were detected for Groups 1 and 2, respectively. However, there were no statistically significant differences in the safety and efficacy indices.

CONCLUSION

Following FS-LASIK, eyes with myopic astigmatism ≥ 1.5 D have approximately four times more chances of undergoing retreatment due to dis-satisfaction caused by residual refractive error compared to eyes with myopic astigmatism < 1.5 D. However, the clinical results after retreatment are highly satisfactory and comparable in both groups.

Postrefractive infectious keratitis: prevention, diagnosis, management, and prognosis

PURPOSE OF REVIEW

Improve outcomes from an elective procedure by preventing a rare but sight-threatening complication.

RECENT FINDINGS

Advancement in anti-infective prophylaxis, and therefore shift in the causative organism permits better diagnostic and empiric management.

SUMMARY

Infectious keratitis presents in different patterns depending on the refractive procedure. Atypical causative organisms may respond poorly to empiric therapy and impair vision. Therefore, microbial identification is of utmost importance and therapy is adjusted accordingly.

Validity of percentage tissue altered as a screening formula for post laser-assisted in-situ keratomileusis ectasia in Indian eyes

Purpose:

To calculate a modified percentage tissue altered (mPTA) in post laser-assisted in-situ keratomileusis (LASIK) eyes and to validate its role as an independent factor to evaluate ectasia in the Indian population.

Methods:

A total of 333 consecutive eyes with normal preoperative corneal topography by combined placido and scheimpflug imaging-based topography system (SIRIUS) who underwent LASIK using a microkeratome between 2011 and 2014 at a tertiary level teaching hospital in south India, were retrospectively analyzed. Preoperatively patient's refraction, flap thickness (FT), ablation depth (AD), residual stromal bed (RSB), and thinnest corneal thickness (TCT) were recorded. The formula used was mPTA = (FT + AD)/TCT. mPTA was grouped into <0.4 (low risk), 0.40 - 0.45 (moderate risk), and >0.45 (high risk). All patients were called for follow-up and underwent a topography to look for ectasia.

Results:

In total 60.1%, 29.1%, and 10.8% patients had mPTA of <0.4, 0.40 - 0.45 and >0.45, respectively. However, after a minimum follow-up of 2 years, none of the patients had any sign of ectasia.

Conclusion:

Careful selection of patients is mandatory before proceeding for LASIK. Factors like corneal thickness, RSB, degree of myopia, and AD are more important. The role of mPTA >0.4 as an independent risk factor for post LASIK ectasia is questionable in Indian eyes. Other factors or a modified formula suitable for Indian eyes needs to be investigated. A larger follow-up period is also required as ectasia has been known to develop even after 2 years.

The Prevalence of Infectious Keratitis after Keratorefractive Surgery: A Systematic Review and Meta-Analysis Study

BACKGROUND

The keratorefractive surgeries (KRS) are one of the most common ocular surgeries. One of the dangerous complications of these surgeries is infectious keratitis (IK), which is the second cause of blindness after cataract surgery. The purpose of this study was to estimate the prevalence of IK after KRS in different parts of the world.

METHODS

In order to obtain relevant studies, all national and international databases including IranMedex, SID, Magiran, IranDoc, Medlib, ScienceDirect, PubMed, Scopus, Cochrane, Embase, Web of Science, and Google Scholar were searched using standard keywords.

RESULTS

IK prevalence after KRS was 0.000496% (0.000145% for the left eye and 0.000149% for the right eye). IK prevalence after KRS in the United States, Europe, and Asia was 0.000667%, 0.000473%, and 0.000045%, respectively, in all of which the common microorganisms were Staphylococci. Meta-regression showed no significant association between IK after KRS and either sample size or publication year of the studies. IK prevalence after KRS in the right eye was more than that in the left one. Also, the probability of IK incidence after LASIK surgery was more than PRK and LASEK. In the evaluation of continents, IK after KRS in the United States was more frequent compared with Europe and Asia.

CONCLUSIONS

This study provided data as to the overall prevalence of IK following KRS and its variations according to the types of eye, surgery, pathogenic microorganism, and geographical location.

Refractive surgery beyond 2020

Refractive surgery refers to any procedure that corrects or minimizes refractive errors. Today, refractive surgery has evolved beyond the traditional laser refractive surgery, embodied by the popular laser in situ keratomileusis or 'LASIK'. New keratorefractive techniques such as small incision lenticule extraction (SMILE) avoids corneal flap creation and uses a single laser device, while advances in surface ablation techniques have seen a resurgence in its popularity. Presbyopic treatment options have also expanded to include new ablation profiles, intracorneal implants, and phakic intraocular implants. With the improved safety and efficacy of refractive lens exchange, a wider variety of intraocular lens implants with advanced optics provide more options for refractive correction in carefully selected patients. In this review, we also discuss possible developments in refractive surgery beyond 2020, such as preoperative evaluation of refractive patients using machine learning and artificial intelligence, potential use of stromal lenticules harvested from SMILE for presbyopic treatments, and various advances in intraocular lens implants that may provide a closer to 'physiological correction' of refractive errors.

