From what I've read, it's usually benign...but in rare cases can cause vision loss. I'm posting some links.
But, remember all of the pharma antibiotics (not just the tetracycline class) we take come with their own 'list' of side effects/risks.
Here's a few links:
www.medsafe.govt.nz/profs/puarticles/bih.htm/www.drugs.com/sfx/doxycycline-side-effects.htmlwww.webmd.com/drugs/2/drug-8773-7073/doxycycline-monohydrate-oral/doxycycline---oral/details#side-effects