Gas-permeable lens options continue to expand

Contact Lenses and Eyewear

Marlane J. Brown

New designs and treatments are continually available for our gas-permeable lens patients. Staying on top of new information from your laboratories may make the difference between success and failure. Additionally, it will help you remain a leader in fitting your patients.

Plasma treatment, a new development for GP lenses, maximizes wettability and may improve initial patient comfort. This treatment is optional and is available on many GP materials, such as Paragon, Boston, Contamac and Menicon.

Originally, plasma treatment was used in cleaning organic and inorganic contaminates from metal, ceramic, glass and silicone in medical devices, circuit boards and electronics. Today it is used in some contact lens materials as well.

A U.S. pre-grant abstract for silicone hydrogel lenses (#20030039748, 2003-02-27) describes the treatment as a “method to provide an optically clear … coating upon the surface of a lens by subjecting [it] to a process comprising plasma treatment, hydration and heat sterilization that is controlled to result in a silicate-containing film.”

The coating process involves a direct application of electrical, magnetic, wave or particulate energy. The cold plasma gas is contained in a reaction chamber; plasma is defined as matter consisting of electrons, positive ions and neutrons in a highly energized state. Plasma can etch a surface, deposit a film, add or modify chemical structures or alter surfaces to control water characteristics. The effect is localized to the surface.

The only performance studies to date have examined wetting properties.

Proposed benefits of plasma

In addition to increasing wettability, plasma coating may repel protein, cell and bacterial adhesion, and it may enhance patient comfort. The treatment removes all residues from the manufacturing process and reduces the wetting angle dramatically. Plasma treatment for IOLs may be beneficial for the protein, cell and bacterial repelling properties on those devices as well.

Because it diminishes initial lens awareness, plasma treatment for GP lenses may help the patient adapt easier. It also provides more crisp vision.

Handling plasma lenses

The lenses are shipped wet, so handle them as little as possible prior to dispensing. Patients should avoid even mildly abrasive cleaners (such as the Boston original cleaner), as they may affect the treatment.

Plasma treatment is not a long-term solution for patients with dry eyes or contact lens intolerance, as the effect diminishes over a few weeks. However, the initial improvement in comfort may be enough to get patients past their early adaptation difficulties.

I recommend this treatment for all patients who are being fitted for new GP lenses or for new orders on patients who have had previous comfort issues.

Soft/GP hybrid lenses

In September 2001, SynergEyes (SynergEyes Inc., Carlsbad, Calif.) began developing a new hybrid lens, which is a union of a GP center with a soft skirt. The GP center consists of Paragon HDS 100 (Paragon, Mesa, Ariz.), which has a Dk of 100 and a soft hydrophilic skirt of a 27% water non-ionic material (Group I.) The lens has a 14.5-mm overall diameter with an 8.4-mm GP center. The posterior surface is aspheric.

The SynergEyes A lens is designed for patients with regular refractive errors and astigmatism. Two additional specialized designs are available for keratoconus, ectatic corneas and either post-surgical or post-traumatic highly oblate corneas. The multifocal was just introduced, and reverse geometry designs are promised in the future.

The hybrid concept is not new. Other hybrid lenses have been available in the past, including the Saturn Lens (1977, Precision Cosmet, Minneapolis) and Saturn II (1985), SofPerm (1989 Sola Barnes Hind,  Sunnyvale, Calif., or CIBA Vision, Duluth, Ga.), with each a progressively better product.

The major drawbacks to these lenses included durability and design. The junction between the GP center and soft skirt was weak, resulting in torn or cracked lenses, and at 14, the oxygen transmissibility (Dk) of the GP center was low. Newer GP materials with high Dks and new technology that forms a reliable soft/GP junction have given the SynergEyes lenses the potential to succeed where the other designs were flawed.

The advantage of a hybrid lens is good centration, better comfort than a GP lens and stability. This lens design may work well for the patient with astigmatism, a first-time wearer, a patient with keratoconus or any GP wearer who may not tolerate his or her current lenses or who are considering dropping out. The optics of a GP lens along with the comfort of a soft lens should allow the patient to see well and be comfortable.

Fitting hybrid lenses

When fitting hybrid lenses, use high molecular-weight fluorescein in the lens before insertion. It is essential that these lenses center well and that they are not fit too flat or loose. A too-tight fit will reveal an air bubble centrally. A lens that is too loose may look adequate but actually will not perform well. The desired fit is one with apical clearance, and the flourescein pattern is essential to determining this. A fitting guide that uses the patient’s keratometry readings and refraction is available online at www.synergeyes.com. This guide will help the practitioner with a starting lens.

I recommend this lens for those patients who have been difficult to fit with traditional GP lenses due to poor centration or poor vision and significant comfort issues. I also recommend them for patients who need to switch from their beloved soft lenses to GP lenses for physiologic or optical reasons.