Incidence and Risk Factors of Opaque Bubble Layer Formation According to Flap Thickness During 500-kHz FS-LASIK

PURPOSE

To present the incidence, risk factors, and effect of opaque bubble layer (OBL) formation during flap creation in laser-assisted in situ keratomileusis (LASIK) with a 500-kHz femtosecond laser on visual performance.

METHODS

In this retrospective study, preoperative characteristics (age, sex, keratometric value, spherical equivalent, and central corneal thickness) and intraoperative surgical factors (used energy, docking type, and flap thickness) were compared between eyes with and without OBL formation during flap creation. Possible risk factors for specific types of OBLs were analyzed.

RESULTS

One hundred thirty-five eyes of 71 patients underwent LASIK, and OBL developed in 98 eyes (72.59%). In the univariate analysis, the greater than 80-µm flap group was associated with a lower OBL occurrence than the 80-µm flap group (P = .0424, odds ratio [OR] = 0.481) and hard docking was associated with increased OBL formation (P = .0001, OR = 6.859). In the multivariate analysis, hard docking was a risk factor for OBL development (P = .0003, OR = 6.329). In the subgroup analysis, hard docking had a marginal effect on OBL occurrence in the 80-µm flap group (P = .086, OR = 3.564), but it had a strong effect in the greater than 80-µm flap group (P = .0018, OR = 10.210).

CONCLUSIONS

Hard docking is a risk factor for OBL development. However, hard docking had a small effect on OBL occurrence in the 80-µm flap group during LASIK. OBL formation did not affect visual performance. [J Refract Surg. 2019;35(9):583-589.].

Impact of Patient Interface Diameter and Vacuum Level on Suction Stability Using a Flat Applanating Interface for Femtosecond Laser-Assisted LASIK

PURPOSE

To investigate the impact of different patient interface (PI) diameters and different vacuum levels on the suction stability during vacuum application for femtosecond laser-assisted LASIK.

METHODS

Break-away forces as a marker for suction stability were measured by an automated test bench set-up. The test bench was based on a customized stamp connected to a digital load cell. Three flat applanating PI with different diameters (8.5, 9.5 and 10.0 mm) and four different vacuum levels (500, 600, 700 and 800 mbar) were investigated using the FEMTO LDV Z8 (Ziemer Ophthalmic Systems AG, Switzerland).

RESULTS

Mean break-away force was 5.23N (±0.99N) using the 8.5 mm PI and 500 mbar vacuum, 8.18N (±1.39N) using the 8.5 mm PI and 800 mbar, 3.37N (±0.56N) using the 10.0 mm PI and 500 mbar, and 6.14N (±0.68N) using the 10.0 mm PI and 800 mbar vacuum (p < .001; CI95%). Increasing the PI diameter from 8.5 to 10.0 mm resulted in a 28.89% (+1.97 ± 1.02N) lower break-away force (p < .001) when using default vacuum settings (700 mbar) compared to increasing vacuum from 500 to 800 mbar, which resulted in a 60.37% (+1.95 ± 1.40N) higher mean break away force (p < .001).

CONCLUSION

The vacuum level and the diameter of the PI showed significant impact on suction stability measured as break-away force during flat applanating docking for corneal and refractive surgery. Break-away forces were inversely related to the PI diameter and directly to the vacuum level. Increasing the PI diameter by one step or reducing vacuum by 100 mbar resulted in a comparable decrease of break-away forces. Therefore, the surgeon could potentially maintain stabile suction by increasing vacuum when choosing a larger PI diameter to obtain a larger treatment zone. Furthermore, reduction of the PI diameter and/or increasing vacuum could help improving suction stability in situations of poor suction and in situations with increased risk of suction loss during LASIK.

Comparison of 9.0 and 9.2 mm Flap Diameter Options of Femtosecond Laser In-Situ Keratomileusis for Hypermetropia and Hypermetropic Astigmatism

Aim

To compare the postoperative one-year outcomes of asphericity (Q) and high order aberration (HOA) values of 9.0 and 9.2 mm diameter flap groups in hypermetropia and hypermetropic astigmatism subjects who underwent femtosecond laser in-situ keratomileusis (LASIK).

