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Queratomileusis in situ asistida por láser (LASIK) con un microquerátomo mecánico en comparación con la LASIK con un láser de femtosegundo para la LASIK en adultos con miopía o astigmatismo miópico

Declaraciones de intereses de los autores

Versión publicada: 07 abril 2020 Historial de versiones

https://doi.org/10.1002/14651858.CD012946.pub2
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Resumen

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Antecedentes

La queratomileusis in situ asistida por láser (LASIK) es un procedimiento quirúrgico que corrige los errores de refracción. Esta técnica crea un colgajo de las partes más externas de la córnea (epitelio, capa de Bowman y estroma anterior) para exponer la parte media de la córnea (lecho estromal) y darle nueva forma con el láser excimer utilizando la fotoablación. Los colgajos pueden ser creados con un microquerátomo mecánico o con un láser de femtosegundo.

Objetivos

Comparar la efectividad y la seguridad del microquerátomo mecánico frente al láser de femtosegundo en la LASIK para adultos con miopía.

Métodos de búsqueda

Se hicieron búsquedas en CENTRAL (que contiene el Registro de Ensayos del Grupo Cochrane de Trastornos de los Ojos y la Visión, Cochrane Eyes and Vision Trials Register) (2019, número 2); Ovid MEDLINE; Embase; PubMed; LILACS; ClinicalTrials.gov y en la International Clinical Trials Registry Platform (ICTRP) de la Organización Mundial de la Salud (OMS). No se aplicaron restricciones de fecha ni de idioma. Se realizaron búsquedas en las listas de referencias de los ensayos incluidos. Se realizaron búsquedas en las bases de datos electrónicas el 22 de febrero 2019.

Criterios de selección

Se incluyeron ensayos controlados aleatorizados (ECA) de la LASIK con un microquerátomo mecánico en comparación con un láser de femtosegundo en pacientes de 18 años de edad o más con más de 0,5 dioptrías de miopía o astigmatismo miópico.

Obtención y análisis de los datos

Se utilizaron los procedimientos metodológicos estándar previstos por Cochrane.

Resultados principales

Se incluyeron 16 registros de 11 ensayos que reclutaron a 943 adultos (1691 ojos) con miopía esférica o esferocilíndrica, que eran candidatos adecuados para la LASIK. Quinientos cuarenta y siete participantes (824 ojos) fueron sometidos a LASIK con un microquerátomo mecánico y 588 participantes (867 ojos) con un láser de femtosegundo. Cada ensayo incluyó entre nueve y 360 participantes. En seis ensayos, los mismos participantes recibieron ambas intervenciones. En general, los ensayos presentaron un riesgo incierto de sesgo en la mayoría de los dominios.

A los 12 meses, los datos de un ensayo (42 ojos) indican que no hay diferencias en la agudeza visual media no corregida (escala logMAR) entre la LASIK con un microquerátomo mecánico y la LASIK con un láser de femtosegundo (diferencia de medias [DM] ‐0,01; intervalo de confianza [IC] del 95%: ‐0,06 a 0,04; evidencia de certeza baja). Se observaron hallazgos similares a los 12 meses después de la cirugía, con respecto a los participantes que lograron 0,5 dioptrías dentro de la refracción objetivo (riesgo relativo [RR] 0,97; IC del 95%: 0,85 a 1,11; 1 ensayo, 79 ojos; evidencia de certeza baja), así como el equivalente esférico medio del error de refracción 12 meses después de la cirugía (DM 0,09; IC del 95%: ‐0,01 a 0,19; 3 ensayos, 168 ojos [92 participantes]; evidencia de certeza baja).

Sobre la base de los datos de tres ensayos (134 ojos, 67 participantes), el microquerátomo mecánico se asoció con un menor riesgo de queratitis laminar difusa en comparación con el láser de femtosegundo (RR 0,27; IC del 95%: 0,10 a 0,78; evidencia de certeza baja). Por lo tanto, la queratitis laminar difusa fue un evento adverso más común con el láser de femtosegundo que con el microquerátomo mecánico, disminuyendo de una tasa supuesta de 209 por 1000 pacientes en el grupo de láser de femtosegundo a 56 por 1000 pacientes en el grupo de microquerátomo mecánico. Los datos de un ensayo (183 ojos, 183 participantes) indican que el ojo seco como evento adverso puede ser más frecuente con el microquerátomo mecánico que con el láser de femtosegundo, aumentando de una tasa supuesta de 80 por 1000 pacientes en el grupo de láser de femtosegundo a 457 por 1000 pacientes en el grupo de microquerátomo mecánico (RR 5,74; IC del 95%: 2,92 a 11,29; evidencia de certeza baja). No hubo evidencia de una diferencia entre los dos grupos para la opacidad corneal (RR 0,33; IC del 95%: 0,01 a 7,96; 1 ensayo, 86 ojos) y el crecimiento epitelial (RR 1,04; IC del 95%: 0,11 a 9,42; 2 ensayos, 102 ojos [51 participantes]). La certeza de la evidencia para ambos resultados fue muy baja.

Conclusiones de los autores

En cuanto a los resultados de la agudeza visual, puede que no haya diferencia entre la LASIK con microquerátomo mecánico y la LASIK con láser de femtosegundo. El ojo seco y la queratitis laminar difusa son eventos adversos probables al utilizar el microquerátomo mecánico y el láser de femtosegundo, respectivamente. No hay evidencia de que la opacidad corneal y el crecimiento epitelial interno sean eventos adversos de cada intervención. El número limitado de resultados informados en los ensayos incluidos, algunos con un riesgo potencialmente significativo de sesgo, hace difícil establecer una conclusión firme con respecto a la efectividad y la seguridad de las intervenciones investigadas en esta revisión.

PICO

Population
Intervention
Comparison
Outcome

El uso y la enseñanza del modelo PICO están muy extendidos en el ámbito de la atención sanitaria basada en la evidencia para formular preguntas y estrategias de búsqueda y para caracterizar estudios o metanálisis clínicos. PICO son las siglas en inglés de cuatro posibles componentes de una pregunta de investigación: paciente, población o problema; intervención; comparación; desenlace (outcome).

Para saber más sobre el uso del modelo PICO, puede consultar el Manual Cochrane.

Eficacia y seguridad de dos tipos de herramientas utilizadas en la LASIK (un tipo de cirugía refractiva) para la miopía

¿Cuál era el objetivo de esta revisión?
El objetivo de esta revisión Cochrane fue evaluar si dos tipos de herramientas para la corrección quirúrgica de la visión (queratomileusis in situ asistida por láser [LASIK]) son efectivas y seguras en pacientes con miopía. Una herramienta utiliza una cuchilla de alta precisión (microquerátomo mecánico) y la otra utiliza ondas infrarrojas (láser de femtosegundo).

