When giving a snellen test, how many letters is the person allowed to miss and still "pass" a line?

Answer 1

Well, for the most part, patients are allowed to miss two letters and still pass that line. However, when dealing with the first three lines, I would make sure that they are correctly answering a majority of the line.

For example, if they miss two letters on the third line, which only has three letters, then they have only answered 33% of the line correctly. I wouldn't count this as passing. The same thing applies to the second line. If they miss two letters, they missed the entire line. This is totally objective, but I would have them move up another line if they missed two on any of the first three lines.

Answer 2

2

Answer 3

Snellen Chart (age 6 years and up)
- check with glasses on (except glasses for reading only)
- heels on line 20'
- occlude the open left eye first
- must read all letters on line above red line
- may miss 2 letters on 20/30 and 20/20 lines
- record last line read correctly
- Do not isolate letters – show whole line

PASS: 20/30 or better without a 2-line difference

RESCREEN: 20/40 or worse or 2–line difference

REFER: Same as rescreen. Don’t refer if 2-line difference has already been evaluated by an eye professional
http://www.health.state.mn.us/divs/fh/mch/hlth-vis/materials/cuesnellen.html