Materials and Methods

The study included 68 eyes of 34 patients. A femtosecond laser platform (Allegrato Wave, Wavelight AG, Erlangen, Germany) was used for flap cutting. Corneal stroma was ablated using Wavelight EX500 with wavefront-optimized profile (WaveLight GmbH, Erlangen, Germany). 9.0 mm flap diameter was randomly chosen for one eye, and 9.2 mm flap diameter was chosen for the fellow eye. Two eyes of the patients who used two different flap diameters were enrolled into two different groups. Corneal stroma was ablated using Wavelight EX500 with wavefront-optimized profile (WaveLight GmbH, Erlangen, Germany). Postoperative one-year outcomes of Q and HOA values of 9.0 and 9.2 mm diameter flap groups were compared statistically.

Results

The preoperative manifest refraction spherical equivalents of the 9.0 and 9.2 mm diameter flap groups were 1.86 ± 1.81 D and 1.69 ± 1.99 D (p=0.754). No intraoperative or postoperative complications were observed. At postoperative one-year, Q values were 0.98 ± 0.13 D and 0.91 ± 0.15 D (p=0.029). HOAs including horizontal and vertical coma, horizontal and vertical trefoil, spherical aberration, and second order vertical coma were not significantly different (p > 0.05 for all). Total HOA values were 1.62 ± 0.14 and 1.40 ± 0.16, in the 9.0 and 9.2 mm diameter flap groups, respectively (p < 0.001).

Conclusion

Both the 9.0 and 9.2 mm diameter flap options in femtosecond LASIK are equally safe and effective. Many of the HOA values are similar in both options, and better results were provided in terms of total HOA and Q values with the 9.2 mm diameter flap option. This study was registered with trial registration number 118-011.

Femtosecond laser in refractive corneal surgery

The introduction of the femtosecond (fs) laser has revolutionized ophthalmic surgery. With the worldwide application of fs-lasers, clinical outcomes and safety in corneal procedures have improved significantly and they have become an ideal tool for ultra-precise corneal refractive surgery. Flap creation in laser in situ keratomileusis (LASIK) is the most common use of this laser. It can also be used for other corneal refractive procedures including channel creation for the insertion of intrastromal corneal ring segments (ICRS), performing astigmatic keratotomies (AK), femtosecond lenticule extraction including small incision lenticule extraction (SMILE), and the insertion of corneal inlays. This article summarizes recent advanced applications of fs laser technology in corneal refractive surgery.

Verification and measurement of the side-cut angle of corneal flap in patients undergoing LASIK surgery using FS 200 kHz femtosecond laser system versus conventional mechanical microkeratome

Introduction: This is a prospective nonrandomized interventional clinical trial conducted to measure and verify the intended versus the achieved LASIK flap side-cut angle in two groups of patients, Femtosecond laser-assisted in-situ keratomileusis (FS-LASIK) using Wavelight FS200 (Alcon Laboratories Inc. Fort Worth, TX, USA) and the conventional mechanical microkeratme (Moria M₂ 90).

Methods: This prospective clinical trial was conducted on 40 eyes of 20 patients (20 eyes in each group) in the interval between December 2017 and August 2018. Heidelberg anterior segment OCT was done for the patients 2 weeks postoperatively to measure the corneal flap side cut angle.

Results: The achieved side-cut angles of all the patients in the first group (the femtosecond laser-assisted in-situ keratomileusis group) were equal to or more inverted than the intended angle (110–115°) in all the study candidates with a minimum angle (110°) and maximum angle (155°). Unlike the achieved side-cut angle in the second group (the mechanical microkeratome group) in which all the achieved side-cut angle were acute with a minimum angle (30°) and maximum angle (65°) which is more acute than the intended side-cut angle (70°).

Conclusion: In our study we found that the femtoLASIK technology was capable of making the flap side-cut angle more obtuse than the intended angle, unlike the achieved flap side-cut angle done using the mechanical microkeratome which was more acute than the intended angle in 100% of cases.

Intraoperative Optical Coherence Tomography-Guided Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty

PURPOSE

To describe the feasibility and outcomes of intraoperative optical coherence tomography (OCT)-guided, femtosecond laser-assisted deep anterior lamellar keratoplasty in which the lamellar and tunnel cuts were completed by laser.

METHODS

The Ziemer Z8 system was used to scan the corneas intraoperatively and guide the stromal lamellar and tunnel cuts created by the laser. Thirty porcine eyes and 3 human cadaver globes were used to evaluate the accuracy of laser-created intrastromal tunnels and the feasibility of achieving big-bubble pneumatic dissection. The tunnel distance above the Descemet membrane (Dt-dm) was set at 100 and 130 μm, and the accuracy of laser cut was assessed by anterior segment OCT and histological sections. Fourteen patients with keratoconus or corneal scars were then included to evaluate the clinical outcomes.

