I've had glaucoma in both eyes for 25 years. I was using eyedrops to control the pressure. But about six years ago, I developed rising pressures and redness, as well as itching, in the eyes. It was thought that I had an allergy to the preservatives in the drops. I was put on Timoptic Preservative-Free drops. This worked very well. Now, I am told that Merck has stopped making this product. Are there any other preservative-free drops out there?

L.L.

Manufacturers put preservatives into bottles of various kinds of eyedrops to prevent the growth of bacteria that could lead to infection. It is thought that the more frequently the drops are used, the greater the risk of patients developing ocular allergies to such preservatives. Because people with severe, dry eyes use artificial tears up to 10-20 times a day, they frequently develop preservative allergies and must turn to preservative-free drops.

In contrast, glaucoma medications are usually used once or twice a day, so allergies to preservatives in glaucoma drops are relatively uncommon. However, if an allergy does develop, glaucoma patients such as yourself have a variety of options -- of which preservative-free Timoptic was just one. The first choice is for your doctor to switch to a similar type of glaucoma medication made by a different company, which may use a different type of preservative that doesn't trigger an allergic reaction in your eyes. Timoptic is a beta-blocker. Similar medications made by different manufacturers include Betimol, Betagan or the generic drug timolol.

In addition, there has been an explosion in the choices of glaucoma medications since you developed your allergy six years ago. New medications include Alphagan, Trusopt, Azopt and Xalatan. These medications work to lower eye pressure differently than Timoptic, and they have fewer systemic side effects than Timoptic.

If it turns out that you are allergic to all types of glaucoma eyedrops, you may want to consider a laser treatment called argon laser trabeculoplasty (ALT). This procedure is very safe, and it lowers the eye pressure to a similar extent as Timoptic. Unfortunately, the effects of the laser treatment seem to wear off after five years or so.

The final option for people who cannot tolerate eyedrops and who do not respond to laser treatment is traditional glaucoma surgery. Glaucoma surgery can effectively lower one's eye pressure, but it does come with a number of risks, including infection and development of cataracts. Your next step should be to see your ophthalmologist to discuss your many options.