Glaucoma Treatment Doesn't Mean Just Adding Medication
BY LEO SEMES, OD, FAAO
A 62-year-old female presented for a second opinion regarding her left eye. She had been told that she had severe glaucoma and that the visual deterioration may be due to a tumor.
Her contributory ophthalmic history included cataract surgery with IOL (OS) one year ago and retinal detachment repair (OS) three or four years ago, secondary to vehicular trauma. For openangle glaucoma she was currently taking the following topical ophthalmic medications: Timoptic, (Merck, timolol 0.5%) b.i.d., Cosopt (Merck, 0.5% timolol and 2% dorzolamide), Xalatan (Pfizer, 0.005% latanoprost) b.i.d. and Lumigan (Allergan, 0.03% bimatoprost) b.i.d. in each eye!
The best visual acuity (VA) was obtained with minimal astigmatic correction in each eye and measured 20/20 and 20/80. Clinical observation estimated that at least 50 percent of the reduced VA in the right eye was due to posterior capsular opacification. The intraocular pressure (IOP) at 11 a.m. on the day of the examination was 15mmHg in each eye.
A Look at the Medications
Apparently the two physicians who had seen this patient did not look carefully at her medications. Instead, they just added additional drops when a target IOP was not achieved or when evidence of apparent progression was observed. Let's look at the lineup.
The combination of a prostaglandin analog (PA) in the evening and a beta-blocker in the morning makes sense. The PA has its peak effect between eight and 12 hours. The onset of action of the beta-blocker is about two hours. When taken in this combination, the objective is to maintain constant and low IOP throughout the 24-hour diurnal cycle and to minimize the typical early morning IOP peak. This pattern doesn't hold for everyone, but it serves as a guideline.
Another reason to use this combination for patients who may not respond to a single agent initially (usually a PA) is mechanisms of action. The major action of a PA is uveoscleral outflow enhancement. Recent evidence suggests that there may be some influence at the level of the trabecular meshwork as well. Betablockers act mainly by suppressing aqueous production, so the combination will produce an additive effect.
Looking at the entire profile of topical IOP-lowering medication for this patient, this case suggests that there may have been misinterpretation of instructions — either given or understood. She was taking two PAs each, twice per day, when the prescribed dosing is only once. In addition, she was taking two doses of timolol for a total of four, and a grand total of eight, drops per day. And her IOP was still 15mmHg.
With each additional drop beyond the initial one, compliance has been reported to be reduced by 50 percent. So, it is logical to expect that this patient's adherence to her prescribed regimen may fall short.
Setting a Target Range
Without knowing the maximum IOP or the IOP at the time of treatment initiation, it is difficult to develop a target range for the patient's IOP. Target IOP could be based on the fact that she showed significant optic disc and visual field damage, especially in the left eye.
I set a target range of 10-to-12mmHg. To achieve a balance between expected outcome and compliance, I asked the patient to use the Cosopt in the morning and the Xalatan in the evening. With this combination offering near maximum medical therapy with minimal dosing (three medications, two drops), I am hoping to combine different mechanisms of action to maximal effect. In addition, she has been scheduled for capsulotomy. CLS
Dr. Semes is a professor of optometry at the University of Alabama at Birmingham School of Optometry.