How do I use pre_option_{option_name} correctly?

I am using a filter to decrypt an api_key that is stored with encryption. I have registered the following hook:

// Decrypt API key after it is retrieved
add_filter('pre_option_percify_api_key', array( __CLASS__, 'decrypt_api_key') );

The problem is, I cannot get at the stored value in the callback:

public static function decrypt_api_key($encrypted) {
  // $encrypted is empty:

  echo($encrypted);
  // ...

Am I calling the function correctly? How do I access the stored value of percify_api_key within decrypt_api_key?