Bachman 1992.

Methods	Cross‐over randomised controlled trial
Participants	29 respondents to an advertisement in the university’s weekly newspaper that asked for presbyopic volunteers who worked at a visual display terminal (VDT) for 20 or more hours per week. Mean age 52.3 years, range 42 to 64 Male/Female: 7/22 Mean time spent at a VDT per day: 5.52 hours ± 1.25 (SD?) (type of computer not described) Refractive error: range of spherical power: +4.75 to −4.75 dpt; range of cylinders: 0 to −2.75 dpt Country: USA
Interventions	Eyeglasses: progressive addition glasses were compared with flat top bifocal glasses in n = 26 participants and with single vision glasses in n = 3 participants, each type of eyeglasses was worn for a period of 4 weeks, followed by a direct comparison for 1 week.
Outcomes	At baseline and during each intervention period patients reported the effect of the intervention on symptoms (headache, eyestrain, back pain, neck pain, nausea and dizziness). Other aspects that were judged by the patients were: clarity of VDU screen work and desk work (paper and other objects), adjustments in position required to see clearly, utility of distance vision, usefulness away from the desk. At the end of the study (week 9) overall preference (intervention or control lens) was assessed. Participants took several measurements at their work station and viewing angle to computer screen was calculated.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised, yet method of randomisation not described.
Allocation concealment (selection bias)	Unclear risk	No information about concealment of allocation.
Blinding of participants and personnel (performance bias) All outcomes	High risk	No information on blinding, however blinding is not possible due to the type of intervention.
Blinding of outcome assessment (detection bias) Primary outcomes	High risk	Participants, who are unblinded, are the outcome assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data of all participants for all outcomes were reported.
Selective reporting (reporting bias)	Unclear risk	No study protocol. However, all outcomes stated in methods were reported at results section of the publication.
Other bias	Low risk	No indication of other bias.