Jaschinski 2015b.

Methods	Cross‐over randomised controlled trial
Participants	23 employees of a tax office, who habitually used general purpose progressive glasses for their office work and indicated higher ocular and musculoskeletal strain in a questionnaire as part of a previous field study. Mean age 55 (standard deviation 4) years; range: 46 to 61 Male/Female: 10/13 Mean daily duration of work (primarily at the computer) 7.9 ± 1.6 hours (range 4 to 10 hours) Refractive error: spherical component was −0.90 ± 2.66 D averaged across the two eyes (range −6.25 D = +4.00 D); cylindrical refraction −0.90 ± 0.69 D (range 0 to −2.75 D); additional power for near 2.06 ± 0.41 D (range 1.00 D to 2.50 D) Country: Germany
Interventions	Eyeglasses: progressive computer glasses vs. general purpose progressive glasses. Participants switched glasses every week over a one‐month period , followed by a period of eight more weeks of free use of the spectacles.
Outcomes	Participant‐reported symptoms of asthenopia at the end of the working day, weekly administration of questionnaire during first four weeks of intervention period. Daily administration of subset of presumably most relevant questions during third and fourth week, the actual test period of the study.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Author correspondence: "the random assignment was produced by the software EXCEL".
Allocation concealment (selection bias)	Low risk	Author correspondence: "The random order was not generated by the experimenters of our research Institute, but by the company ZEISS, that participated in the study. The experimenters were not informed of the assignment of the type of lens to the participants".
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"Neither the experimenters nor the participants were aware of this assignment to ensure a double‐masked condition as much as possible. We intended for the participants to evaluate the two types of lenses purely based on their perception and experience without being influenced by information about the features and purposes of these lenses. The experimenters were neutral, as they were not informed about the type of lenses and did not communicate with the participants about the lenses; however, it was almost inevitable that participants noticed the blurred distance vision with the computer vision PALs, which can occur when looking outside the window. These conditions cannot be avoided, if realistic office conditions are to be investigated."
Blinding of outcome assessment (detection bias) Primary outcomes	Low risk	See Blinding of participants.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Cross‐over study of 23 participants, no information about lost to follow‐up or incomplete outcome data.
Selective reporting (reporting bias)	Unclear risk	No study protocol or trial registration; results were reported for more outcomes than were listed in Methods section of the publication.
Other bias	Low risk	No indication of other bias.