¿Qué se estudió en esta revisión?
La miopía es un trastorno médico en el que las personas pueden ver claramente los objetos cercanos, pero los objetos más lejanos les resultan borrosos. En 2010 la miopía afectaba a alrededor de 2 000 000 000 de personas en todo el mundo. La miopía puede ser tratada con gafas, lentes de contacto o cirugía. La cirugía para la miopía cambia la forma de la estructura transparente de la parte frontal del ojo (córnea). La LASIK es el procedimiento quirúrgico utilizado con mayor frecuencia para corregir la miopía.

El procedimiento de LASIK crea un colgajo en la córnea para darle nueva forma. Este colgajo puede hacerse con un microquerátomo mecánico o con un láser de femtosegundo. El microquerátomo mecánico utiliza una cuchilla para crear el colgajo y el láser de femtosegundo utiliza un láser para crear el colgajo. Los colgajos realizados con los dos métodos son diferentes en cuanto a su grosor y estructura, y los efectos secundarios resultantes de cada método también son diferentes. Se recopilaron y analizaron todos los estudios relevantes para responder esta pregunta. Se encontraron 11 estudios que incluían a 943 participantes (1691 ojos).

¿Cuáles fueron los principales resultados?
No hay evidencia de una diferencia en los resultados de la visión entre el uso del microquerátomo mecánico o del láser de femtosegundo. La certeza de la evidencia es baja. Sin embargo, puede haber una diferencia en los efectos secundarios entre los dos métodos. El grupo de microquerátomo mecánico tuvo más casos de ojo seco y el grupo de láser de femtosegundo tuvo más casos de inflamación de la córnea. En general, debido a la evidencia de certeza baja presentada, es difícil establecer una conclusión general sobre la efectividad y la seguridad de estos dos instrumentos.

¿Cuál es el grado de actualización de esta revisión?
Los autores de la revisión buscaron ensayos que se habían publicado hasta el 22 de febrero 2019.

Authors' conclusions

Implications for practice

Based on the findings of this review, there is no evidence of a difference in visual acuity outcomes in laser‐assisted in‐situ keratomileusis (LASIK) with a mechanical microkeratome or a femtosecond laser. Each intervention may be related to a higher risk of adverse events compared to the other; dry eye with the mechanical microkeratome and diffuse lamellar keratitis with the femtosecond laser. These findings should be reviewed by patients and physicians to choose the intervention that best suits their needs.

Implications for research

There is a clear need for future research comparing mechanical microkeratome with femtosecond laser in LASIK. An important number of included trials had unclear or high risk of bias and each outcome explored in this review was not reported in more than three trials. In order to produce trials with low risk of bias with the possibility of comparing patient‐centered outcomes across trials, we recommend future researchers to:

  • involve patients in defining outcomes;

  • clearly describe a random component in the sequence generation process, the method of concealment prior to assignment of participants, and the process of masking participants and evaluators;

  • clearly describe the amount, nature, and handling of incomplete data;

  • specify the funding source;

  • register a protocol and follow the prespecified methods and outcomes;

  • evaluate participants at one, three, six, and 12 months for any outcome (e.g. visual acuity, refractive error, etc.);

  • document and report adverse events;

  • evaluate patient satisfaction and quality of life with a validated instrument (e.g. Quality of Life Impact of Refractive Correction [QIRC] questionnaire) at 12 months after surgery;

  • Describe the planned flap and excimer laser (e.g. wavefront) characteristics; and

  • stratify patients into degrees of myopia (e.g. low, moderate, high).

As noted previously, we observed a higher risk of diffuse lamellar keratitis with the femtosecond laser. The etiology of this sterile inflammation is suggested to be due to any debris on the interface that initiate an inflammatory reaction (Randleman 2012). Theoretically, the absence of metallic debris from the mechanical microkeratome should reduce the risk of this complication, but we observed the contrary in this review. This finding needs further basic and clinical research.

Summary of findings

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Summary of findings 1. 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

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

Patient or population: adults (18 years) with more than 0.5 diopters of myopia or myopic astigmatism
Setting: eye clinic
Intervention: LASIK with a mechanical microkeratome
Comparison: LASIK with a femtosecond laser

Outcomes

Anticipated absolute effects* (95% CI)

Relative effect
(95% CI)

№ of participants
(studies)

Certainty of the evidence
(GRADE)

Risk with LASIK with a femtosecond laser

Risk with LASIK with a mechanical microkeratome

Mean UCVA, 12 months after surgery (unit LogMAR)
Follow‐up: 1 day to 12 months

The mean uncorrected visual acuity after 12 months surgery in the LASIK with a femtosecond laser group was ‐0.04

MD 0.01 lower
(‐0.06 lower to 0.04 higher)

‐

42
(1 RCT)

⊕⊕⊝⊝
Lowa,b

Proportion of eyes within ± 0.5 diopters of target refraction, 12 months after surgery (unit diopters)
Follow‐up: 1 day to 12 months

925 per 1000

897 per 1000
(786 to 1000)

RR 0.97
(0.85 to 1.11)

79
(1 RCT)

⊕⊕⊝⊝
Lowa,b

Mean spherical equivalent of the refractive error, 12 months after surgery (unit diopters)
Follow‐up: 1 day to 12 months

The mean spherical equivalent of the refractive error 12 months after surgery

in the LASIK with a femtosecond laser group ranged from ‐0.30 to ‐0.31

MD 0.09 higher
(‐0.01 lower to 0.19 higher)

‐

168
(3 RCTs)

⊕⊕⊝⊝
Lowa,b

Corneal haze, any time point

23 per 1000

8 per 1000
(0 to 185)

RR 0.33
(0.01 to 7.96)

86
(1 RCT)

⊕⊝⊝⊝
Very lowb,c

Dry eye, any time point

80 per 1000

457 per 1000
(233 to 899)

RR 5.74
(2.92 to 11.29)

183
(1 RCT)

⊕⊕⊝⊝
Lowa,b

Diffuse lamellar keratitis, any time point

209 per 1000

56 per 1000
(21 to 163)

RR 0.27
(0.10 to 0.78)

134
(3 RCTs)

⊕⊕⊝⊝
Lowa,b

Epithelial ingrowth, any time point

20 per 1000

20 per 1000
(2 to 185)

RR 1.04
(0.11 to 9.42)

102
(2 RCTs)

⊕⊝⊝⊝
Very lowb,c

*The risk in the intervention group (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).

CI: confidence interval; MD: mean difference; RCT: randomized controlled trial; RR: risk ratio; UCVA: uncorrected visual acuity.

GRADE Working Group grades of evidence
High‐certainty: we are very confident that the true effect lies close to that of the estimate of the effect.
Moderate‐certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.
Low‐certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect.
Very low‐certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

aDowngraded one level due to imprecision.
bDowngraded one level due to risk of bias.
cDowngraded two levels due to very serious imprecision.

