Bulging eyes

Our 10 yr old German Shepard just developed bulging eyes.  (7) days prior to us noticing this problem, he was put on Trimethaprim 480mg 1.5 times per day for an anal gland infection.  In conjuction with the bulging eye issue, he was having difficulty walking and was very weak.  Upon returning to the Vet, he tested positive for anaplasma, which he previously showed no signs of.  The vet did a battery of blood and urine tests and all have come back normal - thyroid, kidney function, white and red blood cell count, diabetes, glaucoma etc - all negative.  He did not check for hypertension.
The vet said that the bulging eyes could be a result of pain, but I don't think this is it.  Any thoughts on what we should check for?  He is a very active for his age.
Thanks!

[Aleda M Cheng, D.V.M., C.V.A]

The antibiotic that your dog has been taking for the anal gland infection, Trimethoprim sulfa  can cause a condition called Dry Eye (Keratoconjunctivitis sicca, aka - KCS) in certain dogs.  The medication has the effect of decreasing tear production and the eye could look bulgy,  but, it would also look cloudy and irritated.  This problem can reverse itself once this antibiotic is discontinued, but sometimes the problem is permanent.  There is a very effective treatment for Dry Eye, even if it permanent.  German Shepherds usually don't have this problem, with this antibiotic, and it is uncommon even in the breeds predisposed to developing it, therefore, it is unlikely but still a possibility.

Older dogs eyes tend to begin to look like they bulge due to aging.  The cornea's in older dogs look cloudy and slighly bluish due to nuclear sclerosis or lenticular degeneration, which are just benign aging changes, and usually do not affect the dog's vision very much, but these changes are very gradual and don't show up suddenly in one weeks time.

Dog's eye's can also bulge due to glucoma, which in your dog was not the case, luckily.  Another cause is a tumor behind the eyes that pushes the globe's out, however these tumors are rarely symmetrical, in that both eyes usually do not bulge equally.

Anaplasmosis infection could make your dog weak and sometimes anemic and should be treated with doxycycline.

If your vet is unable to sort this out,  I would ask your vet for a referral to veterinary opthamologist.  Good Luck!