RESULTS

The deviation from the targeted Dt-dm was 5.5% to 8.6% and 0.7% to 9.8% for the 100 and 130 μm groups, respectively. The achieved thickness had a significantly and positively strong correlation with the targeted thickness (r = 0.86; P < 0.001). In all cases, the anterior stromal lamella was removed without difficulty, except in the patients with corneal scars in whom some remaining stromal fiber attachments were observed. A type 1 big bubble was successfully achieved in all patients.

CONCLUSIONS

We present the accuracy and clinical outcomes of femtosecond laser-assisted, intraoperative OCT-guided deep anterior lamellar keratoplasty, in which controlled lamellar and tunnel cuts at desired depths were performed by laser in one step, and a successful big bubble was achieved.

Comparative study of wave-front aberration and corneal Asphericity after SMILE and LASEK for myopia: a short and long term study

Background

The study compares the wave-front aberration and corneal asphericity from multiple perspectives after Small Incision Lenticule Extraction and Laser-assisted Subepithelial Keratomileusis for mild to moderate myopia in a short and long time period.

Methods

This prospective and comparative study included 32 eyes in the SMILE group, with a mean spherical equivalent (SE) of − 4.1 ± 0.9D and 32 eyes in the LASEK group, with a mean SE of − 3.7 ± 1.0D. Visual acuity, refractive error, wave-front aberration, corneal Q value and corneal refractive power were analyzed pre-, 3 months and 3 years post-operatively.

Results

There was no significant difference in refractive error, wave-front aberration, corneal Q value and corneal refractive power before treatment. Three months postoperative, Q value within 6 mm (SMILE: 0.46 ± 0.27, LASEK: 0.63 ± 0.28, p = 0.02), the relative peripheral corneal power (5-8 mm: p < 0.05), change of higher order aberration (SMILE: 0.10 ± 0.16, LASEK: 0.24 ± 0.20, p = 0.004) and spherical aberration (SA, SMILE: -0.07 ± 0.30, LASEK: -0.41 ± 0.40, p < 0.001) were significantly lower in the SMILE than in LASEK group. The visual acuity, refractive error, coma, peripheral Q value, central corneal power had no significant difference between the two groups. Three years post-operation, the corneal power distribution results and SA were similar to that of 3-month, while the Q value had no significant difference between the two groups.

Conclusion

In the early stage after SMILE, the HOAs was lower, the corneal refractive power from central to periphery was more uniform than after LASEK; and in the long-term run, SMILE still preceded LASEK in the corneal asphericity and aberration.

Electronic supplementary material

The online version of this article (10.1186/s12886-019-1084-3) contains supplementary material, which is available to authorized users.

Effect of age on visual and refractive results after LASIK: mechanical microkeratome versus femtosecond laser

AIM

To evaluate the effect of age on visual and refractive results after laser in situ keratomileusis (LASIK) obtained with a mechanical microkeratome or a femtosecond laser.

METHODS

Retrospective, nonrandomized, cohort study. A total of 3826 eyes were included in the study (1725 eyes treated with mechanical LASIK and 2101 eyes treated with femtosecond LASIK). The relationship between patient age and the 3-month postoperative visual and refractive results of both procedures were analyzed by linear regression analysis.

RESULTS

Three months postoperatively, we found a significant correlation between age and the postoperative spherical equivalent (SE; r ²=0.004, P=0.006), efficacy (r ²=0.006, P=0.001), and safety indexes (r ²=0.05, P=0.0001) in the mechanical LASIK group. On the other hand, we found a significant correlation between age and the postoperative SE (r ²=0.02, P=0.0001) and the efficacy index (r ²=0.01, P=0.0001) but not the safety index in the femtosecond laser group. Mechanical LASIK provided slightly but significantly better efficacy and predictability in patients 18 to 40 years of age and femtosecond LASIK did so in patients older than 40 years of age. The femtosecond laser provided better safety results than the mechanical microkeratome in both age groups.

CONCLUSION

A tendency toward undercorrection and less predictability is found with aging after myopic LASIK regardless of whether the flap was created with a mechanical microkeratome or a femtosecond laser. However, femtosecond laser provides significantly better outcomes in terms of efficacy, safety and predictability compared to mechanical microkeratome for the correction of myopia in patients over 40y.

Comparison of changes in refractive error and corneal curvature following small-incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis surgery

Purpose

To compare visual acuity, refractive error, corneal curvature, and the stability of these parameters during the early postoperative period following small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery.

Methods

One hundred and five eyes and 110 eyes were enrolled in SMILE and FS-LASIK group, respectively. Uncorrected and best-corrected distance visual acuity (UCVA and BCVA), manifest refraction, corneal curvature, intraocular pressure, and slit-lamp examinations were performed preoperatively, 1 day, 1 week, 1 month, and 3 months postoperatively.

