Logged in user sees only their own replies.
It is definitely possible...
Open include/staff/viewticket.inc.php
Find this code...
<table align="center" class="response" cellspacing="0" cellpadding="1" width="100%" border=0>
Directly ABOVE, paste in this code....
<? if ($thisuser->getName() == $resp_row){?>
Next find this code...
<tr><td> <?=Format:($resp_row)?></td></tr>
</table>
Directly AFTER, add this code...
<? } ?>
Now logged in user sees only their own replies. This method could also be applied to notes, etc. :