Silicone Hydrogel Lens Trends
Silicone hydrogel lenses offer therapeutic and visual benefits when used in these unique ways.
BY GLENDA SECOR, O.D., F.A.A.O. Huntington Beach, Calif .
lthough silicone hydrogel contact lenses were initially designated by the Federal Drug Agency (FDA) for a specific use and patient population, ginger off-label use by creative eyecare practitioners has allowed several patient populations to benefit from these high-water, high-oxygen lenses — in some cases, even spurring the FDA to expand usage approval. Here, I will discuss the therapeutic and visual benefits these lenses offer when used in the following unique ways.
When used to manage patients who have compromised corneal conditions and those who have undergone ocular surgeries, silicone hydrogel lenses offer these three therapeutic benefits:
• They enhance epithelial adhesion. Researchers and eyecare practitioners have reported that silicone hydrogel lenses in general can reduce corneal edema or corneal hypoxia to enhance epithelial adhesion in the later stages of healing from ocular surgeries, recurrent corneal erosion, bullous keratopathy, corneal abrasions, filamentary keratitis and syndromes or diseases, such as Stevens-Johnson syndrome, which can cause compromised corneal conditions. (See “Stevens- Johnson Patient Fit in a Silicone Hydrogel Lens,” page 68.) The availability of multiple base curves and extensive power ranges allow you to fit almost all corneas with silicone hydrogel lenses that have been FDAapproved for therapeutic usage.
Thus far, these lenses include CibaVision’s Focus Night & Day and Bausch & Lomb’s PureVision. However, the stiffer modulus of these lenses can, at times, cause increased lens awareness for some patients with the aforementioned conditions. In these cases, consider using an offlabel, lower-modulus lens, such as Acuvue Oasys or CibaVision’s O2Optix to enhance epithelial adhesion. Although off-label usage is not against the law, you must nevertheless be judicious in educating your patient on the purpose of trying the off-label lens. Once you do this, document the decision-making process as well as your discussion with the patient, and have him sign a consent form or his own medical record to protect him from any misunderstandings and you from liability.
• They provide elevated comfort post-op. Inserting a silicone hydrogel lens for three to four days of wear following refractive surgery, such as photorefractive keratectomy (PRK), enhances comfort during the initial healing phase because the lens reduces the sensation of the upper lid on the irritated cornea, providing a smoother surface to blink over. (You, the optometrist, can do this, though often the surgeon or his technician inserts the lens immediately after the procedure). Realize, however, the stiffness or modulus of silicone hydrogel lenses vary among different manufacturers, and that should influence your choice of a bandage lens depending on the reason behind it.
So, if protection and pain management are your primary objectives of therapeutic intervention, employ a lower modulus lens, as it provides protection with minimal lid involvement. If, however, the patient requires surface support, use the higher modulus or stiffer lens, as it provides superior assistance to the healing process without excessive lens movement.
To further enhance the patient’s comfort and reduce the risk of a secondary infection, prescribe adjunct pharmaceutical therapy in the form of prophylactic antibiotic and nonsteroidal anti-inflammatory (NSAID) topical drops. Also, inform your patient that his personal hygiene (hand washing), smoking and other behavioral factors, such as swimming while wearing his contact lenses, can also affect the therapeutic outcome, regardless of the chosen lens modality.
• They help seal unrelenting leaking wounds. Although I haven’t needed to employ this use on any of my patients thus far, the concept here to enhance the healing of the wound by offering protection and allowing the wound to heal. This is reported in the medical literature.
• They act as a splint after cataract, penetrating keratoplasty or glaucoma surgery. While I have yet to use this method on any of my patients, the medical literature has shown silicone hydrogel lenses augment healing by offering support to fragile tissues post-operatively during the healing process. Visual benefits When used to manage patients who have various visual problems, silicone hydrogel lenses used in these unique ways offer three benefits:
•They provide vision and comfort for gas permeable lens intolerant patients. The off-label use of a silicone hydrogel lens in a “piggyback” (a cushion lens under a gas permeable lens) application has been very successful in enabling gas permeable (GP) intolerant patients to maintain the vision they require and in providing comfort.
Many patients with irregular corneal conditions, such as keratoconus, require contact lenses that may aggravate a previously compromised corneal epithelium. Using a silicone hydrogel lens that has the patient’s prescription as a base lens for a GP lens, however, may enhance lens wear and offer protection to the cornea.
In addition, using a low-powered or plano silicone hydrogel lens under the original GP lens may sufficiently enhance comfort, temporarily or permanently alleviating the problem of lens intolerance from discomfort and enhancing physiological fitting aspects by providing a smoother ocular surface. (See “Fitting Silicone Hydrogel/Gas Permeable Piggyback Lens Systems,” below.)
Previous attempts at hybrid lenses (gas permeable lenses surrounded by a soft lens skirt) for these patients have been disappointing due to the marginal oxygen transmissibility, cost and problems with handling. However, the latest hybrid lens (SynergEyes) has incorporated newer material technology and addressed the concerns of hypoxia.
Not all GP/silicone hydrogel piggyback lens combinations are useful for keratoconic patients. GP patients who have persistent red eyes often achieve improvement with the addition of a hyper- oxygen transmissible soft lens. As with specialty lenses, it’s often unnecessary to change the original GP lens in this situation. If a lens change is indicated to maximize physiological fitting, however, remember the soft lens profile can help with rigid lens centration issues.