Background

Description of the condition

Refractive errors are an important cause of vision impairment and blindness (Holden 2016). Myopia (nearsightedness) is a type of refractive error that causes blurry vision at distance because abnormal structural conditions of the cornea, lens, or length of the eye prevent the images from focusing properly on the retina (Riordan‐Eva 2011). Myopia affected 1.95 billion people worldwide in 2010 (Holden 2016), with a higher prevalence in urban areas (Morgan 2012). The global economic burden generated by myopia has been estimated at USD 202 billion per annum (Smith 2009), and approximately USD 139 billion in the USA alone (NASEM 2016).

Description of the intervention

Refractive errors can be corrected through non‐surgical (eyeglasses and contact lenses) and surgical methods. The surgical methods are long‐lasting treatments that are used when a person becomes intolerant to contact lenses, encounters visual aberration from high‐powered spectacles, or desires to eliminate or reduce their dependence on glasses or contact lenses (Azar 2002). The eye is an optical system with a refractive power that can be changed by altering the curvature of its refractive surface or the location of elements of the system. Intraocular implants, such as intraocular lenses, can be used to correct refractive errors; however, the most common refractive surgeries performed in the USA are keratorefractive techniques. Keratorefractive surgeries are a group of techniques that modify the refractive power of the cornea by changing its curvature. These techniques include photorefractive keratectomy, laser subepithelial keratomileusis, intrastromal lenticule extraction, and laser‐assisted in‐situ keratomileusis (LASIK) (Bower 2001).

Due its safety and efficacy profile, LASIK is more popular compared with other surgeries. 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 (Ang 2009). LASIK comprises the creation of a corneal flap with an intended diameter that ranges from 7.8 mm to 9.8 mm and a thickness of 90 μm to 180 µm. The flap can be achieved by a mechanical microkeratome or a femtosecond laser (Farjo 2013). The mechanical microkeratome uses an oscillating blade to create the corneal flap (Bower 2001), while the femtosecond laser creates the flap with a focusable photodisruptive laser that delivers ultrashort (10–15 seconds) pulses with a wavelength within the infrared spectrum in a preset pattern (Lubatschowski 2000). This laser ionizes the tissue, causing molecular disruption within the cornea. The beam is focused on a small spot, creating electrically charged particles through multiphotonic absorption which release electrons from the atoms by a process known as avalanche ionization (Azar 2006). The free electrons transfer their energy to the surrounding medium, evaporating the adjacent tissue and forming cavitation bubbles consisting of carbon dioxide, nitrogen, and water (Bashir 2017). When the cavitation bubbles expand, they produce a regular and precise dissection of the corneal flap (Farjo 2013; Huhtala 2016; Sales 2016). The main differences between femtosecond and microkeratome flaps are the thickness and architecture. This Cochrane Review focused on the use of femtosecond laser or mechanical microkeratome in LASIK to correct myopia.

How the intervention might work

The femtosecond laser has some theoretical advantages over the use of a mechanical microkeratome in LASIK. For instance, the thickness of flaps created with the mechanical microkeratome have a significant variation (25 μm to 250 µm) compared with the femtosecond laser (78 μm to 173 µm). The predictability of the procedure to create a flap could be an important factor in the biomechanical integrity of the cornea (Flanagan 2003). Complications associated with the mechanical microkeratome are free or incomplete flaps, buttonholes, and epithelial erosions (Azar 2006). These complications are less common with the femtosecond laser, because it dissects in patterns that allow variation of flap width, depth, and diameter that may lead to better surgical results (Ang 2009; Gil‐Cazorla 2011; Issa 2011; Medeiros 2011). Other proposed benefits of the femtosecond laser use in LASIK are better uncorrected visual acuity (UCVA) (Gil‐Cazorla 2011), lower intraocular pressure during the procedure (Chaurasia 2010), and a lower incidence of dry eye (Salomão 2009).

The creation of the corneal flap with a mechanical microkeratome is free of some complications specific to LASIK with femtosecond laser, such as vertical gas breakthrough, anterior chamber bubbles, and opaque bubble layer (Azar 2006; Courtin 2015; Gatinel 2013; Moshirfar 2010; Stonecipher 2006). Another advantage of the mechanical microkeratome over the femtosecond laser is that it is fully reusable after dismantling and sterilization (the blade is the only single use part of the device), and there is no need to switch the patient to the excimer laser; these factors lower the overall cost of the procedure (Azar 2019). Other reported benefits of the mechanical microkeratome are lower risks of developing corneal haze (Patel 2008), transient light sensitivity (Stonecipher 2006), diffuse lamellar keratitis (Moshirfar 2010), and rainbow glare (Gatinel 2013).

Why it is important to do this review

The number of people with myopia globally is projected to increase to 4.76 billion by 2050 (Holden 2016). The trend has important economic (Corcoran 2015) and public health implications (NASEM 2016). LASIK is one of the most common surgical procedures used to correct refractive errors (Bower 2001). Femtosecond laser technology are often used in high‐income countries, while the mechanical microkeratome are used in low‐income countries (Salomao 2010). Both procedures have some advantages and disadvantages over the other, some of which are controversial (Ang 2009; Azar 2006; Bashir 2017; Farjo 2013). Therefore, it is important to evaluate the comparative effectiveness and safety of both procedure for myopia.

Objectives

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

Methods

Criteria for considering studies for this review

Types of studies

We included randomized controlled trials (RCTs). We did not restrict trial inclusion based on language or publication status.

Types of participants

People aged 18 years or older with more than 0.5 diopters of myopia or myopic astigmatism.

Types of interventions

We included trials that compared mechanical microkeratome with femtosecond laser in LASIK.

Types of outcome measures

Primary outcomes

  • Mean uncorrected visual acuity (UCVA) at 12 months after surgery. We used logMAR for visual acuity analyses.

Secondary outcomes

  • Mean UCVA at one and three months after surgery

  • Mean best corrected visual acuity (BCVA) at one, three, and 12 months after surgery

  • Proportion of eyes within ± 0.5 diopters of target refraction at one and 12 months after surgery

  • Proportion of eyes with loss of two or more lines of BCVA at 12 months after surgery

  • Mean spherical equivalent of the refractive error, measured in diopters, at one and 12 months after surgery

  • Intraoperative and postoperative pain at one day and one week, assessed with any validated measurement scale

  • Quality of life measures, assessed with any validated measurement scale at any point within follow‐up

Adverse outcomes

We considered adverse outcomes as reported by included trials up to 12 months after surgery. Specific adverse outcomes of interest were the following.

  • Corneal haze

  • Dry eye

  • Visual symptoms (double images, glares, halos, starburst)

  • Flap displacement

  • Flap melt

  • Diffuse lamellar keratitis

  • Infectious keratitis

  • Epithelial ingrowth

  • Corneal ectasia

Search methods for identification of studies

Electronic searches

The Cochrane Eyes and Vision Information Specialist (Lori Rosman) searched the following electronic databases for randomized controlled trials. There were no restrictions on language or year of publication. The electronic databases were last searched on 22 February 2019.

