What is the correct distance to keep your eyes from the computer screen ?

Depends: Keep a distance that allows you ease of reading without undue strain both closer or farther away.

There is none: The best distance is that which is most comfortable for you. Some people prefer to be slightly closer, while others prefer to be further back from the monitor. There is no risk for eye damage from modern screens, although staring for long period can cause strain and dry eyes. The key is regular breaks to relax the eyes, and glasses and lubricant eye drops if needed for best comfort.