About Snellen chart?

Question

1) what is the distance from the Snellen chart where i sat and took the test?

2) is 20/20 applicable to night vision?

3) what happened if i failed the 1st 3 rows of the chart (screen generated by machine)

4) I can't see the 3 row (smallest characters) with my left eye but I can with my right eye, am I still consider 20/20?

5) What can i do to improve my vision? (frankly does looking over the green grass etc help?)

6) Been able to read the newspapers or books at my 'arm length' is this considered normal? Or half of my arm length instead?

7) reference the snellen chart : what does rows 9,10,11 means?

9) by having 20/20 basically at standing 20 feet from an object, what are words (minimum height) I likely to read clearly?


http://en.wikipedia.org/wiki/Image:Snellen.svg

Answer 1

1) It depends on the testing set up. Ask the person who tested you. Charts are available for various distances.

2) Acuity is measured with a bright chart when the eye is light adapted. If you wanted to know you dark adapted acuity, you will need to find someone doing research on night acuity who would have a special apparatus for testing that. Humans do not have good night vision, unlike dogs and cats, our eyes do not have special structures that allow for good night vision.

3) Again, charts vary. You will have to ask the person who tested you what acuity level the first three rows measured.

4) Again, you will have to ask the person who tested you what acuity level the smallest row measured and what acuity your eyes each have.

5) Do you mean improve so that you don't need glasses? There are no proven ways to reduce or eliminate refractive error. If you have a specific eye disease that you want to improve, you will have to ask your eye doctor if there is a cure or treatment.

6) Depends on your age. After age 40 it is normal to begin to need reading glasses for closer reading distances.

7) Again, depends on the chart used. Ask the tester.

9) With 20/20 vision and standing 20 ft away, you should be able to just barely read letters just under an inch high.