The visual acuity examination is affected by the contrast between the background of the optotype used
and the letter. Changes in contrast result in unstable visual acuity and affect the examination results
subjectively. The writing of this paper uses a descriptive method using a variety of literature data, one
of which is by David Cline, John R. Hofstetter and Henry W., Griffin, with the title. Dictionary Of
Visual Science, Fourth Edition which explains that contrast in Snellen's optotype affects visual acuity.