为什么这个preg_match不起作用

I need valid numbers between 0.00000001 and 999. I used preg_match:

preg_match('/^[0-9]{1,3}(\.[0-9]{1,8})?$/',0.0000339);

But I don't understand why it doesn't work. If I write a number: 0.0001 it work but 0.00001 or 0.0000001 it doesn't work and 0.11111111 returns true. You can test http://writecodeonline.com/php/ Why?

It work:

$number = 0.0000001; 
echo preg_match('/^[0-9]{1,3}(\.[0-9]{1,8})?$/',"$number");