Table 3 Overview of the included studies
From: Effects of caffeine intake on pupillary parameters in humans: a systematic review and meta-analysis
Study | Study design | Blinding method | Within- or between-subjects design | Sample size | Abstinence duration (in hours) | Method of administration | Caffeine dosing | Type of control | Results |
|---|---|---|---|---|---|---|---|---|---|
Redondo et al. [38] | Crossover study | Double-blind | Within-subjects | 22 | 12 | Oral (capsule) | 4Â mg/kg | Baseline measurement and Placebo | Caffeine significantly increased pupil size compared to placebo |
Lanini et al. [39] | Randomised, placebo-controlled, independent-group design study | Double-blind | Between-subjects | 60 | 12 | Oral (capsule) | Habitual breakfast dose of caffeine (Ranged between 25 and 300Â mg) | Baseline measurement and Placebo | Baseline difference in pupil size between groups; no interaction with time |
Abokyi et al. [40] | Double-blind, placebo-controlled, randomised crossover experimental design | Double-blind | Within-subjects | 50 | 168 | Oral (drink) | 250 mg | Baseline measurement and Placebo | Pupil diameter increased from 3.4 (± 0.4 mm) at baseline to 4.5 (± 0.72 mm) at 90 min |
Krueger et al. [41] | Placebo-controlled, within-subject design | Simple-blind | Within-subjects | 5 | 24 | Oral (drink) | 350Â mg caffeine/75Â kg bodyweight | Baseline measurement and Placebo | No influence of caffeine on pupil dilation caused by pain |
Wilhelm et al. [44] | Open study design | No blinding | Within-subjects | 20 | 9 | Oral (drink) | Caffeine content of 86.85 mg per cup (about 1–1.5 mg/kg) | Baseline measurement | Caffeine caused a reduction of pupillary unrest index (PUI) |
Bardak et al. [42] | Non-randomised design | No blinding | Within-subjects | 30 | 12 | Oral (drink) | 57Â mg | Baseline measurement | tendency of increased pupil size in the caffeine group |
Nicholson et al. [43] | Randomised controlled trial (RCT) | Double-blind | Within-subjects | 6 | 32 | Oral (ingestion) | 300Â mg | Baseline measurement and placebo | No significant changes in pupil size |