Results

No significant differences in postoperative UCVA or BCVA were observed between the SMILE and FS-LASIK groups at any time point. SMILE group had significant better postoperative spherical equivalent (SE) values than FS-LASIK group at 1 day, 1 week, and 1-month follow-up. However, there was no significant difference in postoperative SE values at 3-month follow-up. Significant differences in mean postoperative corneal curvature were observed during all follow-up examinations.

Conclusion

SMILE surgery was associated with more accurate postoperative refractive correction up to 1 month following surgery. SMILE surgery also resulted in less significant corneal curvature changes than FS-LASIK. Furthermore, FS-LASIK was associated with decreased stability of postoperative refractive error and corneal curvature relative to SMILE.

Femtosecond-assisted LASIK flaps resistant to lift secondary to corneal epithelial defects: Case reports and ex vivo studies

PURPOSE

To evaluate why epithelial defects created before femtosecond laser ablation result in laser in situ keratomileusis (LASIK) flaps resistant to lift.

SETTING

Boston Eye Group, Brookline, Massachusetts, USA.

DESIGN

Case reports and ex vivo studies.

METHODS

To examine the mechanism of resistance to flap lift after epithelial defects, flap creation with a femtosecond laser was performed in 30 fresh porcine eyes. Before ablation, the eyes were assigned to 3 groups. Group 1 was a control group with intact corneal epithelium. In Group 2, a central 2.0 mm corneal epithelial defect was created by marking it with a 2.0 mm trephine. In Group 3, a peripheral 2.0 mm epithelial defect was created similarly. After the femtosecond laser procedure was performed, the flaps were lifted and the resistance to lift was documented. The corneas were further examined using anterior segment optical coherence tomography.

RESULTS

In Group 1, no resistance was felt during flap lifts. In Group 2, significant resistance was encountered at the edge of the epithelial defects and the flaps could not be lifted in 7 of 10 eyes. In Group 3, similar significant resistance was encountered in all 10 eyes. Six of 10 flaps could not be lifted. Anterior segment optical coherence tomography from a representative cornea from Group 2 demonstrated a deeper dissection plane in the area where the overlying epithelium was missing.

CONCLUSION

Epithelial defects can interfere with proper LASIK flap creation with the femtosecond laser. This seems to be attributable to a deeper cutting plane under the area of the epithelial defects compared with the surrounding area with intact epithelium.

Clinical outcomes of small-incision lenticule extraction and femtosecond laser-assisted wavefront-guided laser in situ keratomileusis

Small-incision lenticule extraction and wavefront-guided femtosecond-assisted laser in situ keratomileusis (LASIK) provide good visual outcomes and an efficacious correction of myopia or myopic astigmatism with similar levels of safety. Some differences in predictability and the percentage of eyes gaining lines of corrected distance visual acuity are present. A higher level of coma is present after small-incision lenticule extraction, with no clear differences between techniques in spherical aberration. Better contrast sensitivity is achieved in the early postoperative period after wavefront-guided femtosecond laser-assisted LASIK, possibly because of less intrastromal light backscattering and Bowman layer microdistortions. Corneal sensitivity decreased less after small-incision lenticule extraction because of less severe decrease in subbasal nerve density, which has a significant effect on symptomatology and dry-eye tests (P < .05). Significant corneal biomechanical changes occurred after both techniques (P < .05), with no scientific evidence supporting the superiority of 1 technique over the other.

FINANCIAL DISCLOSURE

Dr. Piñero received an unrestricted educational grant from Abbott Medical Optics, Inc. Neither author has a financial or proprietary interest in any material or method mentioned.

Predictive Factors for Successful High Myopia Treatment Using High-Frequency Laser-In-Situ Keratomileusis

Aim

To evaluate the predictive factors of LASIK procedure for high myopia with or without astigmatism using a combination of high-frequency femtosecond-assisted LASIK followed by an excimer laser.

Methods

This study was a retrospective interventional case series study to evaluate myopic eyes undergoing high platform LASIK with FEMTO LDV Z2 intervention, followed by WaveLight®EX500 excimer laser machine. Subjects were divided into 2 groups: high myopia (SE of -6.01 to -9.00 D) and very high myopia (SE of -9.01 D or higher). Myopic eyes (Spherical Equivalent/SE) less than -13 D were included in this study. Visual Acuity (VA) was evaluated 1 day and 60 days after the procedure. Predictive factors, such as age, degree of sphere, degree of astigmatism, keratometric reading and axial length were analyzed to detect any influences affecting the final VA results.

Results

A total of 316 myopia eyes underwent intervention, mean age: 25.3±3.8 years. Target treatment was achieved in 96.1% of patients with high myopia and 69.9% of patients with very high myopia. High degree of sphere and astigmatism constitutes an important factor influencing final VA.

