ABSTRACT.Purpose: Monoamine receptors are found throughout the body. Reports about the presence of monoamine receptors in the human cornea are inconsistent. Methods: Immunohistochemistry, immunofluorescence and immunoblotting were used to localize monoamine receptor sites on human corneal epithelium and endothelium. Results: Antibodies to alpha-1, beta-1 and beta-2 adrenergic receptors and to D1-like and 5HT-7 receptors were bound in corneal epithelium. Antibodies to alpha-1, alpha-2A, beta-1 and beta-2 adrenergic receptors and to 5HT-7 receptors were bound in corneal endothelium.Conclusions: Our data demonstrate the presence of several monoamine receptors in the human cornea. These receptors may play a role in the regulation of fluid transport or corneal homeostasis.

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.

The study provides evidence of the influence of beta receptor antagonists on corneal thickness. This effect may be caused by receptor mediated influences on corneal ion and fluid transport. Further studies are needed to show if the increase of corneal thickness after application of topical timolol has clinical importance.

Our data demonstrate that bovine corneal epithelium and endothelium express a functional D1-like receptor positively coupled to adenylyl cyclase and cAMP production. However, at the present time the physiological role of this receptor remains a matter of speculation.

Topical administration of brimonidine 0.1 % results in a reversible increase in corneal thickness. The question as to whether this increase is of clinical significance has to be answered by larger studies.