  • Cochrane Central Register of Controlled Trials (CENTRAL; 2019, Issue 2) (which contains the Cochrane Eyes and Vision Trials Register) in the Cochrane Library (searched 22 February 2019; Appendix 1).

  • MEDLINE Ovid (1946 to 22 February 2019; Appendix 2).

  • Embase.com (1947 to 22 February 2019; Appendix 3).

  • PubMed (1948 to 22 February 2019; Appendix 4).

  • LILACS (Latin American and Caribbean Health Science Information Database (1982 to 22 February 2019; Appendix 5).

  • US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (www.clinicalTrials.gov; searched 22 February 2019; Appendix 6).

  • World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp; searched 22 February 2019; Appendix 7).

Searching other resources

We searched the reference lists of reports from trials we included in the review to look for additional trials. We did not conduct manual searches of conference proceedings or abstracts specifically for this review.

Data collection and analysis

Selection of studies

Two review authors (NKL, AN) assessed the titles and abstracts of articles identified through the literature search against inclusion criteria (listed in the Criteria for considering studies for this review section) and independently classified these as 'definitely relevant', 'possibly relevant', or 'definitely not relevant'. We used Covidence software to manage the screening process (Covidence). Any disagreement was resolved by a third review author (EGH). We obtained the full‐text copies of all trials classified as 'definitely relevant' or 'possibly relevant'. Each review author independently assessed each trial for inclusion and labeled it as either 'include' or 'exclude'. We contacted the authors of the primary trials via email for clarification whenever necessary. If there was no response within three weeks, we assessed the trial based on the information available. A third review author (EGH) resolved any disagreement. We documented the reason for exclusion of each trial excluded after reviewing the full report in a Characteristics of excluded studies table. We used Google Translate to assess trials written in languages other than English and Spanish. We used a PRISMA flowchart to depicts the flow of information through the different phases of the systematic review (Moher 2009).

Data extraction and management

Two review authors (NKL, AN) independently extracted data from the included trials using data extraction forms developed by Cochrane Eyes and Vision and accessed via Covidence (Appendix 8). A third review author (EGH) resolved any disagreements. We contacted authors of the primary trials via email to obtain missing information or to clarify data. We waited three weeks for a response; in the absence of a response, we used the available information, as provided in published reports. One review author (NKL) entered data into Review Manager 5 (Review Manager 2014), and a second review author (AN) verified the data entered.

Assessment of risk of bias in included studies

Two review authors (NKL, AN) evaluated the risk of selection (random sequence generation and allocation concealment before randomization), performance (masking of trial participants and personnel), detection (masking of outcome assessors), attrition (missing data and absence of an intention‐to‐treat analysis), reporting (selective outcome reporting), and other potential sources of bias using the Cochrane 'Risk of bias' assessment tool as described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2017). We classified the risk of bias as 'low', 'high', or 'unclear' (insufficient information for assessment). We contacted authors of the primary trials when methods were unclear or when additional information about trial design or methods was required to assess the risk of bias. We waited three weeks for a response; in the absence of a response, we assessed the risk of bias based on descriptions provided in published reports. A third review author (EGH) resolved any disagreement between review authors.

Measures of treatment effect

We calculated mean differences (MDs) with 95% confidence intervals (CIs) for continuous outcomes such as mean UCVA after surgery, BCVA after surgery, and mean spherical equivalent of refractive error after surgery. For dichotomous outcomes (e.g. proportion of eyes within 0.5 diopters of target refraction after surgery), we calculated risk ratios (RRs) with 95% CIs. We used logMAR (logarithm of the minimum angle of resolution) for the outcomes that included visual acuity.

Unit of analysis issues

The participant was the primary unit of analysis whenever: only one eye per participant was enrolled in the trial; or two eyes of a participant were treated as a single unit after being administered the same treatment (e.g. mean values, binocular visual acuity). If neither of these conditions was met, the eye was considered the unit of analysis. If two eyes of the same participant were randomized to two different interventions, the correlation between the two eyes must be accounted for in the analysis; and in such case, we would only use the results that have accounted for this correlation.

Dealing with missing data

We contacted trial authors to obtain missing data or data reported unclearly in the trial reports. We allowed three weeks for trial authors to respond and used the available information whenever there was no response. We did not impute missing participant data for analysis.

Assessment of heterogeneity

We compared the participant characteristics, trial interventions, and outcomes across trials to assess for clinical and methodological heterogeneity. We used a visual inspection of forest plots and Chi² test statistics to assess statistical heterogeneity among estimates of effect size from the included trials. We used the I² statistic, which estimates the proportion of variation in observed effects not due to chance, to identify inconsistency among trials; an I² statistic value greater than 50% represented substantial heterogeneity (Higgins 2017).

Assessment of reporting biases

We did not perform a meta‐analysis with 10 or more trials, therefore a visual inspection of funnel plots of the intervention effect estimates for evidence of asymmetry was not meaningful. An asymmetric funnel plot may suggest small‐study effects, which could be the result of reporting bias, heterogeneity, or differences in the methodological quality of trials. We assessed selective outcome reporting as part of the 'Risk of bias' assessment among individual trials.

Data synthesis

We combined the effect estimates from individual trials using the random‐effects model when trials had no substantial clinical or methodological heterogeneity.

Subgroup analysis and investigation of heterogeneity

There were insufficient data from the trials to examine findings by the degree of myopia at baseline among the trial participants: low to moderate myopia (less than 6.0 diopters) and high myopia (6.0 diopters or more).

Sensitivity analysis

We performed sensitivity analyses for primary and secondary outcomes to explore the effects of restricting our analyses to trials in which the authors received no financial compensation from the industry. We also performed a sensitivity analysis for the trials that had at least 80% follow‐up of participants in each group in the trials with high risk of bias and to explore the effects of fixed‐effect versus random‐effects meta‐analyses. Post hoc, we planned to conduct a sensitivity analysis to examine the effects of restricting our analyses to trials for which the unit of analysis was the patient (one eye per participant) or trials that used paired‐eye design and accounted for correlation between the two eyes in their analysis. However, we did not perform this because the only meta‐analysis performed involved only two trials, both of which were paired‐eye design and did not report whether they accounted for correlation between the two eyes in their analysis.

Summary of findings

We summarized the findings of the review using the GRADE approach to assess the strengths and limitations of evidence for both primary and secondary outcomes using the GRADEpro Guideline Development Tool (GDT) software (GRADEpro 2015). Using this approach, we classified the evidence for each outcome as 'high', 'moderate', 'low', or 'very low' and documented reasons for our judgments. We included the following seven outcomes in summary of findings Table 1.

  • Mean UCVA, 12 months after surgery

  • Proportion of eyes within ± 0.5 diopters of target refraction, 12 months after surgery

  • Mean spherical equivalent of the refractive error, 12 months after surgery

  • Corneal haze, at any time point

  • Dry eye, at any time point

  • Diffuse lamellar keratitis, at any time point

  • Epithelial ingrowth, at any time point

In our protocol, we planned to include the following outcomes in this review, but there were insufficient data to include them in the 'Summary of findings' table.

