Is the chart you look at while taking an eye exam called a Snellen chart?

The Snellen distance eye chart is the most common kind of visual acuity testing format. It was developed in 1862 by a Dutch ophthalmologist, Herman Snellen so is quite old and arguably out-of-date.

Improved versions are now available, such as the EDTRS or LogMar chart. These use letter sizes that are slightly different than some of the Snellen chart letters (called Optotypes). For example, the EDTRS has a 20/16 line and a 20/32 line, not the Snellen's 20/15 and 20/32. This way, each additional line read will be an equal relative degree of change (1 log unit) in the letters' size between each line. This may not be critical in regular eye exams, but is important in doing statistical analysis of visual acuity changes as in FDA clinical trials. Eventually all distance eye charts will be some LogMar equivalent with standardized background illumination, not currently the case.

_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic