Effect of Brimonidine on Corneal Thickness

Purpose: Brimonidine, an alpha-2 adrenoceptor agonist, is an effective and safe medication that is widely used in glaucoma treatment. Although it is known that it is quickly taken up by the cornea following topical administration and that the cornea has alpha-2 adrenoceptors, there are only few studies available on the impact brimonidine has on the cornea. Methods: Twenty healthy test persons (12 female and 8 male subjects)-mean age about 33 years (22 to 38 years)-were tested in a double-blind, prospective, randomized study. Intraocular pressure as well as epithelial, stromal, and endothelial thickness was measured before, at 25 days while, and at 5 days after administration of brimonidine 0.1% eye drops twice daily. To check the impact of this medication, placebo (proper solution of preservative) eye drops were administered to the other eye twice daily. Results: Administration of brimonidine 0.1% resulted in a reduction of intraocular pressure from an initial value of 14 to 9 mmHg after 5 days (P = 0.001) as well as an increase in total corneal thickness from 556 mm from the time of the baseline examination to 578 mm (P = 0.001), an increase of epithelial thickness from 58 to 66 mm (P < 0.001), and stromal thickness from 488 to 502 mm (P = 0.008) after 2 days each. Another 2 days later, total corneal thickness was 559 mm (P = 0.276), epithelial thickness 56 mm (P = 0.561), and stromal thickness 493 mm (P = 0.315), which means that the values had returned more or less toward the initial values measured. In contrast, endothelial thickness did not vary following administration of brimonidine 0.1% (P = 0.965). With treatment with brimonidine 0.1%, mean intraocular pressure in thin corneas (< 556 mm) was lower than in the thick corneas (> 556 mm, P = 0.018). Conclusions: Topical administration of brimonidine 0.1% results in a reversible increase in corneal thickness. The question whether this increase is of clinical significance and whether it is the result of epithelial and/or endothelial receptor stimulation cannot be finally answered at the present time.