  • Proportion of eyes with loss of two or more lines of BCVA, 12 months after surgery

  • Postoperative pain, within one week after surgery

  • Quality of life score, 12 months after surgery

Results

Description of studies

Results of the search

As of February 2019, the electronic searches resulted in 6560 titles and abstracts (Figure 1). After removal of duplicates, we screened 4802 records from which we identified 74 trials for full‐text review. We then excluded 57 records after full‐text review because they were either non‐randomized trials (56 records) or did not compare a femtosecond laser with a mechanical microkeratome (1 record). We classified one study as ongoing. There were five records from the Patel_group 2010 and two records from the Manche_group 2008. Overall, we included 16 records from 11 trials that met the inclusion criteria for the review (see Characteristics of included studies table).

Figure 1
Trial flow diagram.

Trial flow diagram.

Included studies

Participant selection

All included trials enrolled adults (aged > 18 years old) with spherical or spherocylindrical myopia who were suitable candidates for Laser‐assisted in‐situ keratomileusis (LASIK) after examination (Buzzonetti 2008; Durrie 2005; Gui‐Hong 2018; Hasimoto 2013; Manche_group 2008; Patel_group 2010; Salomão 2009; Tan 2007; Tran 2005; Zhai 2013; Zhou 2012).There were 943 participants (1691 eyes) enrolled across all trials; 547 participants (824 eyes) received LASIK with a mechanical microkeratome and 588 participants (867 eyes) received LASIK with a femtosecond laser. Each trial included between 9 and 360 participants. Six trials randomized one eye to one intervention and the fellow eye to another (Durrie 2005; Hasimoto 2013; Manche_group 2008; Patel_group 2010; Tan 2007; Tran 2005). The trials were conducted in the USA (5 trials), China (3 trials), and one each conducted in Brazil, Italy and Singapore. Preoperative refraction of participants was up to 7.50 diopters of sphere and 3 diopters of cylinder. The year of publication ranged from 2005 to 2018, with follow‐up time between one day and five years.

Interventions

Trials included in this review assigned participants to receive LASIK with a mechanical microkeratome or a femtosecond laser. One trial randomized 81 participants (161 eyes) into three intervention groups (Zhai 2013), of which two of the three intervention arms involving 60 participants (117 eyes), were relevant to this review. Three trials did not report review specific outcomes of interest (Tan 2007; Zhai 2013; Zhou 2012), therefore we did not include them in the analysis. The remaining eight trials included 482 participants (772 eyes) enrolled across all trials; 270 participants (365 eyes) received LASIK with a mechanical microkeratome and 312 participants (407 eyes) with a femtosecond laser. Among the eight trials that reported review specific outcomes of interest, two trials used a parallel‐trial design (Buzzonetti 2008; Gui‐Hong 2018), and six trials used a within‐person trial design (Durrie 2005; Hasimoto 2013; Manche_group 2008; Patel_group 2010; Salomão 2009; Tran 2005). All eight trials were similar in treatment setting.

Outcomes

Three trials reported the mean uncorrected visual acuity (UCVA) after surgery (Durrie 2005; Gui‐Hong 2018; Patel_group 2010). One trial reported best corrected visual acuity (BCVA) after surgery (Patel_group 2010). Five trials reported the mean spherical equivalent of the refractive error after surgery (Buzzonetti 2008; Durrie 2005; Gui‐Hong 2018; Manche_group 2008; Patel_group 2010), two of these trials reported proportion of eyes within 0.5 diopters of target refraction after surgery (Durrie 2005; Manche_group 2008). Four trials reported adverse events (Hasimoto 2013; Manche_group 2008; Salomão 2009; Tran 2005). We considered the methods used to measure the outcomes to be consistent across trials. None of the trials assessed proportion of eyes with loss of two or more lines of BCVA from preoperative visual acuity, pain, quality of life, visual symptoms, flap displacement, flap melt, infectious keratitis, or corneal ectasia.

Funding sources

Four trials reported source of funding. One trial was funded by the IRCCS‐Casa Sollievo della Sofferenza Hospital and Institue of Ophthalmology of Catholic University (Buzzonetti 2008), another was funded by the National Institutes of Health, Research to Prevent Blindness, and the Mayo Foundation (Patel_group 2010). Salomão 2009 was supported by US Public Health Service grants from the National Eye Institute, and Research to Prevent Blindness. IntraLase Corp funded one trial (Tran 2005), and the remaining seven trials did not report funding sources.

Ongoing Study

We identified one ongoing trial (PACTR201708002498199).

Excluded studies

We reviewed and excluded 57 records. We described the reasons for exclusion in the Characteristics of excluded studies table.

Risk of bias in included studies

A summary of the risk of bias for included trials is presented in Figure 2 and a risk of bias graph is presented in Figure 3.

Figure 3
Risk of bias graph: review authors' judgments about each risk of bias item presented as percentages across all included trials

Risk of bias graph: review authors' judgments about each risk of bias item presented as percentages across all included trials

Allocation

We judged four trials at low risk of bias for random sequence generation because the trial investigators described a random component in the sequence generation process (Durrie 2005; Hasimoto 2013; Manche_group 2008; Zhou 2012). The remaining seven trials did not specify the method for randomization, therefore, we judged the risk to be unclear (Buzzonetti 2008; Gui‐Hong 2018; Patel_group 2010; Salomão 2009; Tan 2007; Tran 2005; Zhai 2013).

Two trials reported using sealed and opaque envelopes to conceal treatment allocation (Hasimoto 2013; Manche_group 2008), and we judged them at low risk of bias. The remaining nine trials did not describe the method of allocation concealment and we judged them at unclear risk of bias

Blinding

One trial specified masking of both participants and trial personnel (Manche_group 2008), and another reported masking of participants (Hasimoto 2013), and we judged them at low risk of bias. Patel_group 2010 stated that "it was not possible to mask patients…", therefore we judged this trial at high risk of bias. The remaining trials included in the review did not specify how masking of participants and personnel was achieved and we judged them at unclear risk of bias.

Three trials described adequate masking of the outcome assessors (Durrie 2005; Hasimoto 2013; Patel_group 2010), and we judged them at low risk of detection bias. The remaining eight trials did not provide a clear description of the measures used to mask outcome assessors or did not address this issue, therefore, we judged them at unclear risk of bias.

Incomplete outcome data

We judged five trials at low risk of bias; Patel_group 2010, Durrie 2005, and Salomão 2009 reported no missing outcome data. Manche_group 2008 described missing outcome data that we considered balanced in numbers across intervention groups with similar reasons for missing data across the two groups. Tran 2005 reported one amblyopic eye that was dropped from the analysis; we considered that reason for missing data unlikely to be related to the outcomes being explored in the review.

