Holz 1993.

Methods	Parallel group RCT Method of allocation: not known Masking: participant ‐ yes; provider ‐ yes; outcome ‐ yes Losses to follow‐up: not known
Participants	Country: UK Number of people randomised: 58 (eyes not known) Number (%) of people followed up: not known Average age (range): 68 years (55 to 82) Percentage women: not known Ethnic group: not known Baseline visual acuity: not known Comorbidities affecting the eye: not known Percentage current smokers: not known
Interventions	Intervention: zinc sulfate 200 mg (daily) 2 x 100 mg tablet 28 people randomised (eyes not known) unknown number people followed up (eyes not known) Comparator: placebo (lactose capsule) 2 x 1 tablet daily 30 people randomised (eyes not known) unknown number people followed up (eyes not known) Duration: 12 to 24 months Similarity between intervention and comparator: not known
Outcomes	Primary: not known Secondary: not known Quote: "Parameters tested included visual acuity, peripheral and macular colour‐contrast‐sensitivity; pattern ERG and dark adaptation. Stereo fundus photographs and fluorescein angiograms were analyzed by investigators in a masked fashion using a standardized grading scheme" Follow‐up: 12 to 24 months Eyes: unclear
Notes	Data available from abstract only: Source of funding: Gertrud‐Kusen‐Stiftung, Hamburg, grant # Ho92/93‐01‐2 Declaration of interest: not known Date study conducted: not known Trial registration number: not known
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomised double‐blind study"
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) Visual acuity	Unclear risk	"randomised double‐blind study"
Blinding of participants and personnel (performance bias) Progression AMD	Unclear risk	"randomised double‐blind study"
Blinding of outcome assessment (detection bias) Visual acuity	Unclear risk	"randomised double‐blind study"
Blinding of outcome assessment (detection bias) Progression AMD	Low risk	"randomised double‐blind study" "Stereo fundus photographs and fluorescein angiograms were analyzed by investigators in a masked fashion using a standardized grading scheme"
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not reported
Selective reporting (reporting bias)	High risk	For visual acuity, trial report states that outcome was analysed but only reports that result was not significant