Patients who have undergone penetrating keratoplasty frequently have an irregular topography due to the “button” placement. When lenses decenter significantly or have excessive impingement regardless of the design, patients and eyecare practitioners become extremely frustrated. A higher minus-powered silicone hydrogel lens has a thicker lens edge profile. This thicker profile may help the centration of the GP lens. As with many piggyback combinations, diagnostic lens fitting often indicates whether the patient can achieve success with the unique piggyback arrangement. Using high permeable materials in both the rigid and silicone hydrogel lens designs offers you reassurance that the cornea is adequately supplied with oxygen.
•They provide vision to myopic patients whose prescriptions extend beyond the norm. By using a silicone hydrogel lens/silicone hydrogel lens piggyback, myopic patients with refractive error corrections outside the CL manufacturers’ standard parameters can achieve their needed power requirements. This is accomplished when you insert the higher-powered lens as the “ocular” lens and the necessary additional powered lens immediately on top of it as the “objective” lens. The higher-power ocular lens helps with centration of the objective lens.
If, however, you evenly divide the necessary power between the two lenses, the combination is less stable and more prone to decentration. Although the combination works in either order, the instability of the lowered power lens under the higher-powered lens usually reduces comfort and is less successful. I have used this method with CibaVision’s O2Optix. When utilizing this piggyback method, instruct the patient to be careful with the handling and care of two lenses for each eye. One can rarely insert or remove multiple lenses as a single unit, and the patient must keep straight which lens goes first. You may want to recommend that the patient have two separate cases marked “first” and “second” to reduce placement errors. (See “Cataract Patient Fit in Silicone Hydrogel/Silicone Hydrogel Piggyback,” below.)
• They reduce the accommodative esotropia in strabismic children. When strabismic children are given contact lenses to reduce their accommodative esotropia, the long-term benefit is the potential avoidance of amblyopia if the child is responsive to the treatment plan. Usually, these children have very high hyperopic prescriptions that don’t respond well to glasses, especially with anisometropic prescriptions. You can also prescribe more plus power in contact lenses and achieve better patient acceptance due to the cosmetic outcome of less eye crossings in strabismic children. Children are very apt and able to use contact lenses, and contact lenses have no age restrictions. However, because the prescription may need to be changed and I want to gauge and reinforce compliance, I recommend seeing the patient every six months.
By using silicone hydrogel lenses in the unique ways described above, you offer your patients the ability to heal comfortably and achieve both the vision and comfort they require. Also, by safely exploring off-label uses for these lenses in patients who have other conditions, you may be able to meet the needs of these and future patients who present with similar conditions. So, offer an open discussion about the potential risks and benefits of these unique uses, and “just do it.”
Stevens-Johnson Patient Fit in Silicone Hydrogel Lens
One of my most rewarding therapeutic silicone hydrogel fits was a 33-year-old man who reported having Stevens-Johnson syndrome since age seven. His history revealed he underwent several cryo-ablations to reduce the entropion appearance of his lids and subsequent trichiasis. The best acuity in his right eye was 20/200 due to the long-term corneal scarring. I employed a silicone hydrogel contact lens to provide him with good acuity and protect his fragile cornea. Unfortunately, it did little to help, so I decided to concentrate on achieving these goals in his left eye, which was 20/25. The result: After 30 days of continuous wear, the patient reported enhanced comfort and the visual acuity he sought. Although I didn’t reduce any of the pre-existing scarring, the use of a silicone hydrogel lens did enable me to solve his 25-year-old problem of persistent lid irritation that past bandage lenses failed to achieve.
Fitting Silicone Hydrogel/Gas Permeable Piggyback Lens Systems
The ability to fit this unique lens system doesn’t require any additional fitting experience than is required to fit traditional GP lenses. If the GP lens is acceptable in fitting, often the addition of a low-powered silicone hydrogel lens is adequate. Again, the higher modulus or stiffer silicone hydrogel lenses may not be best for the base lens because of the propensity for edge fluting or buckling when the lens doesn’t drape over the irregular cornea. Using a lens that has a lower modulus or that has less stiffness may be better because the lens may cover the cornea better, center better and therefore offer improved comfort. Corneal topography or video keratoscopy exposes corneal irregularities, which formally baffled even the most astute slit lamp examiner. The disparity in corneal curvatures indicated by topography can also explain GP lens decentration. Repeating the topography over the silicone hydrogel lens can also give you a starting point for the initial rigid lens base curve selection. One suggestion: Use the radius of curvature 3mm temporal from the central map.You can easily accomplish fluorescein pattern evaluation with the piggyback/GP combination. Keep in mind that some silicone hydrogel combinations are less forgiving of the fluorescein staining and require high molecular weight fluorescein to avoid excessive lens absorption.
Cataract Patient Fit in Silicone Hydrogel/Silicone Hydrogel Piggyback
My most successful silicone hydrogel lens/silicone hydrogel lens piggyback patient is a 75-year-old man whose acuity measured -18.00D. He had cataract surgery in his right eye and was increasingly intolerant of his remaining long-term GP lens in his left eye. I was unsuccessful in refitting his GP lens, and a silicone hydrogel lens/GP lens piggyback failed. Since his acuity was still 20/40 in the contact lens-wearing left eye, he said he was uninterested in surgery until it was required. So, he was receptive to my suggestion of using two silicone hydrogel lenses. I instructed him to first insert a -12.00D followed by a -3.00D Acuvue Oasys lens. The outcome: He said he was “thrilled” with his greatly improved comfort and his ability to be see binocularly again.
Dr. Secor is in private practice in Huntington Beach, Calif. She’s a diplomate and immediate past-chair of the Section on Cornea & Contact Lenses of the American Academy of Optometry and is a member of the Southern California College of Optometry Board of Trustees. She has participated in clinical studies and trials in the past, but has no current affiliations with any contact lens companies. E-mail her at GBSOD@ aol.com.
Optometric Management, Issue: March 2007