Article

CONTACT LENS DESIGN & MATERIALS

MAKING GP LENSES WETTABLE

Rigid GP materials have a number of advantageous properties including durability, deposit resistance, and mechanical stability. These properties make them a great option for those needing sharp optics, masking of surface irregularities, and cost savings over time.

However, one disadvantage of GP materials is the challenge to make the lens surface maintain a viable tear layer so that patients can enjoy good comfort and vision. Modern GP materials can attract proteins and lipids from the tear layer, contaminating the lens surface and making it more hydrophobic (Figure 1). Through the years, GP material manufacturers and finishing laboratories have attempted to improve GP surface wettability by various means.

Figure 1. GP lens surface non-wetting.

Cleaning and Conditioning

Proper GP lens care is essential in maintaining good surface characteristics. Abrasive daily cleaners can help remove protein, while cleaners with solvents can help remove lipid films and deposits.

Periodic use of a deep cleaner containing sodium hypochlorite and potassium bromide can remove more extensive deposits and films. In addition, regular cleaning of the GP contact lens will help maintain a cleaner, more wettable lens surface.

GP soaking solutions not only kill bacteria and fungi but also “condition” the lens to make its surface more wettable. Various wetting agents (e.g., polyvinyl alcohol, polyethylene glycol [PEG], cellulose polymers, hydroxypropyl guar, poloxamer, tyloxapol, etc.) may be included to provide initial wetting of the lens surface. The combination of proper cleaning and conditioning of the GP lens is fundamental to attaining and maintaining good surface wettability.

Plasma Treatment

Plasma treatment is the bombarding of GP lens surfaces with high-energy radio waves in an oxygen-rich ionized vacuum chamber. This process causes oxygen radicals to strike the lens surface, which removes lipids and makes the surface of the lens pristine. It also rearranges the polymer molecules such that the surface becomes more ionized and hydrophilic.

The result is a lens that is more wettable. This has been a helpful option for patients who have had problems with blur and discomfort due to a poorly wetting lens that rapidly attracts lipids and/or proteins.

Surface Coating

A recent innovation in GP manufacturing is the use of a 90% water PEG-based polymer mixture that is bonded to the lens surface. PEG has high lubricity and solvency properties, making it a versatile chemical compound used to bind water in many personal products.

It is applied to the GP contact lens surface as a very thin coating less than 50nm in thickness. The polymer coating is able to bind water better compared to the GP material alone, creating a wetter, more slippery lens surface.

The treated lens surface also resists protein deposits better and increases pre-lens tear breakup time. The result is a GP lens that is more comfortable and allows for longer wear time.

Better Wetting = More Success

Making GP lenses comfortable continues to be a challenge, so utilizing all available technology to improve lens wetting is essential for the continued contact lens wearing success of our patients. CLS