By altering the /openemr/interface/forms/eye_mag/SpectacleRx.php file, you can add the extra text you desire.
My suggestion would be to do something like this around line 751:
replace
<br /><br />
with :
<div style="margin: 0px auto;width: 90%;text-align: center;">
<?php
if ($REFTYPE=='CTL') {
echo xlt('Contacts RX expires in one year.');
} else {
echo xlt('Spectacle RX expires in two years.');
}
?>
</div>
The xlt is the translation engine should anyone use this in another language.
Ray
N.B. I had to edit this reply - as email it mangled the code lines…