Dr. Don Steensma 465 W. Channel Islands Blvd, Port Hueneme, CA 805/486-3585

Vision Self-Test







The top row is 75 pixels high.  The second row is 50 pixels high.  The bottom row is 25 pixels high.  Different computer screens will display the letters in different absolute height, so an adjustment must be made for your monitor to display the letters the right size.  On a standard eye chart at 20 feet, the 20/20 letter is 8.75 mm high (round off to 9 mm for this purpose).

Method #1

Measure the height of the letters in the top row in mm. (Remember 1 inch=254 mm).

Use the Control key on the keyboard with the Scroll key on the mouse to size your computer for a 20 foot view.  Try to get as close to 27 mm. for the height of the top row, thus creating a 9 mm. bottom row.  Now the top row is 20/60, the middle row is 20/40 and the bottom row is 20/20.

Method #2

Measure the height of the letters in the top row in mm. (Remember 1 inch=254 mm).

Use the table below to find the correct distance to test at depending on the size of the top row.

Size of letters in top row in millimeters Test distance in feet
32 mm 23.5 ft
31 mm. 23.0 ft
30 mm. 22.2 ft
29 mm. 21.5 ft
27 mm. 20.0 ft
26 mm. 19.3 ft
25 mm. 18.5 ft
24 mm. 17.8 ft
23.mm. 17.0 ft

Or use the top line letter height in mm. divided by 1.35 to get the correct test distance in feet.

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