ok thanks for the link. i have one question- if i guess the letters that are 20/60 and it is right, does it mean im 20/60 even though it is blurry? or do u have to see the letters clearly to say that u can see it propaly? If u know what i mean :
If I remember correctly, if you get 1/2 of letters on the line right, that's a passing line. Maybe others can confirm?
That's about where I started too, 20/60, yes, they still were blurry to me too.
I'm now between 20/50 and 20/40.
As I understand the normal vision is about 20/15 and 20/20 is average. This is equivalent to a resolution of 1 minute of arc. In other words, the healthy eye can reliably resolve an object that subtends an angle of one minute ( equals 1/60 degrees) at the eye. For an idea, the sun has a visual angular diameter of 31 minutes and the moon has 30 minutes. Most stars have much less than 1/60 of a minute but are still visible because they are sources of light.
If you do the calculations , 1 arc minute works out to a width of approx 1.7 mm at 20 feet. The letters chosen on the Snellen chart are five times this width. Thus. the letters on the 20 line of the Snellen chart are 1.7mm thick and 8.5 mm tall. You can easily make a Snellen chart yourself by calculating the appropriate 30 lines, 40 lines etc.
I believe the standard is that you must read 1/2 the letters correctly to pass the line.
Quote:ok thanks for the link. i have one question- if i guess the letters that are 20/60 and it is right, does it mean im 20/60 even though it is blurry? or do u have to see the letters clearly to say that u can see it propaly? If u know what i mean
In fact, even people at 20/20 will have some blur on the line -- thus the standard of reading 1/2 letters correctly.
Also, the DMV "relaxed" the standard (because so few ordinary people could pass the 20/20 line). Thus they changed
the standard to 20/60 (for Georgia), 20/50 for Texas, and 20/40 for almost all the other states. This is
a matter of reading the chart with both eyes open. Further, the specification sometimes reads that
the better eye must read 20/40.
Also, to "callibrate" your chart for 20 feet -- you should verify that the 20/60 line is 1 inch high.
Obviously at 10 feet the "20/60" line would be 1/2 inch high at that distance.
it is also of value to check outdoors in sunlight.
Hope this clarifies this issue of self-testing your eyes.
