By Cameron Johnston
FT. LAUDERDALE, FL -- May 10, 2007 -- Central corneal thickness (CCT) is known to be a significant risk factor for developing open angle glaucoma. Patients with thinner corneas (<500 microns) are known to develop glaucoma more than people whose corneas are more than 600 microns thick. Also, measuring CCT is a recommended practice when a patient is being examined for the presence or glaucoma or ocular hypertension.
Now, a study presented here at the meeting of the Association for Research in Vision and Ophthalmology (ARVO) has shown that patients with thinner corneas seem to respond to treatment with beta blockers better than they do to drugs such as prostaglandins.
In a retrospective chart review conducted at the Scheie Eye Institute at the University of Pennsylvania, Philadelphia, researchers followed 224 patients with open angle glaucoma for a total of 17 weeks while they used beta blockers, prostaglandin analogues, carbonic anhydrase inhibitors, or alpha2 agonists.
Patients were stratified at the outset according to their CCT: < 520 microns; 520-559 microns, and >/=560 microns. Corneal thickness was measured before and at the end of the study.
Results showed that central corneal thickness did not have a significant impact on a patient's response to any ocular hypotensive drug. Not unexpectedly, prostaglandins as a class resulted in a greater reduction in intraocular pressure than any other type of drug.
Decreases in intraocular pressure (IOP) were 5.79 mm Hg (20%) for prostaglandins; 5.38 mm Hg (13.1%) for beta blockers; 4.12 mm Hg (19%) for alpha2 agonists; and 4.61 mm Hg (15.5%) and for carbonic anhydrase inhibitors.
However, when patients were stratified according to CCT, those with CCT of < 520 microns had a mean decrease in IOP of 20.4% with beta blockers, 19.2% with prostaglandin analogues, 17.5% with alpha2 agonists, and 13.7% with carbonic anhydrase inhibitors.
Among patients with thicker corneas (>560 microns), IOP reductions were 8.41% with beta blockers, 21.2% with prostaglandins, 17.4% alpha2 agonists, and 13.4% with carbonic anhydrase inhibitors.
The differences in IOP reductions achieved with beta blockers compared with other drug classes were statistically significant for the three ranges of CCT. The differences seen with the other IOP-lowering agents were not statistically significant.
According to study presenter Lila Grunwald, MD, ophthalmologist, Scheie Eye Institute, it is now a recommended practice for clinicians to measure IOP when diagnosing a patient with glaucoma, or when starting to treat the patient. Therefore, the clinician could base a chosen treatment on the patient's CCT. Patients with the thinnest CCTs for example, could be initiated on a beta blocker, since the patient would achieve the same IOP-reduction that he or she would see if a prostaglandin was used as drug of first choice. This could be relevant in cases where the patient cannot afford prostaglandins, which are considerably more expensive than beta blockers.
[Presentation title: Effect of Corneal Thickness on Intraocular Pressure Reduction. Poster 1279/B234]
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