Artificial tear delivers high-performance dry eye therapy

Key Points

New York-A new artificial tear product (Systane Ultra, Alcon Laboratories) was developed by formulation engineers to provide extended comfort and protection to patients suffering from dry eye disease, said Peter A. D'Arienzo, MD.

Like the original version (Systane), the new tear contains borate, the gelling agent hydroxypropyl (HP)-guar, and the active demulcents polyethylene glycol 400 and propylene glycol, and its beneficial properties are based on the formation of an HP-guar/borate polymer that adheres to the damaged ocular surface and retains the active demulcents in a protective layer. The new version, however, is formulated at a pH of 7.9 (higher than the original version) and features sorbitol as an added ingredient. These formulation differences, together with divalent ions in the tears and mucin, are the essential elements in the mechanism of action for the intelligent delivery system present in this new artificial tear.

"[The new formulation] represents a new high-performance dry eye therapy, and it is a welcome product introduction considering that dry eye disease continues to be one of the most difficult management problems faced by ophthalmologists in daily practice," said Dr. D'Arienzo, clinical assistant professor of ophthalmology, New York Medical College. "Created with an intelligent delivery system and unique mechanism of action, [the new tear] appears to hold particular promise for bringing patients all of the proven benefits associated with the original [formulation], plus more."

At the slightly alkaline pH in the bottle, he said, the new artificial tear exists as a low viscosity, loosely cross-linked polymer network because sorbitol competes for bonding to borate and reduces its interaction with HP-guar. Shear stress created both as a drop of the artificial tear is squeezed through the bottle tip and as it is distributed by the blinking lid further lowers the viscosity of the newer formulation so that it forms an even, lubricating coat over the ocular surface.

"With its lower viscosity, patients derive the immediate comfort advantages of a gel upon instillation of [the new tear], but with minimized potential for vision-impairing blur," Dr. D'Arienzo said.

Interaction between the new artificial tear on the ocular surface and mucins and divalent ions of the tear film promotes release of sorbitol from borate to enable increased bonding of borate to HP-guar. The more extensively cross-linked HP-guar/borate polymer network represents an enhanced protective coating on the ocular surface, he said. This liquid therapeutic bandage adheres to damaged areas of epithelium and retains the active demulcents in the new formulation in an effort to provide long-lasting ocular surface protection and lubrication.

Research presented at the 2008 annual meeting of the Association for Research in Vision and Ophthalmology demonstrated the unique viscoelastic properties of the new artificial tear and their dependence on its novel formulation and interactions with tear components. Using instrumental testing, the experiments showed the viscosity of the new formulation was reduced by shear stress and that exposure to mucin increased the surface elasticity of the tear.

"This interaction with mucin serves to enhance the qualities of [the new tear] as a liquid bandage," Dr. D'Arienzo said.

Another experiment investigated the lubricating performance of the new tear using a tissue-on-tissue testing protocol. In this model, the friction generated between two articulating tissues was measured when various lubricating test solutions are placed in the interface. A modified solution of the new artificial tear was investigated in which the pH was adjusted and sorbitol was omitted to replicate the formulation in which the tear exists on the eye. The results showed the modified formulation of the new tear had superior lubricating properties compared with a saline control and the competitor artificial tear product with carboxymethylcellulose, glycerin, and a preservative (Optive, Allergan).

"Not only did [the new tear] perform better at reducing tissue-on-tissue friction initially, but it maintained its activity after several rinse cycles, indicating it will provide sustained lubrication and protection on the eye," Dr. D'Arienzo said.