Conclusion

Modern machines provide a more promising efficacy and success of LASIK procedure in high myopia: important predictive factors were a high degree of sphere and astigmatism for achieving the optimal final outcome.

Corneal transplantation trends in France from 2004 to 2015: A 12-year review

Purpose:

The aim of this study was to report the 12-year longitudinal trends in indication and corneal transplantation techniques in France from 2004 to 2015.

Results:

The records of all corneal transplantations performed from 2004 to 2015 in France were retrospectively reviewed. The patient indications and types of transplant performed were analyzed. A total of 46,658 corneal transplantations were performed between 2004 and 2015, with 34,187 (73.3%) penetrating keratoplasty and 10,452 (22.4%) lamellar keratoplasty. The leading surgical indications were secondary endothelial failure (24.3%), keratoconus (18.8%), regraft (13.5%), and Fuchs endothelial corneal dystrophy (15.1%). Endothelial keratoplasty became the preferred technique for endothelial diseases and deep anterior lamellar keratoplasty the preferred technique for keratoconus, surpassing penetrating keratoplasty in 2013.

Conclusion:

Secondary endothelial failure is the top indication for performing a keratoplasty over the 12-year period. There was a shift from penetrating keratoplasty to endothelial keratoplasty performed for Fuchs endothelial corneal dystrophy and secondary endothelial failure, and to deep anterior lamellar keratoplasty, performed for keratoconus. This highlights an important shift in managing corneal diseases toward the application of selective and more conservative surgeries and changes in indications in corneal transplantation.

Topography-guided neutralization technique for the management of flap complication in laser in situ keratomileusis

A 29-year-old male was referred following a flap loss after the creation of a thin, irregular flap with a visual acuity of logMAR 0.1 with -2.0 DS-2.75 DC × 175°. Corneal topography and anterior segment optical coherence tomography revealed an irregular corneal curvature and epithelial profile. Phototherapeutic keratectomy (PTK) followed by Topography - Guided Custom Ablation Treatment (TCAT), as a modification of the topographic neutralization technique protocol, was planned to regularize the corneal surface and treat the residual refractive error. Postoperatively, the patient showed a best-corrected visual acuity of logMAR 0 with a refractive error of -1 DC × 90°. Regularization of topography and epithelial thickness was seen along with a reduction in astigmatism and higher order aberrations. We report the use of PTK followed by TCAT as a novel method to treat a case of intraoperative flap loss during laser in situ keratomileusis.

Comparison of 5468 retreatments after laser in situ keratomileusis by lifting the flap or performing photorefractive keratectomy on the flap

PURPOSE

To assess visual outcomes of retreatment after laser in situ keratomileusis (LASIK) by lifting the flap or performing photorefractive keratectomy (PRK) on the flap, as well as to establish whether there was an increased risk of epithelial ingrowth (EIG) when LASIK and lifting of the flap are separated by a long time interval and to determine the incidence of corneal haze after PRK.

METHODS

Retrospective study of 4077 patients (5468 eyes) who underwent LASIK and subsequent retreatment were reviewed in order to study their visual results and identify cases of EIG and corneal haze.

RESULTS

Enhancements included 5196 eyes from 3876 patients that were retreated by lifting the flap, and 272 eyes from 201 patients that were retreated by PRK on the flap. No statistically significant differences were found between the retreatments in terms of predictability, efficacy, and safety. A total of 704 cases of EIG were found after lifting the flap, for which surgical cleansing was necessary in 70. Surgical cleansing decreased the efficacy index when compared with patients with EIG who did not need cleansing (P=.01). Differences in terms of safety and predictability were not statistically significant. The incidence of corneal haze after ablation of the surface of the previous flap was 14.34%, although none of these cases were clinically relevant.

CONCLUSIONS

Visual outcomes were similar between patients who were retreated by lifting the flap and those who underwent PRK. The incidence of EIG when the flap was lifted was 13.55%. The incidence of EIG increases with the time elapsed between the primary procedure and retreatment.

A sample predictive model for intraocular pressure following laser in situ keratomileusis for myopia and an "intraocular pressure constant"

PURPOSE

To describe a sample predictive model for intraocular pressure (IOP) following laser in situ keratomileusis (LASIK) for myopia and an IOP constant.

METHODS

The records of patients that underwent LASIK for myopia and myopic astigmatism via WaveLight Allegretto Wave Eye-Q 400 Hz excimer laser and Hansatome XP microkeratome were retrospectively reviewed. Patients with no systemic or ocular disease other than myopia or myopic astigmatism were included in the study. Preoperative and postoperative month 1 data and intraoperative data were used to build the predictive model for IOP after LASIK. The IOP constant was calculated by subtracting the predicted IOP from preoperative IOP. The paired samples t test, Pearson's correlation analysis, curve estimation analysis, and linear regression analysis were used to evaluate the study data.