Larger-than-corneal designs

While not an everyday option, I will mention larger-than-corneal designs, as they are becoming more popular. Scleral lenses bear on the sclera instead of the cornea, which eliminates the need for close alignment between the cornea and the lens compared to corneal lenses. The advantages are less movement and more stability, especially for high-powered lenses. It is less important to specify curves for those corneas with irregular topography. Additionally, lid sensation is reduced and there are fewer problems with debris under lenses compared to corneal GP lenses.

According to Pullum and colleagues, scleral contact lenses continue to play a significant role in managing corneal abnormalities, especially those with primary corneal ectasia, such as keratoconus, corneal transplant and ocular surface disease.

There are several types of larger-than-corneal GP lenses. Scleral lenses such as the Jupiter (Medlens Innovations), Innovative, (Innovative Sclerals Ltd, United Kingdom) and Boston Scleral (Boston Foundation for Sight, Chestnut Hill, Mass.) are usually larger than 15 mm in overall diameter, with bearing on the sclera and vaulting the cornea. Corneal scleral designs (i.e., So2Clear, Dakota Sciences, Sioux Falls, S.D., and Macrolens, C&H Contact Lens) are 12.5 mm to 14.5 mm and are designed to equally distribute pressure along the corneal scleral surfaces, providing the optics of a GP lens and stability and comfort approaching a soft lens.

The disadvantages to these designs are that they are usually more expensive lenses, and the larger size can be disconcerting to patients who are used to smaller designs. They are usually removed with a DMV or suction cup remover, and if the patient loses this device there could be some late night phone calls.

Also, because of the larger size, using a soft contact lens solution rather than the thicker GP solution to place the lens on the eye may yield quicker vision. Education on the difference of handling this lens is important not only to the wearer, but also to the staff who may be involved with the patients.

These lenses have shown excellent early potential, but they need to be used more.

Alternating, simultaneous GP bifocal designs

Several designs of GP bifocals are available. The two categories are alternating vision, which includes the segmental designs, and simultaneous vision, which includes the aspheric or diffractive designs. I like the segmental designs because I can see where the actual zones are and feel I have some control in their position to help patients see best.

One of my favorites is X-Cel’s Solutions Bifocal (X-Cel Contacts, Atlanta). This lens boasts a one-piece construction and is monocentric, meaning optic centers near the center of the lens. The lens is prism ballasted and rarely needs truncation. It is available in Fluoroperm 30 or 60.

The lens comes in a wide variety of parameters. Base curves are available in 40 and 47.25, diameters between 8.5 mm and 10.0 mm, distance powers between +6.00 D and -10.00 D and add powers from +0.75 D to +3.50 D. Prism ballast must be specified as minimum, medium or maximum, and segment height is stated as 0.5 mm, 1.0 mm or 1.5 mm above or below the geometric center of the lens.

The translating designs provide specific distance and near zones. Lens translation is necessary to position the correct zone over the visual axis. Stabilization is required, either with prism ballast, truncation or both. Alternating vision is natural vision and similar to our vision system. It allows both eyes to function at distance and near simultaneously.

Lower lid position critical

Lower lid position is critical in fitting these translating, segmented lenses. Positioning the lower lid at or near the inferior limbus will help stabilize the bifocal in the primary gaze. This lid interaction holds the lens in position while the eye alternates from a distance (straight ahead) to a reading (downward) gaze. For alternating lenses to work well, they must move up as the patient looks down.

Translating bifocals perform best on corneas that have with-the-rule astigmatism. During the blink cycle, the lens will follow the path of least resistance along the steeper vertical meridian. For complete translation vertically, it is imperative that the astigmatism is uniform.

Of course, as with any bifocal fitting, a pre-fitting discussion and determination of motivation is necessary. Understanding the patients’ goals as well as the work conditions is critical to success.

This is a challenging category of patient and lens to fit, but the translating bifocals are one of the better designs.

Try these ideas on your next challenging contact lens patient. Fitting the same lens or same design can get boring. Many alternatives exist for the patient who has a complex prescription, an irregular cornea or a dry eye. Most patients will accept an alternative idea, which will make your clinic day more interesting.

For more information:

• Marlane J. Brown, OD, FAAO, is a contact lens specialist and provides surgical comanagement at Minnesota Eye Consultants. She is also on staff in the Ophthalmology Department at the Regions Hospital Eye Clinic and is a former president of the Minnesota Optometric Association. She can be reached at Minnesota Eye Consultants, 710 East 24th St., #106, Minneapolis, MN 55404; (612) 813-3621; fax: (612) 813-3636; e-mail: mjbrown@mneye.com. Dr. Brown has no direct financial interest in the products mentioned in this article, nor is she a paid consultant or employee for any companies mentioned.

Reference:

• Pullum KW, Whiting MA, Buckley RJ. Scleral contact lenses: The expanding role. Cornea. April 2005;24:269-277.