Hasimoto 2013 reported missing outcome data of three participants (6 eyes), one participant (2 eyes) had a head trauma (intervention group was not specified), another participant (1 eye) presented with diffuse lamellar keratitis (femtosecond laser group), and one other participant (1 eye) presented with bleeding from limbal vessels (intervention group was not specified). We considered the missing outcome data likely to be related to true outcomes, therefore we judged this trial at high risk of bias.

The remaining five trials had insufficient reporting of incomplete outcome data and we judged them at unclear risk of bias.

Selective reporting

Outcomes reported in the different reports of the Patel_group 2010 were not prespecified in trial registration, therefore we judged it at unclear risk of bias. We also judged the remaining 10 trials at unclear risk of bias for selective reporting because we did not identify trial protocols.

Other potential sources of bias

Two trials declared financial compensations from the industry directly related to one of the intervention groups (Durrie 2005; Tran 2005), and we judged them to be at high risk of other bias. The remaining trials appear to be free from other sources of bias, and we judged them at low risk for other bias.

Effects of interventions

See: Summary of findings 1 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

See: summary of findings Table 1

Mean uncorrected visual acuity (UCVA) after surgery

One trial provided data of 42 eyes for the primary outcome (Patel_group 2010). The mean difference (MD) of UCVA at 12 months after surgery was –0.01, (95% confidence interval (CI) –0.06 to 0.04). Three trials provided data from 192 eyes for the mean UCVA at one month (Durrie 2005; Gui‐Hong 2018; Patel_group 2010) (MD 0.13, ‐0.08 to 0.33). Two trials provided data of mean UCVA at three months after surgery (Durrie 2005; Patel_group 2010). There was low statistical heterogeneity between the two trials, the I² statistic was 0% and the Chi² test for heterogeneity was not statistically significant (P = 1.00). Therefore, we combined the data of UCVA at three months in a meta‐analysis (72 eyes). The observed MD of UCVA was 0.00 (95% CI –0.03 to 0.03; Analysis 1.1; Figure 4). We did not perform an overall UCVA analysis because two groups included data from the same trial and were based on two clinically different time points. The certainty of evidence for this outcome across the various trials was low; we downgraded for risk of bias and imprecision.

Figure 4
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.1 Mean uncorrected visual acuity after surgery [logMAR].

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.1 Mean uncorrected visual acuity after surgery [logMAR].

Proportion of eyes within ± 0.5 diopters of target refraction after surgery

Data from the trial by Manche_group 2008 comprised 79 eyes and found that the proportion of eyes 0.5 diopters within target refraction was 3% lower after LASIK with mechanical microkeratome 12 months after surgery: risk ratio (RR) 0.97, 95% CI 0.85 to 1.11; low‐certainty evidence; Analysis 1.2; we downgraded for risk of bias and imprecision. Two other trials with 125 participants (Durrie 2005; Patel_group 2010), reported the proportion of eyes within 0.5 diopters of target refraction after LASIK one month after surgery. We combined the data of the two trials because heterogeneity was low, the I² statistic was 0% and the Chi² test for heterogeneity was not statistically significant (P = 0.67). There was no difference between LASIK with a mechanical microkeratome or a femtosecond laser of achieving 0.5 diopters within target refraction one month after surgery (Analysis 1.2; Figure 5). We did not perform an overall analysis because the groups were based on two clinically different time points. However, the certainty of evidence for this outcome across the various time points and trials was low; we downgraded for risk of bias and imprecision.

Figure 5
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.2 Proportion of eyes within ± 0.5 diopters of target refraction after surgery.

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.2 Proportion of eyes within ± 0.5 diopters of target refraction after surgery.

Mean spherical equivalent of the refractive error after surgery

Durrie 2005, Patel_group 2010, and Gui‐Hong 2018 reported mean spherical equivalent of refractive error one month after surgery. There was considerable heterogeneity (I² = 96%, Chi² test for heterogeneity was statistically significant, P < 0.0001) thus, rendered a summary of the pooled effect estimate inappropriate. Point estimates from the three trials showed no evidence of a difference between the two groups: Durrie 2005 (102 eyes, 51 participants); MD 0.40, 95% CI 0.29 to 0.51; Gui‐Hong 2018: (240 eyes, 120 participants); MD –0.01, 95% CI –0.05 to 0.03; Patel_group 2010: (42 eyes, 21 participants); MD –0.06, 95% CI –0.24 to 0.12; Analysis 1.3; Figure 6). However, data from Durrie 2005, which seem to be an outlier, indicate that participants undergoing femtosecond LASIK seem to do better in spherical equivalent of the refractive error. The possible explanation probably has to do with the flap thickness predictability and biomechanics of the corneal flap, which is more efficiently created with the femtosecond laser, and has low spherical aberrations compared to microkeratome LASIK (Bashir 2017). The certainty of evidence across the included trials was low; we downgraded for risk of bias and imprecision.

Figure 6
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.3 Mean spherical equivalent of the refractive error after surgery [diopters].

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.3 Mean spherical equivalent of the refractive error after surgery [diopters].

Three trials reported mean spherical equivalent of refractive error 12 months after surgery (Buzzonetti 2008; Manche_group 2008; Patel_group 2010; 168 eyes, 92 participants). We combined the data of the three trials in a meta‐analysis and observed no evidence of a difference in mean spherical equivalent of refractive error between the two groups (MD 0.09, 95% CI –0.01 to 0.19; I² = 0%; Analysis 1.3; Figure 6). The certainty of evidence was low; we downgraded for risk of bias and imprecision.

Corneal haze

Based on the trial by Manche_group 2008 (86 eyes), the RR of corneal haze was 77% lower with the mechanical microkeratome group compared with the femtosecond laser group (RR 0.33, 95% CI 0.01 to 7.96; Figure 7). The certainty of evidence was very low; we downgraded for risk of bias and very serious imprecision.

Figure 7
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.4 Corneal haze.

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.4 Corneal haze.

Dry eye

The trial by Salomão 2009 (183 eyes, 183 participants) had a RR of 5.74 for the participants assigned to the mechanical microkeratome group compared with the femtosecond laser group (95% CI 2.92 to 11.29; Figure 8). The certainty of evidence was low; we downgraded for risk of bias and imprecision. The trial by Manche_group 2008 described a self‐reported mean dry eye score at preoperative, and one, three, six, and 12 months postoperative time points. We did not include the trial in the quantitative synthesis because 100% of the participants reported dry eye preoperatively. The findings reflected an increase in the mean dry eye score postoperatively in the femtosecond laser group one month after surgery (P = 0.02), the score returned to baseline by six months after surgery. The certainty of evidence was low; we downgraded for risk of bias and imprecision.

Figure 8
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.5 Dry eye.

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.5 Dry eye.