RESULTS

The study included 425 eyes in 214 patients with a mean age of 32 ± 7.8 years. Mean spherical equivalent of the attempted correction (SE-ac) was -3.7 ± 1.7 diopters. Mean post-LASIK decrease in IOP was 4.6 ± 2.3 mmHg. The difference between preoperative and postoperative IOP was statistically significant (P < 0.001). SE-ac, preoperative IOP, and central corneal thickness had highly significant effects on postoperative IOP, based on linear regression analysis (P < 0.001 and R ² = 0.043, P < 0.001 and R ² = 0.370, and P < 0.001 and R ² = 0.132, respectively). Regression model was created (F = 127.733, P < 0.001), and the adjusted R ² value was 0.548.

CONCLUSIONS

Evaluation of IOP after LASIK is important in myopic patients. The present study described a practical formula for predicting the true IOP with the aid of an IOP constant value in myopic eyes following LASIK.

Percent tissue altered and corneal ectasia

PURPOSE OF REVIEW

This article reviews the association of a novel metric, percentage tissue altered (PTA), with the occurrence of ectasia after laser in-situ keratomileusis in eyes with normal corneal topography, and analyses the influence of the variables that comprise it, and its role on eyes with suspicious topography.

RECENT FINDINGS

PTA is derived from [PTA = (FT + AD)/CCT] where FT = flap thickness, AD = ablation depth, and CCT = preoperative central corneal thickness. Our studies revealed that there is a robust relationship between high PTA and ectasia risk in eyes with normal preoperative topography. PTA higher or equal to 40% presented the highest odds ratio and highest predictive capabilities for ectasia risk than each of the variables that comprise it, residual stromal bed or age. Average thicker flaps alone were insufficient to create ectasia unless coupled with greater ablation depths, meaning a high PTA. In eyes with suspicious topography, even low PTA value is sufficient to induce ectasia.

SUMMARY

This new metric, PTA, should be taken into account when screening patients for refractive surgery. Patients with normal topography or tomography, presenting a PTA higher or equal to 40% should be considered at higher risk for post laser in-situ keratomileusis ectasia.

Femtosecond-assisted LASIK: Complications and Management

FS-assisted LASIK has become the preferred method for LASIK flap creation due to the precision, accuracy, and reproducibility of the flap creation. Thinner, planar flaps may help prevent cases of post-LASIK ectasia and may have a superior refractive outcome. However, FS flap creation has several unique complications that require early recognition and optimal timely management for the best visual outcomes.

Intraoperative Flap Complications in LASIK Surgery Performed by Ophthalmology Residents

Purpose:

To report the rate of flap-related complications in LASIK surgery performed by in-training ophthalmology residents and to analyze the risk factors for these complications.

Methods:

We analyzed 273 flap dissections in 145 patients from March 2013 to February 2014. We included all LASIK surgeries performed by 32 ophthalmology residents using a Moria M2 microkeratome. All the flap-related complications were noted. Comparison between both groups with and without complications was performed with an independent Student's t-test and relative risks were calculated.

Results:

There were 19 flap-related complications out of the 273 flap dissections (6.95%). The most common complication was incomplete flap dissection (n = 10; 3.66%), followed by free-cap (n = 5; 1.83%), and flap-buttonhole (n = 2; 0.73%). There was no significant difference between the complicated and uncomplicated cases in terms of the right versus the left eye, pachymetry results, white-to-white diameter, and spherical equivalent. But this difference was significant for mean keratometry (P = 0.008), K-min (P = 0.01), and K-max (P = 0.03) between these groups. Final visual acuity after rescheduling laser treatment was similar in both groups. Relative risks for flap-related complications were 2.03 for the first LASIK surgery (CI 95% 0.64 to 6.48; P = 0.22) and 1.26 (CI 95% 0.43 to 3.69; P = 0.66) for the surgeon's flap-related complications. Female gender presented an odds ratio of 2.48 (CI 95% 0.68 to 9.00; P = 0.16) for complications.

Conclusion:

Flap-related complications are common intraoperative event during LASIK surgery performed by in-training ophthalmologists. Keratometries and surgeon's first procedure represent a higher probability for flap related complications than some other biometric parameters of patient's eye.

Comparison of efficacy, safety, and predictability of laser in situ keratomileusis using two laser suites

Purpose

The main aim of this study was to compare the efficacy, safety, and predictability of femtosecond laser-assisted in situ keratomileusis performed by two different laser suites in the treatment of myopia for up to 6 months.

