Article Date: 9/1/2005

contact lens management
New Polymer For GPs
A novel, rigid silicone-hydrogel contact lens provides durable comfort.

In my practice, I am increasingly fitting larger diameter gas permeable corneal lenses (11mm to 12.5mm) in order to improve comfort and lens centration. But the increase in surface area often results in more surface related problems for many patients. Dry spots on lenses often result in frictional irritation with the blink and serve as a place for tear components to deposit and desiccate. The consequence is that my patients' experiences with such lenses range from annoyance to pain.

In searching for materials that compliment these larger-diameter GPs, I have been disappointed by claims of soft lens comfort from rigid lenses with a "hydrophilic skin" or excellent "wettability." Laboratory measurements that indicate the ability of water to spread over a lens surface often relate very little to lens comfort, as patients will tell you. The real-life, on-eye performance is the only measure of comfort that matters to the patient.

Fortunately, for the past year, my patients and I have had very positive experiences with a new GP material, ONSI-56 (onsifocon A). Made by the Lagado Corporation (, it has the properties necessary to significantly enhance biocompatibility and comfort.

Lagado says its new polymer, ONSI-56, increases patient satisfaction with GP contact lenses.

Three good reasons

ONSI-56 can be described as a silicone hydrogel polymer that cannot absorb water into the interior of the polymer due to it's unique formulation. With a Dk of 56, ONSI-56 provides excellent oxygen transmission without sacrificing comfort, which is a problem we see in some polymers in this range. And ONSI-56 lenses do not require any surface treatment or modification to establish or maintain their hydrophilic surfaces. This is important, because GP lenses are expected to retain wearability for at least a year.

In contrast, hydrophilic surfaces of treated lenses may degrade during normal use, thus shortening expected lens life. ONSI-56 lenses also are quite resistant to surface deposits due to the high proportion of fluoromonomer in the polymer formulation.

Patient pleasers

I also use ONSI-56 lenses to refit current GP wearers, as well as those who have dropped out of GP wear due to comfort issues. Over one-half of my patients refit with the same specifications as their previous lenses say that ONSI-56 lenses are more comfortable. Even those who had no prior comfort problems remark that the lenses are easier to wear for longer hours.

I still use low-Dk GP materials when rigidity is the most important feature. I will also use higher Dk materials, such as Boston XO, when a patient requires a lens with more oxygen permeability. But for most GP patients, I have found that ONSI-56 provides the best balance of comfort, corneal health and sharp visual acuity.

Solving problems

ONSI-56 has been a welcome addition to my practice. It allows me to provide patients with a lens that offers durable comfort and it's the material I choose for routine or problem cases unless otherwise indicated. This advance in contact lens polymers provides an excellent foundation for lenses that can increase the number of patients who enjoy the benefits of GP lenses. It also reduces the number of contact lens drop-outs.



Optometric Management, Issue: September 2005