Professor Snellen's Standard Test letters for testing vision.
Licence: Attribution 4.0 International (CC BY 4.0)
Credit: Professor Snellen's Standard Test letters for testing vision. Wellcome Collection. Source: Wellcome Collection.
Licence: Attribution 4.0 International (CC BY 4.0)
Credit: Professor Snellen's Standard Test letters for testing vision. Wellcome Collection. Source: Wellcome Collection.