Methods

In this two-site retrospective nonrandomized study, myopic eyes that underwent laser-assisted in situ keratomileusis using IntraLase FS 60 kHz formed group 1 and those using WaveLight FS200 femtosecond laser system formed group 2. Ablation was performed with Visx Star S4 IR and WaveLight EX500 Excimer lasers, respectively, in groups 1 and 2. Both groups were well matched for age, sex, and mean level of preoperative refractive spherical equivalent (MRSE). Uncorrected distance visual acuity, corrected distance visual acuity, and MRSE were evaluated preoperatively and at 1 week, 1 month, and 6 months after treatment.

Results

Fifty-six eyes of 28 patients were included in the study. At 6-month follow-up postop, 78.6% of eyes in group 1 and 92.8% of eyes in group 2 achieved an uncorrected distance visual acuity of 20/20 or better (P=0.252). 35.7% and 50% in group 1 and group 2, respectively, gained one line (P=0.179). No eye lost lines of corrected distance visual acuity. Twenty-five eyes in group 1 (92.7%) and 27 eyes in group 2 (96.3%) had MRSE within ±0.5 D in the 6-month follow-up (P>0.999). The mean efficacy index at 6 months was similar in group 1 and group 2 (mean 1.10±0.12 [standard deviation] vs 1.10±0.1) (P=0.799). The mean safety index was similar in group 1 and group 2 (mean 1.10±0.10 [standard deviation] vs 1.10±0.09) (P=0.407). Conclusion: The outcomes were excellent between the two laser suites. There were no significant differences at 6-month follow-up postop between the two laser systems.

Nasal and conjunctival screening prior to refractive surgery: an observational and cross-sectional study

OBJECTIVES

To investigate bacterial flora of clinically healthy conjunctiva and nasal cavity among patients prior to refractive surgery, as well as the characteristics of patients with methicillin-resistant Staphylococcus aureus (MRSA) colonisation.

DESIGN

Observational and cross-sectional study.

SETTING

A single-centre study in Japan.

PARTICIPANTS

120 consecutive patients pre-refractive surgery.

PRIMARY AND SECONDARY OUTCOME MEASURES METHODS

Samples were obtained from the right conjunctival sac and the nasal cavity of 120 consecutive patients prior to refractive surgery and were then measured for the levels of the minimum inhibitory concentration (MIC) of antibiotics. Patients were interviewed regarding their occupation, family living situation and any personal history of atopic dermatitis, asthma, smoking or contact lens wear.

RESULTS

Propionibacterium acnes (P. acnes) (32.5%) and Staphylococcus epidermidis (4.2%) were detected from the conjunctival sac. S. epidermidis was the most commonly isolated (68.3%) in the nasal cavity. Of the 30 patients (25.0%) with colonisation by S. aureus, 2 patients, both of whom were healthcare workers with atopic dermatitis, were found to be positive for MRSA in the nasal cavity. A history of contact lens wear, asthma or smoking, as well as patient gender and age, was not associated with MRSA colonisation.

CONCLUSIONS

There were only 2 patients who were colonised with MRSA, both of whom were healthcare workers with atopic dermatitis. P. acnes was predominantly found in the conjunctival sac. Further study is needed to investigate the involvement between nasal and conjunctival flora, and risk factors for infectious complications.

Ectasia risk factors in refractive surgery

This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient’s age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy.

Opaque Bubble Layer Risk Factors in Femtosecond Laser-assisted LASIK

PURPOSE

To determine the characteristics and risk factors for occurrence of opaque bubble layer (OBL) during femtosecond laser-assisted flap creation for LASIK.

METHODS

One hundred ninety-eight eyes of 102 consecutive patients who underwent LASIK flap creation performed with the Alcon WaveLight FS200 laser (Alcon Laboratories, Inc., Fort Worth, TX) were retrospectively analyzed in a cohort study. Preoperative manifest refraction, corneal keratometry, central corneal thickness, white-to-white corneal diameter, corneal hysteresis, corneal resistance factor, and programmed flaps parameters were collected. Digital images automatically recorded after flap creation were analyzed to measure OBL areas. Correlation tests were performed between preoperative corneal parameters and OBL areas.

RESULTS

The incidence rate of OBL was 48% (103 eyes). The mean OBL area as a percentage of the corneal flap area in the OBL group was 4.25% ± 7.16% (range: 0% to 32.9%). The central corneal thickness, corneal resistance factor, and corneal hysteresis were significantly positively correlated with the OBL area (r = 0.242, P = .001; r = 0.254, P = .028; and r = 0.351, P < .0001, respectively). Corneal hysteresis and OBL area were positively correlated, independently of the central corneal thickness and other confounder factors with standardized coefficient (r = 0.353 ± 0.227, P = .002).

CONCLUSIONS

This study confirms the already known OBL risk factors with a larger cohort and suggests for the first time that an elevated corneal hysteresis is an independent predictive risk for OBL occurrence.