Snellen chart
Snellen chart: history of visual acuity testing from Hooke to ETDRS, with key milestones, optotype design, and contributions from Snellen, Donders, Sloan
Tag Snellen fraction
Herman Snellen
Herman Snellen (1834–1908): Dutch ophthalmologist who created the Snellen chart and standardized visual acuity testing, transforming eye care worldwide