Diffuse lamellar keratitis

Manche_group 2008, Hasimoto 2013, and Tran 2005 (134 eyes, 67 participants) reported diffuse lamellar keratitis. We combined the data of the trials in a meta‐analysis since there was no heterogeneity (I² = 0%, Chi² P = 0.89). The RR for the participants assigned to the mechanical microkeratome group was 73% lower compared with the femtosecond laser group (RR 0.27, 95% CI 0.10 to 0.78; Analysis 1.6; Figure 9). The certainty of evidence was low; we downgraded for risk of bias and imprecision.

Figure 9
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.6 Diffuse lamellar keratitis.

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.6 Diffuse lamellar keratitis.

Epithelial ingrowth

Two trials reported epithelial ingrowth (Manche_group 2008; Tran 2005; 102 eyes, 51 participants). We combined data in a meta‐analysis and observed a RR of 1.04 for the participants assigned to the mechanical microkeratome group compared with the femtosecond laser group (95% CI 0.11 to 9.42; I² = 0%; Analysis 1.7; Figure 10). The certainty of evidence was very low; we downgraded for risk of bias and very serious imprecision.

Figure 10
Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.7 Epithelial ingrowth.

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.7 Epithelial ingrowth.

Sensitivity analysis

The results of the sensitivity analyses of the trials in which the authors received financial compensation from the industry, trials that had at least 80% follow‐up of participants in each group, or trials with high risk of bias, or the use of fixed‐effect versus random‐effects meta‐analysis showed no difference in the findings (data not shown).

Discussion

Summary of main results

We included 16 reports of 11 trials in this review representing 943 participants (1691 eyes). The trials allocated adults 18 years and older, with spherical or spherocylindrical myopia considered suitable candidates for Laser‐assisted in‐situ keratomileusis (LASIK) after examination, to a mechanical microkeratome group or a femtosecond laser group. Based on our assessment of the trials that reported uncorrected visual acuity (UCVA), there was no evidence of a difference in UCVA after LASIK in eyes with the flap created by a femtosecond laser compared to eyes with the flap created by a mechanical microkeratome. There was also no evidence of a difference between the two treatments in terms of achieving within 0.5 diopters of target refraction or in mean spherical equivalent of refractive error 12 months after surgery. The association between corneal haze and epithelial ingrowth with the interventions was uncertain. We observed a lower risk of diffuse lamellar keratitis in the mechanical microkeratome group compared with the femtosecond laser group when combining the results of three trials. Only one trial reported dry eye after the intervention. This trial showed that there may be a higher risk of dry eye in the mechanical microkeratome compared to the femtosecond laser group. We found no trials that reported proportion of eyes with loss of two or more lines of best corrected visual acuity (BCVA) from preoperative visual acuity, pain, quality of life, visual symptoms, flap displacement, flap melt, infectious keratitis, or corneal ectasia. These findings were robust to our sensitivity analysis.

Overall completeness and applicability of evidence

The trials included in the review were not substantially heterogeneous from a clinical point of view. We considered that the trials identified were not sufficient to address all the objectives of the review. For instance, relevant outcomes such as, quality of life, proportion of eyes with loss of two or more lines of BCVA from preoperative visual acuity, as well as intraoperative and postoperative pain should have been investigated.

Potential biases in the review process

Two review authors independently assessed the titles and abstracts and full‐text reports of potentially eligible trials; a third review author resolved any conflicts. The extraction of data and assessment of risk of bias for all trials included in this review were done in the same manner. During the review process, we changed four outcomes in the 'Summary of findings' table specified in the protocol due to insufficient data available from the trials. All outcomes incorporated in summary of findings Table 1 were prespecified secondary outcomes in the protocol. We are aware of no other potential biases in the review process.

Certainty of the evidence

We graded five outcomes reported in summary of findings Table 1 at low‐certainty evidence and two at very low‐certainty evidence. All the trials that reported the seven outcomes had serious risk of bias and we downgraded them. We also downgraded the certainty of evidence of all the adverse events outcomes due to serious or very serious concerns related to imprecision in the results. We identified trial registration in only one trial and there were inconsistencies between trial outcomes defined in the protocol and those reported in the trial publications. Two trials were sponsored by companies related to one of the interventions under investigation and had roles in the design or analysis of these trials (Durrie 2005; Tran 2005). Some investigators reported financial relationships with the company.

Agreements and disagreements with other studies or reviews

Chen 2012 published one systematic review and meta‐analysis comparing IntraLase femtosecond laser versus mechanical microkeratomes in LASIK for myopia. The purpose of the review was to evaluate the safety, efficacy, and predictability of the two interventions. The trials included were randomized and non‐randomized trials. The primary outcomes were loss of more than two lines of corrected distance visual acuity, uncorrected distance visual acuity 20/20 or better, manifest refraction spherical equivalent within 0.50 diopters, final refractive spherical equivalent, and astigmatism. The secondary outcomes were flap thickness predictability, changes in higher‐order aberrations, and complications.

The trial investigators concluded the results showed no differences in visual acuity‐related outcomes between the IntraLase group and the mechanical microkeratomes group. These findings are consistent with the results of this review. Regarding complications, Chen 2012 reported higher events of diffuse lamellar keratitis in the femtosecond laser group, higher risk of loose epithelium in one or two quadrants in the group of mechanical microkeratome, and no significant difference in epithelial ingrowth between groups. Our results were consistent with a higher risk of diffuse lamellar keratitis in the femtosecond laser group as we observed a RR that was 73% lower in the mechanical microkeratome group compared with the femtosecond laser group (Analysis 1.6; Figure 9). Concerning intraoperative epithelial defects, we did not include this adverse event in our prespecified outcomes, therefore, we did not include it in the review. The findings of Chen 2012 regarding epithelial ingrowth were consistent with those presented in this review (Figure 10).

Trial flow diagram.

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Figure 1

Trial flow diagram.

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original image

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Figure 2
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Risk of bias graph: review authors' judgments about each risk of bias item presented as percentages across all included trials

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Figure 3

Risk of bias graph: review authors' judgments about each risk of bias item presented as percentages across all included trials

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.1 Mean uncorrected visual acuity after surgery [logMAR].

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Figure 4

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.1 Mean uncorrected visual acuity after surgery [logMAR].

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.2 Proportion of eyes within ± 0.5 diopters of target refraction after surgery.

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Figure 5

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.2 Proportion of eyes within ± 0.5 diopters of target refraction after surgery.

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.3 Mean spherical equivalent of the refractive error after surgery [diopters].

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Figure 6

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.3 Mean spherical equivalent of the refractive error after surgery [diopters].

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.4 Corneal haze.

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Figure 7

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.4 Corneal haze.

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.5 Dry eye.

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Figure 8

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.5 Dry eye.

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.6 Diffuse lamellar keratitis.

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Figure 9

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.6 Diffuse lamellar keratitis.

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Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.7 Epithelial ingrowth.

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Figure 10

Forest plot of comparison: 1 LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, outcome: 1.7 Epithelial ingrowth.

