Zhou 2012.

Study characteristics
Methods	Study design: randomized controlled trial Study grouping: parallel group Number randomly assigned: 720 eyes, 360 participants Exclusions after randomization: Number analyzed: 720 eyes, 360 participants Unit of analysis: eye Losses to follow‐up: not reported Handling of missing data: not reported Power calculation: not reported Study dates: December 2009 to July 2010
Participants	Country: China Overall mean age: 25.91 years (SD 5.03) Age range: not reported Gender: not reported Setting: Ophthalmic Center, Beijing Tongren Hospital, Capital Medical University Equivalence of baseline characteristics: yes Inclusion criteria: not reported Exclusion criteria: patients with ocular pathologies such as keratoconus, corneal scars, corneal dystrophies, previous ocular surgery, glaucoma, diabetes, or other systemic diseases known to affect the eye were excluded
Interventions	Laser for ablation: Visx S4 excimer laser Intervention 1 Intervention: LASIK with a M2 Moria Microkeratome Flap dimensions: 110 μm thickness, 8.5 mm diameter, superior hinge Number of people randomized: 360 eyes, 180 participants Length of follow‐up: Planned: not reported Actual: 1 week Intervention 2 Intervention: LASIK with an Ziemer LDV femtosecond laser Flap dimensions: 110 μm thickness, 8.5 mm diameter, superior hinge Number of people randomized: 360 eyes, 180 participants Length of follow‐up: Planned: not reported Actual: 1 week
Outcomes	Central corneal flap thickness Intervals at which outcome assessed: 1 day, 3 days, and 1 week. Planned follow‐up: not reported Actual follow‐up: 1 week Scale: μm Instrument for measurement: RTVue OCT system Mean corneal flap thickness Intervals at which outcome assessed: 1 day, 3 days, and 1 week. Planned follow‐up: not reported Actual follow‐up: 1 week Scale: μm Instrument for measurement: RTVue OCT system Nasal and temporal flap thickness Intervals at which outcome assessed: 1 day, 3 days, and 1 week. Planned follow‐up: not reported Actual follow‐up: 1 week Scale: μm Instrument for measurement: RTVue OCT system Flap dimensions and regularity Intervals at which outcome assessed: 1 day, 3 days, and 1 week. Planned follow‐up: not reported Actual follow‐up: 1 week Scale: μm Instrument for measurement: RTVue OCT system Flap thickness accuracy Intervals at which outcome assessed: 1 day, 3 days, and 1 week. Planned follow‐up: not reported Actual follow‐up: 1 week Scale: μm Instrument for measurement: RTVue OCT system
Identification	Sponsorship source: not reported Country: China Setting: Institute of Ophthalmology Comments: none Author's name: Yuehua Zhou Institution: Ophthalmic Center, Beijing Tongren Hospital Email: yh0220@yahoo.com Address: No. 1 Dongjiaomin Ln, Dongchong District, Beijing, China 100730
Notes	Trial registration number: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Based on a randomization table, 180 patients were assigned to the Ziemer LDV (FS laser group) and 180 patients were assigned to the Moria M2 (microkeratome group) for bilateral LASIK"
Allocation concealment (selection bias)	Unclear risk	Comment: method of concealment not described
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: masking of participants and trial personnel not reported
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: masking of outcome assessors not reported
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: no missing outcome data
Selective reporting (reporting bias)	Unclear risk	Comment: no published trial protocol with which to compare
Other bias	Low risk	Comment: trial appeared free of other sources of bias

BCVA: best corrected visual acuity; D: diopter; IOP: intraocular pressure; LASIK: laser‐assisted in‐situ keratomileusis; SD: standard deviation; UCVA: uncorrected visual acuity.