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- Eyeing the Future of Ophthalmic Lenses
- Get to Know Nathan Lighthizer, OD, FAAO
For any type of ophthalmic lens inserted into the eye, whether to enhance vision or simply for cosmetics, wear comfort is based on two primary factors: oxygen permeability and wettability. For manufacturers, achieving these characteristics means utilizing new advanced materials, such as silicone hydrogels. Unfortunately, hydrogels are also inherently “hydrophobic,” meaning they have poor wettability characteristics that can cause discomfort during lens wear.
To overcome this problem, most lenses are surface modified by plasma treatment during the manufacturing process to render them more wettable to tear fluid. A flexible process, plasma treatment is also used to inhibit biofilm accumulation, smooth out lens machining marks, promote bonding and other tasks.
Plasma Treatment's role
Plasma treatment is so common, in fact, that leading equipment providers are able to modify existing, mature tools and technology, complete with fixturing, to deliver what are essentially drop-in solutions for contact and intraocular lens manufacturers. Some providers even provide access to on-site research and development equipment as well as engineering expertise.
Whether to improve vision, or for cosmetic reasons, contact lenses are typically made out of acrylates and siloxanes. In recent years, advances in silicone-hydrogel contact lenses have improved oxygen permeability, enabling up to five times more oxygen to reach the cornea compared to regular soft hydrogel alternatives. As a result, silicone hydrogel lenses now account for approximately two-thirds of all contact lens fittings performed today.
Given the hydrophobic nature of silicone hydrogels, the surface characteristics of the lens must be altered by plasma treatment to render it wettable, or hydrophilic. It is possible to accomplish this by plasma oxidation of the silicone hydrogel to form thin silicate islands across the surface that remain intact when the hydrogel is hydrated (causing it to swell by 10% to 20% by volume) and autoclaved.
Another method involves first plasma activating the lens material, followed by a plasma induced polymerization process of an organic species, which is then oxidized on the surface of the contact lens by an additional plasma step. Plasma treatment provides other positive benefits beyond comfort, most notably the prevention of “cloudy” spots on the lens caused by lipid deposits.
Plasma treatment also plays a critical role by modifying the surface of foldable intraocular lenses used to replace the natural lenses of eyes that have been damaged by trauma or disease, such as cataracts. Advances in technology have brought about the use of silicone and acrylic, both of which are soft foldable inert materials. This allows the lens to be folded and inserted into the eye through a relatively small incision.
This type of lens material , however, has a tendency to adhere to itself, as well as to handling tools. A tacky lens requires more manipulations by the surgeon and increases surgery time.
Plasma surface modification of IOLs removes the surface tackiness, ensuring safe insertion and automatic unfolding of the IOL to its original configuration once inside the eye.
New Market Entrants
For Innovega, a uniquely designed contact lens was the most critical component of its iOptik next generation device for viewing virtual and augmented reality images.
This type of eyewear utilizes optical components that allow the wearer to perceive they are viewing a large computer display in the foreground, while simultaneously allowing them to view real objects at normal distances.
Conventional video eyewear requires the optics to be built into the device, which compromises style, adds weight, and can limit interaction with others. The designers at Innovega felt these barriers were limiting the mainstream acceptance of these products. So the company decided to eliminate the optics from the eyewear and replace it with a contact lens that incorporated a microlens within it. The contact lens could be prescriptive, if necessary.
This design creates a bifocal effect that allows the wearer to simultaneously focus on virtual content from the eyewear and on the entire spectrum of activities in the real world. As a result of moving the optics to the contact lens, the iOptik eyewear is much more comfortable and stylish. This shift in approach, however, meant the company needed to immerse itself in the world of contact lens manufacturing.
To increase its knowledge and expertise in plasma treatment options, Innovega began working with a company that designs plasma systems for surface activation, functionalization, coating, ultrafine cleaning and etching. In addition to providing production-level tools, the company has in-house equipment to run parts and conduct experiments.
Innovega’s technicians visited the lab monthly and ultimately incorporated plasma treatment into a multistep lens molding process. The final system incorporates plasma for surface activation of the molds to facilitate release of the lenses during manufacturing, for bonding microcomponents to the lens, and for surface modification to increase wettability.
Although the bulk of the research and development occurred in the lab, Innovega eventually purchased a production tool of their own. By having access to their lab, it was possible to confirm they had the right process and even do some prototype lenses before making the purchase.
• Head of R&D for PVA TePla America
• Specializes in nanoscale plasma enhanced chemical vapor deposition, silane chemistries, and self-assembled monolayers