Q: I have an advanced glaucoma patient who seems to be allergic to every drop I put her on. She also has cataracts. What are my options?

A: First, you need to determine whether this is a true allergy to the medicine itself or if it’s toxicity or intolerance to the preservatives in the bottle, says Michael Chaglasian, OD, associate professor at Illinois College of Optometry and chief of staff of the Illinois Eye Institute, in Chicago. 

“Quite often, what seems to be an allergy to glaucoma drops is really irritation and toxicity due to the BAK preservative, which is an ingredient in those medications,” he says. “Also, we know that about 60% of our glaucoma patients have concomitant ocular surface disease, which can be exacerbated by the BAK preservative.”1 

Compounding the problem, many glaucoma patients are on two or more medications, which ups the total amount of BAK going into their eyes, Dr. Chaglasian says. 

So, your first option is to address the ocular surface disease. “If it’s not a true allergy—if it’s a sensitivity or intolerance to the preservative—then treat the underlying dry eye disease and that may improve the patient’s tolerability to the glaucoma meds,” he says. 


Lissamine green staining of the conjunctiva and cornea identifies BAK toxicity from a prostaglandin. This patient was switched to a preservative-free prostaglandin analog. His signs and symptoms of dry eye improved over the next three months.

(On a side note, be sure not to mistake hyperemia, which is often caused by prostaglandins, for an allergy or toxicity. Corneal sensitivity and irritation are the hallmarks of the latter; if they’re not present, it’s likely just hyperemia.)

If treating the underlying dry eye doesn’t do the trick, your next option is to switch the patient to a drop that uses a different preservative or is preservative-free:

Travatan Z (travoprost, Alcon), a prostaglandin analog preserved with Sofzia. 
Alphagan P (brimonidine, Allergan), an alpha-agonist preserved with Purite. 
Zioptan (tafluprost, Akorn), a preservative-free unit-dose prostaglandin analog. 
Cosopt PF (dorzolamide/timolol, Akorn), a preservative-free combination of a carbonic anhydrase inhibitor and a beta blocker. 

 (Timolol is also available in preservative-free unit-dose vials, but it can cost up to four times the amount of these other drugs.)

A third option for this particular patient is the iStent (Glaukos), a tiny stent device inserted into Schlemm’s canal that allows aqueous humor to bypass the blocked trabecular meshwork—a procedure performed only in combination with cataract surgery. 

“The iStent is a great option for the right candidate,” Dr. Chaglasian says. “It’s not for everyone, but it’s a simple, safe procedure that helps to lower intraocular pressure even further than cataract surgery alone.”2

If none of the above options succeed or if the patient is not a cataract candidate, the last option would be selective laser trabeculoplasty to reduce the patient’s number of glaucoma medications and therefore reduce the patient’s reaction, Dr. Chaglasian says.

1. Leung EW, Medeiros FA, Weinreb RN. Prevalence of ocular surface disease in glaucoma patients. J Glaucoma. 2008 Aug;17(5):350-5.
2. Samuelson TW, Katz LJ, Wells JM, et al; US iStent Study Group. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011 Mar;118(3):459-67.