Add "Appendix" before "A" in thesis TOC

I am required to insert the word Appendix before the letter A in my dissertation Table of Contents as follows:

Appendix A (title for appendix A)

but the latex thesis cls file I use generates only the letter A followed by the appendix title:

A (title for appendix A)

The thesis cls file defines a "backmatter" command and the appendix is treated as a chapter.

\newcommand\backmatter{\appendix
\def\chaptermark##1{\markboth{%
\ifnum  \c@secnumdepth > \m@ne  \@chapapp\ \thechapter:  \fi  ##1}{%
\ifnum  \c@secnumdepth > \m@ne  \@chapapp\ \thechapter:  \fi  ##1}}%
\def\sectionmark##1{\relax}}

Is there a simple fix to the above code that will add the word Appendix before the letter A in the TOC for Appendix A? There is a related question, How to make 'appendix' appear in toc in Latex?, but the answers did not appear to help in this case.