Contact Lens Design & Materials
Novel Water Gradient Lens Material
BY NEIL PENCE, OD, FAAO
The introduction of a new daily disposable contact lens may signal the need for a new category of lens material. The Dailies Total1 contact lens (Alcon), which was launched in various European markets during the past year, is the first water gradient soft contact lens. What’s unique about this lens is that the water content is not constant throughout the lens, but rather it changes from the main body or core of the lens to the surface. Here’s a brief overview of the key characteristics of this material and the water gradient phenomenon.
Figure 1. Schematic representation of Dailies Total1 water gradient contact lenses
Novel Water Content Properties
Dailies Total1 lenses are manufactured from a new material, delefilcon A, using a modification of Alcon’s Lightstream Technology, the manufacturing process used to produce the Dailies Aqua Comfort Plus daily disposable contact lens. At the core of the Dailies Total1 contact lens, which comprises just over 90 percent of the lens, is a silicone hydrogel material with a water content of 33 percent. The surface of the lens is designed with a water content of over 80 percent. The change in water content and lens structure occurs fairly rapidly in the outer 5 percent of the lens on both sides or surfaces.
Oxygen transmissibility, lens modulus or stiffness and the resultant effect on handling, and lens fitting characteristics are properties determined by the core of a contact lens. With its 33 percent water content core, the Dailies Total1 lens has the highest oxygen transmissibility of any daily disposable lens on the market. It has a Dk of 140 and a Dk/t of 156 for a −3.00D lens with a center thickness of 0.09 mm.
Wettability, lubricity or low coefficient of friction, the ability to resist deposits or soiling and overall biocompatibility with the ocular surfaces are key characteristics of a contact lens surface. A water content of over 80 percent at the surface should result in a wettable, lubricious lens.
With U.S. Food and Drug Administration clearance already secured, 2013 will see the introduction of Dailies Total1 lenses in the United States. The advent of this novel new contact lens material with gradient water content properties and the benefits it may bring will be eagerly awaited. The high oxygen transmission of a silicone hydrogel lens with the surface advantages of a high water content at the surface should be a winning combination for an ever-growing number of patients wearing daily disposable contact lenses. CLS
Dr. Pence is the associate dean for Clinical and Patient Care Services, Indiana University School of Optometry in Bloomington, Indiana. He has received travel expenses, stipend, or reimbursement from Alcon and Bausch + Lomb. You can reach him at email@example.com.