Photina Hedges Losing Leaves?

I have a row of red tip Photina hedges that are losing their leaves rather rapidly. Most years they stay evergreen with the red tips and may occasionally shed a few leaves. I just noticed they are almost bare now and beginning to look rather dead. What could be the problem? Should I cut them back in hopes they'll regrow? They are over 4 years old and at least 7' tall if not taller. Thanks for your input.

Hardiness Zone: 9a

By Nelwyn Mills from Bunkie, LA