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 1: Mean uncorrected visual acuity after surgery

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Analysis 1.1

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 1: Mean uncorrected visual acuity after surgery

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 2: Proportion of eyes within ± 0.5 diopters of target refraction after surgery

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Analysis 1.2

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 2: Proportion of eyes within ± 0.5 diopters of target refraction after surgery

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 3: Mean spherical equivalent of the refractive error after surgery

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Analysis 1.3

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 3: Mean spherical equivalent of the refractive error after surgery

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 4: Corneal haze

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Analysis 1.4

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 4: Corneal haze

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 5: Dry eye

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Analysis 1.5

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 5: Dry eye

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 6: Diffuse lamellar keratitis

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Analysis 1.6

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 6: Diffuse lamellar keratitis

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 7: Epithelial ingrowth

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Analysis 1.7

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 7: Epithelial ingrowth

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Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 8: Best corrected visual acuity after surgery

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Analysis 1.8

Comparison 1: LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser, Outcome 8: Best corrected visual acuity after surgery

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Summary of findings 1. 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

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

Patient or population: adults (18 years) with more than 0.5 diopters of myopia or myopic astigmatism
Setting: eye clinic
Intervention: LASIK with a mechanical microkeratome
Comparison: LASIK with a femtosecond laser

Outcomes

Anticipated absolute effects* (95% CI)

Relative effect
(95% CI)

№ of participants
(studies)

Certainty of the evidence
(GRADE)

Risk with LASIK with a femtosecond laser

Risk with LASIK with a mechanical microkeratome

Mean UCVA, 12 months after surgery (unit LogMAR)
Follow‐up: 1 day to 12 months

The mean uncorrected visual acuity after 12 months surgery in the LASIK with a femtosecond laser group was ‐0.04

MD 0.01 lower
(‐0.06 lower to 0.04 higher)

‐

42
(1 RCT)

⊕⊕⊝⊝
Lowa,b

Proportion of eyes within ± 0.5 diopters of target refraction, 12 months after surgery (unit diopters)
Follow‐up: 1 day to 12 months

925 per 1000

897 per 1000
(786 to 1000)

RR 0.97
(0.85 to 1.11)

79
(1 RCT)

⊕⊕⊝⊝
Lowa,b

Mean spherical equivalent of the refractive error, 12 months after surgery (unit diopters)
Follow‐up: 1 day to 12 months

The mean spherical equivalent of the refractive error 12 months after surgery

in the LASIK with a femtosecond laser group ranged from ‐0.30 to ‐0.31

MD 0.09 higher
(‐0.01 lower to 0.19 higher)

‐

168
(3 RCTs)

⊕⊕⊝⊝
Lowa,b

Corneal haze, any time point

23 per 1000

8 per 1000
(0 to 185)

RR 0.33
(0.01 to 7.96)

86
(1 RCT)

⊕⊝⊝⊝
Very lowb,c

Dry eye, any time point

80 per 1000

457 per 1000
(233 to 899)

RR 5.74
(2.92 to 11.29)

183
(1 RCT)

⊕⊕⊝⊝
Lowa,b

Diffuse lamellar keratitis, any time point

209 per 1000

56 per 1000
(21 to 163)

RR 0.27
(0.10 to 0.78)

134
(3 RCTs)

⊕⊕⊝⊝
Lowa,b

Epithelial ingrowth, any time point

20 per 1000

20 per 1000
(2 to 185)

RR 1.04
(0.11 to 9.42)

102
(2 RCTs)

⊕⊝⊝⊝
Very lowb,c

*The risk in the intervention group (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).

CI: confidence interval; MD: mean difference; RCT: randomized controlled trial; RR: risk ratio; UCVA: uncorrected visual acuity.

GRADE Working Group grades of evidence
High‐certainty: we are very confident that the true effect lies close to that of the estimate of the effect.
Moderate‐certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.
Low‐certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect.
Very low‐certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

aDowngraded one level due to imprecision.
bDowngraded one level due to risk of bias.
cDowngraded two levels due to very serious imprecision.

Figuras y tablas -
Summary of findings 1. 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
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Comparison 1. LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1.1 Mean uncorrected visual acuity after surgery Show forest plot

3

Mean Difference (IV, Random, 95% CI)

Subtotals only

1.1.1 At 1 month

3

384

Mean Difference (IV, Random, 95% CI)

0.13 [‐0.08, 0.33]

1.1.2 At 3 months

2

144

Mean Difference (IV, Random, 95% CI)

0.00 [‐0.03, 0.03]

1.1.3 At 12 months

1

42

Mean Difference (IV, Random, 95% CI)

‐0.01 [‐0.06, 0.04]

1.2 Proportion of eyes within ± 0.5 diopters of target refraction after surgery Show forest plot

3

Risk Ratio (IV, Random, 95% CI)

Subtotals only

1.2.1 At 1 month

2

144

Risk Ratio (IV, Random, 95% CI)

0.87 [0.77, 0.99]

1.2.2 At 12 months

1

79

Risk Ratio (IV, Random, 95% CI)

0.97 [0.85, 1.11]

1.3 Mean spherical equivalent of the refractive error after surgery Show forest plot

5

Mean Difference (IV, Random, 95% CI)

Subtotals only

1.3.1 At 1 month

3

384

Mean Difference (IV, Random, 95% CI)

0.11 [‐0.18, 0.40]

1.3.2 At 12 months

3

168

Mean Difference (IV, Random, 95% CI)

0.09 [‐0.01, 0.19]

1.4 Corneal haze Show forest plot

1

Risk Ratio (IV, Random, 95% CI)

Totals not selected

1.4.1 Any time point

1

Risk Ratio (IV, Random, 95% CI)

Totals not selected

1.5 Dry eye Show forest plot

1

Risk Ratio (IV, Random, 95% CI)

Totals not selected

1.5.1 Any time point

1

Risk Ratio (IV, Random, 95% CI)

Totals not selected

1.6 Diffuse lamellar keratitis Show forest plot

3

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

1.6.1 Any time point

3

134

Risk Ratio (M‐H, Random, 95% CI)

0.27 [0.10, 0.78]

1.7 Epithelial ingrowth Show forest plot

2

Risk Ratio (IV, Random, 95% CI)

Subtotals only

1.7.1 Any time point

2

102

Risk Ratio (IV, Random, 95% CI)

1.04 [0.11, 9.42]

1.8 Best corrected visual acuity after surgery Show forest plot

1

126

Mean Difference (IV, Fixed, 95% CI)

‐0.01 [‐0.04, 0.02]

1.8.1 At 1 month

1

42

Mean Difference (IV, Fixed, 95% CI)

0.00 [‐0.05, 0.05]

1.8.2 At 3 months

1

42

Mean Difference (IV, Fixed, 95% CI)

0.00 [‐0.05, 0.05]

1.8.3 At 12 months

1

42

Mean Difference (IV, Fixed, 95% CI)

‐0.03 [‐0.09, 0.03]
Figuras y tablas -
Comparison 1. LASIK with a mechanical microkeratome versus LASIK with a femtosecond laser
Ir a la tabla de la revisión