Horgen 2004.

Methods	Randomised controlled trial, 4 groups, parallel
Participants	About 360 visual display unit (VDU) users were drawn from the total workforce of Alcatel Telecom and Nexans Companies in Oslo, of which 158 participated. No information about patient characteristics was provided. Country: Norway
Interventions	Eyeglasses: three different types of specially designed VDU progressive glasses (Interview (Essilor), Gradal HR (Zeiss), Technica (American Optical)) were compared with single vision glasses.
Outcomes	At baseline, after six months and one year: questionnaire concerning visual conditions, working conditions and discomfort in different body areas, based on the Nordic Questionnaire with some additional optometric questions. It also dealt with psychological factors at work and at home. Other outcomes: total wearing time per day and possible confounding factors were documented as well.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of randomisation is not described: "The subjects were divided into four test groups by a stratified randomization procedure".
Allocation concealment (selection bias)	Unclear risk	No information on allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"The subjects were not informed about which type of lens they received, only that the lenses were specially designed for computer work".
Blinding of outcome assessment (detection bias) Primary outcomes	Low risk	"The subjects were not informed about which type of lens they received, only that the lenses were specially designed for computer work". Even though symptoms were self‐reported, participants did not know to which group they belonged.
Blinding of outcome assessment (detection bias) Secondary outcomes	Unclear risk	Unclear who assessed secondary outcome.
Incomplete outcome data (attrition bias) All outcomes	Low risk	"There were nine dropouts in the study". These were equally divided over the four intervention groups. No intention to treat analysis.
Selective reporting (reporting bias)	Unclear risk	No study protocol. All outcomes mentioned in the methods section are reported. All results with 95% confidence intervals are presented in figures.
Other bias	High risk	No information on patient characteristics and possible baseline imbalances. Looking at the presented figures, baseline differences are suspected.