contact lens materials
Meeting Patient Needs with Silicone Hydrogel Soft Lenses
BY N. REX GHORMLEY, OD, FAAO

In my November 2004 Contact Lens Colloquy column, I discussed the importance of oxygen to the soft lens patient. The chronic lack of adequate oxygen to the cornea can cause many signs and symptoms of corneal oxygen deficiency. This month, I'd like to review these signs and symptoms, which we all see in clinical practice.

Symptoms of Deficiency

A few of the most common symptoms that I hear from my soft lens patients are:

• "My eyes are always red." Allergies, dry eye, solution sensitivity or corneal oxygen deficiency can cause chronic red eye
• "Vision is blurry at the end of the day." A dirty lens, lens dehydration or corneal oxygen deficiency may cause blurry vision at the end of the day
• "I just can't wear my contact lenses all day anymore." Dry eye, allergies or corneal oxygen deficiency can all result in reduced contact lens wearing time

Signs of Deficiency

Following are some of the many clinical signs of corneal oxygen deficiency:

• Corneal edema
• Corneal staining
• Neovascularization
• Injection of the conjunctiva
• Myopic shift (an increase of >0.50D)
• Endothelial polymegethism, pleomorphism and decreased cell density
• Corneal distortion -- irregular corneal topography

Tackling the Deficiency Problem

We now have the tools to potentially address the signs and symptoms of corneal oxygen deficiency: hyper-Dk/t silicone hydrogel contact lenses. As responsible eyecare practitioners, we should choose these lenses for the majority of our patients because:

• Corneal metabolism varies widely and we don't have a test to predict individual oxygen requirements
• Plus lenses and high-minus lenses have lower oxygen transmissibility compared to the average minus (­3.00D) lenses that we use for published Dk/t values
• Environmental conditions such as altitude and humidity can affect the amount of oxygen that will reach the cornea
• Many patients wear their lenses all waking hours and occasionally sleep in their "daily wear" lenses
• Providing a high level of oxygen transmission may help to eliminate the majority of signs and symptoms of corneal oxygen deficiency

Ideal for Other Conditions

In addition to the clinical signs of corneal oxygen deficiency, many clinicians recommend silicone hydrogel lenses for the following patients:

• Young myopes
• High plus and minus patients
• Pediatric patients
• Those who have a history of corneal injury or disease
• Those who require a bandage lens after corneal trauma
• Post refractive surgery patients
• Patients wearing a "piggyback" lens for keratoconus
• Patients who prefer extended wear up to six nights
• Patients who prefer continuous wear up to 30 nights

Note: The FDA hasn't approved all silicone hydrogel lenses for all of the above-mentioned clinical uses.

With Open Arms

With all of their benefits and indications, why aren't silicone hydrogel contact lenses the lens of choice for the majority of our patients? This material is the future of contact lenses. We all need to adopt this new technology for the benefit of our contact lens patients.

Dr. Ghormley is in private practice in St. Louis, MO. He is a past president of the American Academy of Optometry and is a Diplomate of its Cornea & Contact Lens Section.