Michel, for Windows based installations, its DLL files added to extension directory in PHP, I have seen no issue with PHP 5.5 or even 5.6, in fact there was a small issue (segfault running with moodle) with opcache, and the team behind opcache fixed that for moodle and that is to be included in next coming version of PHP 5.5 and 5.6 with opcache version 7.0.5.
On the link below, you'll find PHP 5.3 and 5.4 with opcache DLL's, all you have to do is download the files and add .dll file to your ext directory. in addition tot that, you'll be adding these lines of code in your PHP.INI file, save it and restart your Apache.
You can change the above values as per your requirement (like increasing memory consumption etc), but these values I have written are default recommended when firing up zend opcache, so even keeping these values will bring substantial improvement.
for opcache version 7.0.3, you can go to this link
for opcache version 7.0.4
for opcache version 7.0.5 (being latest with Moodle bug fixed)
http://windows.php.net/downloads/pecl/releases/opcache/7.0.5/ (only available for 5.3 and 5.4)
Be assured you are downloading NTS (Non-Thread Safe) version, limitation is for 5.3 and 5.4 versions there isnt x64 available.
Just to be assured PHP is now working and enabled in your PHP, open your PHP INFO file in your browser, and you'll see Zend Opcache's logo and settings showing up.
if you'd been using the WIMP combo (I as in IIS) then I could have assisted you more, but on Linux and Apache, my hands are bound, I am pure windows person.